The structure at 150 K of a highly disordered pyrazole: 3-trifluoromethyl-5-(2-thienyl)-pyrazole

The X-ray analysis at 150 K of the title compound, C18H5N2F3S, revealed dis order of the thienyl ring and the CF3 group in the two independent molecule s. The disorder affecting the thienyl substituent consists of two alternati ve orientations, the E and Z with regard to the pyrazole ring. The tautomer present in the crystal is the 1H-3-trifluoromethyl-5-(2-thienyl)-pyrazole and NMR data and DSC experiments. both in the solid state and in solution, are discussed in the light of these results. The secondary structure consis ts of dimers formed by the two independent molecules linked by N-H ... H hy drogen bonds. (C) 2000 Elsevier Science B.V. All rights reserved.