The conversion of phenylpropanedinitrile (phenylmalononitrile) into the carbanion, followed by IR spectra, ab initio and DFT force field calculations

The spectral and structural changes, caused by the conversion of phenylpropanedinitrile (phenylmalononitrile) into the carbanion, have been followed by IR spectra, ab initio HF, MP2 and DFT BLYP force field calculations. In agreement between theory and experiment, the conversion is accompanied with strong frequency decreases (with 114 cm(-1) mean value) of the cyano stretching bands nu(Cequivalent toN), dramatic increases in the corresponding integrated intensities (136-fold, total value), strong enhancement of the nu(Cequivalent toN) vibrational coupling and other essential spectral changes. According to the calculations, the strongest structural changes take place at the carbanionic center: (i) shortenings of the C-Ph and C-CN bonds with 0.064-0.092 Angstrom, and increases in the corresponding bond orders with 0.14-0.21 U; (ii) simultaneous enlargements of the bond angles at the same carbon atom with 7.6degrees-9.7degrees, as from tetrahedral its configuration becomes trigonal. The carbanionic charge is distributed between the two cyano groups (0.44-0.52 e(-)), phenyl ring (0.31-0.34 e(-)) and carbanionic center (0.14-0.25 e(-)). The formation of moderately strong (CH3)(2)S=O-... H-C(CN)(2)C6H5 hydrogen bonds has been found experimentally. (C) 2003 Elsevier Science B.V. All rights reserved.