学习仪器分析双语chapter7ir

Chapter7InfraredSpectrometry,IR22

Introduction

Principle

InstrumentSamplepretreatmentApplicationInfraredSpectrometry(IR)33Theintroductionofinfraredspectrometry44IntroductionofIRTheinfrared(IR)regionofthespectrumpassesradiationwithwavenumbersrangingfromabout128,00to10cm-1orwavelengthsfrom0.78to1000μm.Mostusedwavelengthsusually2.5-15μm(mid-IRregion).55IntroductionofIRAbsorptionofIRradiationisconfinedlargelytomolecularspeciesthathavesmallenergydifferencesbetweenvariousvibrationandrotationalstates.66Almostallthechemicalshaveinfraredabsorption.ToabsorbIRradiation,amoleculemustundergoanetchangeindipolemomentasitvibratesorrotates.IRspectraoforganiccompoundscanofferabundantstructuralinformation.IRspectracanberecordedrapidlyofmaterialsinthesolid,liquid,solution,andvaporphasesoverawiderangeoftemperature.IntroductionofIRIRSpectrumwasobtainedbyrecordingthepercenttransmissionoftheradiationthroughthemoleculevs.thewavenumberoftheradiation.77ThetypicalIRspectrumbandintensitybandnumberbandpositionIRabsorptionspectrumofathinpolystyrenefilmMorecommonunitsarewavenumbers,orcm-1,thereciprocalofthewavelengthincentimeters.88positionThedifferenceofthevibrationalenergylevelsThedegreesoffreedomformolecularvibrationsDipolemomentchangesandtheprobabilityofenergytransitionnumberintensityTheTypicalIRSpectrum9Theprincipleofinfraredspectrometry91010Therelativepositionsofatomsinamoleculearenotfixedbutinsteadfluctuatecontinuouslyasaconsequenceofamultitudeofdifferenttypesofvibrationsandrotationsaboutthebondsinthemolecule.TypesofmolecularvibrationsStretchingbendingBasiccategoriesofvibrations---scissoringrockingwaggingtwisting1111TypesofmolecularvibrationsAstretchingvibrationinvolvesacontinuouschangeintheinteratomicdistancealongtheaxisofthebondbetweentwoatoms.Thebondlengthchangesandthebondangleisconstant.Stretchingvibrations1212TypesofmolecularvibrationsBendingvibrationsarecharacterizedbyachangeintheanglebetweentwobonds.Thebondanglechangesandthebondlengthisconstant.Bendingvibrations1515Theequationofmolecularvibrations1.ThevibrationsandfrequencyofthediatomicmoleculeThevibrationsofthechemicalbondsaresimilartothemovementofthespringconnectingtotwomassesK

-theforceconstant，

-thereducedmassHooke’sLaw1616QuantumtreatmentofvibrationsTheequationcanbeusedtoestimatedthewavenumberofthefundamentalabsorptionband,ortheabsorptionduetothetransitionfromthegroundstatetothefirstexcitedstate,foravarietyofbondtypes.σisthewavenumberofanabsorptionmaximum17ExampleSolution:CalculatetheapproximatewavenumberofthefundamentalabsorptionduetothestretchingvibrationofC=C.K=9.59.9,suppose

