Reexamination of the conformations of dimethyl phosphate anion in water

Abstract

Monte Carlo simulations were employed to calculate the relative free energies of hydration for the gauche-gauche (gg), gauche-trans (gt), and trans-trans (tt) conformers of the dimethyl phosphate anion. Relative to the gg conformer, the free energy of hydration of the gt conformer is 0.2 kcal mol −1 higher, while that of the tt conformer is 2.6 kcal mol −1 lower. In combination with the free energy differences for the isolated molecules (Liang et al., J. Am. Chem. Soc., 115 (1993) 1537), these results indicate that in aqueous solution the gg conformer is most stable, but the gt and tt conformers have comparable stabilities. The entropic contribution to the free energy of hydration is thought to be an important factor.