Spectroscopic Studies and VFF Model calculations on Dynamic and Electrooptic Characteristics of N-H Bonds in Amides

IR spectroscopic studies of propionamide, n-butyramide, benzamide and 2-(F, Cl, Br)- benzamides within the _(NH) and (HNH) absorption range of -NH2 group for the "free" (in CCl4 solutions) molecules and forming complexes with proton acceptor solvents (benzene, toluene, acetonitrile, dimethylformamide, dimethylsulphoxide and hexamethylphosphoramide) have been performed. Modifying the strength of the intermolecular interactions one can achieve the canceling of the primary non-equivalency of the N-H bonds in the -NH2 group of amides. It allows establishing, for the first time, quantitative measures of dynamic (K(NH)) and electrooptic (_/q) characteristics of N-H bonds in amides in framework of the R-NH2 valence force field model. Dynamic and electrooptic non-equivalencies enhance with the increase of the hydrogen bonding strength. For the hydrogen-bonded complexes with acetonitrile, dimethylformamide, dimethylsulfoxide and hexamethylphosphoramide, the dynamic non-equivalency of NH bonds is increased 10-20%, while the electrooptic parameters _1/q1 and _2/q2 grow two or even three times. The electrooptic coupling of the N-H bonds (the parameter _i/qj, where i, j = 1, 2; i _ j) increases with the strength of the hydrogen bonding.