K=9.6N/cmTheC=Cstretchingbandisfoundexperimentallytobe1652cm-11818ThenumberofvibrationsThreecoordinatesareneededtolocateapointinspace.TofixNpointsrequiresasetofthreecoordinates,foratotalof3N.Eachcoordinatecorrespondstoonedegreeoffreedomforoneoftheatomsinapolyatomicmolecule.AmoleculecontainingNatomsissaidtohave3Ndegreesoffreedom.Vibrationalnumber—degreeoffreedom—absorptionbandnumber1919ThenumberofvibrationsIndefiningthemotionofamolecule,weneedtoconsider①Themotionoftheentiremoleculethroughspace;(thetransitionalmotionofitscenterofgravity)②Therotationalmotionoftheentiremoleculearounditscenterofgravity③Themotionofeachofitsatomsrelativetotheotheratoms(itsindividualvibration)20thetransitionalmotion----3therotation----3Thedegreeoffreedominvolvinginteratomicmotion=3N-6,whichrepresentthenumberofpossiblevibrationswithinthemoleculeForthelinearmolecule,therotationaboutthebondaxisisnotpossible,andtwodegreesoffreedomsufficetodescriberotationalmotion.Eachofthe3N-6or3N-5vibrationsiscalledanormalmode.Thedegreeoffreedomforalinearmolecule=3N-5,whichrepresentthenumberofvibrationsforalinearmolecule.TheNumberofVibrations2121Vibrationalcoupling(H2O)H2Oisanonlinear,triatomicmoleculeandhas3n–6=3degreesoffreedomAsymmetricstretchingSymmetricstretchingScissoring2222Carbondioxideisalinearmoleculeandthushas3n–5=4degreesoffreedomVibrationalcoupling(CO2)SymmetricvibrationAsymmetricvibrationBendingvibration(X-Y)Bendingvibration(Y-Z)IRinactive2323AbsorptionpeaknumberDegreeoffreedomTheenergiesoftwoormorevibrationsareidenticalornearlyidenticalThesymmetryofthemoleculesissuchthatnochangeindipolemomentresultsfromaparticularvibrationTheabsorptionintensityissolowastobeundetectablebyordinarymeansThevibrationalenergyisinawavelengthregionbeyondtherangeoftheinstrumentFewerabsorptionbandsarefoundwhen:24FactorsaffectingthewavenumbersInductiveeffectConjugatedeffectStericeffectHydrogenbondvibronic-coupling

theforceconstantDong，P19825R-CORC=O1715cm-1

R-COHC=O1730cm-1R-COClC=O1800cm-1

R-COFC=O1920cm-1

F-COFC=O1928cm-1

Inductiveeffect：

ThemoreelectronegativethegroupX,thehigheristhefrequency.Factorsaffectingthewavenumbers26Conjugatedeffect:

FactorsaffectingthewavenumbersThefrequencyislowerwhenconjugated.C=O27FactorsaffectingthewavenumbersStericeffect---sterichindrance

28Stericeffect----RingstrainFactorsaffectingthewavenumbers29Hydrogenbond

FactorsaffectingthewavenumbersHydrogenbond

causesashiftofX-Hstretchingvibrationtolowerfrequency,whilebendingvibrations

tohigherfrequency.

cm-1

cm-1

cm-1

cm-1C=OstretchingN-HstretchingN-Hbending

cm-1

cm-1FreeH-bond30Coupling：Causedbytheinteractionoftwogroupshavingslightlydifferentfundamentalfrequency.Thepeakspitsintotwo.(Acidanhydride,1820,1760)FactorsaffectingthewavenumbersAsymmetriccouplingSymmetriccoupling31Fermiresonance：Causedbytheinteractionofovertonesandfundamentalfrequency.Thepeakspitsintotwo.(Aldehydes,

C-Hstretching&

C-Hbending,overtone)Factorsaffectingthewavenumbers2740-2720cm-12820cm-132FactorsaffectingthewavenumbersSolventeffect

Thestretchingfrequencyofthepolargroupislowerinthepolarsolvent.

(C=O,NH,OH)33ApplicationsofInfraredSpectrometry3334Groupfrequenciesregion36001250cm-1Fingerprintregion1200600cm-1Manycompoundsshowuniqueabsorptionbandinthisregion,whichisveryusefulforfinalidentification.permitintelligentguessesastowhatfunctionalgroupsarelikelytobepresentorabsentinamolecule.Mid-IRAbsorptionSpectrometryC=C,C=O,C-H,O-H,C

C35GroupFrequenciesforOrganicFunctionalGroups35362．25001900cm-1

triplebondsandcumulateddoublebonds

stretchingfrequenciesregion1．40002500cm-1

X—Hstretchingfrequenciesregion（XisO，N，C，S）3．19001200cm-1doublebondsstretchingfrequencies

4．1200670cm-1

X—Ystretching,X—H

bending37(1)

saturatedC—H—CH32960cm-1

asymmetricstretching

2870cm-1

symmetricstretching

—CH2—2930cm-1asymmetricstretching

2850cm-1symmetricstretching

—C—H2890cm-1

weak<3000cm-1Absorptionfrequenciesofsinglebondstohydrogen38

aromatic

C—H

3030cm-1

C=

C—H30102260cm-1

CC—H3300cm-1>3000cm-1

(2)unsaturatedandaromaticC-H(=C—H,C—H

）Absorptionfrequenciesofsinglebondstohydrogen(3600-2000cm-1)39C-HabsorptionsAbsorptionfrequenciesofsinglebondstohydrogen(3600-2000cm-1)40（3）—O—H36503200cm-1Absorptionfrequenciesofsinglebondstohydrogen(3600-2000cm-1)41（1）RCCH（21002140cm-1）

