Theoretical study on relative stabilities of conformers in the gas phase and in aqueous solution

Abstract

The energies of the conformers of 1,2-dimethoxyethane (DME) in the gas phase are calculated with several levels of ab initio MO calculations. It is found that the energies of the TGT form and the TGG form relative to the most stable isomer (TTT) are 1.1 and 2.9 kcal/mol with the level of HF/6-31G*. They are 0.1 and 1.2 kcal/mol, respectively, with MP2/aug-cc-pVDZ. The energy profile from TTT to TGT is calculated with HF/6-31G* and it is found that the energy barrier is 3.8 kcal/mol. The energy profile from TGT to TGG is calculated with HF/6-31G* and it is found that the energy barrier is 2.5 kcal/mol. The conformations in aqueous solution are investigated with QM/MM method, with HF/6-31G* as QM for DME and TIP3P for the MM water molecules. We take 93 MM water molecules into consideration in the current study. The MD simulation with QM/MM starting from the optimized structure of the TTT form in 93 MM water molecules is performed at 300K, and it is observed that the TTT form changes to the TGT form.