Nonempirical investigations on the azomethine group. 1. The effect of the conjugation with a phenyl ring. A comparison of the electronic structure of the ground and lowest excited states in benzaldimine and N-phenylformaldimine

The possibility of differential effects due to conjugation with a phenyl ring when linked either to the C or N end of the azomethine group is investigated by means of ab initio calculations on the ground and lowest excited states of benzaldimine, N-phenylformaldimine, and the parent compound methylenimine. For the description of the excited states, the electron-hole potential method by Morokuma and Iwata has been adopted. Population analysis shows that the ability of the azomethine group to accept or to donate electrons in a given state is practically the same in molecules 1 and 2. A parallel analysis of the electrostatic molecular potential confirms the results of the papulation analysis and in addition shows differences in reactivity between the two molecules in a given state and among the various states in each molecule.