B Y t V khoa hc v o to

Hp cht hu c n chc v a chc(Sch dng o to dc s i hc) M s: .20.Y.13 Tp I

Nh xut bn Y hc H ni - 2006 1

Ch bin: PGS. TS. Trng Th K Tham gia bin son: ThS. Nguyn Anh Tun TS. Phm Khnh Phong Lan ThS. Th Thu PGS. TS. ng Vn Tnh ThS. Trng Ngc Tuyn Tham gia t chc bn tho

TS. Nguyn Mnh Pha ThS. Ph Vn Thm

Bn quyn thuc B Y t (V khoa hc v o to)

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Li gii thiuThc hin Ngh nh 43/2000/N-CP ngy 30/08/2000 ca Chnh ph quy nh chi tit v hng dn trin khai Lut Gio dc, B Gio dc v o to v B Y t ph duyt, ban hnh cc chng trnh khung cho o to Dc s i hc. B Y t t chc thm nh sch v ti liu dy hc cc mn hc c s v chuyn mn theo chng trnh mi nhm tng bc xy dng b sch chun trong cng tc o to Dc s i hc ngnh Y t. B sch Ho hu c c bin son theo chng trnh o to mn Ho hc hu c thuc chng trnh gio dc ca i hc Y Dc thnh ph H Ch Minh trn c s chng trnh khung c B Gio dc v o to, B Y t ph duyt. Ni dung b sch ch cp nhng kin thc l thuyt v ho hu c, gm 40 chng v chia lm 2 tp trnh by nhng kin thc c bn v danh php, cu trc, c ch phn ng, tnh cht l hc v tnh cht ho hc ca cc hp cht hydrocarbon, cc hp cht n chc, cc hp cht a chc, hp cht tp chc, hp cht thin nhin v hp cht cao phn t. i tng s dng chnh ca b sch ny l cc sinh vin ang theo hc ti Trng i hc Dc khoa Dc cc trng i hc ngnh Y t. ng thi cng l ti liu tham kho tt cho nhng hc vin sau i hc. Sch c bin son da theo chng trnh c B Y t ban hnh. Ni dung sch ch cp nhng kin thc l thuyt v Ho hu c. Sch Ho hu c c cc ging vin giu kinh nghim ca Khoa Dc - i hc Y Dc Thnh ph H Ch Minh bin son. Sch c Hi ng chuyn mn thm nh sch gio khoa v ti liu dy hc chuyn ngnh Dc ca B Y t thm nh v c B Y t ban hnh lm ti liu dy hc chnh thc dng o to dc s i hc ca Ngnh Y t trong giai on hin nay. Trong thi gian t 3 n 5 nm, sch cn c chnh l, b sung v cp nht. V Khoa hc v o to, B Y t xin chn thnh cm n Khoa Dc - i hc Y Dc Thnh ph H Ch Minh cng cc tc gi b nhiu cng sc bin son cun sch ny. V l ln u xut bn nn chc chn cn nhiu thiu st, chng ti mong nhn c kin ng gp ca ng nghip v bn c cun sch ngy cng hon thin.

V khoa hc v o to B Y t

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4

MC LCLi gii thiu M u Chng1: Cu trc in t ca nguyn t carbon v s to thnh cc lin kt trong hp cht hu c ThS. Nguyn Anh Tun 1. Cu trc in t (electron) ca nguyn t carbon 2. S to thnh cc lin kt Chng 2: Cc hiu ng in t trong ha hu c ThS. Nguyn Anh Tun 1. Hiu ng cm ng 2. Hiu ng lin hp (cng hng) 3. Hiu ng siu lin hp (Hyperconjugate effeet) Chng 3: Cu trc phn t hp cht hu c. ng phn v cu dng ThS. Nguyn Anh Tun 1. ng phn phng 2. ng phn lp th - ng phn khng gian Chng 4: Khi nim acid -base trong ha hu c ThS. Nguyn Anh Tun 1. Khi nim acid -base theo Bronsted-Lowry (1923) 2. Khi nim acid -base theo Lewis (1923) 3. Hng s cn bng acid base 4. Yu t nh hng n tnh acid -base ca cht hu c Chng 5: Cc loi phn ng trong ha hu c v khi nim v c ch phn ng ThS. Nguyn Anh Tun 1. Cc loi phn ng trong ha hu c 2. Khi nim v c ch phn ng Chng 6: Cc phng php ha hc v vt l xc nh cu to hp cht hu c ThS. Nguyn Anh Tun 1. Phng php ha hc 2. Phng php vt l Chng 7: Alkan - Hydrocarbon no ThS. Th Thy 1. Ngun gc thin nhin - Cu to, ng phn, cu dng 82 67 68 54 57 67 49 51 51 53 54 31 33 49 22 25 29 3 9 11 11 13 22

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2. Danh php 3. Phng php iu ch alkan 4. Tnh cht l hc 5. Tnh cht ha hc 6. Cht in hnh Chng 8: Cycloalkan ThS. Th Thy 1. Monocycloalkan 2. Hp cht a vng Chng 9: Alken - Hydrocarbon etylenic ThS. Th Thy 1. Cu to ca alken 2. ng phn 3. Danh php 4. Phng php iu ch 5. Tnh cht l hc 6. Tnh cht ha hc 7. Cht in hnh Chng 10: Alkyn - Hydrocarbon acetylenic ThS. Th Thy 1. Cu trc in t 2. Danh php v ng phn 3. Phng php iu ch 4. Tnh cht l hc 5. Tnh cht ha hc 6. Cht in hnh Chng 11: Aren - Hydrocarbon thm PGS. TS. ng Vn Tnh 1. Benzen v nhn thm 2. Danh php v ng phn 3. Phng php iu ch 4. Tnh cht l hc 5. Tnh cht ha hc Chng 12: Hydrocarbon a nhn thm PGSTS. ng Vn Tnh 1. Cu to v danh php 2. Biphenyl 3. Biphenylmetan v triphenylmetan 4. Naphtalen 5. Anthracen 6. Phenanthren

85 86 88 89 93

95 100 102 102 102 104 105 109 110 118 120 120 121 121 123 123 127 129 129 132 133 134 135 150 150 151 153 154 155 156

6

Chng13: H thng lin hp v alkadien PGS. TS. ng Vn Tnh 1. H thng allylic 2. Dien 3. H thng lin hp bc cao 4. Phn ng Diels Alder Chng 14: Dn xut halogen ThS. Trng Ngc Tuyn 1. Danh php 2. ng phn 3. Phng php iu ch 4. Tnh cht l hc 5. Tnh cht ha hc Chng 15: Hp cht c kim ThS. Trng Ngc Tuyn 1. Cu to 2. Danh php 3.Tnh cht l hc 4. Phng php iu ch cc hp cht c kim 5. Cc phn ng ca hp cht c kim Chng 16: Alcol ThS. Trng Ngc Tuyn 1. Monoalcol 2. Alcol cha no 3. Alcol vng 4. Polyalcol alcohol a chc Chng 17: Phenol ThS. Trng Ngc Tuyn 1. Monophenol 2. Polyphenol Chng 18: Ether ThS. Trng Ngc Tuyn 1. Ether mch h 2. Ether vng Chng 19: Aldehyd , Ceton v Quinon ThS. Nguyn Anh Tun 1. Aldehyd v ceton 2. Aldehyd - ceton cha no

158 158 161 164 165 168 168 169 169 173 173 181 181 181 182 182 184 189 189 200 201 201 207 207 215 219 219 223 224 224 245

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3. Aldehyd - ceton a chc 4. Quinon Chng 20: Acid carboxylic ThS. Nguyn Anh Tun 1. Cu to 2. Danh php 3. Phng php iu ch 4. Tnh cht l hc 5. Tnh cht ha hc 6. Acid carboxylic cha no 7. Acid a chc polyacid Chng 21: Cc dn xut ca acid carboxylic ThS. Nguyn Anh Tun 1. Ester 2. Anhydrid acid 3. Ceten 4. Halogenid acid - acyl halogenid 5. Amid 6. Nitril Chng 22: Amin TS. Phm Khnh Phong Lan 1. Cu to 2. Danh php 3. iu ch 4. Tnh cht l hc 5. Tnh base ca amin 6. Cc phn ng ca amin 7. Amin cha no c mt lin kt i Enamin 8. Amin a chc - polyamin Chng 23: Cc hp cht khc cha nit TS. Phm Khnh Phong Lan 1. Hp cht nitro 2. Isocyanat, carbamat v ure 3. Hp cht diazo v mui diazoni Chng 24: Hp cht c lu hunh v phosphor ThS. Th Thy 1. Hp cht hu c c lu hunh 2. Hp cht cha phosphor Ti liu tham kho

250 253 257 257 258 259 261 262 268 270 273 274 279 280 281 283 285 288 288 289 290 292 292 295 300 301 303 303 306 308 313 313 317 319

8

M U

i tng ca ha hc hu c: Ha hc hu c l mn khoa hc nghin cu thnh phn v tnh cht cc hp cht ca carbon. Trong thnh phn hp cht hu c, ngoi carbon cn c nhiu nguyn t khc nh H, O, N, S, P, halogen... nhng carbon c xem l nguyn t c bn cu to nn hp cht hu c. S lc lch s pht trin ca Ha hc hu c T xa xa ngi ta bit iu ch v s dng mt s cht hu c trong i sng nh gim (acid acetic long), ru (ethanol), mt s cht mu hu c. Thi k gi kim thut cc nh ha hc iu ch c mt s cht hu c nh ur, ether etylic... Cui th k 18 u th k 19, cc nh ha hc chit tch t ng, thc vt nhiu acid hu c nh acid oxalic, acid citric, acid lactic ... v mt s base hu c (alcaloid). Nm 1806 ln u tin nh ha hc ngi Thy in Berzelius dng danh t Ha hc hu c ch ngnh ha hc nghin cu cc hp cht c ngun gc ng vt v thc vt. Thi im ny c th xem nh ct mc nh du s ra i ca mn ha hc hu c. Nm 1815 Berzelius a ra thuyt Lc sng cho rng cc hp cht hu c ch c th c to ra trong c th ng vt v thc vt nh mt lc sng ch con ngi khng th iu ch c. Thuyt duy tm ny tn ti trong nhiu nm nhng dn dn b nh bi cc cng trnh tng hp cc cht hu c t cc cht v c. Nm 1824, nh ha hc ngi c Wohler tng hp c acid oxalic bng cch thy phn dixian l mt cht v c. Nm 1828 cng chnh ng, t cht v c amoni cyanat tng hp c ur. Tip theo Bertholet (Php) tng hp c cht bo nm 1854 v Bulerov (Nga) tng hp ng glucose t formalin nm 1861. Cho n nay hng triu cht hu c c tng hp trong phng th nghim v trn quy m cng nghip. Con ngi khng ch bt chc tng hp cc cht ging thin nhin m cn sng to ra nhiu cht hu c, nhiu vt liu hu c cc k quan trng v qu gi m t nhin khng c. Tuy nhin tn gi hp cht hu c vn c duy tr, nhng khng phi ch vi ngha l cc cht c ngun gc ng vt v thc vt m mang ni dung mi: l cc hp cht ca carbon.

9

c im ca cc hp cht hu c v phn ng hu c Mc d ra i mun hn ha hc v c nhng cc hp cht hu c rt phong ph v s lng, chng loi. S lng cht hu c cho n nay nhiu gp vi chc ln cc cht v c bit. Nguyn nhn c bn l do carbon c kh nng to thnh mch di v tn theo nhiu kiu khc nhau. Ni cch khc hin tng ng phn (tc l cc cht c cng thnh phn phn t nhng khc nhau v cu to) l cc k ph bin v c trng trong ha hc hu c. Cu trc phn t ca hp cht hu c c th n gin nhng cng c th rt phc tp, vic xc nh cu trc ca chng nhiu khi rt kh khn, phi s dng nhiu phng php ha hc v vt l hc hin i. Nu nh lin kt ion kh ph bin trong hp cht v c th lin kt ch yu gia cc nguyn t trong phn t hu c li l lin kt cng ha tr. c im ny nh hng nhiu n tnh cht l ha v c bit l kh nng phn ng ca chng. Cc phn ng hu c thng xy ra vi tc chm, khng hon ton v thng theo nhiu hng khc nhau, v vy vai tr ca nhit ng hc, ng hc v xc tc trong ha hu c rt quan trng. Vai tr ca ha hc hu c Cc cht hu c c vai tr rt quan trng trong i sng ca con ngi. Khng nhng hu ht thc phm chng ta n (glucid, protid, lipid), vt dng hng ngy (cellulose, si tng hp, cao su, cht do . . .) l cc cht hu c m nhiu cht hu c cn l c s ca s sng (protid, acid nucleic..). Nhin liu cho ng c t trong, cho nh my nh xng, du l hn hp hydrocarbon mch di ngn khc nhau. Cc vt liu hu c nh, khng han g, tin s dng, nhiu mu sc a dng ang ngy mt thay th cho cc kim loi, hp kim trong nhiu lnh vc, k c nhng lnh vc tng nh khng th thay th c nh bn dn, siu dn. . . Do tt c nhng c im trn, ha hc hu c c tch ra nh mt ngnh khoa hc ring i hi nhng phng php nghin cu v thit b ngy cng hin i hn, i hi n lc khng ngng ca cc nh ha hc khng nhng bt chc thin nhin tng hp nn cc cht phc tp phc v cho nhiu lnh vc ca cuc sng m cn vt xa hn c thin nhin. T c s ha hc hu c, c rt nhiu ngnh nghin cu ng dng ra i: ha cng nghip, ha du, cng nghip dt, ha thc phm, dc phm v ha m phm.

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Chng 1

CU TRC in t CA NGUYN T CARBON V S TO THNH CC LIN KT TRONG HP CHT HU C

Mc tiu 1. Trnh by c cu to in t carbon cc trng thi lai ha sp3, sp2 v sp. 2. Gii thch c cch hnh thnh cc loi lin kt: Cng ha tr Lin kt phi tr Lin kt hydro Ni dung 1. Cu trc in t (electron) ca nguyn t carbon 1.1. Thuyt carbon t din (Vant Hoff- Le Bel 1874) Nguyn t carbon c 4 ha tr. Bn ha tr ca carbon hng ra bn nh ca mt t din. Tm ca t din l nguyn t carbon.o C 109 28'

C

Cc gc ha tr tm u bng nhau v bng 10928'. Khi nguyn t carbon lin kt vi 4 nguyn t hoc 4 nhm th ng nht ta c mt t din u. 1.2. Cu trc in t ca nguyn t carbon 1.2.1. Carbon trng thi c bn2 2 1 1 Carbon c c cu hnh in t C 1S 2S 2px2py 1S22S22p2

1s22s22p2 2 in t n c l px v py. Cn c mt orbital 2pz trng khng c in t 1.2.2. Carbon trng thi kch thch C *1 1 1 1 1S22S 2px2py2pz

1S22S12p3

11

Carbon hp thu nng lng 60-70 kcal/mol, mt in t 2s2 chuyn ln trng thi 2p (orbital 2pz).1s2 2s2 2p2 1s2 2s

2px 2py 2pz

C 1s22s22p2

C 1s22s12p3

Carbon c cu hnh in t 1s22s12p3 l carbon kch thch (1s22s12px2py2pz). Kt qu l carbon c 4 in t n c to lin kt. Carbon lun c ha tr 4. Bn in t ca carbon kch thch c nng lng khc nhau do cc lin kt ca carbon phi khc nhau. Thc t phn t metan c 4 lin kt C _H hon ton ging nhau . 1.2.3. Carbon trng thi lai ha Khi to thnh cc lin kt, orbital 2s v mt s orbital 2p c th t hp li to thnh nhng orbital c dng khc cc orbital ban u v c kh nng xen ph cao hn do lin kt c hnh thnh cng bn hn. S t hp c gi l s lai ha. Lai ha sp3 Kiu lai ha th nht gi l lai ho sp3 (cn gi l lai ha t din). Mt orbital 2s v 3 orbital p t hp vi nhau to thnh 4 orbital lai ha sp3.

