Quantum Mechanical Studies on Chemical Reactivity and Ballistic Chemistry. IV. CNDO/2 Calculations on Azolium Cations and on the Zwitterions Resulting from Their Deprotonation

摘要

It has been found that ring protons in positions alpha-to pyrrole-type nitrogens exchange much faster than those located beta-to such nitrogens. Adding pyridine-type nitrogens to the ring also causes a large increase in rate of exchange. As part of a program of molecular orbital calculations on chemical reactivity and ballistic chemistry, the authors have carried out CNDO/2 calculations on these azolium cations and on the zwitterions resulting from their deprotonation. The calculated total one-and two-atom energy changes and charge distributions suggest that the relative CH acidities of isomeric tetrazolium cations are determined primarily by coulombic effects; but in the case of isomeric diazolium cations, effects operating through the sigma-framework (inductive and hybridization) seem predominant. The importance of solvation and other effects involving the added nitrogen is also considered.