Activation of the SN2 Reaction by Adjacent π Systems: The Critical Role of Electrostatic Interactions and of Dissociative Character

Raphaël Robiette*, Tran Trieu-Van, Varinder K Aggarwal, Jeremy N Harvey

*Corresponding author for this work

Research output: Contribution to journalArticle (Academic Journal)

16 Citations (Scopus)
275 Downloads (Pure)

Abstract

The activation of the SN2 reaction by π systems is well documented in textbooks. It has been shown previously that this is not primarily due to classical (hyper)conjugative effects. Instead, π-conjugated substituents enhance favorable substrate-nucleophile electrostatic interactions, with electron-withdrawing groups (EWG) on the sp2 system leading to even stronger activation. Herein we report computational and experimental results which show that this activation by sp2 EWG-substitution only occurs in a fairly limited number of cases, when the nucleophile involves strong electrostatic interactions (usually strongly basic negatively charged nucleophiles). In other cases, where bond breaking is more advanced than bond making at the transition state, electrophile-nucleophile electrostatic interactions are less important. In such cases, (hyper)conjugative electronic effects determine the reactivity, and EWG-substitution leads to decreased reactivity. The basicity of the nucleophile as well as solvent effects can help to determine which of these two regimes occurs for a given electrophile.

Original languageEnglish
Pages (from-to)734-737
Number of pages4
JournalJournal of the American Chemical Society
Volume138
Issue number3
Early online date3 Jan 2016
DOIs
Publication statusPublished - 27 Jan 2016

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