Molecular orbital calculations of pyrazoles. Part I. Alkyl- and arylpyrazoles

Abstract

The longest π→π* wave absorption band in the u.v. spectra of 40 alkyl- and aryl-pyrazoles has been calculated by the simple LCAO–MO method. With a suitable choice of parameters, a good correlation has been obtained between the calculated and observed frequencies. Angles of twist have been calculated for some sterically hindered pyrazoles, and the stabilities of some tautomeric forms of 1-unsubstituted pyrazoles and the basicities of a number of pyrazoles have also been examined. Electrophilic and homolytic substitution in pyrazole, 1-methyl- and 1-phenyl-pyrazole and their corresponding conjugate acids have been discussed in terms of reactivity indices.