CMR spectra of N-oxygenated pyrazoles I. 3,5-Dialkyl- and 3-alkyl-5- phenyl-4-oxo-4H-pyrazole 1,2-dioxides

Article abstract of DOI:10.3987/com-98-8333

The ¹³C NMR spectra of a series of 3,5-dialkyl- and 3-alkyl-5-phenyl- 4-oxo-4H-pyrazole 1,2-dioxides were determined. Signals for the carbonyl carbon, C4 of the pyrazole, appeared at δ 186.2 to 188.1 ppm, while the C3 and C5 signals were found in the region of 105.8 to 112.8 ppm. The effect of structural variation of the alkyl groups on the chemical shift of C3 in a selected series of these compounds was investigated using published electronic and steric parameters. Strong correlations were observed with electronic parameter sets σ* and E(σ) when augmented with a variety of published steric parameter sets.