A COMPARISON OF THE STRUCTURES OF PYRAZOLE, 3,5-DIMETHYLPYRAZOLE AND 3,5-BIS(TRIFLUOROMETHYL)PYRAZOLE - THEORETICAL CALCULATIONS (STO-3G), MICROWAVE, ELECTRON-DIFFRACTION AND CRYSTALLOGRAPHY

The first two examples of pyrazole structures determined by electron diffraction are reported. These geometries and that of pyrazole itself (known from a microwave study) are discussed in comparison with STO-3G ab initio calculations and with X-ray geometries. Theoretically optimized geometries agree with the experimental ones, both describing consistently the electronic effects and conformation of methyl and trifluoromethyl substituents with regard to the solid state geometries, it appears that 3,5-dimethylpyrazole has a classical C(S) structure in the gas phase consistent with the averaged C2v structure of the crystal (dynamically disordered).