INTERPRETING INFRARED, RAMAN, AND NUCLEAR MAGNETIC RESONANCE SPECTRATo order t his t it le,and f or more informat ion,clickhereByRi char d Ny qui st ,NyquistAssociat es,Midland,Michigan,U. S. A.Descr i pt i onThis book t eaches t he analystwhy itis advant ageous t o obt ain vibrat ional dat a underdifferentphysical phases. Molecular vibrat ions are affect ed by change inphysical phase,and knowledge of how cert ain molecular vibrat ions are affect ed by change in t he chemical environmentimproves t he analyst ' s abilit y t o solve complex chemical problems.This book is invaluable for st udent s and scient ist s engaged in analyt ical and organic chemist ry,since applicat ion of I R and Raman spect roscopy is essent ial in ident ifying and ver ifying molecular st ruct ure.This reference provides analyst s wit h informat ion t hatenables t hem t o acquire t he maximum amountofinformat ion when sampling molecular vibr at ions via I R and Raman spect roscopy.Audi ence Spect roscopist s,analyt ical and organic chemist s, chemical physicist s,bot h in academia and especially indust ry.Cont ent sVolume 1:Theory of Vibrat ional Spect roscopy Experiment al Alkyl Carbon- Hydrogen Vibrat ions Alkenes andOt her Compounds Cont aining C= C Double Bonds Alkynes and Compounds Cont aining C= C Groups Carboxamides,Ureas,Thioureas, I midazolidinones,Caffeine,I socaffeine,Uracils, I mides,Hydant oins,and s- Triazine ( 1H,3H,5H) -Triones Aldehydes Ket onesCarboxylic Acid Est er s Organic Carbonat es,Thiol Carbonat es,Chloroformat es,Thiol Chloroformat es,Acet yl Chloride,BenzoylChloride,Carbamat es, and an Overview ofSolut e- SolventEffect s Upon Carbonyl St ret ching Frequencies Volume 2:Epoxides and Et hers Nit riles,I sonit riles, and Dialkyl Cyanamides Azines,I socyanat es,I sot hiocyanat es,and Car bodiimides Thiols,Sulfides and Disulfides,Alkanet hiols,and Alkanedit hiols ( S- - H st ret ching)Sulfoxides,Sulfones,Sulfat es,Monot hiosulfat es,Sulfonyl Halides,Sulfit es,Sulfonamides,Sulfonat es,and N- Sulfinyl Anilines Halogenat ed Hydrocarbons Nit roalkanes,Nit r obenzenes,Alkyl Nit rat es,Alkyl Nit rit es,and Nit rosamines PhosphorusCompounds Benzene and I t s Derivat ives The NyquistVibrat ional Group Frequency Rule I nfrared Raman andNuclear Magnet ic Resonance ( NMR)Spect ra- St ruct ure Correlat ions for OrganicCompoundsBi bl i ogr aphi c & or der i ng I nf or mat i onHardbound,1068 pages, publicat ion dat e:APR- 2001I SBN- 13:978- 0- 12- 523475- 7I SBN- 10:0- 12- 523475- 9I mprint :ACADEMI C PRESSPr i ce: Order formGBP 435USD 755EUR 630Books and book relat ed elect ronic product s are pri ced in US dollars ( USD) ,euro ( EUR) ,and GreatBrit ain Pounds ( GBP) .USD prices apply t o t he Americas and AsiaPacific.EUR prices applyin Europe and t he Bookcont ent sTable of cont ent sRevi ew sView ot her people' s reviewsSubmityour reviewBookmark t his pageRecommendt his publicat ionOverview of all booksPr oduct sI nt er pr et i ng I nf r ar ed, Raman, and Nu cl earMagnet i c Resonan ce Spect r aBooki nf or mat i onProductdescript ionAudienceAut hor informat ion and servicesOr der i ng i nf or mat i onBibliographic and ordering informat ionCondit ions of saleBookr el at ed i nf or mat i onSubmityour book proposalOt her books in same subj ectareaSuppor t& cont actAboutEl sev i erSel ecty ourv i ewHome |Sit e map |Elsevierwebsit es |Alert sPgina 1 de 2 Interpreting Infrared, Raman, and Nuclear Magnetic Resonance Spectra - Elsevier11/06/2007 http://www.elsevier.com/wps/find/bookdescription.cws_home/675528/description#de...ACKNOWLEDGMENTSIthankthemanagement of TheDowChemical Companyforprovidingmewitharewardingcareer in chemistry for over 41 years. I also thank the management of Sadtler ResearchLaboratories, aDivisionofBio-Rad, fortheopportunitytoserveasaneditorial consultantforseveraloftheirspectralcollectionsofIRandRamanspectra.I thankMarcia Blacksonfor typing the bookmanuscript. Her cooperationandeditorialcommentsareappreciated.ixNYQUIST'SBIOGRAPHYIn 1985, Richard A. Nyquist received the Williams-Wright Award from the Coblentz Societyforhis contributions to industrial IR spectroscopy. He was subsequently named an honorarymember of the Coblentz Society for his contributions to vibrational spectroscopy, and in1989, hewasanational tourspeakerfortheSocietyofAppliedSpectroscopy. TheAssociationof Analytical Chemists honored Dr. Nyquist with the ANACHEMAward in 1993 for hiscontributionstoanalytical chemistry. HeislistedinWho'sWhoinScienceandEngineering,Who's Who in America, and Who's Who in the World. The Dow Chemical Company, from whichDr.Nyquistretiredin1994,honoredhimwiththeV.A.StengerAwardin1981,andtheWalterGraf European Award in 1994 for excellence in analytical chemistry. He has also been a memberof ASTM, and received the ASTM Award of Appreciation for his contributions to the Practice ofQualitativeInfraredAnalysis. In2000, Dr. NyquistwasawardedhonorarymembershiptotheSocietyof AppliedSpectroscopyforhisexceptional contributionstospectroscopyandtotheSociety. Dr. Nyquist received his B.A. in chemistry from Augustana College, Rock Island, Illinois,hisM.S. fromOklahomaStateUniversity, andhisPh.D. fromUtrechtUniversity, TheNether-lands. HejoinedTheDowChemical Companyin1953. Heiscurrentlypresident of NyquistAssociates, andistheauthororcoauthorofmorethan160scienticarticlesincludingbooks,book chapters, and patents. Nyquist has served as a consultant for Sadtler Research Laboratoriesfor over 15 years. In 1997 Michigan Molecular Institute, Midland, Michigan selected him as theirconsultantinvibrationalspectroscopy.xiPREFACEMyintentionincompilingthisbookistointegrateIR, Raman, andNMRdatainordertoaidanalysts in the interpretation of spectral data into chemical information useful in the solution ofproblemsarisingintherealworld.Thereisanenormousamount of IRandRamandataavailableintheliterature, but inmyopiniontherehas not beenenoughemphasis ontheeffects of thephysical environment ofchemicalsupontheirmolecularvibrations.Manipulationofthephysicalphaseofchemicalsbyvariousexperimentsaidsintheinterpretationofmolecularstructure.Physicalphasecomprisessolid,liquid,vapor,andsolutionphases.Inthesolidcrystallinephase,observedmolecularvibrationsofchemicalsare affectedbythenumberofmoleculesintheunitcell,andthespacegroupoftheunitcell.Intheliquidphase,molecular vibrations of chemicals are affected by temperature, the presence of rotationalconformers, andphysical interactionbetweenmolecules suchas hydrogenbonding andaordipolar interaction. In the vapor phase, especially at elevated temperature, molecules are usuallynot intermolecularly hydrogen bonded and are free fromdipolar interaction between likemolecules. However, therotational levels of themolecules areaffectedbybothtemperatureandpressure.Inducedhighpressure(usinganinertgassuchasnitrogenorargon)willhinderthemolecularrotationof moleculesinthevaporphase. Thus, therotational-vibrational bandcollapses into a band comparable to that observed in a condensed phase. Higher temperature willcausehigherrotationallevelstobeobservedin thevibrational-rotationalbandsobservedinthevaporphase.Insolution, thefrequencies of molecular vibrations of achemical areaffectedbydipolarinteractionand/or hydrogenbondingbetweensoluteandsolvent. Inaddition, solute-solventinteractionalsoaffectstheconcentrationofrotationalconformersofasoluteinasolvent.Thenumberof intermolecularhydrogen-bondedmoleculesexistinginachaininsolutiondependsuponthesoluteconcentration. Inaddition, thenumber of moleculesof asoluteinsolutionexistinginaclusterintheabsenceofintermolecularhydrogenbondingalsodependsuponsoluteconcentration.xiiixivPreface I NTRODUCTI ON Infrared(IR)andRaman(R)spectroscopyareessentialtoolsforthestudyandelucidationof the molecularstructuresoforganicandinorganicmaterials.Therearemanyusefulbookscovering bothIR andR spectroscopy(1-14).However,noneof thesebooksemphasizethesignificanceof changesinthemolecularvibrationscausedbychangesinthephysicalstateorenvironmentof thechemicalsubstance.Onegoalofthisbookistoshowhowchangesinthephysical environmentofacompoundaidinboththeelucidationofmolecularstructureandinthe identificationofunknownchemicalcompositions.Studiesofavarietyofchemicalsinvarious physicalstateshaveledtothedevelopmentof theNyquistRule.TheNyquistRuledenoteshow thein-phase-andout-of-phase-orsymmetricandantisymmetricmolecularvibrations(often calledcharacteristicgroupfrequencies)differ withchangestotheirphysicalenvironment.These groupfrequencyshiftdifferencesaidtheanalystininterpretingthedataintousefulchemical information.Anothergoalofthisbookistogatherinformationonthenatureof solute-solvent interaction,soluteconcentration,andtheeffectoftemperature.Thisknowledgealsoaidsthe analystininterpretationofthevibrationaldata.Anothergoalofthisworkwastocompilemany oftheauthors' andcoauthors' vibrationalstudiesintoonecompendium. INTRODUCTIONInfrared(IR), Raman(R), andNuclearMagneticResonance(NMR)spectroscopyareessentialtools for the study and elucidation of the molecular structures of organic and inorganicmaterials.TherearemanyusefulbookscoveringbothIRandRspectroscopy(114).However,none of these books emphasize the signicance of changes in the molecular vibrations caused bychanges in the physical state or environment of the chemical substance. One goal of this book isto show how changes in the physical environment of a compound aid in both the elucidation ofmolecularstructureandintheidenticationofunknownchemical compositions. Studiesofavariety of chemicals in various physical states have led to the development of the Nyquist Rule.The Nyquist Rule denotes how the in-phase- and out-of-phase- or symmetric and antisymmetricmolecularvibrations(oftencalledcharacteristicgroupfrequencies)differwithchangestotheirphysical environment. These group frequency shift differences aid the analyst in interpreting thedata into useful chemical information. Another goal of this book is to gather information on thenatureof solute-solvent interaction, soluteconcentration, andtheeffect of temperature. Thisknowledgealsoaidstheanalyst ininterpretationof thevibrational data. Anothergoal of thiswork was to compile many of the authors' and coauthors' vibrational studies into onecompendium.xiv PrefaceREFERENCES1. Herzberg, G. (1945). MolecularSpectraandMolecularStructureII. InfraredandRamanSpectraofPolyatomicMole-cules,NewJersey:D.VanNostrandCompany,Inc.2. Wilson,E.B. Jr.,Decius, J.C., and Cross,P.C. (1955). Molecular Vibrations,New York: McGraw-Hill Book Company,Inc.3. Colthup,N.B.,Daly,L.H.,andWiberley,S.E.(1990).IntroductiontoInfraredandRamanSpectroscopy,3rded.,NewYork:AcademicPress.4. Potts,W.J.,Jr.(1963).ChemicalInfraredSpectroscopy,NewYork:JohnWiley&Sons,Inc.5. Nyquist,R.A.(1984).TheInterpretationofVapor-PhaseInfraredSpectra:GroupFrequencyData,Phildelphia:SadtlerResearchLaboratories,ADivisionofBio-Rad.6. Nyquist, R.A. (1989). The Infrared Spectra Building Blocks of Polymers, Philadelphia: Sadtler Research Laboratories, ADivisionofBio-Rad.7. Nyquist, R.A. (1986).IRand NMR Spectral Data-StructureCorrelations for theCarbonyl Group, Philadelphia:SadtlerResearchLaboratories,ADivisionofBio-Rad.8. Grifths, P.R. and de Haseth, J.A. (1986). Fourier Transform Infrared Spectrometry, Chemical Analysis, vol. 83, NewYork:JohnWiley&Sons.9. Socrates,G.