N-methylacetamide(NMA),one of the simplest model molecules of peptide group,has been extensively studied using a variety of techniques.1H NMR of NMA-H₂O system was determined by the external reference method in the whole concentration range at different temperatures,and chemical shift data were corrected via the magnetic susceptibilities.The association model was determined by quantum chemical calculation.Dimensionality reduction was also carried out.Based on chemical association theory the association equilibrium constant and the corresponding ΔH and ΔS were obtained by nonlinear least-square fitting.In addition,density functional theory(DFT)was also used to calculate the ΔH of main association forms in NMA-H₂O system.The results calculated by chemical association theory are in good agreement with those calculated by DFT and the literatures.

Key words: NMA-H₂O, chemical association theory, ¹H NMR, DFT