29180-23-2Relevant academic research and scientific papers
ISOMERIC FLUOROBENZYL AND FLUOROTROPYLIUM CATIONS
McLafferty, Fred W.,Amster, Jonathan
, p. 375 - 382 (1981)
The tendency for isomerization of toluene and cycloheptatriene molecular ions, and of benzyl and tropylium product ions, is substantially reduced by fluorine substitution, irrespective of position.This stabilization appears to be due to back-donation of electrons from fluorine, despite its high electronegativity.
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.
Substituent Effect on the Stability of Benzyl Cation in the Gas Phase
Mishima, Masaaki,Arima, Kiyoshi,Usui, Satoshi,Fujio, Mizue,Tsuno, Yuho
, p. 1047 - 1050 (2007/10/02)
Chloride ion affinities of substituted benzyl cations in the gas phase have been determined by means of an ICR mass spectrometer.The substituent effect has been analyzed in terms of the LArSr Eq., giving a p=13.6 and r+=1.31.
Kinetics and Equilibria of Chloride Transfer Reactions. Stabilities of Carbocations Based on Chloride and Hydride Transfer Equilibria Measurements
Sharma, R. B.,Sharma, D. K. Sen,Hiraoka, K.,Kebarle, P.
, p. 3747 - 3757 (2007/10/02)
The kinetics of a number of gas-phase chloride transfer reactions R0(1+)+RCl=R0Cl+R(1+) were measured with a pulsed electron high pressure mass spectrometer.Most of the reactions were found to occur near the collision limit, i.e., with rate constants k ca. 10-9 molecules-1 cm3 s-1.However, several reactions were much slower and were exhibiting negative temperature dependence, i.e., decreasing rate with increasing temperature.Hydride and chloride transfer equilibria were determined for various carbocations R(1+) (R=isopropyl, cyclopentyl, tert-butyl, 1-methylcyclopentyl, substituted benzyls, norbornyl, 2-methyl-2-norbornyl, and adamantyl).Excellent agreement with earlier hydride transfer measurements of Solomon, Meot-Ner, and Field were observed.The chloride affinities generally support conclusions based on the hydride transfer data.Discussion of the data in connection with benzyl cation substituent effects, the norbornyl cation stability, and solvent effects on carbocation stability is presented.The data show that the 2-norbornyl cation is unusually stable.Significant differences between carbocation R(1+) stabilities in gas phase and solution are found which suggest that both differential nucleophilic solvent stabilization and differential nonspecific solvation occur in solution.
