Molecular structure of heterocycles: 4# NMR spectroscopy, X-ray diffraction, and semiempirical MO calculations of 3-phenyl-5-hydroxy-5-trichloromethyl-4,5 dihydro-1H-pyrazole-1-carboxyamide.

A new series of trichloromethylated-4,5-dihydro-1H-pyrazoles has been studi ed. The molecular structure of 5-hydroxy-3-phenyl-5-tn'chloromethyl-4,5-dih ydro-1H-pyrazole-1-carboxyamide (2), synthesized from the reaction of 4-met hoxy-4-phenyl-1,1,1-trichloro-3-buten-2-one (1) with semicarbazide hydrochl oride, was selected and determined by NMR spectroscopy, X-ray diffraction, and semiempirical MO calculations. Proton and carbon-13 NMR data, as one set of signals, shown that only one p air of the enantiomers was obtained. The AM1 calculations showed that 2a (1 S5S/1R5R) is the more stable enantiomers pair. The x-ray diffraction data c onfirmed that only the structure 2a (1S5S/1R5R) was obtained. This was explained by the existence of an intramolecular hydrogen bond betw een the hydroxy group at C(5) and the carbonyl group at N(1), with the form ation a stable six-membered ring. Compound 2 (C11H10Cl3N3O2, M-r = 320.98) crystallizes in the monoclinic space group P2(1)/c with the unit cell dimen sions a = 6.495(1), b = 25.275(5) and c = 8.401(1) Angstrom, beta = 96.88(3 )degrees, R = 3.00 % and wR(2) = 7.71 % for an F-2 refinement on 2012 obser ved reflections with [l>2 sigma(l)].