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1、JcouplingSpin-spinCouplingdipole-dipoleinteraction：magneticdipoleinteractionbetweennucleidirectlySpin-spinCoupling：Itwilloccurbetweentwomagneticallyactivenucleithatareconnectedthroughchemicalbonds.Wecanseeitfortwoatomsdirectlyconnected,orforatomsthat‘see’oneanotheracrossseveralbonds.Couplingsareper
2、hapsthemostimportantparameterinNMR,astheyallowustoelucidatechemicalstructure.ISJ?0ISJ=0ExampleEthanol:CH3CH2OHThreesingletsThespectrumisaresultofspin-spincoupling(scalecoupling)JCouplingEachnucleusactasasmallmagnetandwillaffectthemagneticmomentoftheothernucleinearby(Theenergylevelsofanucleuswillbea
3、ffectedbythespinstateofnucleinearby).Thetwonucleithatshowthisaresaidtobecoupledtoeachother.Thetwonucleicoupleleadingtosplittingofthetwolinesassociatedwitheachnucleus.Notethattheinteractionismutual,andthesamesplittingisobservedforbothresonances.Asplittingofasignalmeansthatwehavemoreenergiesinvolvedi
4、nthetransitionofacertainnuclei.Thestrengthofthecouplingiscalledthecouplingconstant,J–separationbetweenthemultipletlines.IAandIXarethenuclearspinvectorswhichareproportionaltomAandmB,themagneticmomentsofthetwonuclei.JAXisthescalarcouplingconstant.Itdoesnotmatterifwehavea60,a400,oran800MHzmagnet.Theco
5、uplingconstantsarealwaysthesame!JCouplingTheresonancefrequencyofHadependsonwhethertheadjacentHbhasspinupordown.ThefrequencyseparationbetweenthetwopeaksiscalledJ(scalarcouplingconstant)(typically0～15Hz).ThecouplingconstantisindependentofBoandisreportedinHz.JCouplingTheresonancefrequencyofHadependson
6、whethertheadjacentHbhasspinupordown.ThefrequencyseparationbetweenthetwopeaksiscalledJ(scalarcouplingconstant)(typically0～15Hz).ThecouplingconstantisindependentofBoandisreportedinHz.ExampleEthanol:CH3CH2OHSpin-spincouplingtellsushowmanynucleithereareneartoagivennucleus.JCouplingJCouplingPascalTriang
7、le11112113311464115101051JCouplingIfaprotoninteractswithtwodifferentsetsofequivalentprotons,themultiplicitywillbe:—spinsystem,AnMmXp?(m+1)(p+1)ConsiderCH3CH2CH2I—?H=1.02;?H=1.86;?H=3.17-CH3;1:2:1triplet(fro
