SOLVENT-INDUCED FREQUENCY-SHIFTS IN THE INFRARED-SPECTRUM OF ACETONITRILE IN ORGANIC-SOLVENTS

The solvent-induced frequency shifts (SIFS) for the C=N stretching vibration (nu2) in acetonitrile and deuterated acetonitrile have been determined in a wide variety of organic solvents. It is shown that this band is shifted to higher energies in the presence of solvents which are more stronger Lewis acids than acetonitrile itself. On the other hand, in the presence of solvents which are stronger Lewis bases, the nu2 band is shifted to lower energies. This is taken to be evidence that the electronegative end of the Lewis base interacts with the methyl group in acetonitrile. Supporting evidence for this conclusion is reported on the basis of shifts in the symmetrical (nu1) and antisymmetrical (nu5) CD3 stretching bands. The magnitude of the SIFS is shown to correlate either with the solvent's basicity as estimated by the Gutmann donor number or with the solvent acidity as estimated by its acceptor number. Further details of intermolecular interactions in both pure acetonitrile and in its dilute solutions in organic solvents are discussed in terms of the observed vibrational spectra.