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1、OrganicChemistryWilliamH.BrownChristopherS.FooteBrentL.IversonNuclearMagneticResonanceChapter13MolecularSpectroscopyNuclearmagneticresonance(NMR)spectroscopy:aspectroscopictechniquethatgivesusinformationaboutthenumberandtypesofatomsinamolecule,forexample,aboutthenumberandtypesofhydrogenatomsus
2、ing1H-NMRspectroscopycarbonatomsusing13C-NMRspectroscopyphosphorusatomsusing31P-NMRspectroscopyNuclearSpinStatesAnelectronhasaspinquantumnumberof1/2withallowedvaluesof+1/2and-1/2thisspinningchargecreatesanassociatedmagneticfieldineffect,anelectronbehavesasifitisatinybarmagnetandhaswhatiscalled
3、amagneticmomentThesameeffectholdsforcertainatomicnucleianyatomicnucleusthathasanoddmassnumber,anoddatomicnumber,orbothalsohasaspinandaresultingnuclearmagneticmomenttheallowednuclearspinstatesaredeterminedbythespinquantumnumber,I,ofthenucleusNuclearSpinStatesanucleuswithspinquantumnumberIhas2I+
4、1spinstates;ifI=1/2,therearetwoallowedspinstatesTable13.1givesthespinquantumnumbersandallowednuclearspinstatesforselectedisotopesofelementscommontoorganiccompoundsNuclearSpinsinB0withinacollectionof1Hand13Catoms,nuclearspinsarecompletelyrandominorientationwhenplacedinastrongexternalmagneticfie
5、ldofstrengthB0,however,interactionbetweennuclearspinsandtheappliedmagneticfieldisquantized,withtheresultthatonlycertainorientationsofnuclearmagneticmomentsareallowedNuclearSpinsinB0for1Hand13C,onlytwoorientationsareallowedNuclearSpinsinB0Inanappliedfieldstrengthof7.05T,whichisreadilyavailablew
6、ithpresent-daysuperconductingelectromagnets,thedifferenceinenergybetweennuclearspinstatesfor1Hisapproximately0.120J(0.0286cal)/mol,whichcorrespondstoelectromagneticradiationof300MHz(300,000,000Hz)13Cisapproximately0.030J(0.00715cal)/mol,whichcorrespondstoelectromagneticradiationof75MHz(75,000,
7、000Hz)NuclearSpininB0theenergydifferencebetweenallowedspinstatesincreaseslinearlywithappliedfieldstrengthvaluesshownherearefor1HnucleiNuclearMagneticResonancewhennucleiwithaspinquantumnumberof1/2areplacedinanappliedfield,asmallmajorityo
