resumo infravermelho
TRANSCRIPT
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Chapter12,MSandIR1
Chapter12InfraredSpectrophotometry
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Chapter12,MSandIR2
TheIRExperimentStretchingVibrationsAtompositionswithrespecttoeachotherarenotfixed!!Therearerelativemovementstoeachother,whichcanbedescribedbyaspring-model.Consideringtwoatomsresultsinthefollowingmodel
Energy-uptakecanbeaccomplishedbyelectromagnetradiation
StretchingandBendingVibrationsofthreeatomsa)stretching:
Asymmetrical
stretching
as
Symmetrical
stretching
s
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Chapter12,MSandIR3
In-planebending
(scissoring)
s
Out-of-plane
bending(wagging)
Out-of-plane
bending(twisting)
In-planebending
(rocking)
StretchingFrequenciesasafunctionofAtomicWeight:
C-H 3200-2800cm-1
C-O 1200-1050cm-1
C-Cl 800-650cm-1
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Chapter12,MSandIR4
StretchingFrequenciesasafunctionofBondStrengths
Bond Frequency(cm-1)
CH2 H
2960(as),2870(s)
C C
H
3020
C C H 3300
C C
1675-1650
C C
2140-2100
CH2 O 1140-1070
C O
1715
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Chapter12,MSandIR5
SymmetryisanimportantfactorofIR-spectrasinceitisassociatedwithanoscillatingelectricdipole.RingstrainTheeffectofringstraincanbeeasilyobservedinIR:
OO
O
Carbonyl-frequency:1714cm-1 1746cm-1 1783cm-1
C=Cstretching:
1649cm-1 1656cm-1 1677cm-1
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Chapter12,MSandIR6
Stereoisomers:trans-substitutedalkenes:strongbandat~970cm-1
cis-substitutedalkenes:mediumbandsat730cm1and650cm-1
ConformationalIsomers:
H
Cl
O
Cl
H
O
carbonyl:1745cm-1 1725cm-1
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Chapter12,MSandIR7
IRSpectraofAlcoholsCH3CH2OH
CH3 C
CH3
CH3
CH2 CH
CH3
CH2OH
A:O-HB:C-HC:CH2-vibration
D:C-Ostretch
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Chapter12,MSandIR8
IRSpectraofKetones
CH3 C
O
CH3
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Chapter12,MSandIR9
CH3 C
O
CH2CH2CH3
A,B,C:C-HD:C=OE,F,G:CH2-vibration
IRSpectraofAlkenes
H2C CH(CH2)7CH3
A:C-HaliphaticB:C-HolefinicC:C=CstretchD:=CHoutofplaneandCH2
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Chapter12,MSandIR10
IRSpectraofAlkynes
HC CH(CH2)3CH3
A,C,E,duetoalkyne:A:C-HalkyneC:CCstretchalkyneE:CCHbendalkyne
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Chapter12,MSandIR11
IRSpectraofAromaticCompounds
OH
A:O-HB:C-HC:OvertonesD:C=Caromaticringstretch
CH2OH
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Chapter12,MSandIR12
CH3
CH3
AromaticOvertoneandCombinationBands
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Chapter12,MSandIR13
IRSpectraofAminesN-Hstretchof1oamines:doubletat3500,3400cm-1
(verydiagnosticbutweakinintensity)N-Hstretchof2oamines:3310-3350cm-1(weak)N-Hbendof1oamines:1580-1650cm-1(mediumtostrong)N-Hwaggingof1oor2oamines:666-909cm-1(mediumtostrong,usuallybroad)CH3(CH2)6CH2NH2
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Chapter12,MSandIR14
SummaryofIRStretchingFrequenciesFrequency
(cm-1)FunctionalGroup Comments
3300 alcohol O H
alwaysbroad
amine,amide
N H maybebroad,sharp,orbroadwithspikes
alkyne C H alwayssharp
3000
alkane C H
justbelow3000cm-1
alkene C
H
justabove3000cm-1
acid C
O
O H
verybroad
2200 alkyne CC justbelow2200cm-1
nitrile NC justabove2200cm-1
1710
(verystrong)
carbonyl C O
ketones,aldehydes,acids,
estershigher(1735cm-1)amideslower;conjugation
(1650cm-1)
1600-1700
alkene C C
aromaticlower;
conjugation(1600cm-1)
imine C N
strongerthanC=C
amide C O
strongerthanC=C(seeabove)
1000-1200 etheresteralcohol
C O
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Chapter12,MSandIR15