Dipolar repulsion in α-halocarbonyl compounds revisited

Daniela Rodrigues Silva, Lucas De Azevedo Santos, Trevor A. Hamlin, F. Matthias Bickelhaupt*, Matheus P. Freitas, Célia Fonseca Guerra

*Corresponding author for this work

Research output: Contribution to JournalArticleAcademicpeer-review

Abstract

The concept of dipolar repulsion has been widely used to explain several phenomena in organic chemistry, including the conformational preferences of carbonyl compounds. This model, in which atoms and bonds are viewed as point charges and dipole moment vectors, respectively, is however oversimplified. To provide a causal model rooted in quantitative molecular orbital theory, we have analyzed the rotational isomerism of haloacetaldehydes OHC-CH2X (X = F, Cl, Br, I), using relativistic density functional theory. We have found that the overall trend in the rotational energy profiles is set by the combined effects of Pauli repulsion (introducing a barrier around gauche that separates minima at syn and anti), orbital interactions (which can pull the anti minimum towards anticlinal to maximize hyperconjugation), and electrostatic interactions. Only for X = F, not for X = Cl-I, electrostatic interactions push the preference from syn to anti. Our bonding analyses show how this trend is related to the compact nature of F versus the more diffuse nature of the heavier halogens.

Original languageEnglish
Pages (from-to)20883-20891
Number of pages9
JournalPhysical Chemistry Chemical Physics
Volume23
Issue number37
Early online date1 Sep 2021
DOIs
Publication statusPublished - 7 Oct 2021

Bibliographical note

Funding Information:
The authors are grateful to the Netherlands Organization for Scientific Research (NWO), the Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq), the Coorde-nação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES), and the Fundação de Amparo à Pesquisa do Estado de Minas Gerais (FAPEMIG) for financial support.

Publisher Copyright:
© the Owner Societies.

Copyright:
Copyright 2021 Elsevier B.V., All rights reserved.

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