The influence of the nitro group on the solid-state structure of 4-nitropyrazoles: the cases of pyrazole, 3,5-dimethylpyrazole, 3,5-di-<i>tert</i>-butylpyrazole and 3,5-diphenylpyrazole. I. Static aspects (crystallography and thermodynamics)

Abstract

We have determined the enthalpies of sublimation of 3,5-di-tert-butylpyrazole (3), 3,5-diphenylpyrazole (4), 4-nitropyrazo1e (5), 3,5-dimethyl-4-nitropyrazole (6), 3,5-di-tert-butyl-4-nitropyrazole (7) and 3,5-diphenyl-4-nitropyrazole (8); those of pyrazole (1) and 3,5-dimethylpyrazole (2) were already known. the effect of the C-substituents (Me, Bu t , Ph and NO 2 ) on the enthalpies of sublimation of pyrazoles and benzenes are additive and linearly related. Moreover, we report the structure of three of these 4-nitropyrazole derivatives, (5), (7) and (8), which have been solved by X-ray crystallography; those of the remaining five compounds were already known