Cyclic allylamine–enamine systems. Part 7. A theoretical study of the relative energies of isomeric cyclic allylamine–enamine systems

Abstract

The relative energies of a series of isomeric cyclic allylamine–enamine systems have been calculated by MINDO/3 and ab initio MO methods including complete geometry optimisation. The MINDO/3 results are shown to be reliable by comparison with experiment and with the ab initio results. Thus, for a particular pair of N-methyltetrahydropyridine-4-carbaldehyde isomers (12) and (13), both ab initio and MINDO/3 methods give similar optimised geometries and predict the enamine to be more stable than the allylamine by 1.5 and 1.3 kJ mo^–1 respectively. This energy difference is predicted to be increased by up to 3 kJ mol^–1 in water.