M. Georgieva, P. Angelova, I. Binev
Apr 5, 2004
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0
Influential Citations
11
Citations
Journal
Journal of Molecular Structure
Abstract
Abstract The conversion of 3- and 4-hydroxybenzonitriles ( m - and p -cyanophenols) into oxyanions has been followed by IR spectra, ab initio HF, MP2 6-31G(d) and density functional BLYP, B3LYP 6-31G(d) force field calculations. In a general agreement between theory and experiment, the conversion causes a 34 cm −1 frequency decrease in the cyano stretching band, 3.2-fold increase in its integrated intensity and other essential spectral changes in the para -isomer; for the meta -one the corresponding values are 13 cm −1 and 2.3-fold, respectively. According to the calculations, both molecule and anion of 4-hydroxybenzonitrile are more stable (due to the polar resonance) than the corresponding meta -substituted species. The strongest structural changes, caused by deprotonation, are the 0.105 A shortenings of the Ph–O bonds, 0.054 A lengthenings (mean values) of the adjacent CC bonds and essential bond angle changes in the phenylene rings near the oxyanionic centers. In the case of para -isomer these changes are related to the formation of a quasi- para -quinonoidal structure of the phenylene ring in the oxyanion. According to the electronic density analysis, a bit less (Mulliken) or a bit more (natural bond orbital) than halves of the anionic charges remain localized at the oxyanionic centers. Hydrogen bonds have also been discussed.