Experimental and calculated structural parameters of 5-trihalomethyl-4,5-dihydro-1H-pyrazole derivatives, novel analgesic agents

The crystal structures of four novel analgesic agents, methyl 5-hydroxy-3- or 4-methyl-5-trichloro[trifluoro]methyl-4,5-dihydro-1H-pyrazole-1-carboxylate, have been determined by X-ray diffractometry. The data demonstrated that the molecular packing was stabilized mainly by OH⋯O hydrogen bonds of the 5-hydroxy and 1-carboxymethyl groups. The 4,5-dihydro-1H-pyrazole rings were obtained as almost planar structures showing RMS deviation at a range of 0.0052–0.0805 Å. Additionally, computational investigation using semi-empirical AM1 and PM3 methods were performed to find a correlation between experimental and calculated geometrical parameters. The data obtained suggest that the structural data furnished by the AM1 method is in better agreement with those experimentally determined for the above compounds.