alkana, sikloalkana
TRANSCRIPT
KIMIA DASAR
I
SENYAWA ORGANIKMateri tanaman / hewanMakanan, minumanBahan farmasi/ kosmetikPlastik, pipa PVCKomponen minyak bumiPakaian
Unsur kehidupan di atas bumi adalah C
MENGAPA ???
memiliki 4 buah elektron bonding yang
dapat membentuk ikatan kovalen yang kuat,
dapat berupa ikatan tunggal dan rangkap (2
atau 3)
Carbon (C)
H
CH H
H
methane
Carbon has 4 valence electrons
C
H
H
H
H
H C
Ne
Neon
Stable Octet required
Molekul organik paling sederhana:
Covalent Bonding – Atoms Share Electrons
Susunan OKTET yang stabil
metana
ALKANA
C(6) - 1s2, 2s2, 2px1, 2py
1, 2pz0Bentuk dasar
Hibridisasi
C(6) - 1s2, 2s1, 2px1, 2py
1, 2pz1Bentuk
tereksitasi
4 sp3
2s 2px2py 2pz
+ + +
4 X sp3
Struktur tetrahedral pada metana
109.50
Carbon yang menunjukkan hibridisasi sp3 4 buah ikatan C-H yang ekivalen (ikatan )Semua ikatan tunggal dinamakan ikatan
H
CH
HH
Alkana CnH2n+2consist of only carbon and hydrogen bonded by single covalent bonds single
H
CH H
H
H
CH C
H
H
H
H
H
CH C
H
H
C
H
H
H
H
H
CH C
H
H
C
H
H
C
H
H
H
H
CH3
H
CH C
H
H
C
H
H
C
H
H
C
H
H
H
H
methane ethane propane butane
CH3CH3 CH3CH2CH3 CH3CH2CH2CH3
pentane
CH3CH2CH2CH2CH3
Skeletal structure of only carbon atoms
propane
butane
pentane
CH3 CH2 CH2 CH3
CH4
1
4
2 3 4
123
CH3 CH CH2 CH CH2 CH3
CH3CH2 CH3
1 2 3 4 5 6
123456
Contoh :
2-metilbutana
4-etil-2-metilheksana 4 + 2 = 6
3-etil-5-metilheksana 3 + 5 = 8
SIFAT FISIK Senyawa non polar, densitas <1, dengan air
membentuk dua lapisan Larut dalam pelarut organik non polar Alkana C 4, berbentuk gas, Alkana Mr >, berbentuk
cair, Alkana Mr >>>, berbentuk padat Semakin besar jumlah atom C, Mr molekul semakin >,
gaya dispersi tiap molekul >, titik didih semakin tinggi Alkana bercabang td < alkana rantai lurus padanannya Ada pengaruh gaya van der Waals antar molekul Ikatan tunggal mampu berotasi bebas
Melting (blue) and boiling (pink) points of the first 14 n-alkanes in °C.
Isomers – the have the same molecular formula, but a different structuresStructural Isomers – same molecular formula, but atoms are bonded in different orders.
H3C C
CH3
CH3
H
Isobutane
H3C CH
CH3
CH2 CH3
Isopentane
H3C C
CH3
CH3
CH3
Neopentane
Has the same molecular formula as n-pentane, C5H12
Has different Physical Properties : m.p,
b.p.density
C4H10 – has two isomers, n-butane and isobutane (2-methylpropane)
(2,2-dimethylpropane)
(2-methylbutane)
CYCLOALKANES
CnH2n
Bond angles 60°
Bond angles 88°
Bond angles 108°
CyclohexaneBond angles
109.5°
H2C
CH2
CH2C
C
CH
H
H H
H
H Cyclopropane
H2C
H2C CH2
CH2 Cyclobutane
Cyclopentane
H2C
H2C
CH2
CH2
CH2
H2C
CH2
CH2
CH2H2C
H2C
CH3
CH3
CH3
CH3
CH3
C
CH3
1,2-dimetilsikloheksana
tert-butilsiklopentana
metilsikloheksana
How to draw Cyclohexane ?H
HH
H
H
H
put in axial H’s
put in equitorial H’s
H
HH
H
H
H
HH
H
HH
H
H
H
HHH
H
H
H
CH4O2 CO2
H2O energy+ 2 2+ +
RCH2 CH2R RHC CHR H H+alkene
High Temp.catalyst
REACTIONS OF ALKANESCombustion
Dehydrogenation
Halogenation – radical substitution reactions
Br2
Br+ + HBr
light or heat
Halogenation
Substitution Reaction – a reaction in which part of a small reacting molecule replaces an atom or
a group of atoms on the organic molecule
H
CH
H
C
H
H
H + Br2
H
CH
H
C
H
H
Br
Heat or Light or hv
Ethane Bromoethane
HBr+
C
H
H
H + Cl2
Heat or Light or hv
Methane chloromethane
HCl+H C
H
H
ClH
CH2Cl2 and CHCl3may be observed
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Alkyl Halides or Haloalkanes
CH3 CH
Cl
CH CH3
CH3
Cl
CCl Cl
Cl
CH3 CH
Br
CH2 CH2
Cl
F
CH2CH3
BrCl
Cl
CCl F
Cl
F
CCl F
Cl
F
CF
F
C
F
H
H
Naming them
