Dissociation energies of O-H bonds in alkylseleno- and alkyltelluro-substituted phenols

The O-H bond dissociation energy (D (O-H)) has been determined for eight alkylseleno-substituted phenols, one alkyltelluro-substituted phenol, and one alkyltelluro-substituted pyridinol. D (O-H) has been estimated by the intersecting-parabolas method from kinetic data using five reference compounds: alpha-tocopherol (D (O-H) = 330.0 kJ/mol), 3,5-di-tert-butyl-4-methoxyphenol (D (O-H) = 347.6 kJ/mol), 4-methylphenol (D (O-H) = 361.6 kJ/mol), 2,6-di-tert-butyl-4-methylthiophenol (D (O-H) = 336.3 kJ/mol), and 2,6-di-ter-tbutyl-4-methylphenol (D (O-H) = 338.0 kJ/mol). The following D (O-H) values (kJ/mol) have been obtained: 335.9 for 2,5,7,8-tetramethyl-2-phytyl-6-hydroxy-3,4-dihydro-2H-1-benzoselenopyran, 342.6 for 2-methyl-5-hydroxy-2,3-dihydrobenzoselenophene, 333.5 for 2,4,6,7-tetramethyl-5-hydroxy-2,3-dihydrobenzoselenophene, 339.4 for 2-tert-butyl-4-methoxy-6-octylselenophenol, 357.9 for dodecyl 3-(4-hydroxyphenyl) propyl selenide, 348.5 for dodecyl 3-(3,5-dimethyl-4-hydroxyphenyl)propyl selenide, 350.9 for dodecyl 3-(3-tert-butyl-4-hydroxyphenyl)propyl selenide, 338.0 for dodecyl 3-(3,5-di-tert-butyl-4-hydroxyphenyl) propyl selenide, 343.0 for 2,6-di-tert-butyl-4-(tellurobutyl-4'-phenoxy)phenol, and 338.8 for 6-octyltelluro-3-pyridinol. The stabilization energies of phenoxyl radicals containing R substituents (X = O, S, Se, Te) have been compared.