(1994).InfraredCharacteristicGroupFrequenciesTablesandCharts,2nded.,NewYork:JohnWiley&Sons.10. Lin-Vien, D., Colthup, N.B., Fateley, W.G., andGrasselli, J.G. (1991). TheHandbookof InfraredandRamanChar-acteristicFrequenciesofOrganicMolecules,SanDiego,CA:AcademicPress.11. Nyquist, R.A., Putzig, C.L. andLeugers, M.A. (1997). InfraredandRamanSpectralAtlasof InorganicandOrganicSalts,vols.13,SanDiego,CA:AcademicPress.12. Nyquist, R.A., andKagel, R.O. (1997). InfraredSpectraof InorganicCompounds, vol. 4, SanDiego, CA: AcademicPress.13. Nakamoto, K. (1997). InfraredandRamanSpectraof InorganicandCoordinationCompounds, Part A: TheoryandApplicationsinInorganicChemistry,NewYork:JohnWiley&Sons.14. Nakamoto,K.(1997).InfraredandRamanSpectraofInorganicandCoordinationCompounds,PartB,ApplicationsinCoordination,Organometallic,andBioinorganicChemistry,NewYork:JohnWiley&Sons.xvCHAP TER1 Theoryof Vibrational Spectroscopy I.Theory II.Exampl esofMol ecul arStructure A.Li nearmolecules:IA ~O,I B -I c B.SphericalTopMolecules:IA --I 8--I c C.Symmet ri cTopMolecules 1.Prolate:IA eq L~ Variables in Data Interpretation 21 eq L) J O O O r tt3 (0 tt~ .x= O er 22 Theory of Vibrational Spectroscopy e~ eq L~ o o L~ r o t~ P-4 Variables in Data Interpretation 23 ,.-:, e~o o3 co o~5 ~D L) ~o o r o3 o3 ~o tt~ 1,4 ,.Q r ~o o3 o~ g:h d, o _= tt~ 24 Theory of Vibrational Spectroscopy ~0 o ~D o~ 03 o o o4 o4 L~ ~0 Q tth o L~ 03 03 tth o 03 03 t~ o gh CHAPTER2 Experimental I.Solids (ExcludingSingle Crystals)25 A.MullTechnique26 B.PotassiumBromide (KBr) DiskTechniques26 C.Solutions(Solids, Liquids, andGases)27 II.LiquidFilms(See theForementionedI - CforLiquidsinSolution) andCastPolymerFilms27 III.Vapors andGases28 References30 SamplepreparationisaveryimportantpartoftheIRtechnique.Becausechemicalscanexistin thesolid,liquid,vapor,orsolutionphases,differentmethodsof preparationarerequiredinorder tobeabletorecordtheirIRspectra.Thischapterisnotintendedtoincludeallmethodsof obtainingIR spectra.It includesonly themethodsusedtoacquirethedataincludedinthisbook. I.SOLI DS( EXCLUDI NGSI NGLECRYSTALS)SolidsamplesareusuallypreparedasmullsorasKBrpellets.Bothtechniquesrequirethatthe particlesizebesmallerthan2.5 ~t. LargerparticlesscatterIR radiationviaRayleighscatteringin theIRregionofinterest.Forexample,ifparticlesarepresentindecreasingconcentrationfrom 2.5t hrough25 ~t, the baselineof thespectrumwillslopeupwardintheregion2.5to25 ~t (4000- 400 cm -1,theregionmostcommonl yexaminedbychemists). Thus,solidsamplesmustbegroundusingamortarandpestle(orawigglebug)tomeetthe precedingrequirements.Thecloseronegetstoavirtualhorizontalbaseline,thebetterthe qualityoftheIRspectrum.ThebandsofthechemicalsolidstartabsorbingIRradiationatthe pointofthebaselinewheretheirvibrationalfrequenciesoccurinthisregionofthespectrum. Thereisanotherfactorthatcausesdistortionof IR absorptionbands.If therefractiveindexof solidparticlesandthesurroundi ngmedi umdifferappreciably,theChristianseneffectis encountered(1).TheChristianseneffectdevelopsbecausetherefractiveindexofachemical isafunctionoffrequencythathasadiscontinuityineachfrequencyregionofastrong absorptionband.Therefractiveindexfallsrapidlyonthehighfrequencysideoftheabsorption 25 26Experimental maxi mumandonthelowfrequencysidetherefractiveindexfallsrapidlyfromahighvaluetoits valueofnoabsorption.Thiseffectcausespeculiarabsorptionbanddistortionwhenthereare manylargeparticlespresentduetoinadequatesamplepreparation.TheChristianseneffectis minimizedbyareductionof asmanyparticlesaspossiblesmallerthan2 ~insize.However,the effectisnevercompletelyeliminatedwhenrecordingspectraofpowderedcrystallinematerials. A. MULLTECHNI QUE Afterthesamplehasbeenproperlyground,NujoloilorFluorolubeisaddedandmixedinorder tosuspendtheparticlesinthemullingagent.However,itispreferabletogrindthesolidinthe presenceofthemullingagenttohelpinthegrindingprocess.Themullingagentssuspendthe solidparticles,whichhelpstoproduceaclosermatchoftherefractiveindexbetweenthese particlesandthesurroundi ngmedium. NujolisusefulforrecordingIRspectraintheregion 1333- 400cm -1,andFluorolubeisusefulforrecordingIRspectraintheregion4000-1333cm -1.InordertoplacethesemulledsuspensionsintheIRsamplecompart ment ,sodi umchlorideand/ or potassiumbromideplatesarerequired.AFluorolubemullpasteis thenplacedbetweentwosodiumchlorideplatesortwopotassiumbromideplatesusingpressure toobtaintheproperthicknessof thispasteinordertoobtainaqualityIR spectrumintheregion 4000-1333cm -1thatisessentiallyvoidof significantFluorolubeabsorptionbands.Intheregion 1333- 400cm -1theprocessisrepeatedusingtheNujolmullsuspensionbetweenpotassium bromideplates,whichminimizesabsorptionfromNujoloil. B.POTASSIUM BROMIDE(KBr) DISKTECHNIQUE Aftergrindingthesolidtoproperparticlesize,KBrismixedwiththesolidparticles.Aratio somewherebetween50to100 KBr : I ofsolidsampleusuallyproducesaqualityIRspectrum. TheKBr andgroundparticlesarethenthoroughlymixedtoproduceauniformmixture.Furt her grindingofthemixtureshouldbeavoidedbecausethisadditionalgrindingwillusuallyinduce waterintothemixture.Theproperamount of thisKBr preparationisplacedinaspecialdie,and adiskis pressedusingapproximately9600Kg pressure.Thediskis placedinaholderandplaced theninthesamplecompart ment oftheIRspectrometer. BoththemullandKBrpresseddisktechniquecancausechangestothesample.Grinding orincreasedpressureuponthesamplecancausechangesincrystallineformofthesample. Inaddition,thepressedKBrdiskcancausechemicalreactionstooccurbetweenKBrand thesample(e.g.,R- NH+ CI - + KBr ~R- NH+Br-+KC1). Inthemulltechniqueion exchangecanalsooccurbetweenthewi ndowandthesuspendedsample(e.g., R- - NH3 + F- + KBr~R- NH3+Br - ) . Thislatterreactionoccurswhenpressurebetweenthe platestogetherwithplaterotationcausessolidstateinteractionbetweentheplatesandthe sample.Thus,oneshouldbeawarethatthechemistcaninadvertentlyaltertheoriginalsample duringpreparation,therebycausingproblemsinthesolutionofthechemicalproblemathand. TheIRspectraofsolidsobtainedafterevaporatingwatersolutionstodrynesscanalsobe recordedusingthemullorKBrdisktechnique. VariablesinDat aI nt er pr et at i on27 C. SOLUTI ONS( SOLI DS, LI QUI DS, ANDGASES)Solids,liquids,andgasesareoftensolubleinsolventssuchascarbontetrachlorideandcarbon disulfide.Othersolventssuchaschloroform,methylenechloride,or dimethyl sulfoxide(DMSO) canalsobeuseddependingupontheparticularproblem.Since likedissolveslike,themorepolar solventsareusedtodissolvethemorepolarcompounds.Carbontetrachlorideandcarbon disulfideareusedtodissolvethelesspolarcompounds. Carbontetrachlorideisa usefulsolventintheregion4000-1333c m- 1andcarbondisulfideis ausefulsolventintheregion1333-400cm -1.Thisisbecausethesesolventshavetheleast absorptionintheseregions.QualityIRspectracanberecordedusingsamplespreparedat10% byweightineachofthesesolvents,andplacingthesolutionsin0.1-mmsodiumchloridecell ( 4 0 0 0 - 1 3 3 3 c m- 1forCC14 solutions)and0.1-mmpotassiumbromidecell(1333-400cm -1for CS2 solutions).ComparableIR spectrawillberecordedusing1% by weightusing1.0-mmcells; however,absorptionfromthesolventwillbeincreasedbyafactorof10.Variationof concentrationandcellpathlengthcanbeusedtorecordthespectrummostusefulinobtaining usefulchemicalinformation.Forexample,changingtheconcentrationofachemical,insay CC14, canhelptodistinguishbetweeninter-andintramolecularhydrogenbonding.TheOHor NHstretchingfrequenciesremainessentiallyunchangedupondilution,inthecaseofintra- molecularhydrogenbonding,butincreasemarkedlyinfrequencyupondilutioninthecaseof intermolecularhydrogenbonding. Solutionspectraareveryusefulinperformingquantitativeanalysiswhenboththesample concentrationandcellpathlengthareknown,providingtheabsorbanceofabandduetothe presenceof thecriticalanalytecanbedirectly measured.Intheworstcase,interferencefromthe presenceof anotheranalytemayhavetobesubtractedbeforetheanalysiscanbeperformedon thecriticalanalyteinquestion. A solventsuchasCSz isalsousefulforextractingsomechemicalsfromwater.Afterthorough shakingwithwater,thesamplecanbeconcentratedbypartialsolventevaporationinawell- ventilatedhoodcontainingnosourceofignition.ThesampleisthensaltedusingdryNaC1 powderinordertoremove water.TheCS2 is thenplaced ina suitableKBr cell beforethesolution spectrumisrecorded.Thissamesolventcanbeusedtoextractcertainadditivesfrompolymer compositions. I I . LI QUI DFI LMS(SEETHEFOREMENTI ONEDI - C FOR LI QUI DSI NSOLUTI ON) ANDCASTPOLYMERFI LMS a.Liquidfilms betweenKBr platesareeasily preparedby placingadropormoreononeplate andthenplacingthesecondplateontopwithenoughpressuretoformthedesiredfilm thickness.Veryvolatileliquidsarebetterpreparedassolutions. b.IR spectraof polymersareoftenrecordedof freestandingfilmorof filmscastonasuitable IR plate.Freestandingfilmsarepreparedbyheatingpolymericmaterialaboveitsmeltingpoint betweenheatedplatesinasuitablepress.Thefilmisallowedtocooltoambienttemperature beforeremovingitfromthemetalplates.ThefreestandingfilmisthenplacedintheIR spectrometer. 28Experimental c.IRspectraareoftenrecordedofpolymericsubstancescastfromboilingsolutionontoa preheatedKBrplate,oftenunderanitrogenatmosphereinordertoavoidoxidationofthe polymer.Afterthesolventhasevaporated,theplateandfilmareallowedtocooltoambi enttemperaturebeforeplacingintheIRsamplecompart ment . FailuretopreheattheKBrplatewill causeittoshatterwhenfirstincontactwiththehotsolution.Moreover,removaloftheheated castfilmaftersolventevaporationtoaambientenvi ronment wi t hout priorcoolingwillalso causetheKBrplatetoshatter.Organicsolventssuchas1,2-dichlorobenzene,toluene,and dimethylformamideareoftenusedtocastpolymerfilms.Thesolventusedisdependent upon theparticularpolymerorcopolymer,anditssolubilityinthatsolvent. Silverchlorideplatesareoftenusedasthesubstrateforcastingfilmsofwater-soluble polymers.ThewaterisremovedbyheatafterfirstplacingthewatersolutionontotheAgC1 plateplacedunderanIRheatlamp.ItisessentialthatAgC1 platesbestoredinthedarkto preventdarkeningoftheplatesduetotheformationofsilveroxideuponexposuretolight. Itisessentialthatallplatesbecleanedafterbeingusedintheseexperiments.Thepolymer filmcanberemovedfromtheplatesusingthesamesolventsusedtocastthefilms.Itisagain necessarytoavoidsuddentemperaturechangetotheplatesduringthecleaningoperationin ordertoavoidplateshatteringincasessuchasKBr, NaC1,CaF2,etc. III. VAPORS A N D GAS ESQualityIR spectracanberecordedusingpartialpressuresandappropriatecelllengthsequipped, say,withpotassiumbromidewindows.Itshouldbenotedthatcertaininorganiccompounds reactwithKBrandformotherinorganicsaltsonthesurfaceoftheKBr plate.Theirreactionsare readilydetectedbecausetheirreactionproductscannotberemovedwhenthesampleis evacuatedundervacuumfromthecell. TheIR spectraof chemicals withlowvaporpressurecanberecordedusingavariablelongpath length vaporcell either at ambienttemperatureorat elevatedtemperature.It is bestif these variable pathlengthcell wailsarecoated withasubstancesuchaspoly(tetrafluorothylene)tohelpprevent adsorptionof thechemical onthesurfaceof themetallic cell body.It is sometimes necessaryto heat thecell bodyundervacuumtoremoveadsorbedchemicalmolecules.Anothermethodtocleanout adsorbedmoleculespresentinthecellistoflushthecellwithnitrogenordryair. ItisalsopossibletoperformquantitativeanalysisofcompoundswhoseIR spectrahavebeen recordedinthevaporphase.Anoften-usedmet hodistorecordthepartialpressureofthe chemicalinthevapor,andthenbringthetotalpressureupto600-mm Hgusingdrynitrogen. Theconstanttotalpressureof600-mm Hghelpseliminatetheeffectsof pressurebroadeningon theabsorptionbands. 