Open AccessUnderstanding E2 versus S N 2 Competition under Acidic and Basic Conditions
Author(s) -
Wolters Lando P.,
Ren Yi,
Bickelhaupt F. Matthias
Publication year - 2014
Publication title -
chemistryopen
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.644
H-Index - 29
ISSN - 2191-1363
DOI - 10.1002/open.201300043
Subject(s) - chemistry , deprotonation , antibonding molecular orbital , reactivity (psychology) , substitution (logic) , base (topology) , competition (biology) , elimination reaction , homo/lumo , catalysis , medicinal chemistry , quantum chemical , reductive elimination , stereochemistry , organic chemistry , molecule , atomic orbital , ecology , alternative medicine , mathematical analysis , quantum mechanics , programming language , medicine , physics , mathematics , ion , pathology , computer science , biology , electron
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 H 2 O+C 2 H 5 OH 2 + and OH − +C 2 H 5 OH, 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 C 2 H 5 OH 2 + to C β −H antibonding in C 2 H 5 OH.