SS hp 2s v 2p 2p t to hp 2s va

Orbital ho sp Orbital lailai hoa sp

Carbon lai hoa sp3 Carbon lai ho sp3

Cc kt qu tnh ton cho thy rng nu xem kh nng xen ph ca orbital s l 1 th ca orbital p l 3 v ca orbital sp3 l 2.

1

3

2

Lai ha sp2. S t hp orbital 2s vi 2 orbital 2p (2px, 2py) to thnh 3 orbital lai ha sp2 hay cn gi l lai ha tam gic. Trc i xng ca 3 orbital sp2 nm trong mt mt phng v to nn nhng gc 120. Kh nng xen ph tng i ca orbital sp2 l 1,99. 12

120o

Pz

S t hp 2s2s va 2p S to hp v 2p

Carbon lai ho 2sp 2 Carbon lai hoa2sp

2

Orbital 2pz khng lai ho Orbital 2pz khonglai ho

Nh vy trn carbon lai ha sp2 cn c mt in t trn orbital 2pz khng lai ha. Orbital ny c dng hnh khi s 8 ni . Lai ha sp T hp mt orbital s v mt orbital 2px to thnh 2 orbital lai ha sp vi kh nng xen ph tng i 1, 93 v gc to bi trc i xng ca 2 orbital l 180o hay cn gi l lai ha ng thng. Trn carbon lai ha sp cn c 2 in t p khng tham gia lai ha 2py v 2pz

S to h 2s v 2p S t hpp 2s va 2p

Orbital lai ho sp Orbital lai ho a sp

2 Orbital 2py v 2pz 2 Orbital 2pyva 2pz

S lai ha gia orbital s v p cng xy ra trong cc nguyn t oxy, nit ... 2. S to thnh cc lin kt 2.1. S to thnh lin kt cng ha tr - Lin kt v lin kt Lin kt c to thnh do s xen ph cc i ca cc orbital nguyn t thnh orbital phn t. Khi vng xen ph ca cc orbital nguyn t cng ln th lin kt (orbital phn t) c to thnh cng bn v nng lng thot ra khi hnh thnh lin kt cng ln. Khuynh hng ca s xen ph l tin ti cc i, l ni dung ca nguyn l xen ph cc i . Cc orbital nguyn t tng tc c hiu qu vi nhau thnh orbital phn t chng phi tha mn 3 iu kin: Nng lng ca chng gn nhau . S xen ph mc ln. Chng phi c cng mt kiu i xng i vi trc ni hai ht nhn nguyn t. Nh vy 2 orbital s, hoc 1 orbital s v 1 orbital p no c trc i xng trng vi trc ni 2 ht nhn c th tham gia xen ph nhau thnh orbital phn t.

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Ty theo c im i xng ca cc orbital nguyn t, s xen ph ca chng c th theo trc hay bn trc ni gia 2 nguyn t. S xen ph theo trc orbital to lin kt . S xen ph bn xy ra s to thnh lin kt . Xen ph trc - To lin kt

Orbital s

Lin kt

Orbital s

Orbital p

Lin kt

Orbital p

Orbital p

Lin kt

Xen ph bn - To lin kt + Orbital p Lien ket

Orbital p

2.2. Lin kt v lin kt trong cc hp cht hu c 2.2.1. Trong cc hp cht hu c lin kt to thnh do s xen ph Orbital s ca nguyn t hydro vi cc orbital lai ha ca carbon sp3, sp2, sp. Orbital lai ha ca carbon xen ph vi nhau. Orbital lai ha s v p ca nguyn t oxy hoc ca nit vi orbital s ca hydro hoc vi cc orbital lai ha ca carbon sp3, sp2, sp trong cc hp cht c lin kt O-H hoc C-O v trong cc hp cht c lin kt N-H hoc C-N. 2.2.2. Lin kt

c to thnh do s xen ph

Orbital Py hoc Pz ca cc nguyn t carbon xen ph vi nhau tng i mt to thnh lin kt trong C=C hoc trong C C. Orbital p ca nguyn t oxy, nit xen ph vi orbital p ca nguyn t carbon to thnh lin kt trong C=O hoc trong C =N, CN. V d: S to thnh lin kt trong cc hp cht etan, ethylen, acetylen, alcol ethylic c th c minh ha nh sau:

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Cac lien ket Cc lin kt trong trongphn t etan etan phan t

HH H-C-C-H H H

H H Cc lin kt trong phn Cac lien ket C C trong t ethylen etylen H H phan t

Caclin ktket Cc lien trong phn tt acetylen H acetylen trong phan

C C H

Cc lin kt trong Cac lien ket phn t alcol ethylic trong phan t

H H C H

H C H O H

c-c H o-

alccol etylic

c-o

S to thnh lin kt trong phn t ethylen, acetylen c th minh ha nh sau:Lin kt trong ethylen c to thnh do s xen ph cc i v 2 pha ca cc orbital Pz khng lai ha. Lin kt (orbital phn t ) nm trong mt phng thng gc vi mt phng cha cc nguyn t C v H. H H H H Lin kt Lien ket trong ethylen H H trong etylen H H Hai lin kt trong acetylen c to thnh do s xen ph cc i v 2 pha ca cc orbital py v pz tng ng. Cc orbital lin kt nm trong 2 mt phng thng gc vi nhau.

HH

Cac trong phan t acetylen

Lin kt trong acetyle lien ket n

H

H

15

S to thnh lin kt trong h thng alen C=C=C .H H C

S to thnh lin kt trong h thng lin hp C =CC=C.H H

C

H thng lin hp thng thng v n gin l nhng h m hai lin kt v mt lin kt (hoc mt cp in t cha s dng) phn b cnh nhau (lun phin, tip cch). CH2=CH_CH=CH_CH=O ; CH2=CH_CH=CH_CH =CH_OCCH3 Trong h thng lin hp s xen ph bn ca cc orbital p to thnh mt orbital phn t bao trm ln ton b phn t.

S to thnh cc lin kt v trong h thng lin hp lm cho di lin kt ngn i v di ca lin kt di ra. H thng lin hp thng c trong cc cht thuc loi hydrocarbon thm, d vng thm. Cc lin kt trong h thng lin hp lun nm trong cng mt mt phng. 2.3. Tnh cht ca cc lin kt v 2.3.1. S phn cc ca lin kt Khi phn t c dng A _ A ng nht th phn t khng c s phn cc. Ngha l cp in t lin kt hay l orbital phn t lin kt c phn b u gia 2 nguyn t v momen lng cc ()bng khng. V d: H_H ; Cl_Cl ; O=O ; CH3_CH3 ; Cl3C_CCl3 ; CH2=CH2 ; HCCH .

Khi hai nguyn t lin kt vi nhau khng ng nht (phn t c dng A _B) nh H _Cl, CH3_Cl ... cp in t lin kt s lch v pha nguyn t c m in ln hn. Do trng tm in dng v m khng trng nhau v lin kt s c momen lng cc khc khng ( 0). l lin kt cng ha tr phn cc.S phn cc khng nhng xy ra cc lin kt kt (phn t c dng A =B hoc A B).

m cn xy ra cc lin

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Trong cc phn t H2C =O v CH3 _CN, v.v .. c s phn cc ca lin kt . ch s phn cc ca lin kt ngi ta dng mi tn thng ()v s phn cc ca lin kt ngi ta dng mi tn cong ( ). Chiu chuyn dch ca mi tn l chiu chuyn dch in t. Hoc dng k hiu +, - nhm biu th cc phn in tch nh nhng nguyn t tham gia lin kt . V d: CH3 Cl ; CH Cl ; H2C=O ; H2C=O hoc: H2C==O 3 2.3.2. tan Cc hp cht hu c c lin kt cng ha tr (l nhng lin kt c phn cc khng ln) rt t hoc khng tan trong nc, tri li tan nhiu trong cc dung mi hu c. Dung dch cc cht hu c thng l khng dn in. Cc cht c lin kt ion d tan trong nc v khng hoc t tan trong dung mi hu c, dung dch ca chng dn in. 2.3.3. di lin kt Khong cch gia 2 ht nhn nguyn t lin kt thng gi theo quy c l di lin kt. di lin kt c o bng cc phng php vt l hin i nh: phng php nhiu x tia X, ntron, electron, phng php ph hng ngoi. Ngi ta nhn thy rng:

+

+

+

di lin kt cng ha tr gia carbon v mt nguyn t khc trong cng mt phn nhm ca h thng tun hon tng theo s th t ca nguyn t .C_F < C_Cl < C_Br < C_I

di ca lin kt cng ha tr gia carbon v mt nguyn t khc trong cng mt chu k gim khi s th t tng.C _ C > C_ N > C _ O > C_ F

di ca lin kt cng ha tr gia 2 nguyn t cng gim nu s orbital lin kt cng ln.C_C > C= C > CC ; C_O > C=O > CO C_N > C=N > C N ; N_N > N=N > NN

di lin kt gia carbon vi mt nguyn t khc ph thuc trng thi lai ha ca carbon. T l orbital s trong orbital lai ha cng cao th di lin kt cng ngn.

C__H 3sp

C__H 2sp

C__Hsp

17

2.3.4. Nng lng lin ktNng lng ca lin kt A _B l s nng lng thot ra khi hnh thnh lin kt t 2 nguyn t hay 2 gc A v B. cng chnh l nng lng cn thit lm t lin kt A _B thnh 2 nguyn t hay 2 gc A v B.Bng 1.1: Nng lng lin kt (kcal/mol)Lin kt H-H F-F Cl-Cl Br-Br I-I N-N N=N NN P-P C-C C=C CC Si-Si O-H N-H Nng lng lin kt 104,2 36,4 58,0 46,1 36,1 38,4 100,0 226,0 51,3 83,1 147,2 194,0 42,2 110,6 93,6 Lin kt C-H C-F C-Cl C-Br C-I C-O C=O C -O C-N C=N CN H-F H-Cl H-Br H-I+

Nng lng lin kt 98,8 105,4 78,5 65,9 57,4 84,0 171,0 255,8 69,7 147,0 213,0 134,6 103,2 87,5 71,5

Nng lng lin kt l gi tr trung bnh gn ng. Khi dng khi nim nng lng lin kt c ngha l tt c cc lin kt C_H trong phn t alkan u ging nhau (thc t nng lng ph thuc vo cu to phn t). Qua bng 1-1 c th thy rng cc lin kt bi (i = ; ba ) khng c tnh cht bi v nng lng. Nng lng lin kt C =C v C C khng ln gp i v gp 3 ln lin kt C _C. Tri li nng lng ca cc lin kt N =N v N N li gp 3 v gp 6 ln nng lng lin kt N _N. Trong cc phn t c h thng lin hp th gi tr sinh nhit ca n thp hn tng gi tr nng lng lin kt ca cc lin kt c trong phn t c h thng khng lin hp. chnh lch gi l nng lng lin hp hoc nng lng cng hng ca h thng lin hp. Cn phn bit nng lng lin kt v nng lng phn ly. Nng lng phn ly l nhng i lng c trng cho cc lin kt trong phn t. Nng lng cn lm t lin kt CH th nht khng phi bng 1/4 nng lng chung phn ct phn t metan thnh carbon v hydro, cng khng hon ton bng nng lng ca mi lin kt CH trong cc phn t etan v benzen. Mi lin kt trong phn t c mc nng lng phn ly khc nhau (bng 1-2). 18

Bng 1.2: Nng lng phn ly lin kt R-X (kcal/mol)R CH3 CH3CH2 (CH3)2CH (CH3)3C C6H5 C6H5CH2 X H 102 98 89 85 104 77,5 Br 67 65 65 61 71 48 51 52 47 45 57 39 I OH 86,5 87, 84,5 85, 85, 85, CH3 83 82 74 74 91 63 R 83 82 82 60 103 47

HO-OH ---------------------------------

52 (CH3)2 C N = N C (CH3)2 31 CN CN

C6H5COO-OCC6H5 -----------------

30

(C6H5)3C N = N C(C6H5)3 27

2.4. S to thnh lin kt yu hn lin kt cng ha tr 2.4.1. Lin kt hydro Lin kt hydro c bn cht tnh in. Nng lng lin kt nh ( 5kcal/mol).

X___H+ ... Y ; Xiu kin hnh thnh lin kt hydro:

H+ ... Y

X c m in ln hn hydro sao cho X __H phn cc . Y c cp in t t do e . Kch thc ca X v Y u khng ln .X v Y thng l nhng nguyn t ph bin nh F, O, N . Trng hp Y l Cl, S, lin kt th lin kt hydro to thnh s rt yu. C hai loi lin kt hydro:

Lin kt hydro lin phn tLin kt hydro c to thnh gia cc phn t vi nhau. Khi pha long hp cht c lin kt hydro lin phn t trong dung mi tr (khng phn cc), lin kt hydro b ct t dn.Et Et O...H H O ... ...H ... H O O Et Et H__C O ... H O O H ... O C__H

Lin kt hydro ni phn tLin kt hydro c to thnh trong cng mt phn t. Khi pha long hp cht c lin kt hydro ni phn t, lin kt hydro vn c bo ton. hnh thnh lin kt hydro ni phn t ngoi cc iu kin 19

trn, XH v Y phi gn nhau sao cho khi to lin kt hydro s hnh thnh nhng vng 5 hoc 6 cnh. Cc hp cht vng c nhm chc v tr 1, 2 thng d hnh thnh lin kt hydro ni phn t.OH C O O. H H .. . NH2 CH2

. .

O CH2

2.4.2. nh hng ca lin kt hydro n tnh cht l -ha hc v sinh hc S to thnh lin kt hydro nh hng n tnh cht ca hp cht hu c.

Nhit nng chy v nhit siLin kt hydro lin phn t lm tng nhit nng chy tc v tng nhit si tos nhng lin kt hydro ni phn t khng c nh hng ny. V d. Hp cht nitrophenol c 3 ng phn th ng phn p-nitrophenol c lin kt hydro lin phn t c toc l 144C v toc l 241C. ng phn o-nitrophenol (c lin kt hydro ni toc phn t) c toc l 44C v tos l 114C .O N O ... H O N O OH ...O N O OH ...O N O OH

...

