InfraredSpectroscopy(IR)/紅外光譜IRspectroscopycorrespondstotransitionsbetweenthevibrationalenergylevelsofamolecule,involvingthestretchingorbendingofbonds.紅外光譜對(duì)應(yīng)著分子的振動(dòng)能級(jí)躍遷，包含了鍵的伸縮振動(dòng)和彎曲振動(dòng)。Foranorganicchemist,theregionofinterestforIRspectroscopyisofwavelengthfrom2.5to15μm,whichisnormallyexpressedasthewavenumberrange4000-666cm-1

,sincethisistheregioninwhichthemostdiagnosticallyusefulvibrationsoccur.對(duì)有機(jī)化學(xué)家來(lái)講，他們主要對(duì)吸收波長(zhǎng)在2.5-15μm,或者說(shuō)波數(shù)在4000-666cm-1

范圍內(nèi)內(nèi)的紅外光譜感興趣，因?yàn)樽罹咴\斷性的有用的振動(dòng)發(fā)生在這個(gè)區(qū)域。TheselectionrulesforIRtransitions-whichmustbeobeyedifIRabsorptionistooccurforaparticularvibrations–statesthatthemoleculemusthaveadipolemomentandthattheremustbeachangeinthemoleculardipolemomentduringthevibration.IfvibrationresultsinIRabsorption,wesayitisIRactive.IR躍遷的選律，即某種振動(dòng)要發(fā)生紅外光譜吸收所必須遵循的條件：分子必須具有偶極距，且振動(dòng)可以產(chǎn)生瞬間偶極矩變化。有紅外吸收稱為紅外活性。Vibrationalmodeswhichcanbeattributedtoindividualfunctionalgroups(characteristicgroupvibrations)arethemostusefuldiagnosticallytotheorganicchemist.Theycanbebestdescribedmathematicallyifweimaginethetwobondedatomsastwovibratingmassesconnectedbyaspring.有機(jī)化學(xué)家主要利用特征官能團(tuán)的振動(dòng)。如果我們把成鍵的兩個(gè)原子想象成被彈簧連接的兩個(gè)質(zhì)量，這些特征官能團(tuán)的振動(dòng)模式就可以用數(shù)學(xué)很好的描述出來(lái)。Hooke’slaw(胡克定律）k:forceconstant（鍵力常數(shù)）ofthebond(Nm-1),thestrongerthebond,thegreaterthevalueofk；visthefrequency

(Hz);cisthespeedoflight(3*1010cms-1)isthewavenumber(cm-1)μisthereducedmass(折合質(zhì)量）inkg

m1=M1/N,m2=M2/N。

M1、M2為原子量，N為阿佛加德羅常數(shù)。CharacteristicGroupVibrations(特征官能團(tuán)的振動(dòng)區(qū)域）

