INFLUENCE OF SOLVATION ON THE HYDROGEN-BOND IN HYDROGEN MALONATE - ANAB-INITIO AND SEMIEMPIRICAL STUDY

The energy difference Delta E-EZ in vacuo between the closed (E) and o pen (Z) forms of the hydrogen malonate ion was computed at the ab init io HF/6-31G(d,p), 6-311++G(d,p), DFT B3LYP/6-31G(d,p) and B3LYP/6-311+G(d,p) levels. The effects of the polar environment were simulated by attaching discrete water molecules, by the self-consistent reaction f ield model (SCRF) and by the combination of both approaches. These sim ulations were done at the HF/6-31G(d,p) level. The SCRF approach appli ed to both forms of the HM tetrahydrate yields the free energy differe nce of -0.73 kcal mol-l slightly favouring the open form; this contras ts the stabilization by similar to 20 kcal mol(-1) of the E form in va cuo. The metric parameters of the intramolecular hydrogen bond indicat e a slight weakening of the intramolecular H-bond by the influence of hydration. Calculations at the PM3 level did not reproduce the ab init io computed Delta E-EZ values. (C) 1998 Elsevier Science B.V. All righ ts reserved.