O

Lin kt hydro gia cc phn t p -nitrophenol

Lin kt hydro ni phn t o -nitrophenol

tanCc cht c kh nng to lin kt hydro vi nc th rt d tan vo nc. Lin kt hydro lin phn t gia cht tan v dung mi lm tng tan trong dung mi phn cc. Lin kt hydro ni phn t lm tng tan trong dung mi khng phn cc. V d: Alcol methanol, ethanol rt d tan trong nc. p-nitrophenol tan c trong nc, cn o -nitrophenol khng tan trong nc. V vy c th phn ring o -nitrophenol ra khi hn hp bng phng php ct li cun hi nc.

bn ca phn tS to thnh lin kt hydro ni phn t, c bit khi lin kt c kh nng to vng, lm cho ng phn tr nn bn vng hn. V d: Khi 1,2 -dicloethan dng anti bn vng hn dng syn th ethylenglycol dng syn li bn hn dng anti. V syn-ethylenglycol c kh nng to lin kt hydro ni phn t. 20

Anti-dicloetan

Syn-dicloetan

Anti-ethylenglycol

Syn-ethylenglycol

* Thut ng anti v syn s c trnh by chng ng phn.

nh hng n mt s tnh cht khcLin kt hydro lm thay i cc vch c trng trong quang ph hng ngoi (IR), t ngoi (UV), cng hng t ht nhn (NMR), momen lng cc, di lin kt. Lin kt hydro cng c tc dng lm thay i s tng tc ca cc cht trong qu trnh chuyn ha sinh hc trong c th ng vt v thc vt. 2.4.3. Lin kt trong phc chuyn in tch Phc chuyn in tch to thnh do s chuyn dch mt phn mt in t t phn t cho in t sang phn t hay ion nhn in t. Phc chuyn in tch do s chuyn dch mt in t gi l phc .CH 3 NO2 Phc to thnh gia toluen v trinitrobenzen O2N NO2 Phn t nhn

Lin kt trong phc chuyn in tch l lin kt yu. Khong cch gia 2 hp phn vo khong 3 - 3,5 ln hn nhiu so vi lin kt cng ha tr. Phc chuyn in tch c s thay i v phn cc v mu sc ca cc cht ban u. Bi tp 1. V m hnh orbital nguyn t trng thi xen ph cho cc hp cht sau: a- Propan, propylen, methylacetylen, ceten (HC2=C=O). b- Cyclobutan, Cyclopentan, Cyclohexan. c- 1,3-Butadien 2. Hy trnh by mt s nh ngha: a- Th no l lin kt cng ha tr, lin kt hydro ? b- Th no l nng lng lin kt v nng lng phn ly, nng lng cng hng ? 3. Trong hn hp phenol - methanol c bao nhiu "dng" lin kt hydro. Dng no bn nht ? Dng no km bn nht ? Ti sao ? 4. Alcol v ether, cht no d tan trong nc hn. Gii thch ?

21

Chng 2

Cc HIU NG IN T TRONG HA HU C

Mc tiu 1. Nu c cc loi hiu ng cm ng, hiu ng lin hp, hiu ng siu lin hp v tnh cht ca chng. 2. Bit c mt s ng dng ca cc hiu ng trn. Ni dung Mt in t trong lin kt cng ha tr thng c phn b khng ng u gia 2 nguyn t ca lin kt, khi y phn t cht hu c b phn cc. S phn cc c th xy ra ngay trng thi tnh hoc cng c th ch xut hin nht thi trng thi ng (khi phn t b tc ng bi cc yu t ca mi trng). Bn cht ca s phn cc khc nhau cn tu thuc vo cu to phn t (phn t c h thng lin kt nh th no). Nh vy cu to phn t c nh hng n s phn b mt in t. nh hng gi l hiu ng in t trong phn t. C cc loi hiu ng:

Hiu ng cm ng I Hiu ng lin hp C, M Hiu ng siu lin hp H1. Hiu ng cm ng (Inductive effect): K hiu l I Kho st phn t n -propan C3H8 v phn t n-propylclorid C3H7ClH H H H H

C3 C 2 C1 H n-propan n-propanH

H

H H + + + 3 2 1 H C C C Cl 3 2 1 H

H

n-propylclorur n-propyclorid

H

H

Trong phn t n -propylclorid, lin kt C1 Cl b phn cc v pha nguyn t clor v nguyn t clor c m in ln hn. Nguyn t clor mang mt phn in tch m v nguyn t carbon mang mt phn in tch dng +. V C1 mang in tch dng nn cp in t lin kt ca lin kt C2 C1 b dch chuyn v pha carbon C1. Kt qu l lin kt C2 C1 cng b phn cc theo. Nguyn t C2 mang mt phn in tch dng. n lt lin kt C3 C2 cng chu nh hng nh vy v kt qu nguyn t carbon C3 mang mt phn in tch dng. Nhng 1+ >2+ >3+. Cc lin kt cng chu nh hng nh th v kt qu c s phn cc 22

ca lin kt C H. Hydro tr nn linh ng hn. Hin tng ny khng ch xy ra vi phn t propan. Nh vy nh hng s phn cc ca lin kt C -Cl lm cho cc lin kt khc b phn cc theo v ton phn t b phn cc. Nguyn t clor l nguyn t gy nh hng cm ng. S phn cc hay s chuyn dch mt in t trong cc lin kt gi l hiu ng cm ng. Hiu ng cm ng k hiu l I hoc I (ch u ca inductive) phn loi cc nhm nguyn t theo hiu ng cm ng ngi ta quy c rng nguyn t hydro lin kt vi carbon trong C __ H c hiu ng I = 0. Nhng nguyn t hay nhm nguyn t X c kh nng ht in t (CX) mnh hn hydro c coi l c hiu ng - I (hiu ng cm ng m). Nhng nguyn t hay nhm nguyn t Y c kh nng y in t (YC) mnh hn hydro c coi l nhng nhm c hiu ng +I (hiu ng cm ng dng)

Y +I1.1. Hiu ng cm ng + I

C

C

H I=0

C

-I

X

Thng thy cc nhm alkyl (R-) v cc nhm mang in tch m. Trong dy cc nhm alkyl, hiu ng cm ng +I tng theo phn nhnh hay l bc ca nhm .

+I

CH3

CH2 CH3

CH CH3 CH3

CH3 C CH3 CH3

Trong dy cc nhm mang in tch m, nhm c m in nh hn l nhm c hiu ng + I ln hn . -O- < -S- < -Se1.2. Hiu ng cm ng - I L hiu ng rt ph bin cc nhm khng no, cc nhm mang in tch dng v cc nhm ng vi nhng nguyn t c m in ln (nh cc halogen, oxy, nit). S bin thin mc mnh yu ca hiu ng - I trong cc nhm nguyn t tun theo mt s quy lut:

Nguyn t carbon lai ha sp c -I ln hn nguyn t carbon lai ha sp2 v sp3-CCR > -CR1=CR2 > -CR2_CR3.

Nhm mang in tch dng c hiu ng -I ln hn nhm c cng cu to nhng khng mang in tch.-OR2 > -OR+

-NR3 > -NR2

+

23

Cc nguyn t ca nhng nguyn t trong cng mt chu k nh hay trong cng mt phn nhm chnh ca h thng tun hon, hiu ng -I cng ln khi nguyn t tng ng cng bn phi (trong cng chu k) hoc cng pha trn trong cng phn nhm).-F > -Cl > -Br > -I -F > -OR > -NR2 > -CH3. -OR > -SR > -SeR m in cng tng th hiu ng cm ng - I cng ln Biu hin c th ca hiu ng cm ng l nh hng ca cc nhm th khc nhau n lc acid v lc base ca cc acid carboxylic no v ca cc amin. Trn bng 2-1, ngi ta nhn thy rng nu thay th hydro ca acid formic bng cc gc alkyl c + I tng th kh nng phn ly ca acid gim. Cn ln lt thay th cc hydro ca amoniac bng cc gc alkyl c +I tng th tnh base tng ln. Hiu ng + I tng lm cho lin kt O __ H km phn ly.H_COOH CH3 C O O H

Khi thay th hydro ca amoniac bng cc nhm c hiu ng + I, mt in t trn nguyn t nit tng ln do tnh base ca amin tng.CH3 CH3 N: CH3

H_NH2

..

CH3 NH2

..

Bng 2.1. nh hng hiu ng cm ng n tnh acid base

Lc acid giam khi +I tang Acid hu cHCOOH CH3COOH CH3CH2COOH CH3CH2CH2COOH (CH3)2CHCOOH pKa (H2O.25o) 3,75 4,76 4,87 4,82 4,86

Lc base tang khi +I tang Base hu c pKa (H2O.25o)NH3 CH3NH2 CH3CH2NH2 (CH3)2NH (CH3)3N 9,10 10,62 10,63 10.77 9,8*

Ch : *S d tnh base ca trimethylamin khng tng l do hiu ng khng gian.

Hiu ng - I tng, lc acid tng. Khi thay th hydro ca CH3 trong acid acetic bng cc halogen c m in khc nhau th tnh acid thay i. Nguyn t halogen c hiu ng -I ht in t nh hng n s phn ly ca nhm O _H.F CH2 C O H O pKa 2,58 Cl CH2C O H O 2,85 Br CH2C O H O 2,9 I CH2 C O H O 3,16 H CH2 C O H O 4,76

24

c im quan trng ca hiu ng cm ng l hiu ng cm ng lan truyn trn mch lin kt v yu dn khi chiu di ca mch carbon tng ln.CH3CH2CH2COOH 4,82 pKa CH3CH2CHClCOOH 2,86

CH3CHClCH2COOH 4,05

CH2ClCH2CH2COOH 4,42

2. Hiu ng lin hp (cng hng) 2.1. H thng lin hp H thng lin hp l mt h thng:

Cc lin kt bi (i, ba) lun phin vi lin kt n.C=C-C=C-C=C( - ) C=C-C=C-C=O(- ).

H thng cha nguyn t cn cp in t p t do khng lin kt trc tip vi nguyn t carbon c lin kt bi.

-C=C-O-R

..

-C=C-Cl

..

( p- )

Phn t cha h thng lin hp l phn t lin hp. 2.1.1. Phn loi h thng lin hp nh sau:

H thng lin hp - H thng lin hp khng vngCH2=CH_CH=CH2 1,3-Butadien CH2=C_CH=CH2 CH3 2-methyl-1,3-butadien (izopren)

CH2 = CH CH = OAldehyd acrylic

CH2 = CH C NAcrylonitril

CH2 = CH C = OAcid acrylic OH

H thng vng.. O

H thng lin hp p - H thng lin kt lin hp do tng tc gia in t p t do vi lin kt .CH2=CH_Cl Vinylclorid

..

CH2=CH_OCH3 Methylvinyl ether Phenol Anilin

..

:OH

:NH2

2.1.2. c im ca h thng lin hp Trong phn t khng ch c lin kt i hoc lin kt n ring: 25

CH2=CH_CH2_CH=CH2 ;Khng lin hp

CH2=CH_CH=CH_CH3 ;Lin hp

CH=CH_CH2_OCH3Khng lin hp

Cc nguyn t to h lin hp lun nm trong mt mt phng v trc ca cc oirbtal p song song vi nhau v thng gc vi mt phng cha cc lin kt .

Butadien

Benzen

phenol

Phn t lin hp bao gi cng c nng lng thp hn nng lng ca nhng phn t khng lin hp tng ng. V mt in t gn nh gii ta ng u trn cc nguyn t to h thng lin hp v to thnh mt orbital phn t gii ta trn ton b phn t.C C C C

Orbital phn t trong h thng lin hp rt d bin dng v d phn cc khi cu to ca phn t lin hp c mt nguyn t chnh lch v m in. Nh vy trong h lin hp c s tng tc gia cc orbital p vi nhau. S tng tc gi l hiu ng lin hp. 2.2. Hiu ng lin hp C (M) Hiu ng lin hp l hiu ng sinh ra do s phn cc ca lin kt c lan truyn trong h thng lin hp Hiu ng lin hp c k hiu l C (Conjugate effect) hoc M (Mesomeric effect) 2.2.1. Phn loi hiu ng lin hp Cn c vo s dch chuyn in t ca cc in t . C hai loi hiu ng lin hp: Hiu ng lin hp + C v Hiu ng lin hp - C

Hiu ng lin hp - CNu thay th nguyn t hydro trong nhm CH2 ca butadien bng nhm CH = O, nhm ny tham gia lin hp vi orbital phn t ca butadien. Nh c c tnh phn cc ca nhm CH =O nn ton b orbital mi hnh thnh ca phn t b dch chuyn mt phn v pha nguyn t oxy.CH2 CH CH CH CH O

Nhm CH = O c hiu ng lin hp theo c ch ht in t nn c gi l nhm c hiu ng - C.

26

Cc nhm c hiu ng - C l nhng nhm khng no c cng thc chung C =Y, CZ v mt s nhm khc khng cha carbon nh - NO2, - SO3H... Hng chuyn dch in t trong h thng c nhm vi hiu ng - C c m t bng mi tn cong. Nhm c hiu ng -C thng c thm hiu ng cm ng - I. Cc nhm chc c hiu ng -C :C .. O : Cl : ..

..

C O .. H

..

C O .. CH3

..

C O .. : OR ..

..

:OH ..

C O ..

..

: NH2 ..

C O ..

..

C O .. :O ..

..

CR = O > CR > CR = CR2 NO2 > O N > O CR Hiu ng lin hp +C Cc nguyn t hay nhm nguyn t c hiu ng lin hp +C l nhng nhm c kh nng y in t. Cc nhm ny thng c nguyn t mang cp in t p t do. Chnh cp in t p ny lin hp vi cc lin kt trong h thng lin hp.CH2=CH_OCH3

..

CH2=CH_Cl: ..

..

Cc nhm c hiu ng + C :

-NH2 > -OH ; -O- > -OH

-F > -Cl > -Br > -I -NR2 > -OR > -SR > -SeR

Cc nhm c hiu ng + C thng c thm hiu ng cm ng - I.Hiu ng lin hp c ng dng rng ri gii thch c ch phn ng, cc cu to trung gian, bn ca cc ion, tnh acid -base ...

Hiu ng lin hp c nh hng n s dch chuyn in t. Chng c cc cng thc trung gian hay cn gi l cng thc gii hn nh sau:V d: Butadien-1,3:CH2 CH CH CH2 CH2 CH + CH CH2 + CH2 CH CH CH2

Aldehyd crotonic:CH3 CH CH CH O + CH3 CH CH CH O

-

CH3

+ CH

CH

CH O

-

Phenol

:OH-

+OH

+OH

+OH -

OH

-

Hp cht c h thng lin hp cng di th c nhiu cng thc gii hn. bn ca cc cng thc gii hn ph thuc vo khong cch gia 2 in tch tri du. in tch tri du cng xa nhau th cng thc gii hn cng bn. 27

Khc vi hiu ng cm ng, nh hng ca hiu ng lin hp khng b gim i khi h lin hp ko di.V d: Nguyn t hydro trong nhm CH3 ca aldehyd crotonic linh ng do nh hng ca hiu ng lin hp.H

: CH3 CH CH CH aldehid crotonic Aldehyd crotonic

O

Nu ko di mch aldehyd crotonic bng cc nhm vinyl th hydro ca nhm CH3 vn cn linh ng.H

: CH2

CH

CH

CH

CH

CH

CH CH

O

Hiu ng lin hp lm thay i trung tm phn ng:V d: C hp cht sau:..C O CH CH NH2 C OCH CH + NH2

Trong h thng lin hp p -, cp in t p khng lin kt trn nguyn t N lin hp vi h thng lin kt . Nhm NH2 gy hiu ng lin hp + C. Nhm NH2 c tnh base c kh nng tc dng vi proton H+. Nhng do hiu ng lin hp, H+ khng tc dng vo nhm amin NH2 m tc dng vo nguyn t oxy ca nhm carbonyl.C CH CH O + NH 2 + H+ C CH CH OH + NH 2

nh hng ca hiu ng lin hp ch xy ra trong h thng phng:V d: Phenol (I) c tnh acid v nhm OH c hiu ng lin hp +C. p-Nitrophenol (II) c tnh acid mnh hn phenol v nhm -NO2 c hiu ng lin hp - C. Thay 2 nhm CH3 vo v tr orto so vi nhm OH c cht (III). Cht (III) c tnh acid gim cht t so vi (II). Nhng a 2 nhm CH3 vo v tr orto so vi nhm NO2 c cht (IV). Cht (IV) c tnh acid yu hn (II). iu chng t 2 nhm CH3 lm cho nhm NO2 khng c hiu ng lin hp - C nh hng n chc phenol.OH OH CH3 OH CH3 CH3 I OH

pKa

9.98

NO2 II 7,16

NO2 III 7,21

CH3 NO2 IV 8,24

S d c iu v trong (III) nhm NO2 khng nm trong cng mt phng vi vng benzen. Hai nhm CH3 c cn tr khng gian lm cho nhm NO2 b lch ra khi mt phng ca vng benzen. Hiu ng lin hp ca nhm NO2 khng pht huy tc dng. 28

CH3 HO II

..

