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Role of nucleophilic solvation and the mechanism of covalent bond heterolysis
Author(s) -
Dvorko Genrih F.,
Ponomareva Engelsine A.,
Ponomarev Mykola E.
Publication year - 2004
Publication title -
journal of physical organic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.325
H-Index - 66
eISSN - 1099-1395
pISSN - 0894-3230
DOI - 10.1002/poc.757
Subject(s) - chemistry , nucleophile , heterolysis , solvation , solvent , methylcyclohexane , solvent effects , benztropine , photochemistry , medicinal chemistry , computational chemistry , organic chemistry , neuroscience , dopamine , biology , catalysis
Based on data obtained mainly by the verdazyl method, the effects of a solvent on the rates of the heterolyses of 20 substrates ( t ‐BuCl, t ‐BuBr, t ‐BuI, 1‐AdBr, 1‐AdI, 1‐AdOTs, 1‐AdOPic, 1‐chloro‐1‐methylcyclopentane, 1‐bromo‐1‐methylcyclopentane, 1‐chloro‐1‐methylcyclohexane, 1‐bromo‐1‐methylcyclohexane, 2‐bromo‐2‐methyladamantane, p ‐methoxyneophyl tosylate, 2‐chloro‐2‐phenylpropane, p ‐methoxybenzotrichloride, Ph 2 CCl 2 , 7α‐bromocholesterol benzoate, 1‐chloro‐1‐phenylethane, Ph 2 CHBr, 3‐bromocyclohexene) were analyzed in a wide set of protic and aprotic solvents. The heterolysis rate of tertiary substrates decreases with increase in solvent nucleophilicity, but for secondary substrates it does not depend on solvent nucleophilicity. The negative effect of nucleopilic solvation is caused by the solvation of a contact ion pair, which appears before the limiting step. The lack of nucleophilic solvent assistance indicates that a solvent‐separated ion pair of substrates appears after the limiting step. The limiting step involves the interaction of a contact ion pair with a solvent cavity, resulting in the formation of a cavity‐separated ion pair of substrates. Copyright © 2004 John Wiley & Sons, Ltd.