Ab initio, DFT and experimental studies on the IR spectra and structure of propanedinitrile (malononitrile) and its carbanion

The structures of propanedinitrile (malononitrile) and its carbanion have been studied by IR spectra, ab initio HF and MP2, and DFT BLYP and B3LYP calculations. In agreement between theory and experiment, the conversion of the malononitrile molecule into the carbanion results in very essential spectral changes: 134 cm(-1) (mean value) decrease in the cyano frequencies nu(CN), 85 fold (total value) enhancement of the cyano integrated intensities, strong enlargement of the nu(CN) vibrational coupling, etc. According to the calculations, the C-C bond order increases caused by the same conversion, are 2.5-12 fold stronger, than the corresponding Cequivalent toN bond order decreases. The formation of moderately strong (CH3)(2)SO...H2C(CN)(2) hydrogen bonds has been found experimentally. (C) 2003 Elsevier Science B.V. All rights reserved.