N O O

HO IV

..

N O O CH3

3. Hiu ng siu lin hp (Hyperconjugate effect) Ngoi s lin hp - v p - nu trn cn c s lin hp - gia cc orbital ca cc lin kt C H trong nhm alkyl v orbital ca ni i, ni ba hay vng thm.H H H C C C CH3 H 3 lin kt 3 lien ket H H C C C CH3 H 22 lien ket lin kt H H C C C CH3 CH3 H C H

1 lin kt 1lien ket

3 lin kt 3 lien ket

S tng tc lin hp gia orbital ca lin kt C - H vi orbital ca lin kt i, ba hoc h thng lin hp gi l hiu ng siu lin hp.

Hiu ng siu lin hp c k hiu l H. Hiu ng siu lin hp khng nhng lm thay i bn cht ca lin kt i m cn lm thay i c tnh cht ca lin kt n C - H. Hiu ng siu lin hp lm thay i hng cng hp vo lin kt i.V d: Trong phn t 2-penten, nhm C2H5 c hiu ng + I ln hn nhm CH3. Phn t 2-penten cng hp vi HBr ng l phi to thnh 3-bromopentan. Nhng thc t thu c 2-bromopentan. iu chng t nh hng siu lin hp ca nhm CH3 ln hn nh hng siu lin hp ca nhm C2H5 nh hng n hng cng hp.H H C CH CH H CH2 CH3 + HBr H H C CHBr CH2 H CH2 CH3

Hiu ng siu lin hp nh hng n tnh cht linh ng ca lin kt C H trong gc alkyl.V d: Nguyn t hydro trong nhm CH3 ca aldehyd acetic d dng b ct t trong mi trng kim to carbanion.H H C CH H O

+

HO -

H H C CH Carbanion

O + H2 O

Carbanion to thnh c h thng lin hp p - . V vy carbanion ny c th c cng thc gii hn:H H C CH

-

O

H H C CH

O

-

Hin tng trn cn th hin trong hp cht ester ethylacetoacetat CH3COCH2COOC2H5. Lin kt C H ca nhm CH2 c siu lin hp vi nhm 29

carbonyl C =O. Hydro ca CH2 tr nn linh ng v d dng b ct t trong mi trng base to thnh carbanion.CH3 C O H. . C C H O OC2H5

+ OH -

CH3 C

C C OC2H5 + H2O O H O Carbanion

Carbanion to thnh c h thng lin hp p - do c th c cc cng thc gii hn.CH3 C C C OC2H5 O: H O .. Carbanion CH3 C

:O : ..

C H

C O

OC2H5

Hiu ng siu lin hp tng theo s lng lin kt C _H v tr .CH3- > CH3CH2- > (CH3)2CH- > (CH3)3C -

Hiu ng siu lin hp v hiu ng cm ng +I lun xy ra cng hng. Hin tng phn b li mt in t cn c th c trong cc trng hp h thng carbanion v carbocation.V d: Carbocation allylic CH2=CHCH+ v carbanion allylic CH2=CHCH-.+ CH2=CH_CH2

CH2=CH_CH2

Trong carbocation c hin tng dch chuyn in t t lin kt n orbital trng ca nguyn t carbon. Trong carbanion c hin tng dch chuyn cp in t t do ca carbon n lin kt .

Bi tp1. Pht biu nh ngha v hiu ng cm ng, hiu ng lin hp v siu lin hp. 2. So snh hiu ng cm ng v hiu ng lin hp v bn cht, c tnh v quy lut. 3. Cn c vo hiu ng in t c th c so snh v gii thch tnh acid ca cc cht trong cc dy sau: a- n-C4H8ClCOOH, nguyn t clo cc v tr khc nhau . b- m-ClC6H4(CH2)nCOOHn = 0,1,2 . c- m-ClC6H4(CH2)nCOOHn = 0,1,2 4. Vit cng thc gii hn ca sn phm to thnh khi:

a-

NH2 C NH2

Guanidin bC CH2 C CH2 O O + HO -

NH

+ H+

30

Chng 3

CU TRC PHN T HP CHT HU C NG PHN V CU DNG

Mc tiu hc tp 1. Trnh by c cc loi ng phn gp trong Ha hu c. 2. c c tn cu hnh cc hp cht hu c dng Z, E v R,S. 3. Xc nh c cu dng gh ca dn cht cycloalkan.

Ni dungCc hp cht hu c c cu to theo mt trt t xc nh. Cng thc phn t cho bit thnh phn v s lng nguyn t c trong mt phn t. Cng thc cu to phn nh bn cht v th t sp xp cc lin kt trong phn t. Mt cng thc phn t c th c nhiu cng thc cu to khc nhau hoc nhng cht khc nhau. Hin tng mt cng thc phn t ng vi hai hoc nhiu cng thc cu to khc nhau c gi l hin tng ng phn (isomery). Thut ng isomery xut pht t ting Hy Lp "isos" c ngha l "cng" v "meros"c ngha l "phn". Da vo c im cu trc ngi ta chia thnh 2 loi ng phn: ng phn phng v ng phn lp th (ng phn khng gian) 1. ng phn phng Cc nguyn t v nhm nguyn t trong phn t cht hu c u cng nm trong mt mt phng. Cc ng phn ch khc nhau v v tr v th t lin kt gia cc nguyn t to thnh phn t. ng phn phng c cc loi sau: 1.1. ng phn mch carbon C mch carbon sp xp khc nhau. Mch thng hoc phn nhnh.CH3 CH2 CH2 CH3 CH3 CH CH3 iso Butan CH3

n- Butan

CH3 CH3 CH2 CH2 CH2 CH3 CH3 CH CH3 CH2 CH3 CH3 C CH3 neo Pentan CH3

n- Pentan

iso Pentan

31

1.2. ng phn v tr nhm nh chc Nhm nh chc trn mch carbon cc v tr khc nhau. Dng cc ch s ch v tr nhm chc trn mch chnh ca mch carbon.CH3 CH3 CH2 CH2 CH2 OH CH3 CH OH CH CH3 CH3 C OH CH3

1-Butanol CH3 CH2 CH CH2

2- Butanol CH3 CH

2-methyl-2-propanol CH CH3

1-Buten

2- Buten

1.3. ng phn nhm chc C nhm chc khc nhau.CH3 COOH HO CH2 CHO H COOCH3 CH3 CH2 CHO CH3 C O CH3

Acid acetic

Aldehyd glycolic

Ester methyl formiat Aldehyd propionic

Aceton

1.4. ng phn lin kt Cc nguyn t trong phn t c cch lin kt khc nhauCH3 CH2 CH1- Buten

CH2

CH2 CH2 CH2 CH2Cyclobutan

CH2=CH-CH=CH21,3-Butadien

CH3-CH-CCH1-Butyn

CH3-CC-CH32-Butyn

S h bin C cc trng hp cc ng phn vi nhau nhng chng khng bn trong nhng iu kin xc nh v chng c th thay i cho nhau to thnh hn hp cn bng. Hin tng ny gi l s h bin (hin tng tautomer - mesomer) V d: Ester ethyl acetoacetat CH3COCH2COOC2H5 c 2 ng phn. Hai ng phn ny c th phn ring tng cht ch nhit -78C. Hai ng phn c dng ceton v dng enol. nhit cao hn khng th phn ring chng c. Chng tn ti nh l mt hn hp 2 cht trng thi cn bng. Dng ceton lun bin i thnh dng enol v ngc li. Khi nng cc cht trong hn hp c xc nh th chng t n trng thi cn bng. Chng l 2 ng phn h bin (mesomer). 32

CH3 C CH2 COOOC2H5 O Ester ethyl acetoacetat Dng ceton

CH3 C CH COOOC2H5 OH Ester ethyl acetoacetat Dng enol

2. ng phn lp th - ng phn khng gian ng phn lp th hay cn gi l ng phn khng gian c cng cng thc cu to nhng khc nhau v s phn b khng gian (phn b lp th) ca cc nguyn t hay nhm nguyn t trong phn t. Tnh cht v phn ng ca cc cht hu c lin quan cht ch vi s phn b khng gian ca cc nguyn t trong cu trc ca chng. C cc loi ng phn khng gian: ng phn hnh hc ng phn quang hc ng phn cu dng 2.1. ng phn hnh hc 2.1.1. Cu to v danh php ng phn hnh hc C th biu din cng thc ca ethylen theo dng khng gian: H H H HH H H

H

S phn b ca cc nguyn t hydro nm v 2 pha ca mt phng cha lin kt (mt phng ). Cc nguyn t carbon khng th quay t do xung quanh lin kt c v s cn tr ca mt phng . Nu thay th cc nguyn t hydro ca etylen bng cc nguyn t hoc nhm nguyn t khc nhau th s phn b khng gian ca chng so vi mt phng s khc nhau. S phn b v 2 pha ca mt phng cng thng gp trong hp cht vng.H H H H H H H H H HH H H H

S phn b khng gian ca cc nguyn t hay nhm nguyn t v 2 pha ca mt phng hay mt phng ca vng lm xut hin mt loi ng phn. l ng phn hnh hc. ng phn hnh hc l nhng hp cht c cng cng thc phn t nhng c v tr khng gian ca cc nguyn t hay nhm nguyn t khc nhau i vi mt phng hoc mt phng ca vng. 33

2.1.2. Phn loi ng phn hnh hc

C 2 loi ng phn hnh hc: ng phn cis v ng phn trans. + Dng cis ch ng phn c 2 nguyn t hoc nhm nguyn t ging nhau cng mt pha i vi mt phng hay mt phng vng. + Dng trans ch ng phn c 2 nguyn t hoc nhm nguyn t khc pha vi mt phng hay mt phng vng.CH3 C H C H H CH3 CH3 C C CH3 H CH3 C H CH3 Mat phang CH3 C H H

Cis Cis 2-buten

Trans Trans 2-buten

CH

CCH3

Tng qut: Hp cht c lin kt c dng abC =Cab , acC=Cab lun tn ti ng phn hnh hc cis v trans.

abC=Cab a bC C

acC=Cab a bC C

a b

b a

a c

C

C

a b

a c

C

C

b a

Cau hnh cis

Cau hnh trans

Cau hnh cis

Cau hnh trans

V d:H HOOC C C H H HOOC C C COOH H H H HOOC C C COOH C C HOOC cis CH3 Acid isocrotonic CH3 H

cis

trans

H

trans

Acid maleic

Acid fumaric

Acid crotonic

Trng hp hp cht c dng tng qut abC =Ccd cng c ng phn hnh hc vi a,b,c, d l nhng nguyn t hay nhm th hon ton khc nhau v " ln ".

S phn b khng gian cc nhm th ln v mt pha ta c ng phn Z v khc pha ta c ng phn E. Z v E l nhng ch u ca Zusammen (cng pha) v Eintgegen (khc pha).Nu a > b, c > d.a b C C c d abC=Ccd a a>b;c>d b C C d

Cau hnh Z (cis)

c Cau hnh E (trans) H

V d:I Br C C Cl I C C

Br H Cl E Z 1-Brom-1-Iod-2-Cloethylen

I > Br > Cl > H 34

V th I > Br ; Cl > E

OHC H3C C Z C

COOH H

OHC H3C C E C

H COOH

COOH > CHO > CH3 > H

;

CHO > CH3; COOH > H

Nguyn tc xc nh ln ca nguyn t v nhm nguyn t: + Nguyn t c s th t trong bng tun hon cng ln th ln ca n cng lnI > Br > Cl > S > P > F > O > N > C > H -CH2Cl > -CH2OH > -CH2CH3CH OCH3 CH2 CH3

>

OH CH CH2 CH3

+ Nu trong mt nhm nguyn t c mt nguyn t lin kt vi ni i, ni ba th xem nh nguyn t c 2 ln, 3 ln lin kt vi nguyn t kia.CH = CH2 CH C CH2 CCH = O C O O

C

Cho nn:CH CH3 CH2CH3

>

CH

CH2

>

CH

CH3 CH3

-COOCH3 > -COOH > -CONH2 > -COCH3 > -CHO -CN > -C6H5 > -CCH > -CH=CH2 S ng phn hnh hc tng ln nu phn t c nhiu lin kt i V d: Phn t 1,4-diphenyl-1, 3-butadien c 3 ng phn hnh hcC6H5 C H C H C C H C6H5 C H C H C C C6H5 H C C6H5 C H H C C C6H5 H

C6H5 H Trans-trans

H H Trans-cis

Cis-cis

35

ng phn hnh hc trong cc hp cht vngCH3 cis CH3 H H trans H 1,3-Dimethylcyclobutan CH3 H CH3 Cl Cl ClH

H trans Cl H H cis 1,3-Diclocyclohexan

Cc trng hp khc v ng phn hnh hc.ng phn hnh hc trong h thng ethylen phc tpCH3 O CH3 Cis O CH3 O Trans O CH3

ng phn hnh hc trong hp cht c ni i C=N v N =NCH3CH2 CH3 C6H5 OH C N .. Butanoxim Z ( syn ) C6H5 Azobenzen CH3CH2 CH3 C6H5 C N OH

..

E (anti) N .. N

..

N ..

N ..

Z ( syn )

E (anti)

C6H5

Ch : Cc thut ng trans, cis, E, Z, anti v syn l cc h thng danh php gi tn cc ng phn hnh hc. 2.1.3. Tnh cht ca cc ng phn hnh hc Do s khc nhau v khong cch gia nhm th v mc n ng khng gian, hai ng phn hnh hc c nhiu tnh cht l -ha khc nhau.

Tnh cht vt l Nhit nng chy (tnc) : ng phn trans (E, anti ) c nhit nng chy cao hn ng phn cis (Z, syn). Nhit si (ts): ng phn trans (E, anti ) c nhit si thp hn nhit si ca ng phn cis (Z, syn) . Momen lng cc: Tu thuc vo bn cht ca cc nhm th phn b chung quanh lin kt i hoc vng, momen lng cc cc ng phn hnh hc c khc nhau. Nu hp cht c dng aCH =CHa th momen lng cc ca ng phn E (trans) bng khng E = 0 v momen lng cc ca ng phn Z (cis) ln hn khng Z > 0.36

Hp cht c dng aCH =CHb : Nu a v b cng c bn cht in t (ngha l a v b u cng ht hoc cng y in t th Z > E Nu a v b khc nhau v bn cht in t (a ht in t cn b y in t hoc ngc li) th E > Z. Ch : Xc nh momen lng cc theo nguyn tc hnh bnh hnh c th minh ha nh sau:H aCH=CHa a C C H b C a C H a H C C b a H C a C H

z a Z > 0H

E = 0H aHC=CHb a,b u ht electron

E < Zb C a C H a H C C b H

H aCH=CHb a hut, b ay electron

E > Z

Bng 3.1. Tnh cht vt l ca mt s ng phn hnh hc

Hp chatClCH=CHCl PhCH=CHCOOH p-O2NC6H5CH=CHNO2 CH3CH=CHCl

Nhiet o nong chay Nhiet o soi Momen lng cc Trans (E ) Cis (Z) Trans(E) Cis (Z) Trans(E) Cis (Z)-50oc -80,5oc 48,4oc 68,0oc 60,2oc 134,0oc 0D 0,5D 2,0D 2,95D 7,4D 1,7D

bnng phn trans bn hn ng phn cis v nhit . Di tc dng ca nhit ng phn cis c th chuyn thnh ng phn trans. S chuyn i cis transH a C C a H H a C H a Quay a C C H

.

