Solvent effects on the barrier to isomerization for a tertiary amide from ab initio and Monte Carlo calculations

Abstract

The effects of solvation on the free energies of activation for rotation about the carbonyl C-N bond in N,N-dimethylacetamide (DMA) have been examined through a combination of gas-phase ab initio calculations and solution-phase statistical mechanics simulations. The geometries of the planar ground state and the transition states with the nitrogen lone anti and syn to the oxygen were optimized with the 6-31G(d) basis set. Subsequent calculations of the vibrational frequencies and correlation energies (MP4(fc)SDTQ/6-31G(d)//6-31G(d)) predict ΔGs of 14.6 and 18.7 kcal/mol for the anti and syn transition states at 298 K