Studies on aliphatic polyesters I: Ab initio, density functional and forcefield studies of esters with one carboxyl group

Rotations around the neighboring C-C(=O) and C(=O)-O bonds in two esters, H 3C-CH2-C(=O)-O-CH3 (I) and H3C-CH(CH3)-C(=O)-O-CH3 (II) that represent mode l molecules for aliphatic main chain and side group polyesters were studied by ab initio and density functional methods (MP2, B3-LYP and B-LYP) using the standard Gaussian basis set 6-31G(d). The performance of the PCFF force field, developed for polymers, to reproduce the conformational behaviors o f the C-C and C-O rotations in question was evaluated. Disagreements betwee n the quantum chemical and force field results were removed by reoptimizing the PCFF force field torsion parameters of current interest. The conformat ional dependence of geometrical parameters and electrostatic potential deri ved (CHELPG) atomic charges was also studied. (C) 1999 Elsevier Science B.V . All rights reserved.