C

.

H a

cis (Z , syn)

trans (E , anti)

Cc gi tr ph t ngoi, ph hng ngoi ca cc ng phn hnh hc cng khc nhau. 37

Tnh cht ha hc ng phn cis d tham gia mt s phn ng loi nc, to vng.H COOH COOH

to

H H

O C O C O + H2O

H

Acid cis butendioic

Anhydrid maleic

2.2. ng phn quang hc ng phn quang hc l nhng cht ha hc c tc dng quay mt phng nh sng phn cc. Cht c tc dng vi nh sng phn cc l cht quang hot.

nh sng t nhinTheo l thuyt v nh sng th nh sng t nhin gm nhiu sng in t c vect in trng hng theo tt c cc hng trong khng gian v thng gc vi phng truyn sng.Anh sang t nhien Phng truyen song Vect ien trng

nh sng phn cc, mt phng nh sng phn ccKhi cho nh sng t nhin i qua lng knh Nicon hoc mt cht phn cc no (nh HgS, KClO3....) th cc vect in trng s hng theo mt phng dao ng xc nh v vung gc vi phng truyn sng. nh sng i ra khi cht phn cc gi l nh sng phn cc. Mt phng nh sng phn cc (mt phng phn cc) l mt phng vung gc vi phng dao ng ca nh sng phn cc.Mat phang anh sang phan cc Phng truyen song

Anh sang phan cc Anh sang t nhien Lang knh Nicon

Cht quang hot (cht hot ng quang hc)Khi cho nh sng phn cc qua dung dch cht hu c hoc mt cht no , nu cht ny lm quay mt phng nh sng phn cc mt gc c gi tr + hoc - th gi cht l cht quang hot (cht hot ng quang hc). 38

Chat quang hoat

Goc quay

Mat phang phan cc

Mat phat phang phan cc sau khi qua chat quang hoat

c trng kh nng quang hot ca mt hp cht quang hot ngi ta dng i lng quay cc ring hay cn gi l nng sut quay cc ring v k hiu l [].

Trong :

to

= 100 __

LC

l gc quay cc xc nh trn my phn cc k, c th c 2 gi tr .Ga tr + ch mt phng phn cc quay phi. Ga tr - ch mt phng phn cc quay tri. L b dy lp cht quang hot m nh sng phn cc i qua n v tnh l dm. C l s gam cht ha tan trong 100ml dung mi.

l bc sng ca nh sng.t l nhit o. Nh vy tnh quang hot ca mt cht l tnh cht ca phn t gn lin vi cu trc phn t. S phn b khng gian lm cho cu to phn t tr thnh khng i xng l nguyn nhn ch yu gy ra ng phn quang hc. 2.2.1. Phn t c nguyn t carbon khng i xng 2.2.1.1. Phn t c nguyn t carbon bt i xng Nu nguyn t carbon lin kt trc tip vi 4 nguyn t hoc 4 nhm nguyn t hon ton khc nhau th gi l carbon khng i xng (bt i xng, phi i xng).

b*C

b c d hay*C

c d

a

a

a,b,c, d l cc nguyn t hay nhm nguyn t khc nhau. Carbon khng i xng k hiu l C*. Phn t c carbon khng i xng th khng c cc yu t i xng (mt phng i xng, tm i xng v trc i xng) v phn t c ng phn quang hc. 39

V d: Acid lactic c mt carbon bt i xng CH3*CH(OH)COOH.COOH COOH OH CH3 H COOH

CH3CHOHCOOH

C

C H

CH3 OH

hayH

C

CH3 OH

Nu xem m hnh t din ca acid lactic l mt vt tht th nh ca n qua gng l mt vt th th hai. Vt v nh khng bao gi trng kht ln nhau khi quay vt hay nh chung quanh mt phng mt gc 180.Gng phang Gng phng COOH HOOC

C CH3 H OH HO

H3C C H (- )

Vt Vat

(+ )

nh Anh

nh v gng l hai ng phn quang hc ca nhau, c cu to hon ton ging nhau, ch khc nhau l nu vt quay mt phng nh sng phn cc mt gc + th nh quay mt phng phn cc mt gc - . Quan h gia phn t (vt) v nh gng ca n nh bn tay phi v bn tay tri. Vt v nh khng trng ln nhau (chirality). Hai ng phn vt v nh l 2 i quang (2 cht nghch quang). 2.2.1.2. Phn t c mt nguyn t carbon bt i xng Cc ng phn i quang (enantiomer, gc t ting Hy Lp enantio l ngc chiu) c khong cch gia cc nguyn t trong phn t nh nhau. Chng ng nht v cc tnh cht vt l, ch khc nhau v s tng tc vi nh sng phn cc. Hp cht c mt nguyn t carbon khng i xng c 2 ng phn quang hc. Mt ng phn quay mt phng phn cc bn phi vi gc (+) gi l ng phn quay phi (+)hay l ng phn hu tuyn (cn gi l ng phn d = dextrogyre). Mt ng phn quay mt phng phn cc v bn tri (-)gi l ng phn quay tri (-) hay l ng phn t tuyn (trc y gi l ng phn l = levogyre). Nu trn nhng lng bng nhau ca 2 cht i quang (50% ng phn quay phi v 50% ng phn quay tri) s c mt hn hp khng c kh nng quay mt phng nh sng phn cc. Hn hp gi l bin th racemic k hiu l ( ).

40

thun tin khi biu din cc ng phn quang hc, ngi ta biu din cng thc theo hnh chiu Fischer (xem mc ng phn cu dng) nh sau: Cc ng phn quang hc ca acid lacticCH3 CHOH COOH COOHC

COOH H OH CH3 (+ ) Cong thc chieu Fisher

COOH

COOH HO H CH3

H (+ )

CH3 OH

;

H3C HO

C

(- )

H

Cong thc t dien

Cong thc t dien Cong thc chieu Fisher

2.2.1.3. Phn t c nhiu nguyn t carbon bt i xng Hp cht c nhiu carbon bt i xng th s dng phn quang hc tng ln. Trong phn t, cc nguyn t carbon bt i xng c cu to khc nhau th s ng phn quang hc l 2n ; n l s nguyn t carbon bt i xng. V d: Monosachcarid C6H12O6 vi 4 nguyn t carbon bt i xng c 24 = 16 ng phn quang hc . D - Glucose l mt trong 16 i quang .CH2OH CHOH CHOH CHOH CHOH CHO

Phn t acid ,-dihydroxybutyric c 2 nguyn t carbon bt i xng nn c 4 ng phn quang hc. C th minh ha cc ng phn nh sau: Cc ng phn quang hc ca , - dihydroxybutyricCH3 CHOH CHOH COOH

COOH H H OH OH CH3 I HO HO

COOH H H CH3 II H HO

COOH OH H CH3 III HO H

COOH H OH CH3 IV

I v II l 2 i quang, III v IV l 2 i quang vi nhau. Cn I v III, I v IV, II v III, II v IV l cc cp ng phn quang hc khng i quang vi nhau (diastereoisomer). Trong phn t, nhng nguyn t carbon c cu to ging nhau (tng ng nhau) lm cho phn t c mt phng i xng trong phn t th s ng phn quang hc s t hn 2n v c thm ng phn meso. V d: Phn t acid tartaric c 2 nguyn t carbon bt i xng ging nhau nn ch c 2 ng phn quang hc v mt ng phn meso. C th minh ha nh sau: 41

Cc ng phn quang hc v ng phn meso ca acid tartaric* * HOOC CHOH CHOH COOH

COOH OH H HO H COOH I Acid(+) tartaric

COOH HO H H OH COOH II Acid(-) tartaric

COOH OH H OH H COOH III

COOH H HO mp oi xng H HO COOH

IV Acid mesotartaric

Trong : I v II l 2 i quang (2 ng phn quang hc). III v IV c mt phng i xng trong phn t nn chng khng quay mt phng phn cc, chng khng c tnh quang hot. Ngi ta gi l ng phn meso. Ch : III v IV ch l mt cng thc. C th gii thch s ng phn trong cc trng hp s carbon bt i xng c cu to khc nhau v ging nhau nh sau: Carbon bt i xng c cu to khc nhau th gc quay mt phng phn cc khc nhau. Trong trng hp acid ,dihydroxybutyric, gi s gc quay ca mi carbon bt i l a v b, a>b. Acid tartaric c 2 carbon bt i vi cu to ging nhau, gc quay mt phng phn cc ca mi carbon bt i ging nhau (a= b). Gc quay mt phng phn cc l tng gi tr gc quay ca tt c carbon bt i trong phn t. C cc trng hp:CH3CHOHCHOHCOOH

a>b 1 2 2 2 = ( +a ) + (+b ) = = ( -a ) + (-b ) = = ( +a ) + (-b ) = = ( -a ) + (+b ) =(+) (-) 2 oi quang 2 oi quang

HOOCCHOHCHOHCOOH

a=b

( +) ( -)

1 2 3 4

= ( +a ) + (+b) = = ( -a ) + (-b ) = = ( +a ) + (-b) = = ( -a ) + (+b) =

(+) (+)

2 oi quang

(0) mot ong pham meso (0)

Kt qu: Acid , -dihydroxybutyric c 4 ng phn quang hc v acid tartaric ch c 2 ng phn quang hc v 1 ng phn meso. 2.2.2. Danh php ng phn quang hc Danh php ny dng k hiu cu hnh ca nguyn t carbon bt i. C 2 loi danh php: Danh php D, L v danh php R,S 2.2.2.1. Danh php D,L Ngi ta chia cc cht quang hot thnh hai dy: dy D v dy L. Loi danh php ny c tnh cht so snh, ngha l ngi ta ly cu hnh khng gian ca aldehyd glyceric CHOHCHOHCHO lm chun so snh. 42

Aldehyd glyceric c mt carbon bt i xng c 2 ng phn quang hc. Cu hnh ca chng c m t di y: Cu hnh chun ca aldehyd glycericCH2OH CHOH CHO CHOC

CHO H OH CH2OH

CHO

CHO HOH2CC

H

CH2OH OH

va HO

H

D ( + ) Aldehid glyceric

I

HO CH2OH L ( - ) Aldehid glyceric

H

II

Cong thc t dien

Cong thc chieu Fisher

Cong thc chieu Fisher

Cong thc t dien

Trong cng thc I nhm OH bn phi ngi ta quy c n c cu hnh D. Trong cng thc II nhm OH bn tri, quy c n c cu hnh L. Nhng hp cht quang hot c carbon bt i xng vi s th t cao nht c cu hnh ging cu hnh ca D - aldehyd glyceric th chng thuc dy D. Nhng hp cht quang hot c carbon bt i xng vi s th t cao nht c cu hnh ging cu hnh ca L - aldehyd glyceric th chng thuc dy L . V d: D- Glucose v L - Glucose c cu hnh nh sau: Trong phn t glucose carbon bt i xng s 5 (s th t cao nht ca C *) c cu hnh ging D - aldehyd glyceric c gi l D - Glucose v ging L -aldehyd glyceric l L -Glucose. Cu hnh ca D - Glucose v L - GlucoseCH2OH_CHOH_CHOH_CHOH_CHOH_CHO6 5 4 3 2 1

H HO H 4 H 5

H OH OH 6 CH2OH D(+) - Glucose

1CHO 2 OH 3

HO H OH 4 HO H 5 HO H 6 CH2OH L(-) - Glucose

1CHO 2 H 3

Du (+) v du ( - ) ch chiu quay mt phng nh sng phn cc. Danh php D, L cng p dng cho cch gi tn ca cc acid amin. 2.2.2.2. Danh php R, S (danh php Cahn - Ingold-Prelog ). R t ch Rectus (phi), S t ch Sinister (tri). Danh php D, L c nhiu hn ch l khng ch r ht cu hnh ca cc nguyn t carbon trong phn t v c tnh cht so snh. Danh php R, S khc

43

phc iu . Theo h danh php ny th 4 nhm th chung quanh nguyn t carbon bt i xng c sp xp theo th t gim dn v ln" . V d: C*abcd a > b > c > d Xt s phn b cc nhm th a,b,d,c chung quanh carbon bt i xng ca vt v nh trn hnh t din sao cho nhm th nh nht d vo nh t din xa nht so vi mt ngi nhn v ba nhm th a,b,c cn li chim 3 gc ca y t din. Nu theo th t " ln " ca 3 nhm th a,b, c theo chiu quay kim ng h ta c cu hnh R, nu th t ngc chiu kim ng h ta c cu hnh S.

a c*C

a b c*C

a d b d *C bGng phang

a c b*C

c

Ia,b,c theo chieu quay cung chieu kim ong ho Cau hnh R

IIa,b,c theo chieu quay ngc chieu kim ong ho Cau hnh S

V d: Phn t acid lactic c 2 ng phn: acid R- Lactic v acid S LacticCH3_CHOH_COOH o ln cac nhom the OH > COOH > CH3 > H OH *C H3C OHC*

OH H COOH H HOOC *C CH3 HOOC acid S-Lactic

OH *C CH3

COOH

H3C

acid R Lactic

Gng phang

i vi cc hp cht c nhiu carbon bt i xng c danh php theo h thng R, S ngi ta ln lt xc nh cu hnh ca tng carbon bt i. V d: i vi acid tartaric HOOC _CHOH_CHOH_COOH ta c cc ng phn: acid (2R, 3R )-tartaric acid (2S, 3S )-tartaric acid (2R, 3S )-tartaric (aid mesotartaric ).

Phng php xc nh cu hnh R,S Chuyn cng thc dng t din v hnh chiu Fischer. Xt ln lt tng carbon bt i xng vi 4 nhm th c ln khc nhau.

44

Theo qui tc:

Nu thay i v tr nhm th 1 ln th cu hnh thay i. Nu thay i v tr nhm th 2 ln th khng thay i cu hnh.(Ch thay i sao cho nhm th b nht v pha di).

