Hydration thermodynamics of N-methylacetamide

Reliable values for the thermodynamic functions associated with the hydrati on of N-methylacetamide, NMA, in the temperature range 5-100 degreesC, are obtained using experimental data from different investigations. They are an alyzed by means of a suitable theoretical approach. The large and negative hydration entropy values are determined by the excluded volume effect owing to cavity creation in water in order to host the NMA molecule. The large a nd, negative hydration enthalpy values are determined by the NMA-water van der Waals interaction and H-bond energies. The latter are so large in magni tude to overwhelm the work of cavity creation, causing the good solubility of NMA in water. The analysis assumes that the reorganization of H-bonds am ong water molecules in the hydration shell of NMA is characterized by a nea rly perfect enthalpy-entropy compensation, so that such process does not af fect the hydration Gibbs energy change.