title: Understanding E2 versus SN2 Competition under Acidic and Basic Conditions.
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.
authors.affiliation: Department of Theoretical Chemistry, Amsterdam Center for Multiscale Modeling, VU University Amsterdam De Boelelaan 1083, 1081 HV Amsterdam (The Netherlands).
authors.forename: Lando P
authors.initials: LP
authors.lastname: Wolters
authors.affiliation: College of Chemistry and Key State Laboratory of Biotherapy, Sichuan University Chengdu 610064 (P. R. China).
authors.forename: Yi
authors.initials: Y
authors.lastname: Ren
authors.affiliation: Department of Theoretical Chemistry, Amsterdam Center for Multiscale Modeling, VU University Amsterdam De Boelelaan 1083, 1081 HV Amsterdam (The Netherlands) ; Institute for Molecules and Materials, Radboud University Nijmegen Heyendaalseweg 135, 6525 AJ Nijmegen (The Netherlands).
authors.forename: F Matthias
authors.initials: FM
authors.lastname: Bickelhaupt
keywords: activation-strain analysis; density functional calculations; elimination reactions; nucleophilic substitutions; reaction mechanisms