1 Thisrequiresof coursethattheappropriatevacuumlineanddry nitrogen beavailabletothechemist.Alongerpathlengthsettingisrequiredasvaporpressureofa chemicalfalls.Ofcourse,somechemicalsreactwiththemirrors,andthiswilllimitthis applicationfortheseparticularcompounds.Itispossibletodetectlowpartspermillionofchemicalsinairusingthevariablelongpath cells.TheinterpretableregionsoftheIRspect rumaresignificantlyimprovedbyspectral 1The windows (KBr, NaC1, etc) of most glass-bodied cells are adhered tothe glass body by a material such as paraffin wax. Pressures higher than 760-mmHg will blow the windows from the glass body. Thus, 600-mmHg sample pressure is a reasonable total pressure to safely achieve in these laboratory experiments. Va r i a bl e s i nDa t a I n t e r p r e t a t i o n 29 subtractionof absorptionduetothepresenceof H20andCO2.Thiscanbedoneelectronically orbydualcellsplacedinseparatebeamsofadoublebeamspectrometer.InthecaseofFT-IR spectrometers,itis aneasytasktoremovetheseabsorptionbandsduetothepresenceof air.Ina casewherethereisnoIRradiationbeingtransmittedinaparticularregionoftheIRspectrum, detectionof acompoundpresentinair(orinany phase)is notpossibleinthesespectralregions, becausethespectrometeris"dead"intheseregions.Spectralsubtractionwillnotchangethe "dead"regionsofthespectrum. AsimplemethodofobtainingIRvaporspectraofchemicalswithhighvaporpressureisto connectthesamplecontainerusingarubberstopperedhosetoa0. 1-mm(or0.2-mm,etc.) liquidcell.Thestopperisopenedandthechemical vaporis allowedtoflushoutthe0.1-mmcell. Theexit portof thecellisthenstoppered,thesampleconnectionisclosedandremoved,andthe entrancepartofthecellisalsostoppered.Thecellisnowfilledwiththesampleinthevapor phaseatambienttemperatureandpressure.Ofcourse,thisoperationshouldbeperformedina well-ventilatedhood. Gaschromatographyhasbeencoupledtoinfraredspectroscopy(GC/FT-IR)toforma powerfulanalyticaltechniquecapableofsolvingmanyrealworldproblems.Thistechnique requiresthatthechromatographedvaporspasssequentiallyt hroughagold-coatedlightpipe heatedtoatemperatureof over200 oC.Thelightpipepath-lengthmust beshortenoughsothat onlyonechromatographedcomponent isinthelightpipeatonetime.Thistechniquehasa maj or pitfallinthatnotall chemicalcompoundsarestableatthehightemperaturesencountered utilizingthistechnique.Forexample,phthalicacidpresentasonecomponent inamixture wouldnotbedetectedasoneof thechromatographedfractions.Thisis becauseattheseelevated temperatures,watersplitsoutofphthalicacidtoformphthalicanhydride,whichisthe compounddetectedusingthistechnique.Othertypesofchemicalreactionscanoccurifthe chemicalscontacthotmetalsurfaces(excludinggold)duringtheirpatht hroughtheGC/FT-IR system. Inordertoidentify unequivocally a vapor-phaseIR spectrumof achemical,anIR vapor-phase standardspectrumofthiscompoundrecordedundercomparableconditionsmust beavailable for comparison.Thereasonsfor thisare presentedhere.A compoundsuchas aceticacidexistsas ahydrogen-bondedcyclicdimerinthecondensedphaseandinthevapor-phaseattemperatures 150 ~andbelow.At elevatedtemperature,aceticacidexistsasisolatedCH3CO2Hmolecules.In thismonomericstate,theOHstretchingfrequencyexhibitsaweak-mediumsharpbandnear 3580cm -1inthevaporphase,andtheC=Ostretchingfrequencyexhibitsastrongbondnear 1791 c m- 1 . ThesefeaturesareuniquelydifferentfromthecondensedphaseIRspectraof acetic acid.Thismonomericsituationisevenmorecomplicatedinsituationswhereintramolecular hydrogen bondingcanoccurbetweentheprotonof thecarboxylicacidgroupanda basicsitein themolecule.Forexample,pyruvicacid(2-oxo-propionicacid)exhibitstwobandsinthevapor phaseat95~(2).A weakbandnear3580cm -1isassignedtoanunassociatedOHgroupof CO2H.Theweak-mediumbondnear3465 c m- 1 resultsfromtheintramolecularhydrogenbond OHgrouptothefree pairof electronsontheketonecarbonyl grouptoforma5-memberedcyclic ringasillustratedhere: o 0"' "14 30Experimental Othersituationsoccurwheremoleculesthatareintermolecularlyhydrogenbondedinthe condensedphaseformintramolecularhydrogenbondsinthevaporphase.Inaddition,the regionsfor groupfrequenciesinthecondensedorsolutionphaseshaveshiftedfromthoseinthe vaporphase.Therefore,onemust haveathandacollectionof vapor-phasegroupfrequencydata, availabletoenableonetointerprettheseGC/ FT-IRspectrabyspectra-structurecorrelations(3). Acompilationofthevapor-phasegroupfrequencydatahasbeendevelopedfromeditorialwork performedbyNyquistonthe10,000vapor-phasespectrapublishedbySadtlerResearch Laboratories,G.DivisionofBio-RadLaboratories,Inc.ThecollectionoftheseSadtlerspectra areavaluableassetforthoseemployingtheGC/ FT-IRtechniquetosolverealworldproblems. RamanspectraofsolidsandliquidsareroutinelyrecordedutilizingdispersiveorFourier transformsystems. Forexample,Ramanspectraof liquidethynylbenzeneandethynylbenzene-dwererecorded utilizingaHylgerspectrometerand4358 Aradiation(7 A/ mm) filteredthroughr hodami ne/nitritefilters.Depolarizationmeasurement sweremade(4).Thesedepolarizationmeasurement s aidindistinguishingbetweenin-planevibrationalmodesandout-of-planevibrationalmodesin thecaseofethynylbenzene.Thein-planemodesarepolarizedandtheout-of-planemodesare depolarized. Morerecently,Ramanspectraof inorganicsinwatersolutionhavebeenrecordedutilizingthe DilorXYRamantriplespectrographoperatinginthedoublesubtractivemodeandfittedwith 1200 g/ mmgratings.Thedetectorisa3-stagePeltier-cooledEG&GsiliconCCDmodel15305 equippedwithaThomson1024x256chip,operatedat- 6 0 ~(5). SamplefluorescencelimitstheapplicationoftheRamantechniquebecausefluorescenceisa first-orderphenomenon, andtheRamaneffectisasecond-orderphenomenon. Thisfluorescence problemhasbeenovercomerecentlybythedevelopmentofFT/ Raman. Inthiscase,near-IRis usedasthesourceof excitationofthemolecules.Coleyshawetal.reportedonthequalityof FT- Ramanspectraasrelatedtothecoloroftheminerals.Theyreportthatwhite-,gray-,yellow-, pink-,orange-,andred-coloredmineralsyieldgoodFT-Ramanspectra,buttheyhadlittle successwithblue-,green-,ordark-coloredminerals(6).Thisisbecausethesecolorsabsorbred light. ANicoletmodel800FT-IRspectrometer/ NicoletFT-RamanaccessoryequippedwithaCaF2 beamsplitter,Gedetector,andaCVImodelC-95Nd/YAGlasercanbeusedsuccessfullyin recordingtheRamanspectraofmanyorganicandinorganiccompounds. Thebeautyofthis combinationdeviceisthatitcanbeusedtorecordeitherIRorRamanspectra.Other manufacturersalsoproduceFT-Ramansystems. REFERENCES 1.Potts, W. J. Jr.(1963). Chemical Infrared Spectroscopy, New York: John Wiley & Sons, Inc. 2.Welti, D.(1970). Infrared Vapor Spectra, New York: Hyden & Son Ltd. 3.Nyquist, R.A.(1984). TheInterpretation ofVapor-Phase InfraredSpectra: Group Frequency Data, vols.1and2, Philadelphia: Sadlter Research Laboratories, Division of Bio-Rad Laboratories. 4.Evans,J.C. and Nyquist, R. A.(1960). Spectrochim. Acta, 16, 918. 5.Nyquist, R. A., Putzig, C. L., and Leugers, M. A. (1997). Infrared andRaman Spectral Atlas of Inorganic Compounds andOrganic Salts, vol. 1, Boston: Academic Press. 6.Coleyshaw, E. E., Griffith, W. P., and Bowell, R. J.(1994). Spectrochim. Acta, 50A, 1909. CHAPTER3 Alkyl Carbon-Hydrogen Vibrations Summary Othern-AlkaneVibrations 1,2-Epoxyalkanes SodiumDimethylphosphonate(CH3)2P(O)2Na Methyhhiomethyl Mercury,Dimethylmercury(4), andMethyhhiochloroformate(5) Cycloalkanes References FiguresTables Figure3-136(31) Figure3-237(31) Figure3-338(32) Figure3-439(32) Figure3-539(32) Figure3-640(32) Figure3-740(32) Table3-1 Table3-2 Table3-2a Table3-3 Table3-4 Table3-5 Table3-6 Table3-7 Table3-8 Table3-9 Table3-10 Table3-11 Table3-12 Table3-13 *Numbersinparenthesesindicatein-textpagereference. 41(31) 42(32) 43(32) 44(32) 45(32) 45(34) 46(34) 47(34) 47(35) 48(35) 49(35) 50(35) 52(35) 53(35) 32 34 34 34 35 35 35 Thischapterdiscussesalkylcarbon-hydrogenmolecularvibrationsand,insomecases,looksat howthesemolecularvibrationsareaffectedbytheirsurroundi ngchemicalenvironment. However,insomecasesthealkylcarbon-hydrogenvibrationswillbeincludedinthesection thatdiscussestheirmostdistinguishingmolecularvibrations. Theseriesofn-alkanes,CnH2n+2 werepreparedas0.5 wt.%solutionsinCCI4,CDC13, and 54.6 tool%CHC13/CC14.Table3.1liststheIR frequencydataforthevasym.CH3andvsym.CH3 stretchingfrequenciesforC5H12 toC18H38 (1).Figure3.1showsplotsofvasym.CH3vsthe molecular weight(M.W.)of each n-alkaneandFig.3.2showsplotsof vsym.CH3 vs M.W.of each n-alkane.AstudyoftheIRdataandfiguresshowthatvasym.CH3generallydecreasesasthe numberofcarbonatomsincreasesintheorderC5H12 toC18H38 by0.11to0.22 cm -1ingoing fromsolutioninCC14 tosolutioninCDC13. 31 32 Alkyl Carbon-Hydrogen Vibrations Thevsym.CH3modeforthisseriesofn-alkanesshowsthatitgenerallydecreasesby approximately0 . 8 c m-1i nCCI4solutionandapproximately1.2cm -1inCDC13solution progressingintheseriesC5H12t oC18H38ingoingfromsolutioninCCI4t osolutioninCDC13. Table3.2liststheIR absorbancedataforC5H12t oC18H38forthevasym.CH3andvsym.CH3 modes,Fig.3.3showsaplotof(vasym.CH3)/(vasym. CH2)vs A(vsym.CH3)/A(vsym. CH2)in CC14solutionforC5H12 t oC18H38,andFig.3.4showsaplotof(vsym.CH3)/(vsym. CH2)vs A(vasym.CH3)/A(vasym. CH2) inCCI4solutionforC5H12t oC18H38 .Bothplotsshowan essentiallylinearrelationship.Theslightdeviationfromlinearityismostlikelyduetoover- lappinginterferencesinthemeasurementofthesepeakheightabsorbances. Table3.2alistsabsorbanceratios;allof theseabsorbanceratiosforthevCH3 andvCH2 modes generallydecreaseprogressingintheseriesC5H12t oC18H38 . Table3.3listsIRdataforvasym.CH2andvsym.CH2forthen-alkaneat0.5 wt.%inCC14, CDC13, and54.6 mol%CDC13/CC14 solutions.Figure3.5showsplotsofvasym.CH2vsvsym. CH2ineachofthesolventsystems,andFig.3.6showsplotsof vasym.CH3vsvsym.CH3inall threesolventsystems.Theseplotsshowthattheserelationshipsarenotlinearovertheentiren- alkaneseries.Theplotsdopointoutingeneralthatasvasym.CH2decreasesinfrequency,vsym. CH2alsodecreasesinfrequencyprogressingintheseriesC5H~2 toC18H38, andthatthevasym. CH3andvsym.CH3frequenciesshowthesametrend. AstudyofTables3.1and3.3showsomeinterestingtrendsinCC14. CDC13, or54.6 mol% solutionsprogressingintheseriesC5H12 toC18H38. Thevasym.CH3 frequencydecrease ingoing fromsolutioninCC14 tosolutioninCDC13 issmall( ~0. 1cm -1)whileforvsym.CH3the frequencydecreaseismoreinCDC13 solution(1. 2cm -1)thaninCC14 solution(0. 7cm-1). In addition,thefrequencydifferenceforvasym.CH3inCC14 andinCDC13 increasesfrom0.11to 0.22 cm -1andforvsym.CH2inCC14 andinCDC13 decreasesfrom0.45to0.85progressingin theseriesC5H12t oC18H38 .Thevasym.CH2frequencydecreaseingoingfromsolutioninCC14 tosolutionissmall(0.1cm -1)whileforvsym.CH2 thefrequencydecreaseislargeringoing fromsolutioninCC14t oasolutioninCDC13(0. 