Tetrachloromethaneor carbon tetrachloride
2-Chloro-3-methylbutane 3-Bromo-1-chlorobutane
1-Ethyl-2-fluorocyclohexane1-Bromobutane 2-Chloropropane or
Isopropyl chloride
Tend to be Heavier than waterMore Toxic than Alkanes
Trichlorofluoromethane (Freon-11)
Dichlorodifluoromethane (Freon-12) 1,1,1, 2-Tetrafluoroethane
Chlorofluorocarbons (CFCs)Refrigerant Gases, Ozone Depletion, More H’s more degradable
X
C X = F, Cl, Br
-
Nu -
Electronegativity is defined as the ability of atoms to attract shared electrons in a covalennt bond ------------ leads to nucleophilic substitution in alkyl halides
X is readily displaced by nucleophiles
ClCCl ClCl
Symmetrical molecules have no dipole moment or have equal distribution of electrons within covalent bondsTherefore, they are unreactive!
2404/20/23
STEREOCHEMISTRY
Isomers are different compounds that have the same molecular formula
Structural isomers are isomers that differ because their atoms are connected in a different order
Stereoisomers differ only in the arrangement of their atoms in space
Cl H
Cl H
Cl H
H Cl
cis-1,2-Dichloroethene trans-1,2-Dichloroethene
C2H2Cl2
Geometric Isomers
CH3OCH3 ---- dimethyl ether and CH3CH2OH ---- ethanol
Enantiomers are stereoisomers whose molecules are nonsuperimposable mirror images of one another
Objects that are superimposable on their mirror images are said to be achiral
CH3
CH2
CHHO
CH3
CH2
CH
CH3 CH3OH Interchanging any two groups at a
chiral centre (stereocentre) that
bears four different groups converts
one enantiomer into another
Involves a tetrahedral sp3 atom
CH3 C
OH
CH2 CH3
2-Butanol
H
Chiral Centre
One structure can be superimposed on another
If any of the groups attached to the tetrahedral atom are the same, the centre is achiral.
The ultimate way to test for
molecular chirality is to
construct models of the
molecule and its mirror image
and then determine whether
they are superimposable
A molecule will not be chiral if it possess a centre or plane of Symmetry
2-Propanol
CH3
C OHH
CH3
C
CH3HHO
CH3
Screwdriver is achiralSocks are achiralGolf club is chiralGloves are chiral
What is a chiral object?
What is an achiral object?
Properties of EnantiomersEnantiomers have identical melting points and boiling pointsEnantiomers have identical solubilities in solventsEnantiomers have identical spectra and refractive indexEnantiomers interact, and react with achiral molecules in the same mannerEnantiomers interact and react with other
chiral molecules at different ratesEnantiomers rotate plane-polarised light by equal amounts but in opposite directions
Plane-polarised light
Oscillation of electrical field of ordinary lightoccurs in all possible directions
Polarimeter is a devise used to measure the effect of plane-polarised light on an optically active compound
Chiral molecules are optically active
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No Correlation between the direction of rotation of plane polarised light and the absolute configuration of a molecule
Clockwise Rotation (+) – dextrorotatoryAnti-Clockwise Rotation (-) – levorotatory
C
CH2CH3
H2CCH3
HHO
C
CH2CH3
H2CCH3
HCl
(R)-(+)-2-Methyl-1-butanol (R)-(-)-1-Chloro-2-methylbutanol
Same Configuration
An equimolar mixture of two enantiomers is called a Racemic Mixture It is Optically Inactive
3204/20/23
H
O
S-(+)-Carvone
O
R-(-)-Carvone
H
Principle component of Caraway seed oil and responsible for the characteristic odour
Principle component of Spearmint oil and responsible for the characteristic odour
Receptor Sites in the Nose are Chiral