14804-25-2Relevant articles and documents
Ludwig Boltzmann and the Norbornyl Cation
Kramer, G. M.,Scouten, C. G.,Kastrup, R. V.,Ernst, E. R.,Pictroski, C. F.
, p. 6257 - 6260 (1989)
The norbornyl cation is a fluxional species capable of rearranging to as many as 7!*11! degenerate configurations.The process has an associated entropy, depending on how many distinguishable structures are attainable under experimental conditions and this markedly effects the position of hydride-transfer equilibria observable in solution.The equilibration of norbornane with the tert-butyl cation has been observed to be endothermic by 9.6 kcal/mol and be driven toward the formation of the fluxional ion by an entropy change of 34.4 gibbs/mol in the 50-deg span from 193 to 243 K.
Thermodynamic Stabilities of Phenonium Ions Based on Bromide-Transfer Equilibria in the Gas Phase
Mustanir,Mishima, Masaaki,Fujio, Mizue,Tsuno, Yuho
, p. 1401 - 1407 (2007/10/03)
The thermodynamic stabilities of the phenonium (ethylenebenzenium) ion and ring-substituted derivatives were determined based on the bromide-transfer equilibria in the gas phase. It has been shown that the phenonium ion is 2.4 kcal mol-1 more stable than the t-butyl cation, and that the substituent effect on its stability can be correlated with the Yukawa-Tsuno equation with a ρ value of -12.6 and an r+ of 0.62. An r+ value smaller than unity of the α-cumyl(1-methyl-1-phenylethyl) cation suggested that π-delocalization in the phenonium ion is essentially less effective than through a benzylic π-interaction. On the other hand, the ρ value of -12.6 is distinctly larger than that for the ordinary benzylic carbocation systems, but is comparable to that of the benzenium ion. In addition, it has been found that the r+ value of the phenonium ions in the gas phase is in complete agreement with that for the aryl-assisted process in the acetolysis of 2-arylethyl toluenesulfonates. This suggests that the degree of π-delocalization of the positive charge is the same in the transition state and the intermediate cation. It is concluded that an r+ value of 0.6, which is ranked at a unique position in the continuous spectrum of the resonance demand, is characteristic of the bridged structure of the phenonium ion intermediate and the transition state.
Precise Determination of Stabilities of Primary, Secondary, and Tertiary Silicenium Ions from Kinetics and Equilibria of Hydride-Transfer Reactions in the Gas Phase. A Quantitative Comparison of the Stabilities of Silicenium and Carbonium Ions in the Gas Phase
Shin, Seung Koo,Beauchamp, J. L.
, p. 900 - 906 (2007/10/02)
Fourier transform ion cyclotron resonance spectroscopy has been used to examine kinetics and equilibria of hydride-transfer reactions of methyl-substituted silanes with various hydrocarbons having well-established gas-phase hydride affinities.The derived hydride affinities, D(R3Si(1+)-H(1-)), for the silicenium ions SiMeH2(1+), SiMe2H(1+), and SiMe3(1+) are 245.9, 230.1, and 220.5 kcal/mol, respectively, to be compared with the values of 270.5, 251.5, and 233.6 kcal/mol for the corresponding carbonium ions.This indicates that the silicenium ions are significantly more stable than the corresponding carbonium ions in the gas phase with H(1-) as a reference base.