6cm -1)progressingintheseriesC5H12t o C18H38 .Moreover,thesedatashowthatthevsym.CH2modechangesinfrequencyby afactorof approximately5timesmorethanvasym.CH2,vasym.CH3,andvsym.CH3.Inaddition,the vasym.CH2frequencyincreasesinfrequencywhilethevsym.CH2frequencydecreasesin frequencyingoingfromsolutioninCC14t oCDC13. Ingeneraltheselasttwotrendsgenerally decreaseprogressingintheseriesC5H12t oC18H38 . Table3.4liststhefrequencydifferencebetweenvasym.CH3andvsym.CH3andbetween vasym.CH2andvsym.CH2inthethreesolventsystems.Thesedatashowthatthefrequency separationis muchlarger forthetwovCH3 vibrations( ~85 -1)thanforthetwovCH2 vibrations ('-~ 69 cm-1).Figure3.7showsplotsofvasym.CH3--vsym.CH 3vsvasym.CH2 - - v s y m. CH2, whichclearly showsthe behaviorof thefrequency separationof thevCH3 andvCH2 vibrationsin thethreesolventsystems. SUMMARY Forn-alkanes,C5_18H12_38,thevasym.CH3occursintheregion2957.26-2959.55c m -1inCC14 andintheregion2957. 48-2959. 66cm -1inCDC13,andvsym.CH3occursintheregion 2872.35-2873.12c m -1i nCC14andintheregion2871.50-2872.67c m -1inCDC13. Moreover, Variables in Data Interpretation33 vasym.CH2occursintheregion2926. 61-2927. 73cm -1inCC14andintheregion2926. 92- 2928.14cm -1inCDC13, andvsym.CH2occursintheregion2854. 59-2861. 82cm -1inCC14 and intheregion2854.55-2861.21cm -1inCDC13. Inaddition,thesefourvibrationsdecreasein frequencyprogressingintheseriesC5H12throughC18H38. Then-alkanesarenonpolarmolecules,andonewouldexpectthattherewouldbemi ni malsolute-solventinteractionbetweenn-alkanemoleculesandsolventmoleculessuchasCC14 and CDC13.Then-alkanesingoingfromsolutionCC14tosolutioninCDC13solutionshowa frequencyincreaseof 0.11to0.22 cm -1forvasym.CH 3 andforvsym.CH 3 itdecreasesby- 0. 45 to- 0. 85cm -1,withdecreasesforvsym.CH 3progressingintheorderC5H12toC18H38. In addition,thevasym.CH2frequencydifferenceis0.41to0.23 cm -1andforvsym.CH2is- 0. 61 to- 0. 04cm -1.Againthevasym.CH2modeincreasesinfrequencyandthevsym.CH2mode decreasesinfrequencyingoingfromsolutioninCC14 tosolutioninCDC13. Thus,bothvasym. CH3andvsym.CH2increaseinfrequencyandbothvsym.CH3andvsym.CH2decreasein frequencyingoingfromsolutioninCC14tosolutioninCDC13 at0.5 wt.%solutions.Thesedata confirmthattheeffectsofthesesolventsaremi norinthesefourmolecularstretchingvibrations. It is not ewort hythatthevsym.CH2 vibrationshiftsprogressivelytolowerfrequencyintheorder C5H12toC18H38,andthatitdecreasesinfrequencybyafactorofatleast7timesmorethanthe vsym.CH3vibration. Apparently,then-alkaneprotonsformweakintermolecularhydrogenbondswiththefreepair ofelectronsontheC1atomsoftheCC14and/ or CDC13 solventsystem,andanexplanationis neededtodeterminethefrequencybehaviorofthesefourmolecularvibrationsingoingfrom solutioninCC14 tosolutioninCDC13.Asthesevasym.CH3,vasym.CH2,vsym.CH3,andvsym. CH2modesvibrate,theprotonsobtainaweakpositivechargeandthecarbonatomobtainsa weaknegativecharge.Thisistheso-calleddipolemoment changeduringthesemolecular vibrations.Therefore,then-alkaneprotonswouldformweakintermolecularhydrogenbonds withthefreepairof electronsontheC1 atomsoftheCC14 and/ or CDC13 solventsystem.TheC1 atomsofCC14 wouldbeexpectedtobemorebasicthanthoseforCDC13 duetothefactthatthe DatomattractselectronsfromtheC1atoms.Inaddition,thereisintermolecularbondi ng betweenDandC1suchasCC13D: C1CC12D : C1CC13. Therefore,onewouldexpectastronger C- H: C1 bondtobeformedbetweentheprotonsinn-alkanesandtheC1 atomsinCC14 thanfor C1atomsinCDC13. HydrogenbondingalsoweakenstheO- HorC- Hbond,andthevibration vOH: XorvC- H: Xisexpectedtodecreaseinf r equency~t hi siswhat wenotedinthevsym. CH 3andvsym.CH2modes.However,theoppositewasobservedforvasym.CH 3andvasym. CH2,wherebothmodesincreasedinfrequencyingoingfromsolutioninCC14 tosolutionin CDC13.Thisfrequencyincreaseforthevasym,modesneedsanexplanation.Becausethevasym. CH 3 andvasym.CH2modesincreaseinfrequency,itrequiresmoreenergyforthesetwomodes tovibrateingoingfromsolutioninCC14 tosolutioninCDC13.ThetwoCH 3 groupsareisolated by(CH2)~groups,andastheC1 atomsinCDC13 areweakerbasesthantheC1 atomsinCC14 a weakerC- H. . . C1CDC12bondisexpected.Consequently,thevasym.CH3andvasym.CH2 increasesinfrequencywhenCC14 isreplacedbyCDC13. 34Alkyl Carbon-Hydrogen Vibrations Ontheotherhandthereare(CH2),unitspresentinthen-alkaneserieswhicharecapableof formingnunitsof / H "C I ~C'C \/ H.cIineitherCC14 orCDC13 solution.Itisnotedthatvsym.CH3increasinglydecreasesinfrequency progressingintheseriesC5H12 toC18H38 ingoingfromsolutioninCC14 tosolutioninCDC13. ThisindicatesthattheC-H:C1CDC13bondstrengthisincreasedasnisincreasedfor CH3(CH2)nCH3. TheinductiveeffectofadditionalCH2groupsapparentlyweakenstheCH3 bonds,causingvsym.CH2todecreaseinfrequency asthenumberof CH2 groupsareincreasedin then-alkane.AsthenumberofCH2groupsareincreased,thedecreaseinvsym.CH2forn- alkanesdecreasesprogressingintheseriesC5H12 toC10H22 andisrelativelyconstantfrom C9H20toC18H38.ThissuggeststhattheeffectofthenumberofCH2groupsforming intermoleculehydrogenbondswithaCDC13 chainisminimizedaftereightCH2groupsare presentinthattheeffectofthenumberof(CH2)C1CDC13intermolecularhydrogenbonds formedbetweenthen-alkaneandCDC13 isminimizedintheseriesCllH24toC18H38.Itisalso possiblethattheC1 atomsinCDC13 arecloserinspacetotheC-Hbondscomparedtothatfor CC14, andthisfactwouldalsocontributetolowervsym.CH2frequencies. IntheseriesC5H12 toC18H38 thereis acomparatively largechangeinthevsym.(CH2),mode. Thereisadecreaseof7. 23cm -1CC14 and6. 66cm -1inCDC13.Thisisattributedtothe increasingnumberofCH2groupsstretchingin-phaseprogressinginthen-alkaneseries. ThesmoothcorrelationoftheabsorbancevaluesoftheCH2andCH3groupsastheratioof theCH3groupstoCH2groupsdecreasesisjustwhatispredicted.Thereisapparentlyno significantdifferenceinthedipolemoment sof eitherCH2orCH3stretchesprogressinginthen- alkaneseries. OTHERn- ALKANEVI BRATI ONS TheCH2bendasym.CH3bend,andthesym.CH 3bendoccursnear1467,1458,and 1378.5 cm -1inCC14 solution(Table3.5). 1, 2- EPOXYALKANES Table3.6listsIRvapor-phasedataforthealkyl(R)vibrationsof1,2-epoxyalkanes(2).The vasym.CH3modeoccursintheregion2953-2972 cm -1,thevasym.CH2modeintheregion 2920- 2935cm -1,thevsym.CH2modeintheregion2870- 2932cm -1,andthevsym.CH 3 bendingmodeintheregion1363-1388cm -1. SODI UMDI METHYLPHOSPHONATE( CH3 ) 2 P( O) 2 NaTheIRandRamandatingforsodiumdimethylphosphonatearelistedinTable3.7(3).The vasym.CH3andvsym.CH3modesareassignedat2985and2919 cm -1,respectively.Theasym. Variables in Data Interpretation35 (CH3)2bendingmodesareassignedat1428and1413 cm -1andthesym.(CH3)2bendingmodes areassignedat1293and1284 cm -1. METHYLTHI OMETHYLMERCURY, DI METHYLMERCURY(4),AND METHYLTHI OCHLOROFORMATE( 5 )Table3.8listsassignmentsfortheCH3-HgandCH3-Sgroupsforthepreceding3compounds.TheseassignmentsshouldaidthereaderinassigningvibrationsfortheseCH3groupsinother compounds.CYCLOALKANES Table3.9listsIRvapor-phasedataforcycloalkanes(6).Ramandatafortheringbreathingand ringdeformationmodesarealsopresentedforcyclobutaneandcyclopentane.Thevasym.CH2 modeoccursintheregion2930-3100cm -1.Thevsym.CH2modeoccursintheregion2880- 3020cm -1.BothvCH2vibrationsdecreaseinfrequencyastheringbecomeslarger.Thisisthe resultoflesserringstrainwithincreasingringsize.TheCH2bend,CH2wag,CH2twist,CH2 rock,ringbreathing,andringdeformationvibrationassignmentarealsopresented. MI SCELLANEOUSALKYLANDCYCLOALKYLCOMPOUND VibrationalassignmentsforcycloalkylgroupsarepresentedinTable3.10,foralkylgroupsof monomersandpolymersinTable3.11,forcyclopropanederivativesinTable3.12,andfor octadecane,octadecane-D38,tetracosane,andtetracosane-D50inTable3.13. REFERENCES 1.Nyquistl R. A. and Fiedler, S. L.(1993). Appl. Spectrosc., 47,1670. 2.Nyquist, R. A.(1986). Appl. Spectrosc., 40,275. 3.Nyquist, R. A.(1968). J.Mol. Struct.,2,111. 4.Nyquist, R. A. and Mann, J.R.(1972). Spectrochim. Acta,28A, 511. 5.Nyquist, R. A.(1967-68). J.Mol. Struct.,1,1. 6.Nyquist, R. A. (1984). The Interpretation of Vapor-Phase Infrared Spectra: Group Frequency Data, Philadelphia: Sadtler Research Laboratories, A Division of Bio-Rad. 36 Alkyl Carbon-Hydrogen Vibrations ~" ~l ~' ~ ~' ~1 ~ ~ U ~- o0, rr" E "o ~.- -- (1) N C: E 4) --" rn o T" 0 o L) k.) 0 ~ 0 a. u u = t~ 0 > '~" o b.. 0 0 ~ , ,, - l,IL i I I 0 0 0 0 0 0 0 0 0 0 0 ~'~ 0 ~ r I~ CO t.O ,~" CO C~J "" 0 o-r ~0 Variables in Data Interpretation 281 0 u o 4- tl , ~'~ > 9 c ~ o i'... e',',' Q,, 0 t~ N o . co o o o o o 0 o o 0 o ~ t,- 0 ~ gO I'- r4~ ~ ,~- CO 04 ~ C~I 0 o't" 282Aldehydes TABLE13.1AcomparisonofIRdataof nonconjugatedaldehydesindifferentphases Aldehyde 2( C=Ostr.)C=Ostr.C=Ostr.2( C=Ostr.)C=Ostr. vaporvaporCC14soln.neatneat cm-1cm-1cm-1cm-1cm-1 CHstr.2(CHbend)CHbend inER.neatinER.neatneat cm-1cm-1cm -1 Butyr Isobutyr 3- Cyclohexenyl34621741 Phenethyl34521743 Chloroacet Dichloroacet Trifluoroacet1788 Trichloroacet1778 Tribromoacet35011760 1730 .1 1748 .1 1768 .1 34301721282027201390 34301721281027101397 34201731283027001392 34101715281027221400 vaporvaporvapor 285927001365 284126801352 . 1SeeReference1. TABLE13.1ARamandataandassignmentsforaldehydes AldehydeC=Ostr.C- Hstr.inER.2( del t a- C- H) inER.del t a- C- Hgama- C- HC=Cstr. Propion*1723(7,p)2830(9,p)2718(9,p)1337(1,p) Isobutyr*1730(5,p)2813(5,p)2722(9,p) Hexanal*1723(10,p)2723(15,p)1303(7) Heptanal*1723(9,p)2723(14,p)1303(7) Bromal1744(10,p)2850(7,p)1353(2,p) Acrolein*1688(42,p)2812(3,p)1359(32,p) Benz*170128152732 Salicyl *1633 ( 22,P) 849(11,p) 798(14,p) 891(7,p) 895(5,p) 785(9,p) 1618(22,p) * Reference4. TABLE13.2IRdataandassignmentsfor4-X-benzaldehydesinthevaporandCHC13andCCI 4solution C=Ostr.C=Ostr.C=Ostr.[vapor]-[vapor]- 4-X-Benzaldehyde[vapor][CC14 ][CHC13 ][CC14 ][CHC13 ] x-Groupcm -I(A)cm -I(A)cm -1 (A)cm -1cm -1 [CC14 ] - [ CH C13 ]cm -1 NO 21728(1.289)1715.0(0.261)1710.4(0.417)1317.6 CN1713.7"1708.1" CF 31714.6"1707.1" Br1720(1.250)1710.41704.3"19.615.7 C11722(1.250)1709.1"1700.5"12.921.5 C6H 51705.0"1696.7" F1719(1.230)1706.7(0.862)1700.6(0.808)12.318.4 H1707.9"1699.2" CHBS1700.2"1691.1" CH301717(1.240)1697.2"1688.8"19.828.2 HO1715(1.250)1701.1"1688.2"13.926.8 (CH3)2N1711(1.042)1688.1"1671.8"22.939.2 5.4 6.1 8.6 6.1 8.4 12.9 16.3 * CorrectedforFermiRes. Va r i a b l e s i n Da t a I n t e r p r e t a t i o n 283 TABLE1 3 . 