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Wiley Open Access, ChemistryOpen, 1(3), p. 29-36, 2014

DOI: 10.1002/open.201300043

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Understanding E2 versus SN2 Competition under Acidic and Basic Conditions

Journal article published in 2014 by Lando P. Wolters ORCID, Yi Ren, F. Matthias Bickelhaupt
This paper is made freely available by the publisher.
This paper is made freely available by the publisher.

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Abstract

Our purpose is to understand the mechanism through which pH affects the competition between base-induced elimination and substitution. To this end, we have quantum chemically investigated the competition between elimination and substitution pathways in H2O+C2H5OH2 (+) and OH(-)+C2H5OH, that is, two related model systems that represent, in a generic manner, the same reaction under acidic and basic conditions, respectively. We find that substitution is favored in the acidic case while elimination prevails under basic conditions. Activation-strain analyses of the reaction profiles reveal that the switch in preferred reactivity from substitution to elimination, if one goes from acidic to basic catalysis, is related to (1) the higher basicity of the deprotonated base, and (2) the change in character of the substrates LUMO from C(β)-H bonding in C2H5OH2 (+) to C(β)-H antibonding in C2H5OH.