Effects of substituents on activation parameters in SN2 reactions at aliphatic carbon in solution |
| |
Authors: | Vladislav M Vlasov |
| |
Institution: | N.N.Vorozhtsov Novosibirsk Institute of Organic Chemistry, Siberian Branch of the Russian Academy of Sciences, av. Lavrentjev, 9, 630090 Novosibirsk, Russia |
| |
Abstract: | Changes of the activation parameters in aliphatic SN2 reactions with anionic and neutral nucleophiles in various solvents, ΔH≠ and ΔS≠, were correlated with σ constants of the substituents. The resultant δΔH≠ and δΔS≠ reaction constants are linearly related for variations of substituents at the substrate, leaving group and nucleophile. Correlations of δΔH≠ versus δΔS≠ allow the estimation of the contribution of changes of the internal enthalpy, δΔH, to the enthalpy reaction constant, δΔH≠, which gives a single linear dependence on the Hammett ρ reaction constants. The deviations from the dependence of δΔH versus ρ can be interpreted in terms of changes in the transition state structure in SN2 reactions. The results obtained show that the substituent effects on the charge development in the transition state are governed by the magnitude of δΔH. Copyright © 2009 John Wiley & Sons, Ltd. |
| |
Keywords: | activation parameters charge development LFER SN2 reactions substituent effects transition state |
|
|