3 Th e C=Os t r e t c h i n g f r e q u e n c y f o r 4 - X- b e n z a l d e h y d e s i n v a r i o u s s o l v e n t s4-NO 24-CF 3 "I 4- CN*t 4-F4-C1 Solventcm-1cm-1cm-1cm-1cm-1 4-Br*t cm-1 4-H cm -1 Hexane1718.11717.81715.21715.7"1714.81714.81713.3 Diethylether1714.11713.31711.91709.71710.41709.61709.1 Methylt-butylether1713.31713.41711.31706.41709.71708.11708.8 Carbontetrachloride1714.41714.61713.71706.71710.71710.41708.5 Carbondisulfide1712.21713.11712.81705.11708.21709.51706.6 Benzene1711.11710.71709.61703.91706.71707.81705.2 Ace tonitrile1709.21707.61707.61701.61703.91703.61702.5 Nitrobenzene1708.61705.41707.11700.91703.11704.81702.1 Benzonitrile1708.41707.61706.91700.71701.41703.31701.8 M ethylenechloride1710.31707.51708.71698.7"1703.61704.31702.4 Ni t romet hane1708.51706.41707.11698.5"1702.61702.11701.5 t-Butylalcohol1716.21709.61707.91697.3"1712.11706.21710.4 Chloroform1710.41717.11708.11700.61703.41704.31701.9 Di met hyl sulfoxide1703.11699.71702.11697.71697.11697.11697.2 Isopropylalcohol1716.21709.71709.91698.4"1709.11706.91708.6 Ethylalcohol1715.61709.31708.71699.4"1705.61706.41707.1 Methylalcohol1708.81706.11707.21697.5"1704.61705.11705.1 Tetrahydrofuran1709.91710.41704.81705.81707.41705.1 1,2-Dichlorobenzene1703.71708.81702.71705.81705.41703.9 Range(1718.2-1803.1)(1717.8-1699.7)(1715.2-1702.1)(1715.4-1692.7)(1714.8-1697.1)(1714.8-1697.1)(1713.3-1697.2) 4-C 6 H 54-C 6 H 504-CH 3S4-CH 3O* t4-OH4-N (CH 3 ) 2 * ]" Hexane1711.41709.31705.91703.51696.9 Diethylether1707.61704.71700.81698.31696.91690.7 Methylt-butylether1706.71703.51701.21697.11697.41691.1 Carbontetrachloride1706.51703.41700.21695.61700.51684.6 Carbondisulfide1704.61701.11698.51694.71697.11684.4 Benzene1703.51700.71691.21695.91683.8 Acetonitrile1701.11697.51694.11690.61689.11674.1 Nitrobenzene1700.81697.31692.61690.61689.11678.9 Benzonitrile1700.81697.31692.31690.41688.21674.1 Methylenechloride1701.11697.11693.11690.31689.11670.1 Nitromethane1700.81696.21694.71689.11688.81671.1 t-Butylalcohol1698.61693.51685.31686.41681.71668.9 Chloroform1700.51696.61691.11688.81687.61670.6 Dimethylsulfoxide1694.31690.61687.11681.11667.4 Isopropylalcohol1702.41702.31685.31688.11680.91667.7 Ethylalcohol1704.51701.11684.11688.61692.31666.4 Methylalcohol1702.61698.31690.51687.11690.61664.4 Tetrahydrofuran1703.41700.61697.21697.81691.91685.4 1,2-Dichlorobenzene1702.31696.81694.81694.41691.21681.3 Range(1711.4-1694.3)(1709.3-1690.6)(1705.9-1684.1)(1703.5-1686.4)(1696.9-1680.9)(1696.9-1666.4) OverallRangeinall(1718.1-1664.4) solvents DeltaC=O53.7 tSe e t h e e x p l a n a t o r y t e x t o n p a g e 2 6 9 f o r d i s c u s s i o n o f ma t e r i a l d e s i g n a t e d b y a n a s t e r i s k .284Al dehydes TABLE13.4TheCHbendi ngvi brat i onfor4-X-benzaldehydesinCC14andCHCI3sol ut i onsandinthevaporphase 1%(wt./vol.)1%(wt./vol.) 4-X-BenzaldehydeVaporPCC14 ][CHC13 ][ CHC13 ]-[ CC14 ][vapor]-[ CHC13 ] Xcm -1cm -1cm -1cm -1cm -1 NO 21382.921384.791.87 CF 31386.361388.612.25 CN1381.281382.891.61 Br13871383.12 C113811383.61385.82.23 O1387.351390.112.76 F13861385.911388.392.48 C6H 51383.961385.451.49 C6H501386.521388.982.46 OH1393.46 CH 3S1387.341390.032.69 CH 301390.21394.314.11 (CH3)2N13851392.071394.282.21 Range(1381. 28-1392. 07)(1382. 89-1394. 28)(1. 49-4. 11) - 4 . 8- 2 . 4- 9. 3 Variables in Data Interpretation 285 r , L.) O ~ O ~ ~ ,.9o Ou: 4- a, ~ 9 ~ t.) ,~ tN ~ e o .,,~ I ",~ ~ ~ O o z o M % 7a ~ u ~7 L.) t~ bl I"..-00,---4 0 e.q e~,l (-,1 er ,--~ b,. o ~-i fr ~ ,--i ,--i oo o~ ~ oo oo oo oo e~ c~ e'q o'~ I'~. ox I'~ oo N -' 8 N ~ t~ mQ,) '-" ,t ~o r',,I oo oO I ~. I'~ dodod oo oo oo ~o oO oo o ~ o'~ ~,1 exl r-.. ~ m. t-.- (~ n'- !/'~ b.. e-,I t-~ f",l re3 e-,I ~1 ,..,* 8~ ~ .,..~ or< ~ tt~ e'q o6 oo r--- ct3 c'q e'q o~ o0 o~ ee30 ~D o0 r ee~ r--. o0 r--- cq e'q ,---4 r--. o0 t--- c',l c',l o0 o"3 tt~ ~D eq ~D ,.-4 I-,,. tt~ oo oo F-. r,.. r cq ce3 cq t-. r-,- oo r-.. r-.. o4 c,4 oo er tt~ tt~ o~ ~- r--. l--- e-,l cq c'4 oo ~D oo r--. o~ o~ o0 oo r-~ o0 r--. e-4 o4 oq o0 tt~ o'~ r--. o0 c,i o0 oo oO oo ~ #- o u~ oo ~I- u~ I~. ~ e',l ,-.i tr ~ b.. t-~ ~o L~L~ eq 286 Aldehydes t~ ..:t t~ t~ tl .,..~ ,w .,,.~ o~; "'2. ,.--, -A o ~ O II U O ~6 0 ~ e',,I r r r',,I r r r r r r cxl O0 O0 O0 O0 O0 O0 O0 O0 O0 O0 O0 O0 r r r r r cxl r r r C~l C-,I r Cxl r O~ r r ,-~ ,~ G r r ~- ,-~ O0 O0 O0 O0 O0 O0 O0 O0 O0 O0 O0 O0 r,,I Cxl r r r,,I r C',l r r cq r r Z 0 _ = ZOOmOmO ~ ~OO~ CHAPTER1 4Ke t one sSolvent-InducedFrequencyShifts Solute-SolventInteractionAffectedbyStericFactors Inductive,Resonance,andTemperatureEffects OtherChemicalandPhysicalEffects OtherConjugatedCarbonylContainingCompounds Chalcones IntramolecularHydrogenBonding Cycloalkanones Substituted1,4-Benzoquinones ConcentrationEffects References FiguresTables Figure14-1301(288) Figure14-2302(290) Figure14-3303(290) Figure14-4303(291) Figure14-5304(295) Figure14-6305(296) Figure14-7306(296) Figure14-8307(296) Figure14-9308(297) Figure14-10308(297) Figure14-11309(297) Figure14-12309(298) Figure14-13310(298) Table Table Table Table Table Table Table Table Table Table Table Table Table Table Table Table Table Table Table Table Table Table Table Table *Numbersinparenthesesindicatein-textpagereference. 288 289 290 291 291 294 294 295 297 299 299 14-1 14-2 14-2a 14-3 14-3a 14-3b 14-3c 14-4 14-5 14-6 14-7 14-7a 14-8 14-9 14-10 14-11 14-12 14-13 14-14 14-15 14-16 14-17 14-18 14-19 311 312 313 314 315 315 316 316 317 318 319 320 321 322 323 324 325 326 327 328 328 329 329 330 (288) (288) (288) (288) (289) (290) (290) (290) (290) (291) (294) (294) (294) (295) (295) (296) (298) (298) (298) (298) (298) (298) (298) (299) 287 288Ketones Acetoneisthesimplestmemberoftheketoneseries.Itsempiricalstructureis CH3- C( =O) - CH 3.Table14.1listsIRandRamandataforacetoneandacetone-d 6(1,2).The CD 3frequenciesandassignmentsarelisteddirectlyunderthosefortheCH 3frequenciesand assignments.Thefrequency ratiosforCH3/CD 3 vary between1.11and1.38.TheB 1andB2 CH 3 rockingmodetoCD 3 rockingmodefrequencyratiosare1.132and1.108,respectively,andthis indicatesthatthesetwomodesarecoupledwithB 1andB2modes,respectively.Thesedate illustratethatbothIRandRamandataanddeuteratedanalogsarerequiredtomakedetailed assignmentsof molecularcompounds. SOLVENT- I NDUCEDFREQUENCYSHI FTS Hallamhasreviewedtheliteratureconcerningattemptstodevelopanaccuratequantitativeand physicalmeaningfulexplanationof solvent-inducedstretchingfrequencies(3).Kirkwoodetal. (4)and Bauer andMagot(5)relatedtheobservedfrequency shifts andthedielectricconstante of thesolvent.The(K)irkwood(B)auer(M)agotworkresultedintheKBMequation: ( Vva por- - Vsolution/VVapor=A v / v = C [ ( e , - 1)/(2e+1)] JosienandFusonrefinedtheequationtoincludeatermbasedontheindexof refractionofthe solvent(6).Bellamy etal.foundthatA v / v forany soluteplottedvs( A v / v ) foranyothersolvent withinaclassofcompoundsproducedalinearcurve(7).Theythereforepredictedthatgroup frequencyshiftswerelocalassociationeffectsbetweensoluteandsolventandnotdielectric effects.Bellamyetal.proposedthatvhexaneshouldbesubstitutedforvvaporintheKBM equationinordertonegatetheeffectsof phasechange(7).Table14.2illustratestheapplication of theKBM equationusingIR datafor acetonevC=Ofrequenciesinvarioussolvents.Table14.2 showsthattheKBMequationpredictsthevC=Omodewithin- 2. 1to+14. 3c m - 1. Thebestfit isforacetoneinsolutionwithacetonitrileandtheworstfitisfor acetoneinwater.Inthecaseof CHC13andthefouralcohols,thevC=Ofrequencydifferencesbetweenthecalculatedand observedrangearebetween4.3and7.7 c m - 1. Thelargerdifferencesherecomparedtotheother solventsaremostlikelytheresultofintermolecularhydrogenbonding(C=O...HCC13or C=O. . . HOR) .Table14.2acontainsthecalculatedvaluesforA- 1/2A+1andX- Y/ XwhereAandY are equalto0to85andXequals85(seetheKBMequation).Thesetwosetsof dataareplottedin Fig.14.1.Thesedatashowthatany setof numbersusingtheequivalentof theKBM equationor Bellamy'sproposalyieldsamathematicalcurve.Inparticular,thelinearplotX-YvsY isthus meaninglessinpredictingvC--Ofrequencies(8).Intermolecularhydrogenbondinganddipolar interactionbetweensoluteandsolventaswellasdielectriceffectsmustplayaroleinthevC=O frequenciesofcarbonylcontainingcompounds.Stericfactors,whichalsoplayarolebetween solute-solventinteraction,mustalsobeconsideredinpredictingvC--Ofrequenciesinany particularphysicalphase(seeinwhatfollows). Table14.3liststheC=Ostretchingfrequenciesforaliphaticketonesinthevaporphaseand in1%wt./vol,invarioussolvents(9). Inthisseriesof ketones(dimethyl ketonethroughdi-tert-butylketone)thestericfactor of the alkylgroup(s)andthebasicityofthecarbonylgroupbothincrease.Asthestericfactorofthe alkylgroupincreasestheintermoleculardistancebetweenthecarbonylgroupandasolvent Variables in Data Interpretation289 moleculeincreases.Inthecaseofintermolecularhydrogenbondingbetweenasolventanda protonandacarbonylgroup,thestrengthofthehydrogenbonddependsuponatleastfour factors.Theseare,thebasicityof thecarbonyl group,theacidityof thesolventproton,thesteric factorof thedialkylgroupsof thedialkylketone,andthestericfactorof theatomsor groupsof thesolventmoleculesnotinvolveddirectlywiththeintermolecularhydrogenbond. AllofthealiphaticketonesexhibittheirvC=Omodeatitshighestfrequencyinthevapor phase(1699-1742cm-1).Insolution,thehighestvC~Ofrequenciesareexhibitedinhexane solution(1690.3-1727.2 cm -1). Withtheexceptionof dimethylketone(acetone)inhexane,the vC--Ofrequencyfortheotherdialkylketonesdecreasesinfrequencywithincreasingnegative valuesfor botha*(increasingelectron release tothecarbonyl group)and E s (an increasingsteric factorofthealkylgroup)andthesummationofcr*timesthesummationofE s 9 10 -2. Inthecaseof dimethylketone,itsvC~OmodeoccursatahigherfrequencythanvC- Ofor methylethylketoneonlyinthefollowingsolvents,tert-butylalcohol,chloroform,isopropyl alcohol,ethylalcohol,andmethylalcohol.Inthesesolventsthereisintermolecularhydrogen bondingbetweensoluteandsolvent(C~O. . . HORandC-O...HCC13).Moreover,inthese proticsolventsthevC=Ofrequency orderfor methylethyl ketoneanddiethyl ketoneis reversed fromthesequencethattheyexhibitwhenthesedialkylketonesareintheothersolvents. SOLUTE- SOLVENTI NTERACTI ONAFFECTEDBYSTERI C FACTORS Table14.3ashowsacomparisonofthecarbonylstretchingfrequencydifferenceforketonesin hexanesolutionandineachoftheothersolvents(9).Thestrengthofanintermolecular hydrogenbond(C--O. . . HORorC--O..-HCC13)isproportionaltothisfrequencydifference. Thelargerthisfrequency difference,the strongertheintermolecularhydrogen bond.Or, inother words,thestrongertheintermolecularhydrogenbondbetweentheketonesoluteandtheprotic solvent,themorevC--O shiftstolowerfrequency whencomparedtovC- Oforthesameketone inn-hexanesolution.Themostacid protonforthealcoholseriesisthatformethylalcohol,and theleast acidicprotonisthatfortert-butylalcohol.In addition,thestericfactor isthelargestfor tert-butylalcohol,andtheleastformethylalcohol.Themostbasicketonecarbonylgroupisin thecaseofdi-tert-butylketoneandtheleastbasiccarbonylgroupisinthecaseofdimethyl ketone.Neglectingstericfactors,thesefactswouldpredictthatthestrongestintermolecular hydrogenbondswouldbeformedbetweenmethylalcoholanddi-tert-butylketone,andthe weakestbetweentert-butylalcohol,anddimethylketone.StudyofTable14.3ashowsthatthe strongestintermolecularhydrogenisactuallyformedbetweenmethylalcoholanddiisopropyl ketone,andthestrengthof theintermolecularhydrogen bondwithdiisopropylketonedecreases inthe order methyl alcohol,ethyl alcohol,isopropyl alcohol,andtert-butyl alcohol.The strength oftheintermolecularhydrogenbondformedbetweendiisopropylketoneandchloroformfalls betweenthatfortert-butylalcoholandisopropylalcohol.Inthealcoholseries,thestrengthof theintermolecularhydrogenisalsostrongerbetweendiisopropylketonethanbetweendi-tert- butylketone.Thestrengthoftheintermolecularhydrogenbondislessinthecaseofethyl isopropylketonecomparedtodiisopropylketone,butitalsoisstrongerthaninthecaseof di- tert-butylketone.ThesedatashowthatstericfactorsincreasetheC- O. . . Hintermolecular 290Ketones hydrogenbonddistance,thusweakeningthepossiblestrengthofthisintermolecularhydrogen bond. TheketonevC=Ofrequencyshiftsinnonproticsolventsarealsolessinthecaseofdi-tert- butyl ketonevstheother dialkyl ketones.Therefore,stericfactorsof thealkyl groupsalsoplay a roleinthedielectriceffectsofthesolventuponthecarbonylgroup. Table14.3bshowsacomparisonofthecarbonylstretchingfrequencydifferencefordialkyl ketonesinmethylalcoholandotherproticsolvents(9).Inthiscase,thestrengthofthe intermolecularhydrogenbond(C--O--.H)decreasesasthenumberincreases.Thiscomparison showsthatstericfactorsalsoaffectthestrengthoftheintermolecularhydrogenbond. Table14.3cshowsacomparisonofthedifferencesinthecarbonylstretchingfrequenciesof dialkylketonesinhexanesolutionandinalcoholsolutionforsolutemoleculesnotintermo- lecularly hydrogen bonded(9).Thesedata show thatthefrequency differencedecreasesfor these ketonesinalcoholsolution,progressingintheseriesmethylalcoholthroughtert-butylalcohol. Withincreasedbranchingonthe0~-carbon atomoftheC- OHgroup,theintermolecularpolar effect dueto the alcohol oxygen atom is decreased;thus,thereis a lesser polar effect upondialkyl ketonecarbonylgroupssurroundedbyintermolecularlyhydrogen-bondedalcoholmolecules progressingintheseriesmethylalcoholthroughtert-butylalcohol.ThevC=Omodedecreases infrequencyasthepolarityofthesolventincreases. Table14.4listsdatafortheC=Ostretchingfrequenciesforn-butyrophenoneandtert- butyrophenonein 0-100 mol%CHC13/CC14 solutions(2%wt./vol.).ThevC=Omodefor both n-butyrophenone(1691-1682.6 cm -1)andtert-butyrophenone(1678.4-1674.1cm -1)decreases infrequency asthemole%CHC13/CC14 is increasedfrom 0-100 cm -1.However,it is notedthat thevC--Ofrequencyforn-tert-butyrophenonedecreasesinfrequencybyonlyone-half asmuch asthatforn-butyrophenone( 4. 