AB-INITIO AND MOLECULAR MECHANICS (MM2 AND MM3) CALCULATIONS OF POSITIVELY CHARGED CONJUGATED NITROGEN-CONTAINING COMPOUNDS

Ab initio calculations have been carried out on s-trans-N-vinylmethyle neammonium, pyridinium, and related compounds to obtain rotational bar riers, structures, and vibrational frequencies. The restricted Hartree -Fock (RHF) level of theory with 6-31G* basis set was used for these calculations. In addition, the MM2(91) and MM3(94) force fields have b een parameterized to calculate these positively charged nitrogen-conta ining compounds. A bond order term was incorporated in the force field to reproduce accurately the rotational barriers of s-trans-N-vinylmet hyleneammonium and related compounds. Molecular mechanics geometries a nd vibrational frequencies compare well with those calculated by ab in itio methods. (C) 1996 by John Wiley & Sons, Inc.