Medium Effects in Spectroscopy

Due to the fact that a nitrogen atom incorporated in a molecule, exhibits a Lewis basicity which depends on the degree of lone-pair delocalisation, solvent effects are expected to be greater in spectroscopy than in carbon NMR. Examination of Table 5.1 shows that amines, amides (or ureas), nitriles and nitro derivatives are characterized by different values of polarity parameters indicatory of their electron-donating or -accepting abilities. 

As the exchange reactions which involve the nitrogen atom of the various amino derivatives strongly depend on the medium, the borderline between intermolecular effects and chemical reactions may become blurred. This is particularly so for proton exchange reactions which occur as a function of pH in N-H derivatives. However, such processes will be considered in Sect. 8, and only conventional medium effects along with protonation effects will be dealt with now. 

For the sake of brevity, certain abbreviations for the relevant solvents have been used throughout the book. 

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