Molecular structure and interionic vibrations of the ion pairs of N-acetyloxypyridinium halides

The structure and interionic vibrations of the ion pairs of N-acetyloxypyridinium halides were investigated on the basis of joint use of methods of quantum chemistry, molecular mechanics, and long-wave IR spectroscopy. It was established that the indicated salts belong to the class of stereochemically nonrigid molecules, and their most probable geometrical configuration corresponds to a position of the anion above the plane of the pyridine ring in the region adjoining the nitrogen atom. A nonmonotonic dependence of the force constant of the interionic vibrations on the equilibrium distance between ions in N-acetyloxypyridinium halides was predicted theoretically and detected experimentally.Translated from Teoreticheskaya i éksperimental'naya Khimiya, Vol. 22, No. 5, pp. 597–602, September–October, 1986.