RCCR’（21902260cm-1）

R=R’时，

IRinactive（2）RCN（21002140cm-1）

non-conjugated22402260cm-1conjugated22202230cm-1

Absorptionfrequenciesoftripleandcumulateddoublebonds(2300-1930cm-1)42（1）RC=CR’16201680cm-1(w)

R=R’IRinactive

（3）

C=O（18501600cm-1）(s),sharp（2）aromatic

C=C

stretching（16261650cm-1）Absorptionfrequenciesofdouble-bonds(1900-1500cm-1)43C=C44C=O45Groupsabsorbinginthefingerprintregion<1500cm-1

C-H，N-H

bendingvibrations

C-C,C-O，C-X

stretchingvibrations46SummaryofIRAbsorptions4647-CH32960±15(CHνas,s),2870±10(CHνs,s-m)1465±10(CHδas,m),1380(CHδs,m-s)C(CH3)2Aroughlysymmetricaldoublet,1385-1380,1370-1365(m)C(CH3)3Doublet,1395-1385,1370-1365Alkane（烷烃）1380,-CH348-CH22925±10(CHνas,s),2850±10(CHνs，s),1465±20(CHδ,m)(CH2)n,rocking,720-810,n>4,725-720(w)1350-1150,out-planewag,twist(w)495051525354高碳数环易出现双峰55-CH2890±10(CHνs,w),1340(CHδ

，w),C-Cstretching,1200-80056Alkene

（烯）3100-3000(=CHν),1680-1620(C=Cν),TerminalAlkene–CH=CH2,995-980,915-905

C=CH2,

895-885cis-isomer:730-665transisomer:980-9551000-650(=CHδ

)57585960Cycloolefin（环烯）61623340-3260(

CHν,s,sharp),2260-2100(CCν，

m-w),700–610(CH

bending,s)

Alkynes（炔）

636465分子中心对称,无C

C峰663100–3000(=CH)2000-1650(overtone)1625-1450[1600,1580(whentheringisfurtherconjugated),1500，1466]900-650(substitutionpattern)monosubstitution

:770-730,710-690Ortho-substitution:770-735Meta-substitution

:900-860(1H),810-750(3H),710-690(γ)Para-substitution

:860-800……Aromatichydrocarbon

（芳烃）6768693760–3230(OH,ν,s),

freeOH,sharp;H-bondedOH,broad1420-1260(O-Hin-planebending)1390-1200(phenols

C-O,ν)1250-1000(alcohols

C-O,ν)720-600(H-bondedOHout-planedeformation)Alcohols

andphenols（醇和酚）70νc-oδOHνOHνc-oνOH71

Ethers（醚）1150–1050(C-O-C,ν,as),aliphaticethers

1310-1020(C-O-C,ν,as,s),1075-1020(C-O-C,ν,s,w)

aromaticether&vinylether727374

Ketones

（酮）Saturated,1725–1705(C=O,ν)Aryl,1700-1680757677

Aldehydes

（醛）1740–1715(C=O),Saturated1705-1685αβunsaturated1710-1695(C=O

,ν),Aryl2880–2650(CH,ν),2bends(Fermiresonance)78798081醛νCHνC=O

苯νCH82Ketonesand

Aldehydes

83

Carboxylicacids

（羧酸）3550(OH,

ν),2700-2500处常有几个小峰(特殊)1760(C=O)，Aryl，1700-16801350-1180(CH2的面外摇摆)955-915,

特征宽峰,酸的二聚体中OH…O=面外摇摆8485Ester（酯）1750-1735(C=O,

ν)1330-1050(C-O-C)C-O-C(as)C-O-C(s)C=O(ν)86Acidanhydride

（酸酐）1860-1800,1800-1750(C=O,

ν),1250(C-O,ν)(allclasses)1180-1045(C-O,ν)(saturated)1300-1200(C-O,ν)(cyclic)8788红外光谱法应用定性分析谱图解析步骤1、分子式确定2、不饱和度计算3、确定分子中所含基团的类型4、推测分子结构5、验证分子结构标准物质、Sadtler谱图89定性分析-不饱和度分子的不饱和度定义：

