Ab initio MO and experimental studies on the vibrational spectra and structure of 4-hydroxybenzonitrile and of its anion

The structures of 4-hydroxybenzonitrile (p-cyanophenol) and its anion have been studied by IR spectra and ab initio HF and MP2 calculations. In agreement between theory and experiment, the conversion of the 4-hydroxybenzonitrile molecule into the oxyanion leads to essential spectral changes: decrease in the frequency of the cyano stretching band and strong increase in its integrated intensity, strong enhancement of the integrated intensities of the aromatic skeletal bands of v(8) and v(19) types, etc. According to the calculations (MP2 data in italics) the oxyanionic charge is delocalized over the cyano group (0.13e(-), 0.12e(-)), phenylene ring (0.44e(-), 0.39e(-)) and oxyanionic center (0.43e(-), 0.49e(-)). The conversion into the oxyanion results in an additional quinoidization of the phenylene ring. (C) 2001 Elsevier Science B.V. All rights reserved.