3cm- 1/ 9cm- 1=0.48)ingoingfromsolutioninCC14to solutioninCHC13. TheC=Ogroupforthetert-butyroanalogismorebasicthanthen-butyro analog,andonthisbasisonewouldexpectastrongerintermolecularhydrogenbondtobe formedbetweenC=O...HCC13forthetert-butyroanalogthanforthen-butyroanalog,anditis notedthatthis is notthecase.Thereasonforthisisthatthestericeffectof thetert-butyro group preventstheC13CH protonfrom coming as close in spacetotheC=Ooxygen atom inthecase of tert-butyrophenone,whichpreventsitfromformingasstrongaC=O--.HCC13bondasinthe caseofthen-butyroanalogwherethen-butyrogrouphasalesserstericfactor. Figure14.2showaplotofthevC=Ofrequencyfortert-butyrophenonevsthemole% CHC13/CC14.TheresultingcurveisnonlinearduetotheformationofC=O...HCC13hydrogen bonds.Thegeneraldecreaseinfrequencyisduetothedielectriceffectsofthesolventsystem. Thecarbonylstretchingfrequenciesforn-tert-butyrophenoneoccuratlowerfrequencies (1678.4-1674.1cm -1)comparedtothosefordi-tert-butylketone(1685.9-1680.7 cm -1)in0- 100 mol%CHC13/CC14 duetoconjugationof thephenylgroup withthecarbonylgroup,which weakenstheC=Obond(10). I NDUCTI VE, RESONANCE, ANDTEMPERATUREEFFECTS Table14.5listIRdataforacetone,0~-chloroacetone,acetophenone,andbenzophenoneinCS 2 solutionbetween~29and- 100~(11).Figure14.3showsplotsofthecarbonylstretching frequenciesforthesefourcompoundsvsthetemperatureof theCS2solutionin~Theseplots VariablesinDataInterpretation291 showthatall of thevC--Omodesdecreaseinfrequency asthetemperatureis loweredfrom room temperature.Two vC--Ofrequenciesarenotedinthecaseof 0~ -chloroacetone,andbothoccurat ahigherfrequencythanvC--Oforacetone.Theinductiveeffectofan0~-C1 atomincreasesthe vC--Ofrequency,andtheinductiveeffectisindependentofspatialorientation.Thereisafield effectof aC1 atomnearinspacetothecarbonyl oxygen atom,andit alsocausesthevC~Omode toincreaseinfrequency.Thus,rotationalconformerIisassignedtothehigherfrequencyvC--O band,whilerotationalconformerII isassignedtothelowerfrequencyvC~-O bandinthecaseof 0~-chloroacetone.Theconcentrationof rotationalconformerIincreaseswhiletheconcentration ofrotationalconformerIIdecreaseswithdecreaseintemperature(11). Substitutionofoneortwophenylgroupsforoneortwomethylgroupsofacetoneyields acetophenone(vC--O,1689.4cm -1)andbenzophenone(vC--O,1663.3cm-1),respectively. Thus,thefirstphenylgroupcausesvC--Otodecreaseinfrequencyby28.1 c m - 1whilethe secondphenylgroupcausesvC--Otodecreaseinfrequencybyanadditional26.1 c m - 1. The phenylgroup(s)is(are)conjugatedwiththecarbonylgroup,anditweakenstheC--Obond, whichcausesitsvC--Omodetovibrateatlowerfrequency. OTHERCHEMI CALANDPHYSI CALEFFECTS Table14.6 showsa comparisonof thevC--Ofrequenciesfor 2%wt./vol,ketonein0-100mo1% (CH3) 2 SO/CC14solutions.Figure14.4 showsplotsof vC----O vs mole%(CH3) 2 SO/CC14for the samesixketonesasshowninTable14.6.Allsixcurvesdecreaseinfrequencyinalinearmanner asmole%(CH3) 2 SO/CC14isincreasedfrom~30to100mol %(CH3)2SO/CC14.Thisisinthe orderof theincreasingpolarityof thesolventsystem.Allsixketonesappeartobeaffectedinthe samemanner becausethelinearportionof thecurvesis parallel.ThevC----O frequenciesdecrease intheorderacetone,2,4,6-trimethylacetophenone,4-nitroacetophenone,acetophenone,4- methoxyacetophenone,andbenzophenone.Theeffectofconjugationwasdiscussedpreviously. Inthecaseof2,4,6-trimethylacetophenone,thecarbonylgroupandthephenylgrouparenot coplanar;therefore,theC=Ogroupisnotconjugatedwiththephenylgroup.Thus,theC=O groupishigherinfrequencythanthatexhibitedbyacetophenoneby13 c m - 1, butlowerin frequencythanacetoneby14 c m - 1. Hammettcrpvaluesfor4-nitroand4-methoxybenzophe- nonecausethevC~-Omodetobehigherandlowerinfrequency,respectively,thanvC--Ofor acetophenone. OTHERCONJ UGATEDCARBONYLCONTAI NI NG COMPOUNDS Itisinterestingtoconsiderthepossiblemolecularconfigurationsofconjugatedcarbonyl containingcompounds.Lin-Vienet al. (13)havereviewedthepublishedstudiesofthese compounds(14),andthey reportthata planarcompoundsuchas 3-buten-2-oneexistsin s-trans 292Ket ones ands-cisconfigurationsinCC14solution.Thesetwoconformersfor3-buten-2-oneare illustratedhere: 0 s-tmnss-cis CC1_4s o l n , (crn "1)CCl~ sol n. (crn "1) C=OstretchinaC=Ostretchin_a 1687vs1707vs, C=CstretchinaC=Cstretchina 1648w1618m,sh ( C=Ost r . ) - ( C=Cstr,)( C = O s t r . ) - ( C = C str.) 3989 Thesetwoconformersresultfrom180 ~rotationoftheC=CgroupabouttheC2- C 3single bond.Thisnotationadequatelydescribesthemolecular configurationsintheforementionedcase (13-15).InthevaporphasetheC=Ostr.andC=Cstr.frequenciesareassignedat1715and 1627 c m - 1, respectively(16).Thefrequencyseparationbetweenthesetwomodesis88c m-1.Correspondingmodesforthes-transisomerarenotdetectedinthevaporphaseatelevated temperature.Therefore,3-butene-2-oneexistsonlyasthes-cisconformeratelevatedtempera- tureinthevaporphase.TheIR bandsat986and951c m -1c onf i r mthepresenceof theCH=CH 2 group. Similarly,acompoundsuchas3-methyl-3-buten-2-onecanalsobeadequatelydefinedas s-transands-cisconformersasillustratedhere: OO H- C ~\ HH InthevaporphaseatelevatedtemperaturetheIRbandsat1700cm -1and1639cm -1are assignedtoC- OstretchingandC=Cstretching,respectively(16).Thefrequencyseparation betweenthesetwomodesis61 c m -1. Therefore,3-methyl-3-buten-2-oneexistsonlyasthes-cis conformerinthevapor-phaseatelevatedtemperature.TheIRbandat929 c m -1confirmsthe presenceoftheC=CH 2group. Vari abl esi nDataInterpretation293 Letusnowconsiderthenumberofpossibleconformersfor4-methyl-3-buten-2-one" ./\ H3CXXHCH3HC H,HC H3 s-transs-transs-ciss-cis [s-trans,cis CH3][s-trans,transCH3][s-cis, cis CH3][s-cis, transCHa] Herewenotethats-transands-cisdonotdefinethespatialpositionoftheCH 3group. Therefore,theadditionaltermtransCH 3 andcisCH 3 must beusedtoadequatelyspecifyeachof thefour possibleconformersfor 4-methyl-3-buten-2-oneasshownin bracketsintheconformers shownhere. TheC--OandC=Cstretchingfrequenciesfor4-methyl-3-buten-2-oneinCCI 4solutionare givenhere: .s-transconformer(cm ~ )C=Ostr. ( vs) C=Cstr. (m,sh) 1674165 4 ( C = O s t r . ) - ( C = C str,.) ( cm 1 )2 9 s-cisconformer(cm 1)C=Ostr. (s)C=Cst r . (s) 1692163260 Thesedatasupportonlythepresenceofthes-cisors-transpartoftheconformer.NMRdata areneededtohelpestablishthepresenceofacisortransCH 3group,andthesedatawerenot available.SimilarcompoundscontainingthetransCH=CHgroupexhibitaweak-medi umband intheregion974-980cm -1. Asalreadyshown, theC=CandC=Ostretchingfrequenciesfors-cisands-transconformers are very different.Thequestiontoansweris whytheyaredifferent.It is possiblethatinonecase theC=CandC=Ostretchingvibrationscoupleintoin-phaseandout-of-phasestretchingmodes inoneconformerandnotinthecaseoftheotherconformer. Inthecaseof3-methyl-l, 3-pentadienethetwoC=OC- C=Cgroupsarecoupledintoanin- phase(C=C)2vibrationandanout-of-phase(C=C)2vibrationasdepictedhere: . ?H3C H3 HH in-phase( C = C ) 2 s t r . out-of-phase(C=C)2st r .Inthecaseof3-methyl-l, 3-pentadiene, thein-phasestr.modeoccursat1650 c m- 1andthe out-of-phasestr.modeoccursat1610cm -1inthevaporphase.Incasessuchas2-methyl-2- penteneand2,4,4-trimethyl-2-pentenetheC=CbondisnotconjugatedandtheC=Cstretching modeoccursat1665and1658 cm -1,respectively.Therefore,it appearsthatthein-phase(C=C)2 stretchingvibrationoccursnearthatexpectedforisolatedC=Cstretchingvibrationswhilethe out-of-phase(C=C)2stretchingvibrationsoccurconsiderablylowerthanisolatedC=Cstretch- ingvibrations. 294Ketones ThesamebehaviorfortheC=OandC- Cstretchingmodeswasalready notedhereforthes- cisconformers.TheC=Ostr.modeoccurredatafrequencyexpectedforaconjugatedcarbonyl containingcompound,whiletheC=Cstr.modeoccurredat a lowerfrequencythanexpectedfor anisolatedC- Cdoublebond.Ontheotherhand,thes-transconformersexhibitedfrequencies forC=OandC=Cstretchingexpectedfor conjugatedcarbonylcontainingcompoundswhilethe C=Cstretchingfrequencyoccurredatfrequenciescomparabletothoseexhibitedby compounds containingisolatedtransCH--CHgroups.Onthisbasis,webelievethatthesemodesarebest describedasin-phaseandout-of-phaseC- - C- C- - Ostretchingvibrationsinthecaseof thes-cis conformers,andasC=OandC--Cstretchingmodesinthecaseofthes-transconformers. Compoundssuchas3-methyl-4-phenyl-3-buten-2-oneand~-hexylcinnamaldehydecontainthe C--CHgroup,andweareonlyabletoestablishthattheyareinthes-cisconfiguration.Thecis [H,CH 3]andcis[H,C6Hll]areoneofthetwopossibilitiesforthesetwocompounds.The bandsintheregion867-870cm -1supportthepresenceoftheC--CHgroup. Table14.7alsolistsIRvapor-phasedataforchalconeanditsderivatives.TheIRdatais recordedatelevatedtemperature,andallof thedataindicatethatthesecompoundsexistonly as thes-cis,transCH=CHconformer. CHALCONES Chalconeshavethefollowingempiricalplanarstructure: oH Thephenylgroupofthestyrylgroupisnumbered2through6,andthephenylgroupofthe benzoylgroupisnumbered2'through6'.Substitutioninthe2,6-positionswithC12or(CH3) 2 wouldstericallypreventthestyrylphenylgroupfrombeingcoplanarwiththerestofthe molecule.Moreover,substitutionof C12 or(CH3) 2 inthe~,2-positionsonthestyryl groupwould alsosterically preventthestyryl phenylgroupfrom beingcoplanarwiththerestof themolecule. Substitutionof C12 or(CH3) 2 inthe2' ,6' -positionswouldsterically preventthephenylgroupof thebenzoylgroupfrombeingcoplanarwiththerestof themolecule.Thesixchalconesstudied, (seeTable14.6)exhibitvC=Ointheregion1670-1684cm -1,andexhibitvC=Cintheregion 1605-1620cm -1.ThefrequencyseparationbetweenvC=OandvC=Cvariesbetween59and 73cm -1(16).Thesedataindicatethatthesechalconesexistinplanars-cisconfigurations. Noncoplanarchalconeswerenotavailableforstudy. Table14.7a lists somefundamentalvibrationsfortheconjugatedketonesstudied.These group frequenciesaidinidentifyingthesecompoundsbyadditionalspectra-structureidentification. I NTRAMOLECULARHYDROGENBONDI NG Table14.8listsIR datafor 2-hydroxy-5-X-acetophenoneinCC14 solution(3800-1333cm -1)and CS 2 solution(1333-400cm-1).TheintramolecularvOH. . . O=Cand7OH. . . O=Cvibrationsfor 2-hydroxy-5-X-acetophenonewerepresentedinChapter7. Var i abl esi nDat aI nt e r pr e t a t i on295 ThevC=O. . . HOfrequenciesfor2-hydroxy-5-X-acetophenonesoccurintherange1641- 1658cm -1(17).ThesecompoundsexhibitvC=O- . . HOatlowerfrequencyby404- 10cm -1 comparedtononhydrogenbondedacetophenonesduetothestrengthoftheC=O. . . HObond. Inthesolidphase(Nujolmull)thevC=O- . - HOmodeoccurs13to17 cm -1lowerinfrequency thaninCC14 solution. The2-hydroxy-5-X-acetophenonesexhibitcharacteristicvibrationsintherange954- 973cm -1[ C- C( =) - Cstretching],1283-1380cm -1[phenyl-0stretching],and1359- 1380 cm -1[symmetricCH 3 bending]. CYCLOALKANONES InthevaporphasecycloalkanonesexhibitvC=Ofrequenciesintherange1719-1816cm -1(2). Thefrequenciesdecreaseasthenumberof carbonatomsinthecycloalkanoneringincreasefrom 4to8and10(1816,1765,1732,1721,1720,and1719 c m- 1, respectively).Thebehaviorof the vC- OfrequencyisattributedtochangesintheC- C( =) - Cbondangle.Duringacycleof C--O stretching,moreorlessenergy isrequiredtomovethecarbonylcarbonatomastheC- C( =) - C bondanglebecomessmaller orlargerthanthenormalC- C( - - ) - Cbondangleforanopenchain ketonesuchasdimethyl ketone(acetone).Thisis becauseduringacycle of C=Ostretching,the C- C( =) - Canglemustincrease,andasthesizeofthecycloalkanoneC- C( =) - Cangle decreasesfromnormalbondangles(cyclohexanoneforexample),themoredifficultitisfora normalC=Ovibrationtooccur.Conversely, incaseswherethebondangleis largerthannormal, theeasieritisforthevC=Ovibrationtooccur. Table14.9listsIR vapor-phasedataandassignmentsforcyclobutanoneandcyclopentanone. ThevC=Ofrequencieswerealreadydiscussedhere.Itshouldbenotedthatvasym.CH 2,vsym. CH2,CH 2twisting,theringdeformation,andthefirstovertoneofvC=Oalsodecreasein frequencywhiletheCH 2 bendingmodeincreasesinfrequencyastheringsizeisincreasedfrom fourtofivecarbonatoms. Table14.10liststheC=Ostretchingfrequenciesforcyclopentanoneandcyclohexanonein thevapor,neat,andsolutionphases(18). CyclopentanoneexhibitsvC=Oat1765(vapor)and1739. 