Structures and interactions in N-methylacetamide-water mixtures studied by IR spectra and density functional theory

IR spectra have been performed to study the structures and interactions in N-methylacetamide and water mixtures. Because of the competitions of acceptor and donor of the strong hydrogen bonds, some interesting phenomena of red shifts and blue shifts are observed in nCyO and nN–H: It is due to the blue-shifting C–H· · ·O hydrogen bond, the nC–H blue shifts more obviously. Then some representative cluster structures are suggested and further investigated by density functional theory method. The changes in bond length and frequency shift of the structures give good reasons for the red shift and blue shift, which represents excellent agreement with the IR experiment. The investigations of IR spectra and DFT calculations reveal that the weak C–H· · ·O interactions play different roles compared with the classical strong hydrogen bonds in the NMA–water mixtures. q 2004 Elsevier B.V. All rights reserved