Quantum-chemical study of nitrosonium complexes derived from nitrogen-containing heterocycles

The affinities of a series of azines for nitrosonium ion (A(NO+)) were calculated by quantum-chemical methods, AMI and ab initio. The A(NO+) values were found to increase as the number of nitrogen atoms in the ring decreases and the donor power of substituents increases; ring fusion also increases ANO+. The best agreement between the calculated and experimental A(NO+) values was attained with the use of AM I calculations and ab initio methods with split polarization or diffuse functions. Substituted pyridines showed linear correlations between the calculated A(NO+) values and substituent constants sigma or sigma(+) or overall charges on the NO group in the complex. Linear cot-relations were also found between the calculated A(NO+) values of azines and their experimental proton affinities.