有机光谱.docx
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有机光谱
IdentificationofOrganicCompounds
OUTLINE
●Massspectrometry
●absorptionspectroscopy
⏹Infraredspectroscopy
⏹Ultravioletandvisiblespectroscopy
●NMRspectroscopy
spectraldatamolecularstructure
ElectromagneticSpectrumandmolecularSpectroscopy
statesinvolvedenergyregion
nuclearspinstatesradiofrequency
vibrationalstates
Molecularvibrationsandcorrespondingenergy
springshaveanaturalvibrationalfrequencydeterminedbyHooke’slaw:
forthesemotions,theirenergychangematchesthatofaphotonwithwavelengthintheIRregion
Infrared（IR）AbsorptionSpectra
VibrationFrequencyandBondStrength
C≡OC=OC-O
Stretchingfrequency2143cm-11715cm-11100cm-1
Thestrongerthebond,thehigherthefrequency
InformationfromtheX-HRegion
theX-HregiondistinguishesC-H,N-H,andO-Hbonds
bond
reducedmassμ
bondstrength
IR
C-H
12/13=0.92
435
2800-3200
N-H
14/15=0.93
450
3300-3500
O-H
16/17=0.94
500
C-HStretchingFrequenciedCorrelatedtoBondStrength
C-Hbondtype
bondstrength
IR
sp
548
3340-3250
sp2
460
3095-3010
sp3
410
3000-2840
3000
haveabsorptionabove3000cm-1Doublebond,triplebond,aromaticring
nothaveabsorptionabove3000cm-1alkane,cycloalkane
InterpretingInfraredSpectra
4000–28002800–20002000–15001500–
N-HO-HC-HC≡NC≡CC=OC=NC=CFingerprintregion
FuntionalGroup
Absorption
Intensity
FuntionalGroup
Absorption
Intensity
alkaneC-H
2850-2960
Medium
alkene
=C-H
C=C
3020-3100
1640-1680
Medium
Medium
Ph-H
3030
alkyne
≡C-H
C≡C
3300
2100-2260
N-H
C-N
3300-3500
1030-1230
alkylhalide
C-Cl
C-Br
600-800
500-600
C=O
COO-H
CO-H
1670-1780
2500-3100
2800
alcohol
O-H
C-O
3400-3650
1050-1150
-C≡N
NO2
2210-2260
1540
arene
C-H
3030
aromaticring
1660-2000
1450-1600
IRAbsortionsofanAlkane
Besidesthestretchingmode,anothertypeofmolecularvibrationisthebendingmode
非端基炔三键振动吸收弱（振动会影响分子偶极从而吸收）
R-NH2hasbothantisymmetricstretchandSymmetricstretch
酚羟基吸收窄，醇羟基吸收稍宽，分子间氢键会使峰变宽
O-HstretchusuallystrongerthanN-Hstretching
Hydrogenbondingbroadensandshiftstheabsorptionband
Hydrogenbondingreducesthebondstrength
Carboxylicacidcanfromahydrogenbondeddimer
Thedoublebondregionhasthreeimportantabsorptions
group
IR
absorptionstrength
-NO2
twobands1550&1350
intense
thestrengthofIRabsorptionsdependsondiploma
IRStretchingFrequencyandConjugatedDoubleBonds
ConjugationlengthensandweakenstheC=O;comparetheketoneandamideC=Ostretchingfrequencies
acetone:
1715cm-1acetamide:
1650cm-1
MolecularInterpretationofIRData
C=O
formaldehyde>acetaldehyde>acetone
175017271715
σ-πhyperconjugation
acetone:
1715acetamide:
1681ethylacetate:
1746acetylfluoride:
1870
F吸电子效应远大于给电子共轭效应
O吸电子效应略强于给电子共轭效应（二者比较接近），在反应中不同（会摇摆）
acetone:
1715cyclopentanone:
1750CH3CH=CHCOCH3:
1690Acetophenone:
theringmakesthehyperconjugationweaker
（thecarbon-carbonbondcannotrotate）
177017501800
Thelong-pairelectroninOatomconjugatetothedoublebondandthustheelectron-withdrawingeffectoftheOatomisstronger.
massspectrum
质谱分为低分辨与高分辨，低分辨也能区分同位素
100个碳则很可能出现13C分子离子峰
UltravvioletandVisible（UV-Vis）Spectroscopy
UV-VisSpectraRevealExtentofConjugation
Ethene:
171nm1,4-pentadiene:
178nm1,3-butadiene:
217nm
NMRSpectroscopy
Inamagneticfield,nucleiwithnuclearspinquantumnumber≠0,alignparallelofantiparalleltotheappliedfield.Theenergydifferencebetweenthesespinstatesisequivalenttoradiofrequency,andisdirectlyproportionaltoB0,themagnitudeofthemagneticifeld,andacharacteristicofthenucleiknowasthegyromagneticratio,γ.
