Aprotic Solvent Effects upon the Fundamental Vibrational Peak of the Nitrile Group in Benzonitrile

The characteristic IR peak at 2230 cm −1 (298 K) for the C=N group in benzonitrile shows a modest shift with changing solvent. A solvent reaction field model (SCRF-MO) perturbation model applied earlier to carbonyl species was tested with the V max (C=N) data for aprotic nonpolar, aprotic dipolar, aprotic highly dipolar, and aromatic liquids. For all the dielectric continuum functions tested as components in that model, there is evidence that solvent dipolarity and solvent polarizability are responsible for the nitrile band shift. However, as a solvent class, the aromatics exhibit a greater perturbation in V max (C=N) than predicted by any of the continuum descriptions.