NMR譜特征：位置，形狀，寬窄影響因素

提供分子結(jié)構(gòu)、運(yùn)動(dòng)信息NMR譜（頻域）：I()第三章：核磁共振譜Chapter3NMRSpectroscopyI強(qiáng)度隨頻率分布3.1簡(jiǎn)單脈沖序列

（SimplePulseSequence）sfid(t)=

Meqexp(iω0t)exp{?t/T2}fouriertransformationt

T2,1/T2:transverserelaxationtime,rateExperimentalT2:Fidorlinewidth

FID(時(shí)域）NMR譜(頻域）勻場(chǎng)？frequency,11/2Fullwidthathalf-height.absorptionLorentzianangularfrequency,Fullwidthathalf-height=1/(T2)~1/T2relaxation

rate

3.2SimplespectrumFIDDecay:指數(shù)衰減：xp{?t/T2}

Lorentzian吸收線型線寬3.3SpectralFrequencies3.3譜頻率(labframe靜止):ref00Cos(reft)RelativeSpectralFrequencies:0=ω0?ωref

=ω?ωreftheresonanceoffsetortheLarmorfrequencyintherotatingframeRelativeSpectralFrequencies:CaseofPositiveGyromagneticRatio3.4相對(duì)譜頻率(rotatingframe旋轉(zhuǎn)):3.5InhomogeneousBroadeningDifficult:aperfectlyhomogeneousmagneticfieldThesampleitselftendstodistorttheappliedmagneticfield,becauseofitsmagneticsusceptibility.

*InsomeNMRexperiments,spatiallydependentmagneticfieldsaredeliberatelyapplied,usingspeciallydesignedadditionalfieldcoils.Thisisthecasein,forexample,NMRimagingexperiments.非均勻?qū)捇?00*106Hz/11.7T=4274Hz/G=0.4Hz/0.0001G500MHz(11.7T)譜儀0.4HzB~0.0001G磁場(chǎng)均勻度例1：不均勻磁場(chǎng)（外磁場(chǎng)，樣品（外部形狀，內(nèi)部空洞等））purewaterχ=?9.05×10?6.Binduced=-0M=-B0~1G形狀各向異性因子=4,4/3,….0Binduced=-0MM非均勻退磁場(chǎng)BinducedB0InhomogeneousBroadening樣品不同位置，取向，化學(xué)環(huán)境等rf照射Burningahole燒個(gè)洞

非均勻?qū)捇瘜W(xué)位移各向異性Thechemicalshiftδscalealwaysincreasesfromrighttoleftinplottedspectra.106（ppm)40ppm40X100(Hz)400MHz譜儀DefinitionReference1H與磁場(chǎng)無(wú)關(guān)Couplewithnequivalentnuclei:1H:2nI+1=(n+1)splittingr=0,1,…n與N個(gè)等價(jià)核（l=1/2)偶合:2Nl+1

peaks(2nI+1)分裂0,J(Hz)JItotal=1，0Itotal=I1+I2….Abs(I1-I2)兩個(gè)角動(dòng)量組合：2D:自旋I=11storderapproximationi.CouplewithN-nonequivalentnuclei:(I=1/2)splitto2Nii.Couplewithnequivalentnuclei:(n+1)(2nI+1)Coefficientsofbinominalexpansion(relativeintensity)iii.CenterνiSplitingJiv.noJsplittinginspectrabetweenequivalentnuclei3.9HeteronuclearDecoupling13CspectrumoftheCH2regioninethanol.HCH3CH2exchange-decoupling異核去偶rfHCH2射頻異核去偶“Improved”Stern-GerlachExperimentSpin?particle(e.g.silveratoms)Wha