Effect of substituents on activation parameters in aliphatic S(N)2 reactions. A DFT study

The Journal of Organic Chemistry
Ferenc Ruff, Odön Farkas

Abstract

The activation parameters and optimized structures of the reactants and transition states in the S(N)2 reactions of substituted pyridines and N,N-dimethylanilines with methyl iodide were computed at the DFT level in different solvents. The measured and calculated deltaG/deltaH/deltaS versus sigma plots proved to be linear, and their slopes, the deltadeltaG, deltadeltaH, and deltadeltaS reaction constants, were determined. The least solvent-dependent deltadeltaG reaction constants can be computed with acceptable accuracy. The calculated deltadeltaS data decrease only very slightly with the jointly increasing electron-withdrawing effect of the substituents and tightness of the transition states. The measured deltadeltaS values are influenced mainly by the change of solvation in the reactions, and deltadeltaH is also influenced by the reorganization of the solvent. Consequently, the experimental and calculated deltadeltaS and deltadeltaH reaction constants may deviate considerably from each other. In dipolar aprotic solvents the measured deltadeltaS was less than zero, and in protic solvents it was greater than zero. The ordering of the solvent molecules around the transition state with increasing charge is increased in the former...Continue Reading

References

Feb 19, 2002·Chemical Reviews·Mikhail V. Rekharsky, Yoshihisa Inoue
Feb 17, 2005·Journal of the American Chemical Society·Faraj HasanaynRasha Al-Rifai

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Citations

Mar 10, 2016·Inorganic Chemistry·Rameswar BhattacharjeeAyan Datta

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