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 estima ted using molecular mechanics and Monte Carlo/stochastic dynamics (MC/ SD) simulations. The torsional parameters of the Amber and OPLS* forc e fields were modified to reproduce high-level ab initio data describi ng DME conformer energies in the gas phase. Predicted conformer popula tions from gas-phase molecular mechanics and simulations are in agreem ent with theoretical calculations and with previous electron diffracti on data. For simulations in chloroform and aqueous solution an implici t solvation model (GB/SA) was used. The GB/SA treatment gives the TGT as the most populated conformer in aqueous solution, providing the maj or 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 TG G' conformer. These results are compared to previous work in solution and in vacuo and with ab initio results.