Work

Exploring the Preference for Tertiary Substrates in E2 Reactions: Beyond Transition State Stability

Year: 2025

Type: article

Abstract: The fundamental bimolecular elimination (E2) reactions are often taught with the assumption that more substituted alkenes are favored due to the stability of the alkene-like transition state. However, this quantum-chemical study shows that in a model E2 reaction involving 2-bromo-2-methylpropane and 1-bromo-2-methylpropane, both yielding 2-methylpropene, the tertiary substrate does not kinetically favor the reaction. The faster reaction with 2-bromo-2-methylpropane is instead attributed to a probability factor, given the greater number of antiperiplanar β-hydrogens. When this factor is absent, as in the case of 2-bromobutane, the Saytzeff product dominates, consistent with the stability of more substituted alkene-like transition states. Therefore, textbooks and curricula should include this probabilistic effect as a key factor explaining the preference for the E2 reaction in the substrate order: primary < secondary < tertiary.

Source: Journal of Chemical Education

DOI: 10.1021/acs.jchemed.5c00102

Author: Matheus P. Freitas

Institutions: Universidade Federal de Lavras, Institute of Natural Sciences

Language: English

Topic: Chemical Reaction Mechanisms

Subfield: Organic Chemistry

Field: Chemistry

Domain: Physical Sciences

Open Access status: hybrid

Estimated APC paid: $4,500

Funders: Coordenação de Aperfeiçoamento de Pessoal de Nível Superior, Conselho Nacional de Desenvolvimento Científico e Tecnológico, Fundação de Amparo à Pesquisa do Estado de Minas Gerais