Calculation of solvent effect on conformation stability and anomeric effect in dimethoxymethane

Abstract

Solvent effect has been investigated on relative stability of the dimethoxymethane (DMM) conformers formed by rotation about the central C-O bonds. Potential energy of the isolated molecule in the whole conformation space determined by torsion angles (φ1, φ2) has been calculated by the PCILO semiempirical quantum-chemical method. For determination of potential energy of DMM in solvent environment the procedure by Sinanoglu has been used in which the solvation energy is divided into electrostatic, dispersion and cavity terms. The calculation predicts that DMM in CCl4 solution as well as in vapour phase exists almost exclusively in its most stable(sc, sc) conformation with slight population of the (ap, sc) conformations. On the contrary, in aqueous solution an almost exclusive occurrence of the (ap, ap) conformation can be expected. The predicted abundances of the DMM conformers agree well with the available experimental data for DMM and similar molecules. Also the role of environmental factors on the anomeric (gauche) effect has been analyzed which makes itself in preference for sc to ap conformations in a number of polar molecules. It has been shown that the original intramolecular preference for the sc conformation can be compensated by intermolecular solute-solvent interactions, and the anomeric effect can disappear with increasing solvent polarity. The calculated solvation energies have been used for estimation of dilution enthalpies of DMM, too.