chemical shift 化学位移.ppt

ChemicalShiftChemicalShiftω=γB0Forasamekindofnucleus,the0shouldbethesame!icfieldfeltbythenucleusisnotthesameasappliedfieldThee--icshielding,B=B0(1-)=B0(1-)=B0-Bloc=B0(1-)HO-CH2-CH3wolowfieldhighfieldExampleethanolChemicalShiftScaleω=γB0ν=B0(1-)γ/2π△ν=B0(1-2)γ/2π1)B0isconstantδ=(νS-νR)/νR=(S-R)/(1-R)=(S-R)(R<<1)2)ν0isconstantδ=(BS-BR)/BR=(S-R)/(1-R)=(S-R)(R<<1)δ=(S-R)ppm(10-6)StandardReferences=poundistetramethylsilane,anicsolvents,isinert,volatile,,socan’tbeusedinaqueousmedia,thenuse2,2-dimethyl-2-silapentane-5-sulfonicacid,DSS(=)Otherreferencescanbeused,suchastheresidualsolventpeak,,(ic):icfieldopposingBofromtheelectronsimmediatelysurroundingthenucleus(sorbitals).spara(ic):generatedbyelectronsinporbitals(aswellasbonds…).:whichisduetoneighboringgroups,anditcanaddorsubtractfromB0,(andthereforechemicalshifts).Originsofs(Bloc)s=sdia+spara+upied(lowerenergythanporbitalsin1H…)1H13C1Hhasonlya1sorbital,sdiawilldominate