Inlookingatcharacteristicgroupvibrations,itisconvenienttoconsidertheIRspectrumasbeingdividedinto5regions:4000-2300cm-1:Vibrationsofsinglebonds(單鍵）toH(C-H,O-H,N-H,S-H)2300-1850cm-1:Vibrationsoftriple(三鍵）andcumulative(累計(jì)雙鍵）bonds1850-1500cm-1:VibrationsofC=X1500-1000cm-1:Fingerprintregion1000-666cm-1:UnsaturatedC-Hbending4000-2300cm-1:VibrationsofsinglebondstoHAbsorptionbandsinthisregioncorrespondtothestretchingvibrationsofsinglebondstohydrogen:C-H,O-H,N-H,S-H.這個(gè)區(qū)域的吸收帶對(duì)應(yīng)著含H單鍵的伸縮振動(dòng),如…………….。C-H(3100-2700cm-1)C-H振動(dòng)很少用到，因?yàn)樗杏袡C(jī)物都含C-H,并且大多數(shù)環(huán)境下C-H的伸縮頻率幾乎一樣；另外，由于C-H鍵的偶極距小，所以C-H的伸縮很弱。ThemostusefulC-Hstretchesarethoseforanaldehyde(醛）andanalkyne（炔）.IRspectrumofbenzaldehyde(苯甲醛）Ingeneral,strongabsorptionsabove3100cm-1indicateeitherO-HorN-Hvibrations.3100cm-1以上的強(qiáng)吸收基本上可以表明O-H或者N-H振動(dòng)的存在。O-H(3600-2500cm-1)N-H(3500-3300cm-1)O-H(3600-2500cm-1)注意：樣品中水分的存在也會(huì)導(dǎo)致出現(xiàn)強(qiáng)O-H吸收ThepositionoftheO-Habsorptionisverysensitivetohydrogenbonding(氫鍵）.Ingeneral,themoreconcentratedasolution,thegreatertheextentofhydrogenbondingand,sincehydrogenbondingweakenstheO-Hbond,thesmallerthevalueofk(theforceconstant)andsothelowerthefrequency(orwavenumber)ofthevibration.O-H吸收位置對(duì)氫鍵敏感，氫鍵減弱O-H。溶液濃度越高，氫鍵程度越大，O-H鍵力常數(shù)越小，振動(dòng)頻率（或者波數(shù)）越小。IRspectrumof4’-hydroxyacetophenone.3304cm-1:O-H(非氫鍵的）3158cm-1:O-H(氫鍵的）IRspectrumofparacetamol.3165cm-1(O-H)，3325cm-1(N-H)Carboxylicacids(RCO2H)oftenformdimersandtendstohaveahigherdegreeofhydrogenbonding,sotheyusuallyabsorbtowardsthelowerendofthisregion.Becauseofthehydrogenbonding,carboxylicacidtendtohaveanumberofweakabsorptions(correspondingtodifferentbondstrengths)whichcoverarangeoffrequencies.羧酸中的O-H：傾向于朝該區(qū)域（3600-2500cm-1)的低波數(shù)吸收。并且傾向于在不同的波數(shù)處出現(xiàn)多個(gè)弱吸收峰（對(duì)應(yīng)著不同的鍵結(jié)合強(qiáng)度）O-Hincarboxylicacid:multiplepeaksbetween3010-2560cm-1(O-H)Multiplepeaksbetween3005-2550cm-1Solidordilutesolutions(稀溶液)ofphenols,alcoholsandcarboxylicacidshavealesserdegreeofhydrogenbondingandsoabsorbinthe3600-3200cm-1.固體或者稀溶液狀態(tài)的苯酚，醇或者羧酸氫鍵程度較低，所以O(shè)-H在3600-3200cm-1發(fā)生吸收。N-H(3500-3300cm-1)N-HabsorptionsappearinmuchthesameregionasO-H,butitisusuallypossibletodistinguishtheN-Habsorptionsastheyaregenerallysharperowingtoasmallerdegreeofhydrogenbonding.N-H氫鍵程度較O-H小，一般情況下N-H吸收峰更尖。IndistinguishN-HfromO-Hvibrations,itisusefultonotethatforanN-Hstretchingvibration,thereshouldbeacorrespondingbendingvibrationat1650-1550cm-1(normallyweak)區(qū)別N-H和O-H的振動(dòng)：N-H的伸縮振動(dòng)對(duì)應(yīng)著1650-1550cm-1

的彎曲振動(dòng)（弱）N-Habsorptionsarereasonablystrong,andwecaneasilydistinguishprimaryamines(RNH2)andprimaryamides(RCONH2)fromsecondaryamines(R2NH)andsecondaryamides(RCONHR).Primaryaminesandamideshavetwo(veryoftenthree)stretchesinthisregioncorrespondingtothesymmetricalandasymmetricalstretchesofthetwoN-Hbondsinthesefunctionalgroups,whilesecondaryaminesandamideshaveonlyoneN-Hstretchingvibration.區(qū)別伯胺，伯酰胺與仲胺，仲酰胺：前兩者有兩個(gè)（經(jīng)常三個(gè)）伸縮振動(dòng)峰，分別對(duì)應(yīng)著兩個(gè)N-H的對(duì)稱伸縮和不對(duì)稱伸縮振動(dòng)，后兩者只有一個(gè)伸縮振動(dòng)峰。SymmetricandasymmetricstretchesofaprimaryamineN+-H(3300-2250cm-1)Forsaltsofamineswecanobtainstrongbandsforboththestretchingvibrationsandtheassociatedbendingmode.銨鹽中的N+-H

伸縮振動(dòng)和伴隨著的彎曲振動(dòng)都給出強(qiáng)吸收峰。S-H(2700-2400cm-1)與O-H比較，典型的S-H吸收弱，并且發(fā)生在較低波數(shù)（或者頻率）。因?yàn)镾的原子量大，所以折算質(zhì)量大。并且S-H的鍵能?。ㄦI力常數(shù)k?。?。按照胡克定律，伸縮頻率小。2300-1850cm-1:vibrationsoftripleandcumulativebonds(三鍵和累積雙鍵的振動(dòng)）Mostoftheseabsorptionbandsaremoderatetoweak;inparticular,thealkyne(炔）bandsdecreaseinintensitywithincreasingsymmetryinthemolecule.大部分這類吸收帶都是較弱的；特別是炔類，吸收峰隨著分子對(duì)稱性的增加而強(qiáng)度減弱。IRspectrumofbenzonitrile(苯腈）：2228cm-1duetoCN.1850-1500cm-1:vibrationsofC=XThisisprobablythemostusefuldiagnosticregionasitincludesthestretchingvibrationsforthosecommonfunctionalgroupswhichcontainadoublebondtocarbon(C=C,C=N,C=O).Theabsorptionsforcarbonylgroups(羰基）areparticularlyuseful,sincetheyarestrongandtheirpositionisverysensitivetothetypeoffunctionalgrouppresent,aswellastoanyhydrogenbondingorconjugationpresentinthemolecule.重要區(qū)域！尤其是羰基的吸收（吸收強(qiáng)，吸收位置對(duì)官能團(tuán)，氫鍵，共軛情況都很敏感）！1.C=O

