Computational investigation of the effect of alpha-alkylation on SN2 reactivity: acid-catalyzed hydrolysis of alcohols
Ruggiero, G. D. and Williams, I. H., 2001. Computational investigation of the effect of alpha-alkylation on SN2 reactivity: acid-catalyzed hydrolysis of alcohols. Journal of the Chemical Society: Perkin Transactions 2
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Computed potential energy barriers (HF, B3LYP and MP2/6-31G*; vacuum and PCM water) for simple S(N)2 identity reactions H2O + R-OH2+ --> +H2O-R + OH2 tend to decrease along the series R = Me, Et, Pr-i and Bu-t, in contrast with those calculated for Cl- + R-Cl-->Cl-R + Cl-. The S(N)2 reaction profile for H2O + Bu-t-OH2+ shows a sequence of three steps, each with a transition structure corresponding to the internal rotation of a single methyl substituent. The same three rotations also appear in the S(N)2 reaction profile for Cl- + Bu-t-Cl, but as distinct stages of a concerted process with a single transition structure; only the second methyl group undergoes internal rotation in the transition vector itself. Simulation of reactions H2O + R-OH2+, using the AM1/COSMO method for treatment of aqueous solvation, illustrates the changing energy surface topography accompanying S(N)2/S(N)1 mechanistic changeover along the series R = Me, Et, Pr-i and Bu-t, and permits determination of kinetic isotope effects for both pathways with each alkyl group. Mechanistic change occurs by alteration of the relative energies of the TSs along these competing paths. Computational modelling allows investigation of experimentally unobserved reaction mechanisms, such as S(N)1 for primary substrates.
|Creators||Ruggiero, G. D.and Williams, I. H.|
|Departments||Faculty of Science > Chemistry|
|Additional Information||ID number: ISI:000168123900005|
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