55708-37-7Relevant articles and documents
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Kovats,E. sz.
, p. 2705 - 2731 (1963)
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A comparison of substituent effects on the stability of α,α-dimethylbenzyl carbocations in aqueous solution and in the gas phase: How significant is nucleophilic solvation?
Richard, John P.,Jagannadham, Vandannapu,Amyes, Tina L.,Mishima, Masaaki,Tsuno, Yuho
, p. 6706 - 6712 (2007/10/02)
Rate and equilibrium constants for conversion of ring-substituted cumyl alcohols in acidic solutions of 50:50 (v/v) trifluoroethanol/water (I = 0.50, NaClO4) to an equilibrium mixture of the corresponding cumyl alcohol, cumyl trifluoroethyl ether, and α-methylstyrene and the fractional yields of cumyl trifluoroethyl ether obtained from partitioning of the cumyl carbocation intermediates of these reactions between capture by water and by trifluoroethanol have been determined. These data and estimates of absolute rate constants for the reaction of ring-substituted cumyl carbocations with water in 50:50 (v/v) trifluoroethanol/water30 have been used to calculate equilibrium constants KR and Kp respectively for conversion of ring-substituted cumyl carbocations to the corresponding cumyl alcohols and α-methylstyrenes and the changes in Gibbs free energy (△Gx)sol for deprotonation of ring-substituted cumyl carbocations by α-methylstyrene. A plot of (△Gx)sol against (△Gx)gas for the corresponding reactions in the gas phase is linear with a slope of 0.70, in contrast to the previously reported unitary slopes of correlations of substituent effects on carbocation stability in solution and in the gas phase. We conclude that there is a modest increase in the stabilization of ring-substituted cumyl carbocations by solvation as their stability is decreased, but that this is much smaller than the change in stabilization by solvation with the changing stability of pyridinium and anilinium ions. The possible relevance of these data to the stabilization of carbocations by nucleophilic solvation is discussed.
Photochemically Generated Ion and Radical Pairs. Self-Destructive Charge-Transfer Complexes
Maslak, Przemyslaw,Chapman, William H.
, p. 6334 - 6347 (2007/10/02)
Irradiation of CT complexes between 4-methoxy-4'-X-bicumenes, 1a-e (X = H, a; OMe, b; Me, c; CF3, d; CN,) and tetranitromethane (2) results in efficient generation of radical and ion pairs (Φ ca. 0.20).The identity of the final products depends on the dynamics of these pairs, which in turn is dramatically influenced by substitution and solvent.In all cases, 2*- dissociates rapidly ( - (4-) and NO2*.In CH2Cl2, 1a*- reacts with 4- (aromatic trinitromethylation) and undergoes C-C bond fragmentation before diffusional separation of fragments can occur.Thus, a tetrad of reactive intermediates (cumyl radical, NO2*, p-methoxycumyl cation and 4-) are produced in a single solvent cage.The cumyl radical is oxidized by 2, and both cumyl cations undergo α-trinitromethylation.The cumyl cations undergo trinitromethylation in the original solvent cage which is kinetically equivalent to a contact ion pair (CIP).In CH3CN the fragmentation is accompanied by aromatic nitration (radical collapse).In this solvent, the p-methoxycumyl cations produced by cleavage reaction undergo trinitromethylation at the CIP stage, but cumyl cations produced by thermal oxidation of the cumyl radicals are trapped by 4- at the solvent-separated ion pair stage.In CH2Cl2, 1b-c*+ undergo exclusively fragmentation, completely within the solvent cage.The cleavage of 1d-e*+ is much slower, and the radical cations undergo instead aromatic trinitromethylation.The observed substituent effect on the rate of cleavage ( ρ+ = -2.2) indicates significant charge transfer across the scissile bond in the transition state for this process.The products of these reactions are predominantly derived from ion annihilation.The radical coupling processes are limited to radical cation/radical collapse that lead to nitrated products.
