An ab initio Study of the Equilibrium Structures of Prop-2-ynamine (Propargylamine) and the Transition Structures Connecting Them

Abstract

Optimization with the 3-21G and 3-21G(N*) basis sets finds, in agreement with previous ab initio studies and the experimental result, the anti conformation of prop-2-ynamine to be of lowest energy and, after zero-point vibrational -energy ( E_zpv ) corrections, the gauche form to lie 11 kJ mol^-l higher; by vibrational analysis, both are confirmed as equilibrium structures. The synform was not able to be optimized with the 3.21G basis set but, with the 3-21G(N*) basis set, is found to lie 8.6 kJ mol^-1 (after E_zpv corrections) above the gauche form, and is shown by vibrational analysis to be a transition structure connecting enantiomeric gauche forms by internal rotation about the N-C bond. The transition structure connecting gauche and anti forms by internal rotation lies 6.3 kJ mol^-1 (after E_zpv corrections) above the gauche form, and the transition structure for inversion at the nitrogen atom lies 31.1 kJ mol- l (after E_zpvcorrections) above the anti form.