Xt chiu theo th t gim dn ln ca cc nhm th.V d: Xt cu hnh ca aldehyd D Glyceric HOCH2 _ C*HOH _ CHO. C mt carbon bt i v 4 nhm th chung quanhC* l HO > CHO > CH2OH > HHOCH2_CHOH_CHO Cong thc t dien CHO *C H CH2OH OH H CHO *C CH2OH OH H CHO * OH CH2OH CH2OHI

Cong thc chieu Fisher CHO * OH CH2OH OH CHO

H oi v tr lan 1II

H oi v tr lan 2III

R

R

T cng th t din chuyn v cng thc chiu Fischer (I). Cu hnh I l cu hnh ca aldehyd D -glyceric. T (I) thay i v tr ln 1 thu c (II). i v tr tip tc ln 2 ta c (III). Cho H l nhm th b nht v pha di. Cu hnh ca (III) l cu hnh ca (I) Xt chiu quay ca 3 nhm th OH, CHO, CH2OH. Ta c OH CHO CH2OH theo chiu kim ng h. (III) c cu hnh R v suy ra (I) phi c cu hnh R. Vy D- aldehyd glyceric l R - aldehyd glyceric . 2.2.2.3. Danh php Erythro v Threo phn bit cc ng phn quang hc khng i quang ca cc hp cht quang hot c 2 nguyn t carbon bt i xng ngi ta gi tn theo danh php erythro v threo. Dng erythro l dng trong 2 i nhm th tng t nhau c th a v v tr che khut, cn dng threo ch c mt i nhm th tng t nhau c th v tr che khut V d: 2-Phenyl -2-butanol c dng ng phn erythro v threo nh sau:

45

CH3_CH(Ph)_CHOH_CH3 CH3 H HS R

OH Ph

CH3 HO PhR S25

CH3 HO HR R25

CH3 H Ph H PhS S25

H H

OH H

CH3 [] = -0,69o25

D

[] = +0,69oD

CH3

[] = -30,2oD

CH3

[] = +30,2oD

CH3

2 ong phan erythro

2 ong phan threo

2.2.3. Cc ng phn quang hc khng c carbon bt i xng C mt s hp cht trong phn t khng c carbon bt i xng, nhng do s cn quay lm cho phn t tr thnh bt i xng nn phn t c tnh quang hot (c ng phn quang hc). Cc hp cht thuc dy allen, diphenyl, paracyclophan, thuc loi cht quang hot khng c carbon bt i xng.a b Hp chat allen cC C C d R' R''' R R"

O(CH2)n

O

Hp chat diphenyl

Hp chat paracyclophan

2.3. ng phn cu dng Cu dng hay cn gi l hnh th (Conformation) ca mt phn t dng ch cc dng cu trc khng gian c th hnh thnh khi cc nhm th quay t do chung quanh lin kt n. Mt cht hu c c th c trnh by theo cc dng cng thc sau: Cng thc t din Cng thc chiu Fischer Cng thc phi cnh Cng thc Newman V d: Phn t etan c th c trnh by cc dng cng thc:H H H H H H H H H H H H CT phoi canh H H H H H H H H H H

H CT t dien

H CT chieu Fisher

CT Newman

46

Cng thc phi cnh v cng thc Newman thng c dng bin din cu dng cc cht hu c. Cng thc phi cnh c m t trong khng gian 3 chiu, lin kt gia 2 nguyn t carbon hng theo ng cho t tri sang phi v xa dn ngi quan st. C 2 loi cng thc phi cnh l dng xen k v dng che khut.

a bC

c c

C

b b

aC

a c bC

a

c

Dng xen k

Dng che khut

a,b,c l nhng nguyn t hoc nhm nguyn t phn b chung quanh nguyn t carbon. Cng c th m t theo ng m nt ( ),ng chm chm .....)v ng nht (__). ng m nt ch r lin kt hng v pha trc mt ( phng. ng chm chm hng v pha sau mt phng. ng nt nht nm trong mt phng.

a bC

c c

C

b b

aC

a c bC

a

c

Dng xen k

Dng che khut

Cu dng xen k c nng lng thp hn (bn hn) cu dng che khut (km bn). T cng thc phi cnh c th m t theo cng thc Newman bng cch nhn phn t theo dc trc lin kt C1 C2. Ta biu din C2 b che khut bng vng trn, cn C1 tm vng trn. Ba lin kt xut pht t mi nguyn t carbon to nn nhng gc 120 trn mt phng giy.

a bC1

c c

2

C

b

c a b b1 2

aa b b1 2

a bC1

aC2

a

CT phoi canh

CT Newman

a

c

cc

c b

c

CT Newman

CT phoi canh

Dang xen ke

Dang che khuat

Trong cc hp cht vng cc nguyn t khng phn b trn cng mt phng. Chng c cc cu dng khc nhau. Phn t cyclohexan c hai loi cu dng: cu dng gh v cu dng thuyn.

47

H H H H H H

H

H H H H

H HH

H HH

H H H

H H

H

Cau dang ghe

Cau dang thuyen

dng gh cc nguyn t hydro trn 2 carbon cnh nhau phn b theo cch xen k. Cn dng thuyn cc nguyn t hydro trn 2 carbon cnh nhau phn b theo cch che khut. V vy cu dng gh bn hn cu dng thuyn (xem phn cycloalkan). 2.4. Tc dng sinh hc ca cc ng phn quang hc Cc ng phn quang hc ng vai tr quan trng trong i sng t nhin ca con ngi v th gii sinh vt. Cc cht chuyn ha, cc cht men l nhng h thng hp cht quang hot. Thay i cc dng i quang dn n s thay i qu trnh v c ch ca s chuyn ha. Acid Lactic tn ti (+) Lactic, (-)Lactic v L () Lactic (racemic). Chng c cc tc dng sinh hc khc nhau. D -(+)-glucose l ng c tc dng sinh hc lm cht tim truyn. Ngc li L -(-)-glucose hon ton khng c tnh cht ...

Bi tp1- Cng thc phn t mt hydrocarbon l C7H14. Bao nhiu ng phn c th c ? 2- Cng thc phn t C5H12. Bao nhiu ng phn c th c? 3- Vit cng thc cu to cc ng phn hnh hc ca cc cht sau: a- 2-Penten ; b-2-Phenyl-2-buten ; c- 1,2-Dimethylcyclopentan. d-1-Phenyl-1-clo-2,3,3-trimethyl-1-buten. Cho bit danh php cu hnh ca cc ng phn . Dng ng phn no bn hn. Gii thch. 4- C hp cht CH2Cl-CHOH-CHOH-CH2Cl. a- Hp cht ny c bao nhiu nguyn t carbon i xng, bt i xng . b- Hp cht c bao nhiu i quang v c loi ng phn no. c- V cng thc t din, cng thc chiu Fischer, cng thc phi cnh v cng thc Newman . d- Gi tn cc ng phn theo danh php D, L; danh php R, S v danh php Erythro -Threo . 5- V cc cu dng gh v thuyn ca cc cht sau y: a- cis-1,2-dimethylcyclohexan c- cis-1,3-dimethylcyclohexan e- cis-1,4-dimethylcyclohexan 48 b- trans-1,2-dimethylcyclohexan. d- trans-1,3-dimethylcyclohexan f-trans-1,4-dimethylcyclohexan

Chng 4

KHI NIM ACID -BASE TRONG HA HU C

Mc tiu hc tp 1. Trnh by c cc quan nim v acid v base trong ha hu c. 2. Gii thch v so snh c mnh tng i tnh acid hoc base ca mt s hp cht hu c. 3. Nm c khi nim acid -base lin quan n phn ng ca cc hp cht hu c. 4. S dng khi nim acid -base ca Bronsted - Lowry v Lewis trong ho hu c gii thch v tnh acid -base ca cc cht v c ch phn ng. Ni dung 1. Khi nim acid - base theo Bronsted -Lowry (1923) Acid l nhng tiu phn c khuynh hng cho proton. Base l nhng tiu phn c khuynh hng nhn proton. V d c cht HA cho proton H+.

HA

A- + H+

Theo phng trnh trn th s phn ly to H+ l mt qu trnh thun nghch. HA l acid v cho proton H+. A to thnh gi l base, v A nhn proton to thnh acid HA. V vy c th gi HA l acid lin hp ca base A v A l base lin hp ca acid HA. Trong bng 4-1 trnh by mt s acid -base lin hp.Bng 4.1. S phn ly ca cp acid base lin hpHA

+ H ProtonH+ H+

+

A Base lien hpCH3COO CH3O-

Acid lien hpCH3COOH CH3OH NH +4

+ CH3_O_CH3 H

H+ H+

NH3 .. CH _O_CH3

..

-

3

49

Theo bng trn khi BH+ phn ly to thnh base khng c in tch ( - )

BH

+

H + B+ -

+

Kt hp c 2 trng hp ta c

HA + B

BH + A

Vy phn ng gia mt acid HA v mt base B l s chuyn dch proton t acid sang base hay l phn ng proton ha. Tnh cht ca acid hoc base khng ph thuc in tch ca tiu phn. Nh vy c nhng phn t acid khng mang in (H2SO4, HCl, CH3COOH), c phn t acid tch in dng (NH4+, [CH3OCH3]H+), c phn t base mang in tch m (CH3COO-, CH3O-), c phn t base khng c in tch (NH3, CH3OCH3) . Acid ha tan vo nc c s tng tc acid base: Nc l dung mi c tnh base.

CH3COOH + H2O Acid Base

H3O+ + CH3COOAcid Base

Ho tan mui ca acid hu c vo nc, c s tng tc acid -base : Nc l dung mi c tnh acid.H2O + CH3COO Base Acid CH3COOH + HO Acid Base

Nc l mt dung mi lng tnh ph thuc vo tnh cht ca cht ha tan.Mt s phn ng ha hc c xc tc acid, thc cht l s tng tc acid - base. V d: Phn ng to ether t alcol c xc tc acid l s tng tc acid (H+) vi base (alcol) to cht trung gian khng bn trc khi hnh thnh ether.

H2SO4 + R_O_H Acid Base

+ R_O_H + HSO 4 H Base Acid

Phn ng cng hp nc vo olefin c xc tc acid cng l qu trnh tng tc acid -base, to carbocation trung gian trc lc to thnh alcol.H3PO4 + CH3 CH=CH2 Acid Base + CH3CH_CH3 + Acid H2PO4 Base

-

Mt s phn ng c xc tc base cng c qu trnh tng tc acid base to carbanion trung gian.CH3_CHO + HO Base Acid

H2O + CH2_CHO Base (carbanion) Acid

Ch : Mt acid rt mnh th base lin hp ca n l mt base rt yu. Mt acid rt yu th base lin hp ca n l mt base rt mnh. 50

CH3 + Acid rt yu-

CH2 B BH+

-

+Base rt mnh

Base rt mnh-

Acid rt yu

HO , CH3O l nhng base mnh H2O, CH3OH l nhng acid yu

2. Khi nim acid - base theo Lewis (1923) Base l phn t c kh nng cung cp cp in t (c cp in t khng lin kt). Acid l phn t c nguyn t m in t lp ngoi cng cha y (c kh nng kt hp vi cp in t ca base). Cc cht sau y l nhng base Lewis:R_O_R

..

.. .. .. ; R_NH2 ; R_OH ; NH3 ; HO- ; RO -

Cc cht sau y l acid Lewis:+ BF3 , AlCl3 , FeCl3 , ZnCl2 , SO3 ,NH4

Acid Lewis c kh nng to lin kt cng tr (lin kt phi tr cng l mt dng ca lin kt cng tr) vi cc base Lewis nh H2O, R2O, NH3 .H .. N H : ..: HBase Lewis

+

F Acid Lewis

F .. B ..: F

H F .. .. N :..: F H: .. B H F

3. Hng s cn bng acid - base Acid phn ly trong nc. Cc ion b hydrat ha (solvat ha)

HA

H+ + A- hay HA( nc )

H+(nc) + A- (nc)

S solvat ha H + (nc) v A - (nc) c th minh ha:H2O H + O H + H3O (H2O)n OH2 H OH2 H O H H O H H O H H

A-

H O A- 2O)n (H

51

Bng 4.2. Gi tr pKa ca mt s cht hu cHp chat CH3CONH2 H2O CH3OH (CH3CH2)2 O CH3COOH CH3COOC2H5 CH3CHO CH3COCl CH3CN Acid lien hp + OH CH3 C NH2 + H3O + CH3OH2 + (CH3CH2)2 OH + OH CH3 C OH + OH CH3 C OC2H5 + OH CH3 C H + OH CH3 C Cl + CH3 C NH 00 -1.7 -2.2 -3.6 -6.0 -6.5 -8.0 -9.0 -10.7 pKa

Hng s cn bng ca phn ng:HA( nc )K

Ka =

H+(nc) + A-(nc) [H+][A-]

[HA]

Ka > 1 thuc nhng acid mnh Ka < 10-4 thuc nhng acid yu Gi tr Ka rt b thuc nhng acid rt yu S dng i lng pKa = -logKa nh gi mnh yu ca acid pKa cng b th acid cng mnh v ngc li pKa < -1 thuc acid mnh . pKa > 3 thuc acid yu. Tng t ta c hng s cn bng ca base.

B + H2O Kb =

Kb

BH + + HO-

[ BH +][HO-] v [H2O] = 55,5 M [B]

S dng i lng pKb = - logKb nh gi mnh ca base. Kb cng ln th tnh base cng yu pKb cng ln th tnh base cng mnh v ngc li 52

Bng 4.3. nh hng ca cc hiu ng n tnh acidAcid Ka ,M pKa

CH3COOH FCH2COOH F3CCOOH ClCH2COOH Cl2CHCOOH Cl3CCOOH BrCH2COOH

1,8.10-5 2,6.10-3 0,59 1,4.10-3 5,5.10-2 1,3.10-3 6,7.10-4 1,5.10-4 2,9.10-4 4,5.10-5 4,8.10-4 1,3.10-5 3,4.10-3 4,9.10-5 0,23

4,74 2,59 0,23 2,86 1,26 0,64 2,90 3,18 3,83 3,54 4,35 3,32 4,87 2,46 4,31

ICH2COOH

HOCH2COOH CH3OCH2COOH CH2=CHCH2COOH CH3CH2COOH NCCH2COOH HC CCH2COOH

C6H5CH3COOH

Ch : Tnh acid v tnh base ca mt cht l mi quan h bin chng. Mt cht c tnh acid mnh th n l mt base yu. Mt cht c tnh base mnh th n l mt acid yu. Ether ethylic C2H5OC2H5 l mt base yu, v vy n ch tc dng vi mt s acid mnh .

.. CH3CH2OCH2CH3 + H+

CH3CH2OCH2CH3 H

+

4. Yu t nh hng n tnh acid -base ca cht hu c Cu trc in t ca phn t nh hng n tnh acid -base Cc nguyn t, nhm nguyn t gy nh hng cm ng, nh hng lin hp, nh hng siu lin hp c nh hng n tnh acid -base. Hiu ng - I, - C lm cho tnh acid ca mt cht tng (tnh base gim). Hiu ng + I, + C lm cho tnh acid ca mt cht gim (tnh base tng). Cc s liu ghi trong bng 4-3 chng t iu .

Bi tp1- Vit cng thc ca cc base lin hp ca cc acid sau: C6H5COOH, C6H5CH2COOH, CH3CH2NO2, C6H5OH, (CH3)3NH+ 2- Vit cng thc cc acid lin hp ca cc base sau: NH3, C6H5NH2, CH3OCH3, CH3COCH3, HCC-, RO3- V sao AlCl3, ZnCl2, NH4+, BF3 l nhng acid. 53

Chng 5

CC LOI PHN NG TRONG HA HU C v KHI NIM V C CH PHN NG

Mc tiu hc tp 1. Trnh by c cc c ch phn ng thng gp trong ha hu c. 2. Vit v gii thch c cc c ch phn ng: th (S), cng hp (A), tch loi (E) Ni dung C nhiu phng php phn loi phn ng trong ha hu c. Trong gio trnh ny cc phn ng c phn loi theo hng phn ng. C cc loi phn ng nh sau: 1. Cc loi phn ng trong ha hu c 1.1. Phn ng th (Substitution) Phn ng th (k hiu S) l phn ng trong mt nguyn t hay nhm nguyn t trong phn t c thay th bng mt nguyn t hay nhm nguyn t khc.R_I + CN- R_CN + IR_Li + H2O R_H Tng qut: R_A + Y + LiOH R_Y +A

A l nhm b th (nhm i ra) A = I-, Li+ , ... Y l nhm th ( nhm i vo) Y = CN-, H+ Trong ha hu c tn gi ca mt s phn ng c lit k trong bng 5-1.Bng 5.1. Tn gi mt s phn ng thRA+YNhom the Y Halogen X NO2 SO3H R' Ar R'CO CHO N=N_Ar R'COO

RY+A San pham the R_Y Ten phan ngR_X R_NO2 R_SO3H R_R' R_Ar Phan ng halogen hoa Phan ng nitro hoa Phan ng sulfonic hoa. Phan ng alkyl koa Phan ng aryl hoa Phan ng acyl hoa Phan ng formyl hoa Phan ng azo hoa Phan ng ester hoa

R'CO_R R_CHO R_N=N_Ar R'COO_R

54

Mt s phn ng th c km theo s loi nc, alcol, amoniac ...cn gi l phn ng ngng t. V d: R_CHO + CH3COC6H5

R_CH=NR' + H2O

RCOOC2H5 + CH3COC6H5 RCOCH2CO C6H5 + C2H5OH Tu theo c ch phn ng v tc nhn phn ng, phn ng th cn chia thnh cc loi phn ng th khc nhau:

Phn ng th i nhn. Phn ng th gc t do. Phn ng th i in t.1.1.1. Phn ng th i nhn SN

R-A + Y

-

R-Y + A

-

Y- gi l tc nhn i nhn V d: CH3Cl + HO-

CH3OH + Cl-

1.1.2. Phn ng th gc t do SR

R-A + R .

