Ab initio and molecular mechanics (MM2 and MM3) calculations of nonconjugated positively charged nitrogen‐containing compounds

High‐level ab initio calculations have been performed on N‐methyl‐N‐methyleneammonium and related compounds to obtain accurate rotational barriers, structures, and vibrational frequencies. The 6‐31G** basis set has been utilized at the Hartree‐Fock level of theory for these calculations because little experimental data are available. The MM2(91) and MM3(94) force fields have been parameterized to include these nonconjugated charged nitrogen‐containing compounds. Molecular mechanics geometries and vibrational frequencies compare well with the ab initio results.