Inportantactivenuclei:
1H,13C,15N,19F,31P
磁场强度大，信号强
Variationsinthedistributionofelectronsaroundanucleus（duetodifferentchemicalbondsandconnectedatoms）affecttheeffectivemagneticfieldthatthenucleusexperiences.
电子自旋，跟电子云密度有关
密度高，产生磁场强，抵消外部磁场多
TwoNucleiinDifferentEnvironments
1.deshieldednuclei:
thesehydrogenssensealargereffectivemagneticfieldsocomeintoresonanceatahigherfrequency
2.thesehydrogenssenseasmallereffectivemagneticfieldsocomeintoresonanceatalowerfrequency
Lowfield（largechemicalshift）:
lowelectronclouddensity
Resonancepositionsarealwaysreferencedtoastandard.For1HNMR,thestandardistetramethylsilane（TMS）.ThepositionofTMSisdefinedasthezeropoint.
Positionsarethesame（ppm）regardlessoffieldstrength（B0）
Resonancecondition:
v=（γ/2π）B0
analysisofNMRSpectra
Thegoal:
●Tocorrelateaspectrumtoitsexpectedproduct
●Toelucidateanunknownstructurefromspectra
StepI
Identifythenumberofresonancesignals.Eachsetofchemicalshift……
ChemicalShiftEquivalency
ResonanceIntegration:
correspondtothenumberofHatoms
StepIII
PositiontheChemicalShift
ChemicalShift:
methyl0.8-1.21.2-1.51.4-1.751.6-2.25
Electronwithdrawinggroupsteduceelectrondensityatneighbotinghydrogens,whichdecreasestheabilityofnearbyelectronstoshieldthenucleus……
烷烃：
2以下，和O相连：
3点几
alkene:
4.5-5.5;conjugated（carbonylgroup）alkene:
7-8;phenyl:
7-8;aldehyde:
9-10;alkyne:
2.2-2.8
CHCl3:
7.26（canreplaceTMS）
benzene（unsubstituted）:
7.2
9以下只有醛基，形成氢键的羧酸，酰胺，后二者会宽化。
α-Hofcarbonylgroup:
2-2.5
烯烃在去屏蔽区，炔烃在屏蔽区
SplittingofSignals
Protonsonneighboringcarbonatomsinteractwithoneanotherandaplittheresonancethroughamechanismknownasspin-spincoupling
SplittingofSignals
structure
signalofHa
signalmultiplicity
Ha
||
—C—C—
||
1
singlet
HaHb
||
—C—C—
||
1:
1
doublet
HaHb
||
—C—C—Hb
||
1:
2:
1
triplet
HaHb
||
—C—C—Hb
||
Hb
1:
3:
3:
1
quartet
A对B的裂分等于B对A的裂分
PredictingMultiplicity
Thenumberofpeaksinamultipletfollowsthen+1rulewhere“n”isthenumberofadjacentprotons（mustbeequivalent）.
StrengthofSpin-SpinCoupling
Thestrengthofspin-spincouplinginteractionisknownasJ,thecouplingconstantwithunitsofHz.
Thecouplingconstantsarereciprocal:
JAB=JBA
RepresentativeJValuesforOrganicCompounds
HaHb
||
—C—C—
||
6-8Hz
8-140-50-5
11-185-100-3
HaHbHc
|||
—C—C—C—Jab>JbcDoubletofdoublets（dd）
|||Jab=JbcTriplet
||
|Jab||Jab|
|Jbc||Jbc||
|Jbc|Jbc|
向心效应，非一级裂分
NMRCharacteristicofAromaticCompounds
SummaryofNMR
●Thenumberofsignalsindicatesthenumberofsetsof
ProtonEquivlaence
13CNMRspectrumgivesinformationonhowmanydifferentsetsofcarbonsthereareinthemolecular.
IndexofHydrogenDeficincy（IHD）
i.e.DegreeofUnsaturation
Calculatingthenumberofringsandpibondsbasedonthemolecularformula
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