P 93 Protolytic equilibrium of the isomeric phenyl-1,2,4-triazines [Electronic resource] / I. V. Khabibulina, A.P. Volovodenko, R. E. Trifonov, G. V. Yashukova, N. N. Mochul`skaya, V. N. Charushin, G. L. Rusinov, D. G. Beresnev, N. A. Itsikson, V. A. Ostrovskii // Chemistry of Heterocyclic Compounds. - 2003. - Vol. 39, № 5. - P616-623 Рубрики: ХИМИЧЕСКИЕ НАУКИ Аннотация: The protonation constants for the first and second stages (pK BH+, pKBH2+) of a series of 1,2,4-triazines with a phenyl substituent at various positions in the ring were determined in aqueous solution by a spectrophotometric method. The values of the basicity constants characterizing the first protonation of the heterocycles investigated was in the range of acidity of the medium of pH 3.5 to H0 -2, and the second from H0 -7.3 to H0 -8.7. The position of the phenyl substituent proved to have a significant effect on the size of pK BH+. According to the results of ab initio calculations using HF/6-31G** for the heterocycles investigated the 1H+ form is thermodynamically most stable among the monocations, with the exception of 6-phenyl-1,2,4-triazine for which the existence of the monocation in the 1H+ and 2H+ forms are equally probable. In the case of the dications of all the triazines the 2,4-H,H2+ tautomer is the most preferred. The aromaticity of the 1,2,4-triazine ring is changed insignificantly on mono- and diprotonation. \\\\Expert2\\nbo\\Chemistry of Heterocyclic Compounds\\2003, v.39, N 5, p.616. .pdf |