Understanding E2 versus SN2 Competition under Acidic and Basic Conditions

ChemistryOpen

Lando P. Wolters¹  Prof.𠁝r. Yi Ren² 

[1] Department of Theoretical Chemistry, Amsterdam Center for Multiscale Modeling, VU University Amsterdam, De Boelelaan 1083, 1081 HV Amsterdam (The Netherlands);E-mail address: 关键词: activation-strain analysis;    density functional calculations;    elimination reactions;    nucleophilic substitutions;    reaction mechanisms;   

DOI  :  10.1002/open.201300043

来源: Wiley

【 摘 要 】

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.

【 授权许可】

CC BY-NC   
© 2014 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA.

Creative Commons Attribution-NonCommercial License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited and is not used for commercial purposes.