R-R + A

.

R l gc t do (nhng gc c mt in t) V d: SO2Cl2 + C6H5 C6H5Cl + SO2Cl 1.1.3. Phn ng th i in t SE R _ A + E+

R_ E

+ A+

E+ l tc nhn i in t+ V d: Ar _ H + NO2 Ar _ NO2 + H+

Trong phn c ch phn ng s cp v cc qu trnh xy ra phn ng th. 1.2. Phn ng cng hp (Addition) Phn ng cng hp (k hiu Ad) l phn ng trong hai phn t (hoc ion) kt hp vi nhau thnh mt phn t (hoc ion) cht mi. Phn ng thng xy ra trong cc hp cht c ni i, ni ba: C=C, CC, C=O, C=NH, CN. Phn ng cng hp xy ra c s thay i trng thi lai ha ca nguyn t carbon. HCCH + HCl R_CH=CH2 + Br2 H2C=CHCl: Carbon trng thi sp thnh sp2

R_CHBr_CH2Br: Carbon trng thi sp thnh sp3

55

Ty theo cu to cht phn ng, ngi ta chia phn ng cng hp thnh cc loi:

Phn ng cng hp i in t P (AdE , AE ) Phn ng cng hp i nhn P (AdN , AN) Phn ng cng hp gc P (AdR , AR )1.2.1. Phn ng cng hp i in t (AdE , AE)R_CH=CH2 + H2O R_CHOH_CH3

1.2.2. Phn ng cng hp i nhn (AdN , AN )R_CH=O + HCN R_CH(CN)_OH

1.2.3. Phn ng cng hp gc (AdR , AR ). + Cl

Cl

.

;

Cl

.

+ Cl2

Cl . + Cl Cl

Phn ng cng gc c nh sng lm xc tc l phn ng dy chuyn. Phn ng cng hp hydro vo lin kt i, ta cn c th gi l phn ng hydro ha hay phn ng kh. 1.3. Phn ng tch loi (Elimination) Phn ng tch loi (k hiu E) l phn ng m 2 nguyn t hay nhm nguyn t tch ra khi phn t v khng c nguyn t hay nhm nguyn t no thay th. Phn ng xy ra c s thay i trng thi lai ha ca nguyn t carbon. H_CH2_CH2_OH CH2=CH2 + H2O: Carbon trng thi sp thnh sp2. Br_CH2_CH2_Br + Zn CH2=CH2 + ZnBr2: Carbon trng thi sp thnh sp2 1.4. Phn ng chuyn v (Rearrangement) Trong cc loi phn ng k trn c lc c th xy ra s chuyn v lm chuyn ch mt nguyn t hay nhm nguyn t no trong phn t. Phn ng xy ra c s chuyn i v tr trong phn t gi l phn ng chuyn v.

R R C CH2 X -XR

Chuyen v tr R .. + + R C CH2 R C CH2 R R R

Mt s phn ng th, tch loi, cng hp c th xem l phn ng oxy ha kh. V trong qu trnh phn ng c s thay i s oxy ha ca mt hay nhiu nguyn t trong phn t. Cc phn ng c s tng v gim s oxy ha (hay s nhng v thu in t) gi l phn ng oxy -ha kh.

56

2. Khi nim v c ch phn ng Phng trnh ha hc thng thng ch trnh by cc cht u v cui ca h phn ng m khng cho bit qu trnh ha hc c thc hin bng cch no v tin trnh din bin ca phn ng. C ch phn ng ha hc l con ng chi tit m h cc cht phn ng phi i qua to ra sn phm. Cc qu trnh phn nh cc bc c bn ca phn ng, s ct t lin kt, s hnh thnh lin kt mi, hnh thnh cht trung gian v phc hot ng (trng thi chuyn tip); tin trnh lp th, s solvat ha ... 2.1. Ct t lin kt v hnh thnh cc tiu phn phn ng Mt lin kt c th b ct t theo kiu d ly hoc ng ly. V d c lin kt cng ha tr gia hai nguyn t hoc hai nhm nguyn t A v B: 2.1.1. S ct t d ly Khi lin kt b ct t, cp in t lin kt thuc A hoc B

. A__B .A+ v B- l cc ion.

A+ + B-

hoac

. A__B .

A- + B +

Nu tiu phn to thnh A+ hoc B+ l R+ th tiu phn gi l carbocation. Nu tiu phn B - hoc A - l R - th tiu phn gi l carbanion. Carbocation v carbanion l nhng tiu phn ng vai tr quan trng trong cc phn ng th, cng hp v tch loi.2.1.2. S ct t ng ly Khi lin kt b ct t, cp in t c phn i. Trn mi tiu phn mang mt in t t do. Cc tiu phn gi l gc t do.

. A__B .. CH3-CH2 ,

. . A + Bla cac goc t do

. CH2=CH-CH2

Cc gc t do tham gia cc phn ng theo c ch gc.2.1.3. Cu to v tnh cht tiu phn to thnh khi ct t lin kt

Carbocation Carbocation (k hiu R+) l nhng cation m trung tm in tch dng nguyn t carbon (trn orbital p khng c electron - orbital trng). Carbocation c to thnh khi ct t d ly lin kt cng tr hoc khi cng hp proton H+ vo ni i, ni ba.57

CH3CH=CH2

+

H

+

CH3CH_CH+

Carbocation c cu trc phng. Ba lin kt ca carbon C+ nm trong mt mt phng. Orbital trng (khng c in t) c trc i xng thng gc vi mt phng . Carbanion

Carbanion (k hiu R) l nhng anion m in tch m (2 in t) tp trung ch yu nguyn t carbon (trn orbital p c 2 in t). Carbanion c to thnh khi ct t d ly lin kt cng ha tr . H_CH2CHO + HO- -CH2CHO + H2O

Carbanion c cu trc hnh thp, tm l nguyn t carbon v 4 nh l 3 nhm th v cp in t. Gc t do

Gc t do (k hiu R) l nhng tiu phn c cha 1 in t t do (khng cp i) nguyn t carbon (trn orbital p c 1 in t). Gc t do c to thnh do s ct t ng ly lin kt cng tr di tc dng ca nh sng hoc nhit. Gc t do c cu trc phng. Ba lin kt ca carbon C . nm trong mt mt phng. Orbital p cha mt in t thng gc vi mt phng . Hnh 5.1 minh ho trng thi khng gian ca carbocation, carbanion v gc t do.+

CH3CHCH3CH3

CH3CHCH3CH3

-

CH3CHCH3CH3

.

CH3

CCH3 H H CH3

:H CH3

CH3

H

Cau truc phang cua carbocation orbital p khong co eletron

Cau truc hnh thap cua carbanionorbital p vi 2 electron

Cau truc phang cua goc t do orbital p vi 1 elctron

Hnh 5.1. Cu trc khng gian ca carbocation, carbanion v gc t do.

Carben

Carben k hiu RR'C: l tiu phn c 2 in t khng lin kt lp ngoi cng ca nguyn t carbon .V d: H2C: , Cl2C: , CH2=CHCH:

Nu 2 in t phn phi trn 2 orbital p, carben dng lng gc. Nu 2 in t cng phn phi trn mt orbital p, trn carbon c mt orbital p trng khng c in t. Carben c dng mt ion dng ng vai tr mt tc nhn i in t .

58

Ion dng

Lng goc

H H

orbital trong orbital sp2 H H

Hnh 5.2. Cu trc ca carben H2+C: v lng gc CH2

bn ca cc tiu phn

bn ca cc tiu phn ph thuc vo cu trc in t. Mt in tch trn carbocation v carbanion cng gim th nng lng ca chng cng thp v chng cng bn (d tn ti trong cc qu trnh phn ng). Cc hiu ng electron I, C v H lm gim mt in tch c nh hng quyt nh n bn vng ca cc tiu phn.+

Carbocation bn vng kh in tch dng c gii ta. Cc hiu ng +I v C c tc dng lm cho carbocation bn vng hn.V d: CH3+ < CH3CH2+ < (CH3)2CH+ < (CH3)3C+ do hiu ng +I ca CH3.

CH3+ < C6H5CH2+< (C6H5)2CH+ < (C6H5)3C+ do hiu ng +C ca C6H5 Carbanion bn vng khi c cc nhm ht in t . Hiu ng -I v -C lm tng bn ca carbanion.V d: CH3 < (CF3)2CH- < (C6H5)2CH

CH3 CH2CH2- < CH2 = CH CH2 < (CH2=CH)2CH Cc gc t do km bn v c kh nng phn ng cao. Cc nhm alkyl, aryl lm tng bn. Gc phenyl C6H5 - c kh nng c hiu ng +C hoc -CV d: CH3. < CH3CH2. < (CH3)2CH. < (CH3)3C

CH3. < C6H5CH2. < (C6H5)2CH. < (C6H5)3C. Cc nhm th c hiu ng I , C v H v tr para trong gc p-X-C6H4CH2. lm cho bn ca gc tng ln.2.2. Tc phn ng

Tc v ca phn ng A + B C c th c th hin qua phng trnh .v = k [A].[B] = k c

Trong : c = [A].[B]k l hng s tc phn ng .

[A],[B] l nng ca cc cht A v B . Theo phng trnh Arrhenius ta c .

k = P.Z .e

EA RT

59

Theo th k t l thun vi s va chm Z. Nhng khng phi tt c cc va chm u dn n phn ng ha hc. V vy cn c mt nng lng ti thiu EA gi l nng lng hot ha a cc phn t n " trng thi kch thch " lm cho cc phn t thnh cc tiu phn giu nng lng (carbocation, carbanion, gc t do). xy ra phn ng, s cc tiu phn c nng lng ti thiu bng nng lng hot ha EA c xc nh bi nh lut phn b nng lng Boltzmann. Kt qu l tc phn ng ph thuc mnh vo nhit T. Theo phng trnh trn, khi nhit tng ln khong 10oC th tc cc phn ng ha hc tng ln gp 2 n 3 ln. Khi cc tiu phn nng lng cn thit th ch c nhng va chm ca cc tiu phn nhng v tr khng gian thch hp mi lm cho phn ng xy ra. Tr s k thc nghim thng nh hn rt nhiu so vi gi tr tnh ton c t EA, T v Z. Gi tr k l thuyt v k thc nghim khc nhau bi mt i lng P. i lng P c gi l h s khng gian hay l h s xc sut . Khi nghin cu v c ch phn ng, tc phn ng cn c tnh ton theo l thuyt phc cht hot ng (hay cn gi l trng thi chuyn tip) gii thch cc trng thi ng hc ca phn ng. L thuyt ny gi thit rng trn bc ng n sn phm cui cng, cc phn t tham gia phn ng hp li vi nhau thnh mt phc cht hot ng (hay l trng thi chuyn tip). Trng thi chuyn tip c c trng bng mt cc i nng lng (im A trong hnh 5-3a) ca cc phn t tham gia phn ng. Phc cht hot ng khng phi l mt cht trung gian v n khng c cc tiu nng lng. Cc tiu nng lng ca cht trung gian trnh by trn hnh 5-3b (im B).

E

ANang lng hoat hoaEA

EEA1

A1 Phc chat hoat ong A1 A2 Phc chat hoat ong A2 EA1

Chat trung gian B

B

Chat ban au

AH Chat cuoi (b)

Tin trnh phn ng

Tin trnh phn ng

(a)

Hnh 5.3. Gin nng lng v tin trnh phn ng

C th xem nng lng hot ha EA tng ng vi entanpi hot ha H. Mc trt t khng gian trng thi chuyn tip c c trng bi i lng Entropi S hot ha. Gi tr S hot ho ca trng thi chuyn tip cng m s phn nh mc cc cht phn ng tng tc a phn t hay n phn t. Bit gi tr S v H tc l bit c tin trnh v c ch phn ng xy ra.

60

Thc t khng phi nng lng hot ha EA m l nng lng t do F hot ha mi l yu t quyt nh chuyn phn t t trng thi u ln trng thi chuyn tip . F = H - T S 2.3. C ch phn ng th 2.3.1. C ch phn ng th i nhn

Phn ng th i nhn xy ra theo 2 c ch chnh. C ch lng phn t SN2 v c ch n phn t SN1. C ch SN2

C ch lng phn t SN2 th hin trong phng trnh tc phn ng c nng ca 2 cht phn ng. Phn ng xy ra mt giai on v c trng thi chuyn tip gia cht phn ng v tc nhn i nhn Y -.V d: CH3Cl + HO- CH3OH + Cl-

Phng trnh tc phn ng: v = k [CH3Cl] [HO-] Trng thi chuyn tip:H HO + H H Tac nhan ai nhan Chat phan ng C Cl

HO

H

H H

Cl

HO

H C H San pham cuoiH + Cl

Trang thai chuyen tiep

trng thi chuyn tip lin kt c sp b ct t v lin kt mi sp to thnh. Tc nhn i nhn HO - (tng qut Y -) tn cng vo carbon t pha sau ca Cl (nhm i ra X) Sn phm ca phn ng c thay i cu hnh. Nu cht phn ng ban u c cu hnh R th sn phm phn ng s c cu hnh S v ngc li.

C ch SN1

Xy ra theo 2 giai on. Giai on chm l giai on quyt nh tc phn ng. Trong phng trnh tc phn ng ch c nng ca cht phn ng. Giai on chm quyt nh tc phn ng l giai on to ra carbocation trung gian R+.V d: HO- + (CH3)3C_Br

(CH3)3C_OH + Brv = k [(CH3)3C_Br]

Phng trnh tc phn ng: Giai on chm: (CH3)3C_Br

(CH3)3C+

+

Br -

Giai on nhanh: (CH3)3C+ + HO - (CH3)3C_OH

61

Phn ng xy ra theo c ch SN1 c s racemic ha. C s racemic ha v carbocation R+ to ra giai on chm c cu trc phng v tc nhn i nhn HO tn cng vo carbon v 2 pha ca mt phng vi kh nng nh nhau. V vy c 2 sn phm vi cu hnh ngc nhau c to thnh v c s racemic ha. C th minh ha qu trnh lp th nh sau:HO CH3 HO C CH3 CH3CH3 CH3 CH3

HO -

C+

CH3 CH3 CH3

C

OH

San pham cuoi

Carbocation+

San pham cuoi

Phn ng xy ra theo c ch SN1, c carbocation R hnh thnh nn kh nng c s chuyn v v to thnh sn ph l th hoc tch loi (xem thm phn alcol). Cc tc nhn i nhn Y trong phn th i nhn c th l anion (HO-, Cl-, Br -, I-), carbanion (-CH2CHO ...), cc tiu phn c cp in t lin kt (anion CH3O- ..), hoc cc phn t c cp in t khng lin kt (NH3...)Ch : Tnh base ca Y- cng mnh th tnh i nhn ca Y- cng mnh.

