Premium
Effects of substituents on activation parameters in S N 2 reactions at aliphatic carbon in solution
Author(s) -
Vlasov Vladislav M.
Publication year - 2010
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.1634
Subject(s) - chemistry , enthalpy , nucleophile , substituent , reaction rate constant , computational chemistry , standard enthalpy of reaction , hammett equation , carbon fibers , medicinal chemistry , thermodynamics , kinetics , organic chemistry , catalysis , physics , quantum mechanics , materials science , composite number , composite material
Abstract Changes of the activation parameters in aliphatic S N 2 reactions with anionic and neutral nucleophiles in various solvents, Δ H ≠ and Δ S ≠ , were correlated with σ constants of the substituents. The resultant δ Δ H ≠ and δ Δ S ≠ reaction constants are linearly related for variations of substituents at the substrate, leaving group and nucleophile. Correlations of δ Δ H ≠ versus δ Δ S ≠ allow the estimation of the contribution of changes of the internal enthalpy, δ Δ H ≠ int , to the enthalpy reaction constant, δ Δ H ≠ , which gives a single linear dependence on the Hammett ρ reaction constants. The deviations from the dependence of δ Δ H ≠ intversus ρ can be interpreted in terms of changes in the transition state structure in S N 2 reactions. The results obtained show that the substituent effects on the charge development in the transition state are governed by the magnitude of δ Δ H ≠ int . Copyright © 2009 John Wiley & Sons, Ltd.