The Concept of Chemical Shift and Its Dependence on Adsorption Interactions

THE CONCEPT OF CHEMICAL SHIFT AND ITS DEPENDENCE ON ADSORPTION INTERACTIONS 

The spectral technique of nuclear magnetic resonance is ba.sed on the phenomenon of absorption of radio-frequency energy by a sy.stem of magnetic nuclei. In an external magnetic field nuclei with a nonzero spin / are oriented discretely so that the spin projection to the field direction (m) takes on 2/ -I- I values 

21 + 1 sublevels. The difference in energy between the sublevels is defined by the relationship 

When using the NMR method, transitions between these sublevels are investigated by applying an additional high-frequency field B[ with angular frequency to. In this case the resonance absorption of energy takes place under the condition 

In order to characterize the quantity of magnetic screening characteristic of a concrete nucleus, use is made of the value of the chemical shift, i.e., the difference between the constant screening of a standard substance (Oi) and the screening of the substance studied (a). The chemical shift (5) is measured in millionth parts of the magnetic held strength of a NMR spectrometer  

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II. The Concept of Chemical Shift and Its Dependence on Adsorption Interactions... 

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