Conformations of 1,2-dimethoxyethane in gas and solution phase from molecular mechanics and Monte Carlo/stochastic dynamics simulations

The conformations and energies of 1,2-dimethoxyethane (DME) are estimated using molecular mechanics and Monte Carlo/stochastic dynamics (MC/SD) simulations. The torsional parameters of the Amber* and OPLS* force fields were modified to reproduce high-level ab initio data describing DME conformer energies in the gas phase. Predicted conformer populations from gas-phase molecular mechanics and simulations are in agreement with theoretical calculations and with previous electron diffraction data. For simulations in chloroform and aqueous solution an implicit solvation model (GB/SA) was used. The GB/SA treatment gives the TGT as the most populated conformer in aqueous solution, providing the major contribution to the observed gauche effect around the C-C dihedral. Significantly, the energy of the TGT conformer is lower than that of the TTT structure in solution, and it is stabilized relative to the TGG' conformer. These results are compared to previous work in solution and in vacuo and with ab initio results.