有机光谱.docx
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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:
methyl 0.8-1.21.2-1.51.4-1.751.6-2.25 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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