The electron distribution in crystalline α-pyridone

Abstract

The electron density in crystals of a-pyridone has been measured with sufficient accuracy in two projections to establish the existence of the molecule in the pyridone form which differs from its tautomer, the hydroxy form, only in the position of one hydrogen atom. The molecular electron density is satisfactorily explained within the experimental error by an assemblage of isolated atoms, each with its own temperature factor, and possessing the electron distribution calculated by McWeeny using analytical approximations to atomic wave functions. Bond lengths have been measured with a standard deviation of 0.010/~ and can be explained in terms of a resonance struc= ture in which polar forms of the molecule play an important part. The hydrogen atom responsible for tautomerism is concerned in an intermolecular NO hydrogen bond, which, repeated throughout the structure, links molecules into endless helices.