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Towards mechanisms of bimolecular nucleophilic reactions in solution—probing the variation of the activation parameters in the reactions of aromatic compounds
Author(s) -
Vlasov Vladislav M.
Publication year - 2012
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.1912
Subject(s) - chemistry , substituent , enthalpy , nucleophile , reaction rate constant , hammett equation , reaction mechanism , nucleophilic substitution , computational chemistry , kinetics , thermodynamics , medicinal chemistry , organic chemistry , catalysis , physics , quantum mechanics
Variation of the activation parameters in the S N 2, acyl‐transfer, S N Ar, S N V, and Ad N reactions offers a uniquely useful probe for the mechanistic features of these reactions in solution. New approach uses the substituent effects on the aromatic ring to the variation of the activation parameters, Δ H ≠ and Δ S ≠ , in the above reactions in the frameworks of the Hammett‐like equations in order to evaluate the resultant δ Δ H ≠ and δ Δ S ≠ reaction constants. Compensation relationships of δ Δ H ≠ versus δ Δ S ≠ allow one to estimate the contribution of changes of the internal enthalpy, δ Δ H ≠ int , to the enthalpy reaction constant, δ Δ H ≠ , that is inherent to bimolecular nucleophilic reactions and gives a single linear dependence on the Hammett ρ reaction constants for these reactions. The deviations from dependence of δ Δ H ≠ int versus ρ serve as useful points of interpretation of changes of the transition state structure or reaction mechanism. The results obtained show that the substituent effects in the substrates, nucleophiles, and leaving groups on the mechanistic features in bimolecular nucleophilic reactions are governed by the magnitude of δ Δ H ≠ int . Copyright © 2011 John Wiley & Sons, Ltd.