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Theoretical insights into the E1cB/E2 mechanistic dichotomy of elimination reactions

Ortega, Daniela E. and Ormazábal-Toledo, Rodrigo and Contreras, Renato and Matute, Ricardo A. (2019) Theoretical insights into the E1cB/E2 mechanistic dichotomy of elimination reactions. Organic and Biomolecular Chemistry, 17 (46). pp. 9874-9882. ISSN 1477-0520. https://resolver.caltech.edu/CaltechAUTHORS:20191111-082331901

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Abstract

E1cB and E2 eliminations have been described as competing mechanisms that can even share a common pathway when the E1cB/E2 borderline mechanism operates. A suitable case study evincing such a mechanistic dichotomy corresponds to the elimination reaction of β-phenylmercaptoethyl phenolate, since its mechanism has been thought to be an E2 elimination. Nonetheless, according to the computational assessment of the substituents on the leaving group, we demonstrate that the reaction proceeds via a borderline E1cB mechanism. Stabilization of the carbanion was provided not only by substituent effects tuning the nucleofugality of the leaving group, but also by a base, since distortion/interaction–activation strain and Natural Bond Order (NBO) analyses suggest a stabilizing interaction between the base and C_β of the E1cB intermediate. In order to gain insights into these results in a more general context, we have rationalized them with a qualitative picture of the E1cB/E2 mechanistic dichotomy using simple relationships between diabatic parabolas modeling the potential wells of reactants, intermediates, and products. In this Diabatic Model of Intermediate Stabilization (DMIS), the borderline E1cB mechanism for the elimination reaction of β-phenylmercaptoethyl phenolate was discussed in terms of bonding and dynamic stepwise processes. The conceptual model presented herein should be useful for the analysis of any reaction comprising competing one- and two-step mechanisms.


Item Type:Article
Related URLs:
URLURL TypeDescription
https://doi.org/10.1039/c9ob02004gDOIArticle
http://www.rsc.org/suppdata/c9/ob/c9ob02004g/c9ob02004g1.pdfPublisherSupplementary Information
ORCID:
AuthorORCID
Ortega, Daniela E.0000-0002-0724-4206
Ormazábal-Toledo, Rodrigo0000-0003-1777-0426
Contreras, Renato0000-0001-6137-9534
Matute, Ricardo A.0000-0002-0644-3799
Additional Information:© 2019 The Royal Society of Chemistry. The article was received on 13 Sep 2019, accepted on 29 Oct 2019 and first published on 30 Oct 2019. This paper is dedicated in memory of the late Dr Erwin Buncel. The authors acknowledge the FONDECYT Grant No. 1181260, No. 11160780, and No. 1160061. D. E. O. acknowledges the financial support from the Postdoctoral FONDECYT Grant No. 3190252. There are no conflicts to declare.
Funders:
Funding AgencyGrant Number
Fondo Nacional de Desarrollo Científico y Tecnológico (FONDECYT)1181260
Fondo Nacional de Desarrollo Científico y Tecnológico (FONDECYT)11160780
Fondo Nacional de Desarrollo Científico y Tecnológico (FONDECYT)1160061
Fondo Nacional de Desarrollo Científico y Tecnológico (FONDECYT)319025
Issue or Number:46
Record Number:CaltechAUTHORS:20191111-082331901
Persistent URL:https://resolver.caltech.edu/CaltechAUTHORS:20191111-082331901
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:99767
Collection:CaltechAUTHORS
Deposited By: Tony Diaz
Deposited On:12 Nov 2019 22:24
Last Modified:27 Nov 2019 18:01

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