A Semi‐empirical Theoretical Study of the Structure of Pyrazolidinones and Related Compounds

Abstract

INDO and AM1 calculatlons with complete optimization of the geometrv have been performed on seven pyrazolldinones (neutral, cations and zwitterions) and the corresponding pyrazolinones. The geometrles, dipole moments and energies are discussed. Both methods yield acceptable results, INDC being better for the energies and A111 for the geometrles.Pyrazolidinones are a rather neglected family of heterocyclic compounds although they inclucie one of the most studied heterocycles, phenidone (l-phenylpyrazolidin-3-one), and a new class of antibiotics where the pyrazolidinone ring replaces the B-lactam.' In particular, no theoretical studies have been carried out, with the exception of a CND0/2 and a MIND0/3 calculation of the molecular and electronic structure of azomethinimine 7a. * We report here the use of IND03 and AM1 semi-empirical methods4 for the study of 3-hydroxypyrazoline l a , pyrazolidin-3-one 2a, pyrazolidin-4-one 3a, both possible salts of pyrazolidin-3-one 4a and 5a, the betaine 6a, and the azomethinimine 7a. For comparative purposes, the corresponding unsaturated compounds (b series) have also been calculated. These much more conmon derivatives, pyraz~linones,~ will not be discussed in detail, only their dipole moments and energies will be reported.