RELATIVE ENERGIES AND STRUCTURAL FEATURES OF SMALL AMINES AND THEIR AMMONIUM ANALOGS - RESULTS FROM 6-31G-ASTERISK OPTIMIZATIONS AND AN MM2AMMONIUM FORCE-FIELD

An MM2 force field that reproduces the structural features and relativ e energies of quaternary aliphatic amines as derived from ab initio ca lculations at the 6-31G level has been completed, The purpose of the study is to provide Medicinal Chemists with a method of evaluating the structures and conformational energies of ammonium species typically found in pharmaceuticals. Full Cartesian coordinate geometry optimizat ions at the 6-31G level are followed by single-point Moller-Plesset P erturbation calculations through the MP3 level, which were performed o n CRAY X-MP/4, CRAY Y-MP/464, and VAX 8800 machines using Gaussian 80( UCSF). Methyl-, ethyl-, propyl-, and ethylmethylamines, N-Methylpiperi dine, 2-Methylpiperidine, and corresponding ammonium systems are used to evaluate changes in structure, barrier heights, and relative energi es resulting from quaternization.