An Example of Polynomial Expansion: The Reaction of 3(5)-Methyl-1 H-Pyrazole with Chloroform and Characterization of the Four Isomers

Molecules. 2019 Feb 4;24(3):568. doi: 10.3390/molecules24030568.

Abstract

The reaction in phase-transfer catalyzed conditions of 3(5)-methyl-1H-pyrazole with chloroform affords four isomers 333, 335, 355 and 555 in proportions corresponding to the polynomial expansion (a + b)³, with a = 0.6 and b = 0.4, a and b being 3-methyl and 5-methyl proportions. The up (u) and down (d) conformation of the pyrazolyl rings with regard to the Csp³⁻H atom was established by X-ray crystallography and by ¹H-, 13C- and 15N-NMR in solution combined with gauge-including atomic orbitals (GIAO)/B3LYP/6-311++G(d,p) calculations. A comparison with other X-ray structures of tris-pyrazolylmethanes was carried out.

Keywords: GIAO calculations; NMR spectroscopy; X-ray crystallography; phase transfer catalysis; pyrazoles; pyrazolylmethanes; theoretical calculations.

MeSH terms

  • Chloroform / chemistry*
  • Crystallography, X-Ray
  • Isomerism
  • Magnetic Resonance Spectroscopy
  • Models, Molecular
  • Models, Theoretical
  • Molecular Conformation
  • Molecular Structure
  • Pyrazoles / chemistry*

Substances

  • Pyrazoles
  • Chloroform