Quantum chemical studies on some potentially tautomeric oxazolidin-4-one derivatives and their thio and azo anologs

The basicities and nucleophilicities along with prototautomerism of biologically active oxazolidin-4-one and its thio and azo analogs were investigated by semi-empirical methods. The oxo and thion protonation were found to be easier than that of azo protonation for 4-oxo and 4-thion derivatives whereas amino protonation was found to be easier than imino and azo protonation in 4-imino derivative. The preferred tautomeric form for 4-oxo and 4-thion derivatives were found to be the keto and thion forms, respectively, whereas the amino form was found to be preferred in 4-imino derivatives. An acceptable correlation between gas phase proton affinities and aqueous phase acidity constants as well as the correlation between nucleophilicity and acidity constants was observed.