SN2 versus E2 Competition of Cyclic Ethers

Author:

Hansen Thomas1ORCID,Vermeeren Pascal1ORCID,Zijderveld Kim W. J.1ORCID,Bickelhaupt F. Matthias123ORCID,Hamlin Trevor A.1ORCID

Affiliation:

1. Department of Chemistry and Pharmaceutical Sciences Amsterdam Institute of Molecular and Life Sciences (AIMMS) Vrije Universiteit Amsterdam De Boelelaan 1108 1081 HZ Amsterdam (The Netherlands

2. Institute for Molecules and Materials (IMM) Radboud University Heyendaalseweg 135 6525 AJ Nijmegen (The Netherlands

3. Department of Chemical Sciences University of Johannesburg Auckland Park Johannesburg 2006 South Africa

Abstract

AbstractWe have quantum chemically studied the influence of ring strain on the competition between the two mechanistically different SN2 and E2 pathways using a series of archetypal ethers as substrate in combination with a diverse set of Lewis bases (F, Cl, Br, HO, H3CO, HS, H3CS), using relativistic density functional theory at ZORA‐OLYP/QZ4P. The ring strain in the substrate is systematically increased on going from a model acyclic ether to a 6‐ to 5‐ to 4‐ to 3‐membered ether ring. We have found that the activation energy of the SN2 pathway sharply decreases when the ring strain of the system is increased, thus on going from large to small cyclic ethers, the SN2 reactivity increases. In contrast, the activation energy of the E2 pathway generally rises along this same series, that is, from large to small cyclic ethers. The opposing reactivity trends induce a mechanistic switch in the preferred reaction pathway for strong Lewis bases from E2, for large cyclic substrates, to SN2, for small cyclic substrates. Weak Lewis bases are unable to overcome the higher intrinsic distortivity of the E2 pathway and, therefore, always favor the less distortive SN2 reaction.

Funder

Nederlandse Organisatie voor Wetenschappelijk Onderzoek

Publisher

Wiley

Subject

General Chemistry,Catalysis,Organic Chemistry

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