Affinement de la structure cristalline du pyrazole

Abstract

The study of pyrazole, C3H4N2, whose structure has been determined by Ehrlich [Acta Cryst. (1960). 13, 946] from equatorial projections, has been restarted with three-dimensional diffractometric analysis of reciprocal space (copper Kct radiation) with a view to obtaining a better precision in the interatomic bond lengths. In general the structure is confirmed. Nevertheless, a greater uniformity is observed in the lengths of the 5 covalent bonds of the ring, so it becomes difficult to give the same interpretation of the molecular structure in terms of resonance: the betaine form does not seem to be the principal form as was proposed before.