不饱和度是指分子结构中达到饱和所缺一价元素的“对”数。如：乙烯变成饱和烷烃需要两个氢原子，不饱和度为1。计算：

若分子中仅含一，二，三，四价元素（H，O，N，C），则可按下式进行不饱和度的计算：

=（2+2n4+n3–n1

）/2

n4，n3，n1

分别为分子中四价，三价，一价元素数目。90定性分析作用：

由分子的不饱和度可以推断分子中含有双键，三键，环，芳环的数目，验证谱图解析的正确性。例：

C9H8O2=（2+29

–8）/2=6=1

双键or

饱和环=2

叁键=4

苯（一个环加三个双键）=（2+2n4+n3

–

n1

）/2应用示例例1

某化合物的分子式为C6H14，红外谱图如下，试推测该化合物的结构。

从分子式可看出该化合物为烃类，计算不饱和度

=（2＋6×2－14）/2=0---饱和烃类解：从谱图看，谱峰少，峰形尖锐，谱图相对简单，可能化合物为对称结构。由于1380cm-1的吸收峰为一单峰，表明无偕二甲基存在。775cm-1的峰表明亚甲基基团是独立存在的。因此结构式应为

=（2+2n4+n3–

n1）/2C6H14由于化合物相对分子量较小，精细结构较为明显，当化合物的相对分子质量较高时，由于吸收带的相互重叠，其红外吸收带较宽。谱峰归属(括号内为文献值)。

3000~2800cm-1：饱和C-H的反对称和对称伸缩振动

(甲基：2960cm-1和2872cm-1，亚甲基：2962cm-1和2853cm-1)。

1461cm-1：亚甲基和甲基弯曲振动(分别为1470cm-1和

1460cm-1)。

1380cm-1：甲基弯曲振动(1380cm-1)。

775cm-1：乙基中-CH2-的平面摇摆振动(780cm-1)。谱峰归属例2

试推测化合物C8H8O2的分子结构。

＝（2＋8×2－8）／2＝5计算不饱和度

＝（2＋8×2－8）／2＝5不饱和度大于4，分子中可能有苯环存在，由于仅含8个碳，因此该分子应含一个苯环一个双键。1610cm-1、1580cm-1、1520cm-1、1430cm-1：苯环的骨架振动（1600cm-1、1585cm-1、1500cm-1、1450cm-1）。证明苯环的存在。825cm-1：

对位取代苯（833～810cm-1）。解：1690cm-1：醛基－C=O伸缩振动吸收（1735cm-1～1715cm-1，由于与苯环发生共轭向低频率方向位移）。2820cm-1和2730cm-1：醛基的C-H伸缩振动（2820cm-1

和2720cm-1）。1465cm-1和1395cm-1：甲基的弯曲振动（1460cm-1和

1380cm-1）。1260cm-1和1030cm-1：C-O-C反对称和对称伸缩振动（1275cm-1～1010cm-1）。由以上信息可知化合物的结构为97C7H6O298C4H6O299C9H10例C8H10例C9H10OC9H10OC8H8109TheInstrumentationofInfraredSpectrometry109110110TypesofIRInstrumentationDispersivespectrophotometerwithagratingmonochromatorFouriertransformspectrometersemployinganinterferometerNondispersivephotometersusingafilteroranabsorbinggas111DispersivespectrophotometerIRsourceSamplecompartmentmonochromatordetectorrecorderDispersivespectrophotometer112113ComponentofDispersiveSpectrophotometerSiliconcarbiderod,NernstglowerLightSourcePrism,Raster,Filter

MonochromatorDetectorThermocouplevacuumgauge,Pyroelectricinfrareddetectors,Mercurycadmiumtelluridedetector

