Etudes de bromures de thiazolium à –150°C. II. Bromure de méthyl-3 tert-butyl-2 thiazolium

Abstract

The crystal structure determination of CaH20NSBr has been carried out by X-ray diffraction techniques. The crystals are orthorhombic (Pnma) with a=26-64, b=6-73, c=10.72 A~ and Z=8. As the two molecules of the asymmetric unit are related by a pseudocentre of symmetry, special constraints were applied during the refinement process to avoid correlation effects. The final R value is 0.051 for the 892 observed reflexions. This study shows that there are striking structural analogies between this structure and that of BTB4T [P6pe & Reboul, Acta Cryst. (1976), B32, 2631-2633]: molecules form doublets which are enclosed in a Br framework. In contrast to similar compounds the Br atom occupies a singular position in relation to the thiazolium ring. The t-butyl group has the hydrogen atoms on the methyl groups in staggered positions. The molecular conformation corresponds to a minimization of steric interactions between the substituents. On the basis of the N-methyl bond deformations a hypothesis is derived for the nitrogen atom reactivity in thiazolic compounds.