3-Methyl-5-phenylpyrazole: a neutron diffraction study

Abstract

A single-crystal neutron diffraction study of the title compound (734 reflections, R0.08) has located the tautomeric N–H hydrogen atoms; the two molecules in the asymmetric unit are closely related to a second pair generated by a crystallographic two-fold axis, the ‘tautomeric’ protons bridging adjacent N ⋯ N groups to form a hydrogen bound cyclic tetramer. Within each of the three remarkably short independent N ⋯ N contacts, the tautomeric hydrogen atoms are almost linearly co-ordinated and symmetrically disposed.