Ngc li tnh i nhn ca Y- mnh khng nht thit n l mt base mnh.V d: HO l mt base mnh ng thi HO cng l mt tc nhn i nhn mnh.

Ngc li ion I l mt base rt yu nhng n l mt tc nhn i nhn mnh. C ch phn ng th SN1 xy ra c tnh cht ion gia tc nhn i nhn Y- v carbocation R+ (hnh thnh giai on chm). Phn ng th nhm X trong phn t R _X v tc nhn i nhn Y-, nu X gn trc tip vi carbon bc nht RCH2 _ X phn ng ch yu xy ra theo c ch SN2 RCH2_X + HO- RCH2_OH + X-: c ch SN2. Phn ng th nhm X trong phn t R X v tc nhn i nhn Y-, nu X gn trc tip vi carbon bc ba (R)3C X phn ng ch yu xy ra theo c ch SN1 (R)3C_X + HO- (R)3C_OH + X- c ch SN1 Phn ng th nhm X trong phn t R _X v tc nhn i nhn Y-, nu X gn trc tip vi carbon bc hai (R)2CH_X phn ng xy ra theo c ch SN1 hoc SN1 ph thuc vo cc yu t cu trc hoc dung mi. (R)2CH _ X + HO- (R)2CH_OH + X- c ch SN1 hoc SN2

Dung mi c nh hng n c ch phn ng. Dung mi phn cc lm cho phn ng u tin xy ra theo c ch SN1. Dung mi khng hoc t phn cc lm cho phn ng u tin xy ra theo c ch SN2.

62

2.3.2. C ch phn ng th i in t SE

Phn ng th i in t ch yu xy ra cc hp cht ca hydrocarbon thm v d vng thm (xem thm phn hydrocarbon thm v d vng). Tc nhn i in t Y + l nhng tc nhn mang in tch dng (+NO2, Br+) hoc phn t thiu in t (SO3, CO2...). Cht phn ng l nhng hp cht vng c cu trc thm Ar -H (ph hp vi cng thc Huckel) .Phc H E+

E

Phc + E Chat trung gian Chat phan ngH H

H E

San pham

E

Tien trnh phan ngHnhHnh 5.4: c qua trnh cua phaphngng th in t t 5-4. CaCc qu trnh ca n n the ai ie in

Phn ng th i in t xy ra qua nhiu giai on. Giai on tng tc gia E+ v Ar -H to phc . Giai on chuyn phc hnh thnh phc . Giai on to sn phm cui cng.

Thc t trong phn ng th i in t thng c vai tr ca xc tc (xem phn hydrocarbon thm).H E+ Phc H + E Phc + H E E + H+ San pham

+ E+

T cht phn ng ban u n sn phm cui tri qua s hnh thnh cc phc hot ng (trng thi chuyn tip ng vi cc cc i nng lng trn gin nng lng (hnh 5-4).2.3.3. C ch phn ng th gc t do SR

Phn ng th theo c ch gc l phn ng dy chuyn c ba giai on: Giai on khi mo. Giai on pht trin mch v to sn phm. Giai on tt mch v kt thc phn ng .

63

V d: Phn ng clor ha alkan xy ra nh sau .

Giai on khi mo: Giai on pht trin mch:

Cl_Cl

Cl. + Cl.

R_H + Cl. R. + HCl tip tc...............................

Giai on tt mch v kt thc phn ng: R. + R. R _ R Cl. + Cl. CL - CL Giai on quyt nh tc phn ng l giai on pht trin mch . Gc t do c cu trc phng, phn t Cl2 tn cng t 2 pha ca mt phng (tng t c ch th SN1) v vy sn phm phn ng dn n s racemic ha.2.4. C ch phn ng cng hp (k hiu Ad) 2.4.1. C ch phn ng cng hp i in t AdE

Phn ng cng hp xy ra gi phn t E _Y v cht phn ng c lin kt i C =C v lin kt ba C C l phn ng cng hp i in t c cc giai on: Giai on to tc nhn i in t E+ v anion Y - t phn t E Y Tng tc ca E+ vi cht phn ng c ni i, ba to thnh carbocation R+ Tng tc gia carbocation R+ v Y- v to thnh sn phm cng hp.

Tng tc ca E+ vi cht phn ng c ni i, ba to thnh carbocation R+ xy ra chm nn n l giai on quyt nh tc phn ng.V d: Phn ng cng hp ca HBr vo propylen CH3CH=CH2 xy ra nh sau:

H_Br

H+

+ Br+ H+

H+ l tc nhn i in t E +; Br l Y -.CH3 CH3 + CH + CH2 CH3 CH2 H +

CH3

CH

CH2

Cham

hoac CH3

CH

CH2

CH3 CH3

+ CH CH2

CH3 + Br + CH2 + Br -

CH3 CH3

CHBr CH2

CH3 CH2Br

Nhanh

Carbocation to thnh l vng tam gic cu to phng. Mt in tch dng trn hai nguyn t carbon l nh nhau. Y - (Br-) tn cng v hai pha ca mt phng vi xc sut nh nhau. V vy cng lc hai sn phm cng hp c to thnh. Gii thch iu theo s di y:H

CH3

CH Br

CH2

CH3

CH Br -

H +

Br Br

CH2

CH3

CH H

CH2

64

Dung mi v cu to phn t E _Y c nh hng quyt nh n s hnh thnh tc nhn i in t E+.2.4.2. C ch phn ng cng hp i nhn

Phn ng cng hp i nhn thng xy ra gia tc nhn i nhn Y - vi cc hp cht c ni i C =O, C=N_ .... Phn ng c cc giai on nh sau: S tng tc gia tc nhn i nhn Y - vo trung tm mang in tch dng ca carbon trong nhm carbonyl ( C=O +C O) to thnh ion mang in tch m trn oxy.

RCH=O + Y- +

RCHY_O-

Ion m to thnh s kt hp ion dng (H ) to thnh sn phm cui cng.

RCHY_O- + H+ RCHY_OH Nhiu hp cht c cha nhm chc carbonyl tham gia phn ng cng hp i nhn v ng thi km theo s tch loi. C th xem loi phn ng ny nh l mt loi phn ng th hoc phn ng cng v tch''O R C X + YO R C Y + X-

in tch dng trn nguyn t carbon ca C =O cng ln th kh nng phn ng cng cao. Thay X bng nhm th c nh hng in t th kh nng phn ng thay i.O R C Cl > O R C O O C R' .. O

> R C O H > R C O R' > R C O .. .. -

O

O

2.5. C ch phn ng tch loi (k hiu E)

Phn ng tch loi to lin kt i xy ra theo 2 c ch: c ch lng phn t E2 v c ch n phn t E1.2.5.1. C ch tch loi E2

Phn ng xy ra theo cc giai on. Tng tc gia mt base mnh vi cht phn ng hnh thnh trng thi chuyn tip. S tch loi xy ra v to sn phm c lin kt i.Tng qut:Y- + Base manh H C C X Y H C C X

YH + C

C + X-

Chat phan ng

Trang thai chuyen tiep

San pham

65

V d: Phn ng tch loi HBr t ethylbromid di tc dng ca C2H5O l mt base mnh to thnh ethylen c c ch nh sau:H CH3 C2H5O + H Br H H H CH3 C C Br

C

C

H

H H C2H5O Trang thai chuyen tiep

H

CH3 + C2H5OH

C

C

H

+ Br H

iu kin v ha lp th cho c ch E2 xy ra khi 4 trung tm phn ng (H C C Br) trn mt mt phng. H v Br v tr trans vi nhau (v tr anti). Minh ha c ch theo cch biu din hnh chiu Newman:CH3 HH

Br

H H

+ C2H5O -

CH3 H

Br

H H

- Br - C2H5OH

CH3 H

C

H

C H

H

2.5.2. C ch tch loi E1

Phn ng xy ra theo 2 giai on. Cht phn ng to carbocation R+ l giai on chm. Tch H+ v to ni i l giai on nhanh.Tng qut:H C C X H C C+ + XCham

Chat phan ng H C C+

Carbocation C C San pham + H+ Nhanh

Carbocation

V d: Tch HBr khi 2-Brom-2,3-dimethylbutan .CH3CH3 H C C Br CH3 CH3

- Br -

CH3 CH3 H C C+ - H+ CH3 CH3 Carbocation

CH3 CH3

C

C

CH3 CH3

Cc phn ng c s cnh tranh ln nhau. Khi tin hnh phn ng th thng km theo phn ng tch loi. Cc iu kin nh dung mi, nng , nhit c nh hng ng k n c ch phn ng.

66

Chng 6

CC PHNG PHP HA HC V VT L XC NH CU TO CHT HU C

Mc tiu hc tp 1. Hiu v bit cch s dng cc phng php ha hc v vt l xc nh cu trc ca phn t 2. ng dng ca quang ph t ngoi, hng ngoi v cng hng t ht nhn trong vic xc nh cu trc phn t.

Ni dungMt cht hu c c ng dng trong thc t phi bo m tinh khit, phi tha mn v thnh phn cc nguyn t ha hc v cng thc cu to. Xc nh cng thc cu to ca mt cht hu c tch/chit c t ngun gc thin nhin hay tng hp c l cng vic rt cn thit v quan trng trong ha hu c. C th xc nh cu to cht hu c bng phng php ha hc hay vt l.1. Phng php ha hc ng dng phng php php ha hc xc nh cng thc phn t v nhm chc ha hc bng cc phn ng c trng. 1.1. nh tnh v nh lng nguyn t

nh tnh v nh lng cc cht hu c l xc nh s hin din cc nguyn t v thnh phn nh lng ca cc nguyn t trong mt cht hu c.1.1.1. nh tnh cc nguyn t v nhm chc

xc nh s c mt cc nguyn t c trong cht hu c, thng tin hnh v c ha, ngha l chuyn cc nguyn t v dng ion v dng cc phn ng nh tnh xc nh cc ion . V d: V c ha hp cht hu c th carbon s chuyn thnh CO2 hoc CO32-, nguyn t halogen (X ) chuyn thnh X -, nguyn t N chuyn thnh CN - ... Dng cc phn ng nh tnh c trng xc nh cc ion CO32-, ion X-, ion CN-. nh tnh cc nhm chc bng cc phn ng c trng. V d: Chc OH alcol tc dng vi natri c hydro thot ra. Chc aldehyd cho phn ng trng gng vi thuc th Tollens... Ngy nay c cc phng php vt l xc nh cc nhm chc mt cch nhanh chng v chnh xc. 67

1.1.2. nh lng cc nguyn t

Xc nh thnh phn phn trm v khi lng cc nguyn t trong cht hu c theo 2 phng php ch yu sau: Phng php Dumas

nh lng cc nguyn t C, H, N, S v halogen c trong cc cht hu c.Nguyn tc: t chy cht hu c bng mt lung kh oxy. Cc nguyn t chuyn thnh CO2, H2O, N2, SO2, X2. Hp thu cc kh sinh ra vo cc cht thch hp. Xc nh khi lng cc kh v suy ra thnh phn phn trm cc nguyn t c trong hp cht hu c. Ngy nay c cc my mc tinh vi nh lng chnh xc cc nguyn t.

Phng php Kjendallng dng phng php Kjendall nh lng nguyn t nit c trong cc cht hu c. Phng php ny rt ph bin xc nh nit trong cc cht amin v acid amin. Nguyn tc ca phng php Kjendall l chuyn nit v dng NH3 hay NH4+ sau dng phng php chun xc nh hm lng NH3 hay NH4+ v suy ra thnh phn phn trm ca nit c trong cht hu c. 2. Phng php vt l ng dng cc phng php vt l xc nh cc tiu chun v tinh khit v xc nh cc nhm chc, cc lin kt c trong hp cht hu c. 2.1. Cc tiu chun vt l 2.1.1. Nhit nng chy v nhit si

Nhit nng chy

Cc cht hu c dng rn tinh khit c nhit nng chy xc nh. Nhit nng chy ca mt cht l nhit m tng rn v tng lng nng chy ca cht trng thi cn bng vi nhau. Nhit m tt c cc tinh th u nng chy c coi l im kt thc ca khong nhit nng chy. Nhit si

Cht hu c lng tinh khit c c trng bng nhit si. Nhit si ca mt cht l nhit m ti cht lng bin thnh hi. Tng lng v tng hi trng thi cn bng. Nhit si ca cht lng ph thuc vo p sut. Cht lng tinh khit lun c nhit si xc nh. Nhit nng chy, nhit si l nhng tiu chun xc nh tinh khit ca cht rn hoc cht lng.2.1.2. Ch s khc x

Ch s khc x l mt tiu chun nh gi tinh khit ca cht lng. Theo nh lut Snellius, nu nh sng n sc b khc x ti b mt ranh gii gia hai mi trng ta c: 68

Moi trng 1 Moi trng 2

n=

sin sin

= C1C2

C1 va C2 la toc o ang sang trong moi trng 1 va 2

Thng ngi ta ly khng kh lm mi trng so snh. Ch s khc x ph thuc vo nng , nhit v bc sng ca nh sng.2.2. Cc phng php sc k

S dng cc phng php sc k tch ring cc cht trong hn hp v cn dng phng php sc k xc nh tinh khit ca mt cht. Sc k l mt phng php vt l dng tch cc thnh phn ra khi hn hp bng cch phn b chng thnh 2 pha: mt pha c b mt rng gi l pha c nh v pha kia l mt cht lng hoc cht kh gi l pha di ng, di chuyn i qua pha c nh. C 2 loi sc k: sc k lng v sc k kh.2.2.1. Sc k lng

Sc k lng l phng php sc k dng cht lng lm pha di ng. Trong sc k lng c cc k thut: Sc k giy: Pha tnh (pha c nh) l giy. Sc k lp mng: Pha tnh l mt lp mng cht hp ph c trng bng phng v u n trn mt tm knh hoc kim loi. Sc k ct: Pha tnh l cht rn c nhi thnh ct. Trong k thut sc k ct, ty theo bn cht ca cht rn lm ct cn c chia thnh: + Ct c in: Ct n gin vi cht hp ph thng thng v c hoc hu c.

Ct trao i ion: Ct l cht trao i ion m (anion) hoc dng (cation).+ Ct gel hoc lc gel (gel filtration) : Pha c nh l mt loi gel tng hp c l xp xc nh dng lc cc cht c kch thc phn t khc nhau. Sc k lng cao p (high pressure liquid chromatography) cn gi l sc k lng hiu nng cao HPLC (high performance liquid chromatography).2.2.1. Sc k kh

Sc k kh l phng php sc k dng cht kh lm pha di ng. Da vo pha c nh, cn chia ra: Sc k kh -rn: Pha c nh l cht rn. Sc k kh -lng: Pha c nh l cht lng.

69

2.3. Cc phng php ph

Khi mt cht hu c hp th nng lng bc x in t th phn t c th tri qua nhiu dng kch thch. Cc kch thch c th l kch thch chuyn dch in t, kch thch quay, kch thch lm thay i spin ht nhn nguy