- Ion-Pair Recombination of a Carbocation and Hydroxide Ion Observed in Solvolytic Media by Laser Photolysis of 9-Aryl-9-xanthenol
-
9-p-Methoxyphenyl-9-xanthenylium ion is generated by laser photolysis of the corresponding xanthenol in aqueous ethanol.The time-dependent absorbance change shows a biphasic first-order decay with halflives of 10-4 and 10-2 s.The rapid reaction is ascribed to the ion-pair recombination.
- Okuyama, Tadashi,Ueno, Kenji,Morishima, Yotaro,Kamachi, Mikiharu,Fueno, Takayuki
-
-
Read Online
- 9-Phenylxanthen-9-ylium and 9-phenylthioxanthen-9-ylium ions: Comparison of o- and p-substitutions in the 9-phenyl group by cyclic voltammetry and visible spectra
-
9-Arylxanthen-9-ylium (3a-i) and 9-arylthioxanthen-9-ylium (4a,b,e-i) perchlorates [aryl = 2,4,6-(MeO)3C6H2 (a), 2,6-(MeO)2C6H3 (b), 2-MeOC6H4 (c), 4-MeOC6H4 (d), 3-Br-2,6-(MeO)2C6H2 (e), 2,4,6-Me3C6H2 (f), 2-MeC6H4 (g), 4-MeC6H4 (h), C6H5 (i)] were prepared by the reactions of 9-arylxanthen-9-ols or 9-arylthioxanthen-9-ols with perchloric acid. Their LUMO and HOMO levels were estimated from the redox potential (E0) in cyclic voltammetry and λmax in the UV-visible spectra measured for a 1,2-dichloroethane solution, and were compared with those of 9-aryl-1,8-dimethoxyxanthen-9-ylium ions (8b,i). We found that 1) both the LUMO and HOMO levels varied almost in the same order of substituent on the 9-phenyl group; 2) the MeO-group on the 9-phenyl group was more effective to raise both the HOMO and LUMO levels than the Me-group; 3) the HOMO levels of 3 and 4 were more sensitive than the LUMO levels to the change in the 9-aryl group; 4) p-substitution by MeO- or Me-groups was more effective to raise the HOMO and LUMO levels than o-substitution; 5) the presence of two o-MeO groups was more effective to raise the HOMO and LUMO levels than one o-MeO group; 6) a m-bromination of 9-aryl group in 3b or 4b greatly lowered both LUMO and HOMO levels, as observed for 3e or 4e; 7) both the HOMO and LUMO levels of 8b and 8i were higher than those of 3b and 3i, respectively; 8) the LUMO level of 3b was higher than that of 8i, the isomer.
- Erabi, Tatsuo,Asahara, Masahiro,Miyamoto, Masahumi,Goto, Keisuke,Wada, Masanori
-
p. 1325 - 1332
(2007/10/03)
-
- Triarylmethanes and 9-arylxanthenes as prototypes amphihydric compounds for relating the stabilities of cations, anions and radicals by C-H bond cleavage and electron transfer
-
Thermodynamic stability properties of 11 p-substituted trityl and seven 9-phenylxanthyl carbocations are reported in sulfolane and of their conjugate carbanions in DMSO. The cations are compared by calorimetric heats of hydride transfer from cyanoborohydride ion, their first and second reduction potentials, their pK+Rs in aqueous sulfuric acid, 13C chemical shifts and free energies of methoxy exchange. Carbanions are compared by their heats and free energies (pKHA) of deprotonation and their first and second oxidation potentials. Radicals are compared by their oxidation and reduction potentials. Their bond dissociation energies are derived by alternative routes: from the carbocation and its reduction potential and from the carbanion and its oxidation potential. The various properties are correlated against each other and against appropriate Hammett-type substituent parameters. Correlations between the different measured properties reported here range from fair to excellent. Despite their importance as historic prototypes for the three trivalent oxidation states of carbon, trityl and xanthyl systems are atypical models for comparing transmission of electron demand in other series of carbocations, radicals or carbanions with significantly different structures. The 9-arylxanthyl series is especially poor because of its insensitivity to substituent effects. The effects of substituents on various properties which represent the stabilities of R+s correlate surprisingly well against those for corresponding R-s. Accordingly, compensating effects on the oxidation and reduction of a series of related R.s may lead to a nearly constant electron transfer energy and absolute hardness for the series. In contrast, the free energies for interconversion of the carbocations and carbanions which determine the gap between pKR+. and pKHA are very sensitive to structural change.
- Arnett, Edward M.,Flowers II, Robert A.,Ludwig, Richard T.,Meekhof, Alison E.,Walek, Stuart A.
-
p. 499 - 513
(2007/10/03)
-
- Synthesis of 2'-thioadenosine
-
Reaction between 5-N-benzoyl-9-adenine (12a), prepared from 9-(β-D-arabinofuranosyl)adenine, and 9-(4-methoxyphenyl)xanthene-9-thiol (AXT, 7b) in the pr
- Marriott, Jonathan H.,Mottahedeh, Mina,Reese, Colin B.
-
p. 257 - 269
(2007/10/02)
-
- Electrophilic Reactions of Xanthylium Carbocations Produced by Flash Photolysis of 9-Xanthenols
-
The xanthylium ion and eight 9-aryl derivatives (p-MeO, p-Me, m-Me, H, p-F, m-MeO, p-Cl, and p-CF3 phenyl) were produced in 1:4 acetonitrile/water by flash photolysis of the corresponding 9-xanthenols.The identifications of the transients as xanthylium ca
- McClelland, Robert A.,Banait, Narinder,Steenken, Steen
-
p. 2929 - 2935
(2007/10/02)
-