Effects of Protonation on the Electronic Structure and Spectra of Nitrogen Heterocycles

Abstract
The self-consistent electronegativity method has been applied to calculate the electronic structure and spectra of some protonated nitrogen heterocycles. This method may be regarded as an improvement of our method ii which has led to poor agreement with experiment because of the neglect of the inductive displacement in σ-core caused by protonation. The calculated results with the present method, however, are in rather poor agreement with experiment, and it is only a small improvement of the method ii. Comparing the present results with the previous ones obtained with method i and ii, some discussions about the nature of the protonation effect on the electronic structure of these molecules have been given. In addition, formulae which represent the magnitude of inductive effect on each atom as a function of the distance or number of bonds from the protonated atom have been given.