The C-N rotation barrier of the lithium enolate of acetamide: An ab initioand density functional theory investigation

Semiempirical (PM3), ab initio (HF/6-31+G(d) and MP2/6-31+G(d)), and densit y functional (pBP/ DN*) calculations are used to investigate the rotation b arrier of the carbon-nitrogen bond in a simple enolate anion: lithium aceta mide, 1. For comparison, the amidate anion 2, vinylamine 3, and a simulated dimer 4 were also calculated. In all systems, the barrier to rotation was found to be less than 10 kcal mol(-1) in agreement with experiment. The cor related calculations show the barrier to be lowest for the anion 2. The res ults show conjugation effects in 1 and 2 comparable to that in vinylamine 3 and imply that polarization effects are more important than charge transfe r in amine conjugation.