Organic chemistry hyperconjugation

The phenyl cation (134) firstpostulated by Waters335 is a highly reactive species oflow stability and plays a fundamental role in organic chemistry—for example, in the chemistry of diazonium ions. According to gas-phase studies and calculations, its stability is between that of the ethyl cation and the vinyl cation.336 Since it is an extremely electrophilic and short-lived species, it could not be isolated or observed directly in the condensed phase. For example, solvolytic and dediazoniation studies under superacidic conditions by Faali et al.337,338 failed to find evidence of the intermediacy of the phenyl cation. Hyperconjugative stabilization via orf/zo-Me3Si or... 

For a discussion of hyperconjugation, see M.B. Smith and J. March (2000) March s Advanced Organic Chemistry Reactions, Mechanisms and Structure, 5th edn, Wiley, New York. 

For an example of such interaction in the TS of non-catalyzed alkyne/azide cycloaddition (click reaction), see Gold, B., Shevchenko, N. E., Bonus, N., Dudley, G. B., Alabugin, 1. V. (2012). Selective Transition State Stabihzation via Hyperconjugative and Conjugative Assistance Stereoelectronic Concept for Copper-Free Click Chemistry. The Journal of Organic Chemistry, 77(1), 75-89. 

Mo, Y., Jiao, H., Schleyer, P. v. R. (2004). Hyperconjugation Effect in Substituted Methyl Boranes An Orbital Deletion Procednre Analysis. Journal of Organic Chemistry, 69, 3493-3499. 

Alabugin, I. V., Manoharan, M. (2004). Effect of Double Hyperconjugation on the Apparent Donor Ability of o-Bonds Insights from the Relative Stability of 5-Substituted Cyclohexyl Cations. Journal of Organic Chemistry, 69, 9011-9024. 

For a discussion of the role of polarizibility in donor abihty, see (a) Taft, R. W., Topsom, R. D. (1987). The Nature and Analysis of Substitutent Electronic Effects. Progress in Physical Organic Chemistry, 16, 1-83 (b) Exner, O., B6hm, S. (1997). Baker-Nathan effect, hyperconjugation and polarizability effects in isolated molecules. Journal of the Chemical Society, 6, 1235-1240. 

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