Electrical effects in substituted thiazoles. pKa Values of some 5-substituted 2-aminothiazoles and 5-substituted 2-NN-dimethylaminothiazoles
Abstract
Comparison of the pKa values of some 5-X-aminothiazoles with those of the corresponding 5-X-2-NN-dimethylaminothiazoles allows the assignment of the aromatic amino form to 2-aminothiazole derivatives. A Hammett plot of pKa values against σmeta substituent constants is linear as required if the protonation centre is the endocyclic nitrogen in all cases. Cross-conjugation between the amino groups in position 2 and the substituents in position 5 is present only when the nitro-group is the substituent. Conjugative interaction between the amino group and the ‘aza’ group is also discussed.