ChemInform Abstract: Electronic Absorption Spectra of Pyrazoles. Part 3. Semiempirical Calculations and the Problem of Tautomerism of 3(5)‐Phenylpyrazole.

Abstract

structure structure (organic substances) K 9000 -063Electronic Absorption Spectra of Pyrazoles. Part 3. Semiempirical Calculations and the Problem of Tautomerism of 3(5)-Phenylpyrazole.-The structures of pyrazole, 3-phenylpyrazole, its 5-phenyl tautomer, 4phenylpyrazole and 3,5-diphenylpyrazole adopted in solution are investigated by UV and low temp. 13C NMR spectroscopy and semiempirical calculations. The NMR spectra reveal that the 3-phenyl tautomer is the major component in the tautomeric couple with its 5-phenyl tautomer. A mathematical model is presented for the comparison of the experimental and calculated electronic spectra. -(CATIVIELA, C.; GARCIA LAUREIRO, J. I.; ELGUERO, J.; ELGUERO, E.; Gazz.

STUDIES IN THE AZOLE SERIES. CIV.1 EXPERIMETAL AND CALCULATED DIPOLE MOMENTS OF 3(5)‐PHENYLPYPRAZOLES

“…(7~8) The main conclusions of We have been interested in the structure and PhY-these studies will be briefly summarized here. All the sical Properties of C-PhenY IPYrazoles; these studies pyrazoles needed for the following discussion are recomprised electronic spectra, (2,3) NMR spectros-presented below. …”

“…In solution, there is 75-8070 of 4a -20-25% of 4b (AE = 2.3 kJ mol-1). (4) Finally, electronic spectroscopy coupled with theoretical calculations (2,3) lead to the conclusion that 3-phenyl tautomers 3a and 4a are predominant in ethanol solution and that 3-phenyl substituents are planar (0, = 0") while 5-phenyl substituents are twisted (0, -30°), the twist angle €I5 increased when there is a methyl group at position 1 (9, 11, 12).…”

1-Vinyl-3- and 1-vinyl-5-pyrazolecarboxylic acids. Synthesis and anti-burn activity of their chitosan salts

“…No products of N-alkylation are formed under these conditions. Transvinylation of the esters of 3(5)-pyrazole carboxylic acid (II) with vinyl acetate in the presence of catalytic amounts of mercury(II) sulfate gave a mixture of isomeric esters of 1-vinyl-3-and 1-vinyl-5-pyrazole carboxylic acids III, IV in total yield of 80% and the ratio of isomers 3 : 2, respectively [8]. The isomers were separated by conventional distillation.…”