2cm -1inneatphaseafter correctionforFermiresonance(18).Inallsolutions,vC--OhasbeencorrectedforFermi resonance.CyclopentanoneexhibitsvC=Oat1750.6cm -1inn-hexanesolutionandat 1728.8cm -1inwatersolution.CyclohexanoneexhibitsvC=Oat1723cm -1inn-hexane solutionandat1701c m- 1inethylalcoholsolution.AftercorrectionforFermiresonance, vC--Ofor cyclopentanonedecreasesinfrequency by approximately17.1 c m- 1progressinginthe seriesof solventshexanethroughmethyl alcohol(18).Progressinginthesame seriesof solvents, vC=Ofor cyclohexanonedecreasesinfrequency by approximately22 c m- 1.TheC=Ogroupfor cyclohexanoneismorebasicthantheC=Ogroupforcyclopentanone,andthisisgivenasthe reasonthatthereismoreof asolute-solventinteractioninthecaseof cyclohexanonethaninthe caseofcyclopentanone(18).ThevC=Ofrequenciesforthesetwocycloalkanonesdonot correlatewellwiththesolventacceptornumbers(AN),andthisisattributedtostericfactorsof thesolventsthathindersolute-solventinteraction. Figure14.5showsaplotofvC=Oforcycohexanonevsmole%CHC13/n-C6H14. Definite breaksintheplotarenotedat~2. 5to1,~6to1,~50to1,and~62. 1to1molofCHC13 to imolcyclohexanone.ThecauseofthesevC=Ofrequencyshiftsismostlikelyaresultof 296Ketones different hydrogen bonding complexes betweenC- OandCHC13 whichchanges withincreasing CHC13concentration,thatis, (CH2)sC=O...HCCI3 (CH2)sC=O''" H C C 13(HCCI3)n CHCCI3(HCCIs)n (CH2)sC=O CHCCI3(HCCI3)n ThegeneraldecreaseinthevC=Ofrequencymostlikelyistheresultofcontinualchangein solventdielectriceffect.Figure14.6showsaplotofvC=Oforcyclohexanonevsmole% CC14/n-C6H14. Thislinearplotdecreasesinfrequencyasthemole%CC14/n-C6H14 increases. Thedielectriceffectofthissolventmixtureincreasesasthemole%CC14/n-C6H14 increases, causingvC--Otooccuratlowerfrequencyinalinearmanner.UnlikeCHC13, thereareno differentCC14 solutecomplexesasnoted. Figure14.7showaplotofvC=Ofor0.345mo1%acetoneinCHC13/CC14 solutionvsthe mole%CHC13/CC14 (19).Thisplotshowsthatitislinearoverthemole%CHC13/CC14 range of~17- 100%. Extrapolationofthelinearplottozeromol%CHC13 indicatesthatthevC=O frequencyforacetoneintherange0-17%ratioCHC13/CC14 variesfromlinearityby~1cm -1. ThemolefractionofCHC13isinexcessofthe0.345mo1%acetonepresent,evenatthe 1.49 mol%ratioCHC13/CC14 wheretheCHC13 protonsforms weak hydrogen bonds betweenC1 atomsof otherCHC13 moleculesandCCI4 moleculesaswellaswiththecarbonyloxygenatom (19). F i g u r e 1 4 . 8s h o w s ap l o to ft h ev C - O f r e q u e n c y for a c e t o n ev st h er e a c t i o nfield for e a c h o fthemole%CHC13/CC14 solutions.ComparisonofFig.14.7withFig.14.8showsthatthe ( e - 1)withethedielectricconstantofeachcurvesareidentical.ThereactionfieldJR]2e +n 2' solvent,andntherefractive indexof eachsolvent.A plotof mole%CHC13/CC14 vs thereaction field yields a linear curve(19).Therefore,it appearsasthoughtherefractiveindexof thesolvent aswellasthedielectricvalueofthesolventsystemtogetherwithintermolecularhydrogen bondingwithC=OofthesoluteaffectstheinducedfrequencyshiftofvC=Oinsolutionwith CHC13/CC14.Insummary,thefrequencybehaviorofthesolvent-inducedketonecarbonyl stretching vibration,vC=O,is affected by thereactionfield,inductiveeffects,andsolute-solvent intermolecularhydrogenbonding(29). Table14.11listsIR datafor14H-dibenzo[a, j]xanthen-14-oneinCHC13/CC14 andinvarious solvents(20).Thisketonehasthefollowingempiricalstructure: " ~o/ / "I Variables in Data Interpretation297 Forsimplicity,thiscompoundisgiventhenameDX-14-O.Themaxi mumsymmetryfor DX-14-OisC2v. ThevC--OmodebelongstotheA 1speciesifithasC2vsymmetry.TheDX- 14-OhastwosignificantIRbandsintheregionexpectedforvC--O,andasolutionstudyin CHC13/CC14solutionwasusedtohelpexplainthepresenceofthesetwoIR bands.Inorderfor vC=OtobeinFermiresonanceinthecaseof DX-14-Oboththecombination(CT)orovertone (OT)andvC--OmustbelongtotheA 1 symmetry species.Inaddition,theCT orOTwoul dhave tooccurintherangeexpectedforvC=O.It isobviousfromtheketonestructuregivenherethat theIRdoubletcouldnotbeduetothepresenceofrotationalisomers. Figure14.9showsIR spectraof DX-14-Ointheregion1550-1800cm -1. Spectrum(A)isfor asaturatedsolutioninhexane,spectrum(B)isforasaturatedsolutionincarbontetrachloride, andspectrum(C)isfora0.5%solutioninchloroform.InhexanetheIR bandsoccurat1651.9 and1636.8cm -1,incarbontetrachloridethebandsoccurat1648.9and1634. 9cm -1,andin chloroformthe bandsoccurat1645.4and1633.1cm -1. Inspectionof theirIR spectrashowsthat theabsorbanceratioofthelowfrequencybandtothehighfrequencybandincreasesinthe solventordern-C6H14 ,CC14,CHC13. Figure14.10showsaplotofvC--OandtheOT orCTin Fermiresonance,andvC=OandOTorCTcorrectedforFermiresonance.Thecorrecteddata showthat unperturbedvC--Ooccursat higherfrequencythanunperturbedOT orCT at mole% CHC13/CC14below~28%; atmole%CHC13/CC14above~28%unperturbedvC=Ooccursat a lowerfrequencythanunperturbedOT orCT. WithoutFR correction,eachIR bandresultsfrom somecombinationofvC=OandtheOT orCT.Atthe~28mol %CHC13/CC14,bothIR bands resultfromequalcontributionsofvC=OorOT orCT. Figure14.11showsplotsofvC--OandOTorCTandtheircorrectedfrequenciesvsthe solventacceptornumber(AN)foreachoftheeightsolvents,numbered1-8,andlisted sequentically.TheseplotsshowthatingeneralthetwomodesinFermiresonanceand unperturbedvC=OdecreaseinfrequencyastheANofthesolventisincreased.Thescattering ofdatapointssuggeststhattheANvaluesdonottakeintoaccountthestericfactorofthe solvent,whichcausesvarianceinthesolute-solventinteraction.Itshouldbenotedthat unperturbedvC=OoccursatlowerfrequencythantheOCorOTinonlychloroformand benzonitrilesolutions. SUBSTI TUTED1, 4- BENZOQUI NONES Theketone1,4-benzoquinonehasthefollowingplanarstructure: IthastwoC--Ogroups,andthesecoupleintoanin-phase(C--O)2stretchingvibration, rip(C--O)2,andanout-of-phase(C--O)2stretchingvibration,Vop(C=O)2.InCC14 solution,1,4- benzoquinoneexhibitsastrongIR bandat1670 cm -1andamedi umstrongbandat1656 cm -1. Withoutconsiderationofthemolecularsymmetryof1,4-benzoquinone,itwouldseemreason- abletoassignthe1670cm -1bandtoVop(C--O)2andthe1656cm -1bandt oYip(C--O)2. However,1,4-benzoquinonehasacenterofsymmetryandithasVhsymmetry.The30 fundamentalsaredistributedas6Ag,1Big,3B2g, 5Blu ,52u, and3B u.OnlytheuclassesareIR 298Ketones active,andonlythegclassesareRamanactive.TheVop(C=O)2modebelongstothebluspecies, andtheVip(C=O)2modebelongtotheAgspecies.Ofcourse,1,4-benzoquinonecannothave rotationalconformers.Therefore,oneoftheforementionedIRbandseitherresultsfromthe presenceofanimpurity,orelseitmustresultfromaBlucombinationtoneinFermiresonance withthe~,op(C=O)2, blufundamental.ItcouldnotbeinFermiresonancefromanovertoneof a lowerlyingfundamental,becauseafirstovertonewouldbelongtotheAgspecies.TheRaman bandat1661.4cm -1inCC14 solutionisassignedtotherip(C--O)2,Agmode. Figure14.12showsplotsofVop(C=O ),bluandtheCTBlumodesinFermiresonance,and theirunperturbedfrequenciesaftercorrectionforFermiresonancefor1,4-benzononein0.5% wt./vol,orlessin0-100mo1%CHC13/CC14.ThetwoobservedIRbandfrequenciesinFermi resonanceinthiscaseincreaseinfrequencyasthemole%CHC13/CC14isincreased.However, unperturbedVop(C--O)2 decreasesinfrequencyasthemole%CHC13/CC14increases,andthisis alwaysthecaseforothercarbonylcontainingcompoundsasthemole%CHC13/CC14is increased.ItisnotedthattheunperturbedCTblumodeincreasesinfrequencyasthemole% CHC13/CC14isincreasedfrom0-100%. Inthiscase,at~,25mol %CHC13/CC14bothIR bands resultfromequalcontributionsfromVop(C--O)2 andtheCTblumode. Table14.12listsIRandRamandataforseveral1,4-benzoquinonesinCCI 4andCHC13 solutions(at0.5%wt/vol,orlessduetosaturation).Thepointgrouppertainingtotheir molecularsymmetryisgivenforeachoftheseketones.Noneoftheother1,4-benzoquinones showIRevidencefortheVop(C=O)2modebeinginFermiresonance.TheVop(C=O)2modefor these1,4-benzoquinesoccursintherange1657-1702. 7cm -1inCC14 solutionandatslightly lowerfrequencyinCHC13 solution.InCHC13 solution,Vip(C=O)2occursintherange1666.9- 1697.7cm -1.Theincreasinginductiveeffectofthehalogenatoms(progressingintheorderBr, C1,F)togetherwiththeirfieldeffectincreasebothVop(C=O)2andVip(C=O)2 frequencies(22). Tables14.13-14.17listIRdatafortetrafluoro-l,4-benzoquinone,tetrachloro-l,4-benzoqui- none,tetrabromo- 1,4-benzoquinone,chloro- 1,4-benzoquinone,and2,5-dichlorobenzo-quinone inthreedifferentsolventsystems. IntheIR,tetrafluoro-l,4-benzoquinoneexhibitsstrongIRbandsat1702.7and1667.6cm -1 inCC14solutionandat1701.4and1668.4cm -1inCHC13solution.Inallcasesthehigher frequencybandhasmoreintensitythanthelowerfrequencyband.ThesetwoIR areassignedto Vop(C=O)2andVop(C=C ),respectively.Figure14.13showsplotsof Vop(C--O)2andVop(C=C)2 for1,4-tetrafluorobenzoquinonevsmole%CHC13/CC14.TheVop(C=O)2modedecreasesin frequencyasexpectedasthemole%CHC13/CC14isincreased.TheVop(C=C)2ringmode increasesinfrequencyasthemole%CHC13/CC14isincreased. Thefrequencybehavioroftheothersubstituted1,4-benzophenonesisdiscussedindetailin Reference21,andthereaderisreferredtothispaperforfurtherinformationontheseinteresting solute-solventinteractions. Table14.18listsIRdatafor3, 3', 5, 5' -tetraalkyl-l ,4-diphenoquinonesinCHC13 solutionand inthesolidphase(22).The3,3' ,5,5' -tetraalkyl-l,4-diphenoquinoneshavethefollowing empiricalstructure: RR' /\ RR' VariablesinDataInterpretation299 Whenthe3,3' ,5,5' positionsaresubstitutedwithidenticalatomsorgroups,thecompounds haveD2hsymmetry(22).Thesemoleculeshaveacenterofsymmetry,andonlytheVop(C-O ), B3ufundamentalisIRactive.TheVop(C----O)2, AgfundamentalisonlyRamanactive.The Vop(C--O)2modeforthe3,3' ,5,5' -tetraalkyl-l,4-diphenoquinonesoccursintherange1586- 1602cm -1inthesolidphaseandintherange1588-1599cm -1inCHC13solution.The compound3,3' -dimethyl,5,5' -di-tert-butyl-l,4-diphenoquinonehasCzvsymmetry,andinthis case bothVip(C=O)2areIR activeas wellasRamanactive.InthiscasetheIR bandat1603 c m - 1 isassignedtobothVop(C-O)2andrip(C-O)2.ThefrequenciesinbracketsinTable14.18are calculated.Allofthesefive3, 3', 5, 5' -tetraalkyl-l ,4-diphenoquinonesexhibitaweakIRbandin therange3168-3204cm -1inthesolidphaseandintherange3175-3200cm -1inCHC13 solution.ThesebandsareassignedtothecombinationtoneVop(C--O)2+rip(C--O)2.Usingthe observedVop(C--O)2 andcombinationtonefrequenciesforthesecompounds,therip(C-O)2 frequenciesarecalculatedtooccurintherange1579-1601c m - 1inthesolidphaseandinthe range1583-1602cm -1CHC13 solution(22).Thesedataconfirmapreviousconclusionthat diphenoquinonesexhibita strong IR bandnear1600 c m - 1,whichmustincludestretchingof the C--Obond(23).Thus,itispossibletodistinguishbetween4,4' -diphenoquinonesand1,4- benzoquinones,sincethelattercompoundsexhibitcarbonylstretchingmodes30to80 c m - 1 higherinfrequency(21). CONCENTRATI ONEFFECTS Table14.19listsdatathatshowthedependenceof thevC=Ofrequencyof dialkylketonesupon thewt. / vol. %ketoneinsolutionwithCC14or CHC13 (10).InCC14solution,thevC=Omode for diisopropylketonedecreasesmoreinfrequencyingoingfrom~0. 