Amide hydrogen bonding in organic medium

Thermodynamic parameters for the self-association of N-methylformamide and N-methylacetamide in CCl4 solvent have been determined by infrared spectroscopy. The pure base calorimetric method was used to determine the enthalpy of hydrogen bond complex formation of N-methylformamide and N-methylacetamide with N,N-dimethylformamide, N,N-dimethylacetamide, ethyl acetate, and dioxane. Comparison of the calorimetric and spectroscopic results show that the dimers of N-methylformamide and N-methylacetamide are linear with hydrogen bond enthalpies of −2.9 and −3.9 kcal mol−1 respectively. The carbonyl group of N-methylacetamide was found to be a better proton accepter than the carbonyl of N-methylformamide in agreement with theoretical predictions. N-methylacetamide was found to be a better proton donor than N-methylformamide in disagreement with theoretical predictions. The dimer self-association constants appear to be larger than previously reported.