56683-65-9Relevant academic research and scientific papers
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.
Stability and reactivity of the benzyl and tropylium cations in the gas phase
Sharma, D. K. Sen,Kebarle, P.
, p. 1592 - 1601 (2007/10/02)
A measurement of equilibrium : t-C4H9+ + BzCl = t-C4H9Cl + C7H7+ led to equilibrium constants K4 which are fair agreement with earlier work by Abboud at al.However, the present temperature dependence predicts a ΔS40 which is sufficiently different from that by Abboud et al. to put in question the identification of C7H7+ as Bz+ on the basis of the measured ΔS40 value.Therefore experiments were made to confirm that C7H7+ produced in is Bz+ and not the tropylium cation.A C7H7+ cation was produced by hydrid abstraction from 1,3,5-cycloheptatriene.The behaviour of that C7H7+ ion was entirely different from C7H7+ produced by chloride abstraction from BzCl or hydride abstraction from toluene.While the benzyl derived C7H7+ engaged in a number of reactions like hydride abstraction, chloride abstraction, addition, condensation, etc., the C7H7+ from the heptatriene remained completely unreactive.On this basis the C7H7+ ions were identified as Bz+ and tropylium+, respectively.Rate constants for several reactions of Bz+ were determined.It is concluded that a rearrangement from benzyl to tropylium cations and vice versa does not occur at least up to 300 deg C.The ions also retain their identity if they are produced with considerable internal excitation energy.