8%to5.25%thanitdoes for di-tert-butylketoneatcomparablewt./vol,ketoneinCC14solution( - 0. 19to--0.08 c m - 1at5.25%wt./vol.).InCHC13 solution,theshiftof vC- Oisintheoppositedirectiontothatnoted forCC14solutions.At5.89%wt./vol,inCHC13solution,vC=Oincrease0. 38c m- 1for diisopropylketoneandat5.78wt./vol.inCHC13fordi-tert-butylketonetheincreaseis 0.1 r - 1. ThesmallervC- Ofrequencyshiftsinthecaseofthedi-tert-butylanalogcompared tothediisopropylanalogisattributedtostericfactorsof thealkyl group.Thestericfactorof the tert-butylgroupsdoesnotallowasmuchsolute-solventinteractionbetweenC- Oandthe solventasitdoesinthecaseofthediisopropylanalog.Withincreaseinthewt./vol,of ketone/CHC13vC=Oincreasesinfrequency,indicatingthatthestrengthoftheC---O...HCC12 C1--.(HCClzC1)nintermolecularhydrogenbondbecomesweakerasnbecomessmaller. REFERENCES 1.Schrader, B. (1989). Raman/Infrared Atlas of Organic Compounds, 2nd ed., Weinheim, Germany: VCH. 2.Nyquist, R. A. (1984). The Interpretation of Vapor-Phase Infrared Spectra: Group Frequency Data, Philadelphia: Sadtler Research Laboratories, a Division of Bio-Rad Labortories, Inc. 3.Hallam, H. E.(1963). Infra-Red Spectroscopy andMolecular Structure, p. 420, M. Davies, ed., New York: Elsevier. 4.Kirkwood,J.G., West, W., and Edwards, R. T. (1937). J.Chem. Phys., 5,14. 5.Bauer E. and Magot, M. (1938). J.Phys. Radium, 9, 319. 300Ketones 6.JosienM.L.andFuson,N.(1954).J.Chem. Phys.,22,1264. 7.Bellamy,L. J.,Hallam,H.E.,andWilliams,R.L.(1959).Trans. Farad. Soc., 55,1677. 8.Nyquist,R.A.(1989).Appl. Spectrosc.,43,1208. 9.Nyquist,R.A.(1994).Vib. Spectrosc.,7,1. 10.Nyquist,R.A.,Putzig,C.L.,andYurga,L.(1989).Appl.Spectrosc.,43,983. 11.Nyquist,R.A.(1986).Appl. Spectrosc.,40,79. 12.Nyquist,R.A.,Chrzan,V., andHouck, J.(1989).Appl.Spectrosc.,43,981. 13.Lin-Vien,D.,Cohhup,N.B.,Fatelely,W.G.,andGrasselli,J.G.(1991).TheHandbookofInfraredandRaman CharacteristicGroupFrequencies of Organic Molecules,SanDiego:AcademicPress,Inc. 14.Bowles,A. J.,George,W.O.,andMaddams,WE(1969) J.Chem.Soc., B,810. 15.Cottee,EH.,Straugham,B.P.,Timmons,C. J.,Forbes,WE,andShilton,R.(1967). J.Chem. Soc., B,1146. 16.(1982)SadtlerStandardInfrared Vapor phaseSpectra,Philadelphia:SadtlerResearchLaboratories,aDivisionof Bio- Rad,Inc. 17.Nyquist,R.A.(1963).Spectrochim.Acta,19,1655. 18.Nyquist,R.A.(1990).Appl. Spectrosc.,44,426. 19.Nyquist,R.A.,Putzig,C.L.,andHasha,D.L.(1989).Appl.Spectrosc.,43,1049. 20.Nyquist,R.A.,Luoma,D.A.,andWilkening,D.,(1991).Vib. Spectrosc.,2,61. 21.Nyquist,R.A.,Luoma,D.A.,andPutzig,C.L.(1992).Vib. Spectrosc.,3,181. 22.Nyquist,R.A.(1982).Appl. Spectrosc.,36,533. 23.Gordon J.M.andForbes, J.W(1968).Appl.Spectrosc.,15,19. Variables in Data Interpretation 301 o. o o ( ,, I I I ~| El (sg=x) 0L- o q I II x ~-X o. o o o u~ ~. r oi ,..: o A ! I 'l I' " R D ~ i -, 0 o , '~ + c~ I _ I I I I 1 ! o. o Q o q o ( o. 0 >- 0 --J 0 0 ~+V~ 0~. ------- L-V rq Q o o u E p, u ~u0 = "0 = o o u u~ p. Q < ~o E = ~J Q o 'd- U.I 302Ketones 100 80 70 o6 0-,,,, :i:7 .950 r C Q 0 30 20 10 0 167416751676167716781679 vC = O , c m "~inCHCI~an d/o r CCI 4 s o l ut i o nFIGURE14.2AplotofvC=Ofortert-butyrophenone(phenyltert-butylketone)vsmol%CHC13/CC14. VariablesinDataInterpretation303 ~ 3O 2 01 0. -- 1 0 - - 2 0- -U o - 30- -~. 5 0 _- 6 0 -- 70I - --150 w1 o II c 112C H3 I o I Ic c , , C . ; 'l rIII'C' cn 3 IIII. . . . . . I II 0 - 1 1 0 1 7 6 0 1 7 5 0 1 7 4 0 1 7 3 0 1 7 2 0 1 7 1 0 1 7 0 0 1 6 9 0 1 6 8 0 1 6 7 0 1 6 6 0 1 6 5 0v C - O i nCS2S o l u t i o n , c m "1 FIGURE14.3PlotsofthevC=-Ofrequenciesforacetone,cc-chloroacetone,acetophenone,andbenzophenoneinCS2 solutionbetween-~29and-100 oC. 1 7 2 0 . _ =0 0 ~ ' o o )e - . -" I-j /( A)B en z 0phen o n e e ( B) (O)( D) 2, 4 , 6- t r i met hy l4 - met ho x y - A c et o phen o n e4 - n i t r o - ac et o phen o n e ac et o phen o n eac et o phen o n e 1700IIIIIiIIIII 1 6501 66016701 6801 6901 700 vC = O , c m "1in ( C H3) zSO an d/o r C C I 4 s o l ut i o n1710 FIGURE14.4PlotsofvC=Ofor2%wt./vol,solutionsof(A)benzophenone,(B)4-methoxyacetophenone,(C) acetophenone,(D)4-nitroacetophenone,(E)2,4,6-trimethylacetophonone,and(F)acetoneinmole%(CH3)SO/CC14 solutions. 304 Ketones | r O r c- O I 02 0 0 c 0 0 0 -r 2 ID e- 0 c. 0 C c. e- U 0 o --- I 3 o U 9 ~ 2 0 0 if) 2 C 0 c | r 0 0 o I 0 m. 2 e/'e 143 ,,f-,. O u3 ,,- =~ ~J o~ O E U3 ;> ~J ~U ~ ~ ;> O 9II O O < ,r.. l.,u 1 I ! ! I I I I ! ! I I ! I I I I I I 1 (3) oO O t, LHgO-u/~IOHO 0/o elo~ Variables in Data Interpretation 305 ',r'- c- O E c- O I i I I I i ] l I I I I I I I l l I I I A I/

9 0 0 Q 0 ,,i =- LJ o-.0. 0 p, T E -~ u c~ II --.:.. Q ~ 9II 0 .,o 0 < ~'~HeO-UP'lO0 % elOlN 306Ket ones 0 oo 0 100 I 90 8 0-7 0-6 0-5 0-4 0- 3 0 -2 0 -1 0 . -\ 0 171017111 71 2 1 7 1 3 1 7 1 4 1 7 1 5 1 7 1 6 1 71 7 VC = O , c m -1 FIGURE14.7AplotofvC=Ofor0.345 mole%acetonevsmol%CHC13/CC14solutions. 1718 VariablesinDataInterpretation307 0. 3 3 - -0. 3 2 -0. 3 1 -0. 3 @-0. 2 9 - -0 . 2 8 - -R E A0. 27- -C T I0 . 2 6 - -0 N 0 . 2 5 - -F I E0.24-- L D 0 . 2 3 - -0. 22" -0. 21-" 0. 2~-0. 19-" 0 . 1 8 ,1710 @ . . . . . . . . =. . . . . . =~-ti. . . . . ~. . . . . . ~ 1 71 1 1 71 2 1 71 31 71 4 1 71 51 71 61 71 7 l!1718 A C E T O N E CARBONYLF R E Q U E N C Y (CM-I) FIGURE14.8AplotofthereactionfieldvsvC--Ofor0.345 mole%acetoneinCHClffCC14solutions. 308Ketones m 80 g g 4O 20 100 0iiIii 180016001800160018001600 cm--tcrl l .-1cm-1 l ! Ii FIGURE14.9IRspectrafor14H-dibenzo[a,j]Xanthen-14-one.(A)Saturatedsolutioninhexane;(B)saturated solutionincarbontetrachloride;(C)0.5% wt./vol,solutioninchloroform. 1 0 0 - -0- ' -80- -O70- 0 5 0 - o4 0 - 3 0 - 2 0 - -1 0 - 0 1 6 3 2N VC=O c o r r e c t e df o r Fe r m ioRe s o n a n c e0 (3 C C ( , . . . ,~6a4 O To r C T c o r r e c t e df o r Fe r m iRe s o n a n c eIII~! I 1 6 3 6 1 6 3 8 1 6 4 0 1 6 4 2 1 6 4 4 1 6 4 6 1 6 4 8 1 6 5 0c m -1 FIGURE14.10Plotsof vC=OandOT orCT inFermiresonanceandtheir correctedunperturbedfrequenciesfor14H- dibenzo[a,j]xanthen-14-onevsmole%CHC13/CC14.Thesolidsquaresandopensquaresrepresentuncorrected frequency data,thesolidcirclerepresentsvC--OcorrectedforFermiresonanceandtheopencirclesrepresentOT orCT correctedforFermiresonance. VariablesinDataInterpretation309 24 - -22- -20[ 18 16 14 12 10 8 6 4 2 0 1632 N VC = Oco r r ect edf orFermi R e s o na nc e77e 5 16341 6 3 68\. .O T o r C T\ 6c o r r ec t ed~, 96 f o rFer mi R e s o na nc e' ~ 1 I....II ' ~ ~ _ 1 i" ~ _ 1I 1 638 cm-1 FIGURE14.11PlotsofvC--OandOTorCT uncorrectedandcorrectedforFermiresonancefor14H-dibenzo[a,j]- xanthen-14-onevsthesolventacceptornumber(A)for(1)hexane;(2)carbontetrachloride;(3)carbondisulfide;(4) benzene;(5)tetrahydrofuran;(6)methylenechloride;(7)nitrobenzene;and(8)chloroform. / f90 - - 1, 4-B enz oq u i none 80- - ~/ L .inFermiRest /ot-' o' Cong A B,,,CT Mok) % CHCI=/CCI. 50 - -4 0- -30- -o_,. . . . . I _ __ 1654165616581660166216641666166816701672 vop(O-O)s, cm" FIGURE14.12Plotsof Vop(C=O) 2 andBluCT inFermiresonanceandtheirunperturbedfrequenciesafter correction forFermiresonancefor1,4-benzoquinonevsmole%CHC13/CC14. 310Ket ones 100 Tet r af l uo r o - 1 , 4 - B en z o qul n o n e 90 8O 70 vop(C=C)2vop(C,,,O)2 Mole %~ CHCIs/CCI4,I ( :f 2 0! q 10 0_,.. ! I..IIII,I 166516701675168016851690109517001705 c r I R - 1FIGURE 14.13Plots of Vop(C=O)2 andVop(C=C)2 fortetrafluoro-1, 4-benzoquinonevs mole % CHC13/CC14. Variables in Data Interpretation 311 ~o o o o ~5 oT s ~T S ~To ~S ~T ~S S ~T s 0o U on r ~': -8 o o ,-.-~ ~_~ ~-~ ~. ~. ~-4 . ~-~ o o~ o o o 00 o ,.-~ o ~-~ o ,~, ,~, ,-~ o ,.~ o oo ~-~ o v o ,-~ o o ~~ ~ ~. o ~. o ~. o ~. ~. ,-~ o --~ o ~ o eq eq o e5 tt~ eq o eq e5 te~ ,0- o 312Ketones TABLE14. 2Applicationof theKBMequationusi ng IRdataf oracetoneC=Ostretching f requenciesinvarious solvents Foracetone [ C=O( hexane) - C=O( s ol n. ) ] / x10(3)CalculatedC=OdeltaC=O(obs. )-C=O(cal c. ) Solvent[C---O(hexane)]cm-1cm-1 Hexane Diethylether2.3221715.9-2.1 Benzene4.6451717.93.9 Toluene2.9041717.83.8 Carbontetrachloride2.322 Pyridene5.2261714.21.2 Nitrobenzene5.2261713.70.7 Acetonitrile5.2261713.50.5 Dimethylsulfoxide6.9691713.43.4 Methylenechloride5.3881714.52.5 Chloroform6.3881715.64.6 t-Butylalcohol6.9691714.34.3 Isopropylalcohol7.5491713.74.9 Ethylalcohol8.131713.75.7 Methylalcohol8.7111814.77.7 Water13.361713.314.3 , ,VariablesinDataInt erpret at i on313 TABLE14.2AThecalculatedvaluesfor A-1/ 2A4-1andX-Y/XwhereAandY equal0to85andXequals85[theKBM equation] x-Y/X AorYA- 1/ 2A4-1[X--85] 0- 11 100.988 20.220.976 30.2860.964 40.3330.953 50.3640.941 60.3850.929 70.40.918 80.4120.906 90.4210.894 100.4280.882 150.4520.824 200.4630.765 250.470.706 300.4750.647 350.4780.588 400.4810.529 450.4830.471 500.4850.412 550.4860.353 600.4880.294 650.4890.235 700.48940.176 750.490.118 804910.058 850.49120 314Ke t one sTABLE14.3TheC=Ostretchingfrequenciesforaliphaticketonesinthevaporphaseandvarioussolvents Solvent DimethylMethylethylDiethylEthylisopropylDisopropylDi-t-butyl ketoneketoneketoneketoneketoneketone cm-1cm-1cm-1cm-1cm-1cm-1 AN [Vapor]173517421731173017261699 Hexane1722.41727.21725.11721.41720.31690.3 Diethylether1719.617231721.41718.21717.81687.7 Carbontetrachloride1717.71721.31719.61716.517161685.9 Carbondisulfide1716.31720.11718.31715.21714.51684.9 Benzene1715.81718.61717.417141713.51684.5 Acetonitrile1713.317141713.71710.61707.81681.6 Nitrobenzene1712.81714.31713.81710.61707.61681.7 Benzonitrile1712.71713.91713.21710.21706.81682.2 Methylchloride17121712.61712.51709.61706.41680.5 Nitromethane1712.21712.41712.41709.51706.31680.6 t-Butylalcohol1711.81711.21711.81709.21705.61678.5 t-Butylalcohol *11722sh .21722.5sh1718.8sh1718sh1687.0sh Chloroform1710.61710.21710.71708.21705.31680.8 Dimethylsulfoxide1709.21709.71710.11707.41704.61680.1 Isopropylalcohol1710.31709.81710.31707.71704.21677.9 Isopropylalcohol *11720.5sh1720.5sh1716.2sh1717sh1687sh Ethylalcohol17091708.51710.11706.11703.11676.8 Ethylalcohol *11717sh1719.4sh1717.8sh1715.4sh1716sh1686.4sh Methylalcohol17081707.51707.71704.81701.11675.2 Methylalcohol *11716.2sh1718.6sh1717.0sh1715sh1715sh1684.8sh Y~6* 9 Y~0~- 10 -200.72.815.735.7184.8 E6*0- 0. 1- 0. 2- 0. 29- 0.