Solvation Free Energies of Amides and Amines: Disagreement between Free Energy Calculations and Experiment

Abstract

We present molecular dynamidfree energy calculations on the molecules acetamide, N-methylacetamide, N,N-dimethylacetamide, ammonia, methylamine, dimethylamine, and trimethylamine. Unlike the experimental data, which suggest a very non-additive solvation free energy (N-methylacetamide and methylamine having the most negative free energy of solvation), the calculations all find that the free energy of solvation monotonically increases as a function of methyl addition. The disagreement with experiment is surprising, given the very good agreement (within 0.5 kcaYmo1) with experiment for calculation of the solvation free energy of methane, ethane, propane, water, methanol, and dimethyl ether.