Spectrochemical, ab initio and density functional studies on the conversion of 2-hydroxybenzonitrile (o-cyanophenol)...

The spectral and structural changes caused by the conversion of 2-hydroxybenzonitrile (o-cyanophenol) into the corresponding oxyanion have been followed by IR spectra, ab initio and density functional force field calculations. In agreement between theory and experiment, the conversion is accompanied by a 29 cm(-1) frequency decrease of the cyano stretching band, 2.7-fold increase in its integrated intensity, 5.8-fold (total value) intensification of the aromatic skeletal bands of Wilson's 8 and 19 types, and other essential spectral changes. According to the calculations, the strongest structural changes are the shortening of the Ph-O bond with 0.10 A, lengthenings of the adjacent CC bonds in the phenylene ring with 0.06 A and bond angle variations near the oxyanionic center. All these changes are connected with the formation of a quasi-ortho-quinonoidal structure of the o-phenylene ring in the oxyanion. According to the electronic density analysis, 0.41 e(-) (Mulliken) or 0.56 e(-) (natural bond orbital, NBO) of the anionic charge remain localized at the oxyanionic center. Conformations and hydrogen bonds have also been discussed on the basis of experimental and theoretical data.