REEXAMINATION OF THE CONFORMATIONS OF DIMETHYL-PHOSPHATE ANION IN WATER

Monte Carlo simulations were employed to calculate the relative free e nergies of hydration for the gauche-gauche (gg), gauche-trans (gt), an d trans-trans (tt) conformers of the dimethyl phosphate anion. Relativ e to the gg conformer, the free energy of hydration of the gt conforme r is 0.2 kcal mol(-1) higher, while that of the tt conformer is 2.6 kc al mol(-1) lower. In combination with the free energy differences for the isolated molecules (Liang et al., J. Am. Chem. Sec., 115 (1993) 15 37), these results indicate that in aqueous solution the gg conformer is most stable, but the gt and tt conformers have comparable stabiliti es. The entropic contribution to the free energy of hydration is thoug ht to be an important factor.