Chapter13SpectroscopyUntilthesecondhalfofthe20thcentury,thestructureofacompound,suchasnaturalproduct,wasdeterminedusinginformationobtainedfromchemicalreaction（functionalgroupreaction,chemicaldegradation,qualitativetest,etc).Instrumentalmethodsofstructuredeterminationoforganiccompoundshavereplacedthatofchemicalmethods.Themostimportantamongthesestructuredeterminationtechniquesare:NuclearMagneticResonance(NMR)SpectroscopyInfrared(IR)SpectroscopyUltraviolet-Visible(UV-VIS)SpectroscopyMassSpectroscopy(MS)§13.1PrinciplesofMolecularSpectroscopy:ElectromagneticRadiationParticle-likeproperties:Aparticleofenergyiscalledaphoton.Eachphotonhasadiscrete(不连续的,离散的)amountofenergy:aquantum(量子)Wave-likeproperties:Itisimportanttounderstandwavelengthandfrequencyandhowtheyrelatetooneanother.TherelationofenergyofaphotontoitsfrequencyisexpressedbyPlanck’sequation:Electromagneticradiationispropagatedatthespeedoflight(c=3.0×108m/s).§13.2QuantizedEnergyStatesQuantisationofEnergy:Innuclearmagneticresonance(NMR)spectroscopyDE=twodifferentspinstatesofanatomicnucleusIninfrared(IR)spectroscopy:DE=twodifferentvibrationalenergystatesInultraviolet-visible(UV-VIS)spectroscopy:DE=twodifferentelectronicenergystates§13.3ProtonMagneticResonance(1HNMR)SpectroscopyNuclearSpinStates粒子在磁场中的进动B，氢原子核的自旋与进动SpinstateA:thenuclearmagneticmomentisparalleltotheappliedfieldH0NuclearMagneticmomentantiparalleltoH0n:Frequency(Hz),H0:FieldStrength(gauss,G)g:磁旋比,对于质子=26,750Nuclearmagneticresonancespectrometer§13.4NuclearShieldingandChemicalShift屏蔽(shield)：电子围绕质子本身的环流所产生的磁场与外加磁场的方向相反（愣次定律），使质子实际所感受到的磁场受到减弱的现象（质子实际感受到的有效磁场应是外加磁场强度减去感应磁场强度）。屏蔽效应：需要较高的外磁场强度才能发生核磁共振。去屏蔽(deshield)：电子围绕质子本身的环流所产生的磁场与外加磁场的方向相同，使质子所感受到的磁场受到增强的现象。（质子实际感受到的有效磁场应是外加磁场强度加上感应磁场强度）。去屏蔽效应：在较低的外磁场强度下就能发生核磁共振。ChemicalShift(化学位移)：Achemicalshiftisthechangeintheresonancepositionofanucleuswhichisbroughtaboutbyitsmolecularenvironment.不同环境中的氢核其外围的电子在外磁场的感应下产生不同程度的屏蔽或去屏蔽作用，使原子核实际所受的磁场略有降低或增加，从而引起核磁共振谱吸收位置的移动，这种现象称化学位移。—即同种核由于在分子中化学环境不同而在不同共振强度下