Solvolytic Displacement Reactions

The increase in rate owing to MeO-5 participation in the acetolysis of secondary p-bromobenzenesulfonates [cf. compounds (11) and (15) in 

Compound EtOH (75°C) AcOH (25°C) HCO2H (75°C) EtOH AcOH HCO2H 

The slightly greater rate of acetolysis of t/ir o-5-methoxy-2-hexyl p-bromobenzenesulfonate (14) relative to its erythro isomer (13) probably results from steric retardation in formation of the cyclic oxonium ion from 

According to the mechanism postulated, (11) and (12) should yield the same oxonium ion (18), and if counterion effects are unimportant, their products also should be identical. Allred and Winstein have conducted detailed studies showing that both the rate constants (Table 2) and the product ratios are nearly identical for the acetolyses of (11) and (12) at 25°C. 

It is somewhat surprising that the rate constants for acetolysis and ethanolysis are so similar for (11) and (12). These similarities have been rationalized in terms of the blending of and substituent effects. Since (11) and (12) are interconverted during acetolysis, attack on (18) may be partly rate limiting. 

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A. Streitwieser, Jr., Solvolytic Displacement Reactions, McGraw-Hill, New Tfcrk, 1962 J. F. Bunnett, Annu. Rev. Phys. Chem. 14 271 (1963). 

A Strdtwieser, Jt, Solvolytic Displacement Reactions, McGraw-Hill, New York, 1962. 

Spieth. F.. quoted by Streitwieser, A., Jr. Solvolytic Displacement Reactions McGraw-Hill New York, 1962 p 53. 

For reviews, see L. Melander, Isotope Effects on Reaction Rates, Ronald Press, New York, 1960 F.W. Westheimer, Chem. Rev., 61, 265 (1961) Streitwieser, A., Jr., Solvolytic Displacement Reactions, McGraw-Hill, New York, 1962 E. H. Halevi,Prog Phys. Org. Chem., 1, 109 (1963) C. J. Collins and N. S. Bowman, eis.. Isotope Effects in Chemical Reactions, Van Nostrand Reinhold Co., New York, 1970. 

Streitwieser, A, jr. Solvolytic displacement reactions at saturated carbon atoms. Chem. Reviews 56, 675 (1956). 

A. Streitwieser, Solvolytic Displacement Reactions at Saturated Carbon Atoms," Chem. Rev. 56, 571 (1956). 

Comprehensive reviews of S 2 substitution can be found in (a) S. R. Hartshorn, Aliphatic Nucleophilic Substitution, Cambridge University Press, London, 1973 (b) A. Streitwieser, Solvolytic Displacement Reactions, McGraw-Hill, New York, 1962 (c) C. K. Ingold, Structure and Mechanism in Organic Chemistry, 2nd ed., Cornell University Press, Ithaca, N.Y., 1969. 

These values are from Streitwieser, A. Solvolytic Displacement Reactions, McGraw-Hill, NY, 1962, p. 43, where values are also given for other conditions. Methyl bromide reacts faster than ethyl bromide (and in the case of 60% ethanol, ispropyl bromide) because most of it (probably all) reacts by the Sn2... 

Streitwieser, Jr., A. Solvolytic displacement reactions. New York McGraw-Hill 1962... 

Solvolytic displacement reactions can be affected by solvents in several ways, including nucleophilic solvent assistance (NSA) and electrophilic solvent assistance (ESA). NSA can be defined as electron donation from solvent to the developing positive dipole of a reacting C-X bond, and ESA can be defined as electron acceptance by the solvent from the leaving group, I. 

George Hammond began his independent research career as a physical organic chemist studying the benzidine rearrangement. He studied the effects of remote substituents in solvolytic displacement reactions and was one of the first to point out the existence of systematic deviations from the Hammett equation. He also undertook studies of the reactions of free radicals and... 

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