有机波谱分析双语课件 (15).pdf
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1、核磁共振氢谱 I 有机波谱分析 Organic Spectroscopic Analysis 1H NMR Spectroscopy I 2 How to produce NMR phenomena?1.Nuclei I0 2.There is a external magnetic field B0.Radio frequency electromagnetic waves in the vertical direction of B0.3.When the frequency of the radio frequency electromagnetic wave is the same a
2、s the Larmor frequency of the spin nucleus,the nucleus absorbs the energy of the radio frequency wave and transitions from the low energy state to the high energy state,that is,nuclear magnetic resonance occurs.Resonance Frequency:=Bo/2 Nuclear magnetic dipole Oscillator coil Precessional orbit Low
3、energy spin state(+1/2)Precessional orbit High energy spin state(-1/2)Oscillator coil transmits radiofrequency 3 A Simple NMR Machine An NMR machine consists of:(1)A powerful,supercooled magnet(stable,with sensitive control,producing a precise magnetic field).(2)A radio-frequency transmitter(emittin
4、g a very precise frequency).(3)A detector to measure the emission of radiofrequency by the sample.(4)A recorder(to plot the output).4 NMR System 5 NMR Machine 6 The NMR magnet is of superconducting(超导的)type and has to be immersed in liquid helium.It is the most expensive component.NMR System 7 Why s
5、hould the proton nuclei behave differently in the NMR experiment?The answer to this question lies with the electron(s)surrounding the proton:Since electrons are charged particles,they move in response to the external magnetic field(0)so as to generate a secondary field that opposes the much stronger
6、 applied field.This secondary field shields the nucleus from the applied field Chemical Shift Phenomenon 8 Chemical Shift Phenomenon The electron density around each nucleus in a molecule varies according to the types of nuclei and the bonds in the molecule.The opposing field and therefore the effec
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