PROTON-EXCHANGE AND TEMPERATURE STUDIES OF PYRAZOLE IN DIMETHYL-D6 SULFOXIDE BY C-13 NMR

The 13C NMR shifts of all the carbons in pyrazole have been observed at room temperature. This paper reports the kinetic data available from the temperature-induced collapse of the C-3, C-5 NMR peaks. ΔG≠ ≃ 14.8 kcal/mol, ΔH≠ ≃ 7.0 kcal/mol, and ΔS≠ ≃ -25.0 cal/deg for the virtual tautomerism of pyrazole in Me2SO-d6 Temperature-induced 13C shifts for the solvent and for pyrazole were also determined to be +1.47 X 10-3 and +2.0 X 10-3 ppm/deg for C-4 and the center of the C-3, C-5 peaks, respectively. The solvent shift for 13C with temperature is +11.59 ± 10-3 ppm/deg for the CD3 in Me2SO-d6 and +3.22 X 10-3 ppm/deg for the deuterium in Me2SO-d6 Rapid exchange of pyrazole observed earlier by several workers in the solvent Me2SO-d6, is attributed to acid impurities present in previous samples. © 1979, American Chemical Society. All rights reserved.