不同官能團(tuán)中羰基的伸縮振動(dòng)Ingeneral,themoreelectronegativethegroupXinRCOX,thestrongertheC=Obond,andsothehigherthewavenumber(frequency)forthestretchingvibration.一般來(lái)說(shuō)，X的電負(fù)性越大，C=O鍵越強(qiáng)，伸縮振動(dòng)的波數(shù)（頻率）越大。WecanpartlyexplainthisincreaseinwavenumberbyimaginingaresonanceformforRCOXinwhichtheC-Xbondisbrokenasaresultoftheelectron-demandoftheXgroup.ThemoreelectronnegativethegroupX,themorelikelythisistohappenand,sinceoneofresonanceformshasaCC(andhencealargervaluefortheforceconstantk),thiswillleadtoastrongerC=Obond,andsoincreasedstretchingfrequency.

IRspectrumofaceticanhydride(乙酸酐）（由于CH2COO-的電負(fù)性強(qiáng)，與乙醛相比，C=O振動(dòng)波數(shù)大）(1822,1762cm-1duetoasymmetricandsymmetricC=Ostretches)Electron-donatinggroups(particularlythosecapableofresonancestabilization)willdecreasetheC=Obondstrengthandsoleadtoadecreaseinthestretchingfrequency(wavenumber).供電子集團(tuán)（尤其是那些能使共振穩(wěn)定的）會(huì)降低C=O鍵強(qiáng)度，導(dǎo)致伸縮振動(dòng)頻率或者波數(shù)降低。Oneinterestingfeatureofprimaryandsecondaryamidespectraisthepresenceoftwoabsorptionbandsinthisregion-referredtoasamideⅠ(essentiallythecarbonylband)andamideⅡ(acombinationbandessentiallyduetoN-Hbending),theamideⅡbandisgenerallylessintensethanamideⅠandisoftenabout80cm-1lowerthantheamideⅠband.伯酰胺和仲酰胺：在這個(gè)區(qū)域有兩個(gè)吸收帶，一個(gè)是C=O伸縮振動(dòng)，一個(gè)是N-H彎曲振動(dòng)。N-H吸收較弱，而且吸收波數(shù)比C=O大約小80cm-1.1654cm-1(amideⅠband)and1564cm-1(amideⅡband)Bondorder（鍵級(jí)或鍵序）Bondorderisthenumberofchemicalbondsbetweenapairofatoms.Forexample,indiatomicnitrogenN≡Nthebondorderis3,whileinacetyleneH?C≡C?Hthebondorderbetweenthetwocarbonatomsisalso3,andtheC?Hbondorderis1.Bondordergivesanindicationtothestabilityofabond.描述分子中相鄰原子間成鍵強(qiáng)度的物理量。表示鍵的相對(duì)強(qiáng)度。鍵級(jí)高，鍵強(qiáng)。一般來(lái)說(shuō)，鍵級(jí)越大，分子越穩(wěn)定。1741and1721cm-1duetoconjugation.1725and1709cm-1stillduetoconjugation分子內(nèi)氫鍵不受樣品濃度限制，分子間氫鍵隨濃度的升高氫鍵程度升高，伸縮頻率降低。(a)Intramolecularhydrogenbonding;(b)Intermolecularhydrogenbonding.Theeffectofringstrain(環(huán)張力）Thesmallertheringbecomes,themorestrainedthering(asthebondanglesbecomeincreasinglyremovedfromtheidealizedangleof120o

foransp2hybridizedcarbonatom),andthehigherthestretchingfrequencyofthecarbonylgroupinboththelactonesandlactams(biggerk).Thevalue(stretchingfrequencyorwavenumber)forthesix-memberedringsisusuallyclosetothatfortheacyclicsystems,sincethisring(andlargerrings)haveverylittleringstrain.2.AlsopresentinthisregionaretheC=CandC=Nstretchingvibrations,buttheyaregenerallymuchweakerthanthecarbonylabsorptions.1611and1605cm-1duetoC=Cstretches.3.Finally,inthisregionaretheN-Hbendingvibrations(1650-1550cm-1),whichwillhavecorrespondingstretchingvibrationsbetween3600and3200cm-1.TheseabsorptionsareoftendifficulttodistinguishfromC=Cvibrations.Why?C=Cstretchingvibrations(1650-1590cm-1)Somebandscanonlybeattributedtovibrationsofthewholemolecularskeleton;thesebandsoccurbetween1500and1000cm-1andarecha