IR spectra and structure of (4-nitrophenyl)acetonitrile and of its carbanion: experimental and ab initio studies

The structures of (4-nitrophenyl)acetonitrile and of its carbanion were studied on the basis of both quantitative LR spectra and ab initio force field calculations. The spectral and structural changes, which take place in the course of the conversion of the parent molecule into the carbanion, are essential and spread over the whole species. In agreement between theory and experiment, the conversion studied causes strong frequency decreases (down to 136 cm(-1)) and intensity increases (up to 90-fold) of the cyano and nitro stretching bands. The molecule --> carbanion conversion is accompanied by both quinoidization of the phenylene ring and a change in the configuration of the methylenic carbon atom: from tetrahedral in the molecule it becomes planar in the carbanion. The carbanionic charge is delocalized over the carbanionic center (0.40 e(-)), phenylene (0.24 e(-)), nitro (0.21 e(-)) and cyano (0.15 e(-)) groups. (C) 2000 Elsevier Science B.V. All rights reserved.