Molecular Structure of Heterocycles: 4^# NMR Spectroscopy, X-Ray Diffraction, and Semiempirical Mo Calculations of 3-Phenyl-5-Hydroxy- 5-Trichloromethyl-4,5-Dihydro-FH-Pyrazole-1-Carboxyamide

Abstract

A new series of trichloromethylated- 4, 5-dihydro-1H-pyrazoles has been studied. The molecular structure of 5-hydroxy-3-phenyl-5-trichloromethyl-4,5-dihydro-7H-pyrazole-1-carboxyamide (2), synthesized from the reaction of 4-methoxy -4-phenyl-1,1,1-trichloro-3-buten-2-one (1) with semicarbazide hydrochloride, 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 pair of the enanfiomers was obtained. The AM1 calculations showed that 2a (1S5S/1R5R) is the more stable enantiomers pair. The x-ray diffraction data confirmed that only the structure 2a (1S5S/1R5R) was obtained.

This was explained by the existence of an intramolecular hydrogen bond between the hydroxy group at C(5) and the carbonyl group at N(1), with the formation a stable six-membered ring. Compound 2 (C₁₁H₁₀CI₃N₃O₂, M_r = 320.98) crystallizes in the monoclinic space group P2₁/c with the unit cell dimensions a = 6.495(1), b = 25.275(5) and c = 8.401(1) A, p = 96.88(3)°, R = 3.00 % and wR₂ = 7.71 % for an F² refinement on 2012 observed reflections with [l>2σ(l)].

Key Words:

• 1H-Pyrazole-1-carboxyamides
• NMR
• X-ray Structure Investigation
• MO calculations, AM1