title: Experimental (13C NMR) and theoretical (ab initio molecular orbital calculations) studies on the prototropic tautomerism of benzotriazole and some derivatives symmetrically substituted on the benzene ring.
abstract: The prototropic tautomerism in anhydrous DMSO of benzotriazole and six derivatives symmetrically substituted on the benzene ring (5,6-dichloro, tetrachloro, 4,7-dibromo, tetrabromo, 5,6-dimethyl, and tetramethyl), was followed by both experimental (13C NMR and UV spectroscopy) and theoretical methods. In all of the analyzed systems, predominance of the asymmetric form, N(1)/N(3) protonated, was found. The rates of the N(1)-H<-->N(3)-H prototropic equilibrium, estimated by 13C NMR techniques, were in the medium exchange regime of 300-3000 s(-1), and are correlated with the spectroscopically determined pKa values in aqueous medium, and the anionic forms are the putative rate-limiting intermediate states.
authors.affiliation: Institute of Biochemistry and Biophysics, Polish Academy of Sciences, 5a Pawińskiego St. 02-106 Warszawa, Poland. jarek@ibb.waw.pl
authors.forename: Jarosław
authors.initials: J
authors.lastname: Poznański
authors.forename: Andzelika
authors.initials: A
authors.lastname: Najda
authors.forename: Maria
authors.initials: M
authors.lastname: Bretner
authors.forename: David
authors.initials: D
authors.lastname: Shugar
mesh_terms: D001555:Benzene Derivatives / Q000737:chemistry*; D002247:Carbon Isotopes; D009682:Magnetic Resonance Spectroscopy; D008956:Models, Chemical; D015394:Molecular Structure; D013237:Stereoisomerism; D013816:Thermodynamics; D014230:Triazoles / Q000737:chemistry*
chemical_list: D001555:Benzene Derivatives; D002247:Carbon Isotopes; D014230:Triazoles; C012771:benzotriazole