J耦合、谱分析以及偶极耦合

《J耦合、谱分析以及偶极耦合》由会员上传分享，免费在线阅读，更多相关内容在教育资源-天天文库。

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