Issue 37, 2021

Dipolar repulsion in α-halocarbonyl compounds revisited


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.

Graphical abstract: Dipolar repulsion in α-halocarbonyl compounds revisited

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Article information

Article type
04 Jun 2021
31 Aug 2021
First published
01 Sep 2021
This article is Open Access
Creative Commons BY license

Phys. Chem. Chem. Phys., 2021,23, 20883-20891

Dipolar repulsion in α-halocarbonyl compounds revisited

D. Rodrigues Silva, L. de Azevedo Santos, T. A. Hamlin, F. M. Bickelhaupt, M. P. Freitas and C. Fonseca Guerra, Phys. Chem. Chem. Phys., 2021, 23, 20883 DOI: 10.1039/D1CP02502C

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