Molecules (Feb 2019)

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

  • Vera L. M. Silva,
  • Artur M. S. Silva,
  • Rosa M. Claramunt,
  • Dionisia Sanz,
  • Lourdes Infantes,
  • Ángela Martínez-López,
  • Felipe Reviriego,
  • Ibon Alkorta,
  • José Elguero

DOI
https://doi.org/10.3390/molecules24030568
Journal volume & issue
Vol. 24, no. 3
p. 568

Abstract

Read online

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