Tautomerism of pyrazolidine-3,5-diones. II. Infrared spectra

Abstract

The tautomerism of a number of N¹- and N¹,N²-substituted monotriazolylpyrazolidine-3,5-diones and their phenyl analogues has been examined by infrared spectroscopy. The diketo tautomer is the predominant form, both in the solid state and in chloroform solution. Monosodium salts of 4,4-dialkyl-1-triazolylpyrazolidinediones show unusual absorption which indicates strong hydrogen bonding in the compounds; a three-centre hydogen bond is proposed to explain the observed spectra.