113114DispersiveSpectrophotometerSchematicdiagramofadouble-beam,dispersiveIRspectrophotometer.Theheavyblacklinesindicatemechanicallinkages,andthelightlinesindicateelectricalconnections.Theradiationpathisdesignatedbydashedlines.114115NondispersivePhotometerAtypicalnondispersiveinstrumentdesignedtodeterminecarbonmonoxideinagaseousmixture115116IRSourcesSource:consistofaninertsolidthatisheatedelectricallytoatemperaturebetween1500and2200K.TheNernstGlower:composedofrareearthoxidesformedintoacylinderhavingadiameterof1to3mmandalengthof2to5cm.TheGlobar:isasiliconcarbiderod,about5cmlongand5mmindiameter.Incandescentwiresource:isatightlywoundspiralofnichromewireheatedtoabout1100Kbyanelectricalcurrent,lowerintensitybutwithlongerlife116117Themercuryarc:consistsofaquartz-jacketedtubecontainingmercuryvaporatapressuregreaterthan1atmosphere,forthefar-IRregionTheTungstenfilamentlamp:isaconvenientsourceforthenear-IRregionThecarbondioxidelasersource:isformonitoringtheconcentrationsofcertainatmosphericpollutantsandfordeterminingabsorbingspeciesinaqueoussolutionsIRSources118IRTransducersPyroelectrictransducers(焦热电）:

exhibitresponsetimesthatarefastenoughtoallowthemtotrackthechangesinthetime-domainsignalfromaninterferometerandusedinphotometers,someFTIRspectrometersanddispersivespectrophotometers118119IRTransducersPhotoconductingtransducers:

consistofathinfilmofasemiconductormaterial,depositedonanonconductingglasssurfaceandsealedinanevacuatedenvelopetoprotectthesemiconductorfromtheatmosphere,usedinmanyFTIRinstrument.119120Thermaltransducers:

whoseresponsesdependontheheatingeffectofradiation,areusedinolderdispersivespectrometersfordetectionofallbuttheshortestIRwavelengths.IRTransducers121121Itisameasurementtechniquewherebyspectraarecollectedbasedonmeasurementsofthecoherenceofaradiativesource,usingtime-domain

orspace-domain

measurementsoftheelectromagneticradiationorothertypeofradiation.Itcanbeappliedtoavarietyoftypesofspectroscopyincludingopticalspectroscopyinfraredspectroscopy(IR)Fouriertransformnuclearmagneticresonance(NMR)massspectrometry(MS)electronspinresonancespectroscopy(ESR)FourierTransformSpectrometers122122PhotoofaBasicFTIRSpectrometerSpectraarerecordedinafewsecondsanddisplayedontheLCDpanelforviewingandinterpretation.Thespectramaybestoredinamemorycardforlaterretrievalandanalysis,ortheymaybeprinted.123123DiagramofaBasicFTIRSpectrometerRadiationofallfrequenciesfromtheIRsourceisreflectedintotheinterferometerwhereitismodulatedbythemovingmirrorontheleft.Themodulatedradiationisthenreflectedfromthetwomirrorsontherightthroughthesampleinthecompartmentatthebottom.Afterpassingthroughthesample,theradiationfallsonthetransducer.Adata-acquisitionsystemattachedtothetransducerrecordsthesignalandstoresitinthememoryofacomputer.DiagramofaBasicFTIRSpectrometerinterferometerSourceSamplecompartmentdetectordisplayplotcomputerinterferogramIRFTS傅里叶变换红外光谱仪工作原理图

迈克尔干涉仪工作原理图

127InterferometerinanFTIRSpectrometerThemajorityofcommerciallyavailableFTIRinstrumentsarebasedontheMichelsoninterferometer.127128Single-BeamFTIRSpectrometerAtypicalprocedurefordeterminingtransmittanceorabsorbancewiththistypeofinstrumentistofirstobtainareferenceinterferogrambyscanningareferencetwentyorthirtytimes,coaddingthedataandstoringtheresultsinthememoryoftheinstrumentcomputer.128129Double-BeamFTIRSpectrometerThebeamemergingfromtheinterferometerstrikesmirrorM1,whichinonepositiondirectsthebeamthroughthereferencecellandintheotherpositiondirectsitthroughthesamplecell.MirrorM2,whichissynchronizedtoM1,alternatelydirectsthereferencebeamandthesampletothetransducer.129130AdvantagesofFTSpectrometersBettersignal-to-noiseratiosthanthoseofagood-qualitydispersiveinstrument,usuallybymorethananorderofmagnitudeTheoretically,theopticsprovideamuchlargerenergythroughput(onetotwoordersofmagnitude)thandodispersiveinstrumentsTheinterferometerisfreefromtheproblemofstrayradiation130131SamplePretreatmentforInfraredSpectrometry131132MajorapplicationofIRspectrometry133ThedemandforthesampleThechoiceofsamplingtechniquedependsuponthegoaloftheanalysis,qualitativeidentificationorqu