A COMPUTATIONAL STUDY OF LITHIO AZAALLYLIC SYSTEMS

Ab initio and semiempirical PM3 calculations were performed on lithioi mines as a model system for molecules in which Lithium is (3) eta boun d to the aza-pi-allylic system, such as the growing poly (2-vinylpyrid ine) chain end. Comparison to the ab initio calculations and published x-ray crystal data showed that the semiempirical calculations perform ed reasonably well for these systems. The PM3 calculations overestimat e the lithium bond distances to the atoms in the allylic system by abo ut 0.1 A, and underestimate the dimerization energies of lithioimines by about 7 kcal/mole, compared to the ab initio results. The solution structure of these molecules is largely determined by steric hindrance and the solvation suite. Lithioimines have been found to aggregate in to dimers, and in some cases two or more aggregated species coexist in equilibrium with the monomer.