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Isolating Free Carbenes, their Mixed Dimers and Organic Radicals

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Published on: April 19, 2019

Dipolar repulsion in α-halocarbonyl compounds revisited.

Daniela Rodrigues Silva^1,2, Lucas de Azevedo Santos^1,2, Trevor A Hamlin¹

¹Department of Theoretical Chemistry, Amsterdam Institute of Molecular and Life Sciences (AIMMS), Amsterdam Center for Multiscale Modeling (ACMM), Vrije Universiteit Amsterdam, De Boelelaan 1083, 1081 HV Amsterdam, The Netherlands. f.m.bickelhaupt@vu.nl.

Physical Chemistry Chemical Physics : PCCP

|September 16, 2021

Summary

This study reveals that molecular orbital theory, not just simple dipolar repulsion, explains rotational isomerism in haloacetaldehydes. Pauli repulsion, orbital interactions, and electrostatics dictate conformational preferences, with fluorine behaving uniquely due to its compact nature.

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Area of Science:

Organic Chemistry
Computational Chemistry
Quantum Chemistry

Background:

Dipolar repulsion models, while useful, oversimplify molecular conformations.
Understanding conformational preferences is crucial in organic chemistry.

Purpose of the Study:

To develop a causal model for rotational isomerism in haloacetaldehydes using quantitative molecular orbital theory.
To analyze the influence of Pauli repulsion, orbital interactions, and electrostatic forces on molecular conformations.

Main Methods:

Relativistic density functional theory (DFT) calculations were employed.
Analysis of rotational energy profiles for haloacetaldehydes (OHC-CH2X, X = F, Cl, Br, I).
Bonding analyses were performed to understand electronic structure differences.

Main Results:

Rotational energy profiles are governed by a combination of Pauli repulsion, orbital interactions (like hyperconjugation), and electrostatic effects.
Fluorine's unique behavior stems from its compact nature, influencing electrostatic contributions to conformational preference.
Heavier halogens (Cl, Br, I) exhibit different conformational preferences compared to fluorine due to their more diffuse electron clouds.

Conclusions:

A more accurate model for molecular conformation involves integrating Pauli repulsion, orbital interactions, and electrostatics.
The study highlights the distinct electronic properties of fluorine compared to heavier halogens in determining molecular structure.
Quantitative molecular orbital theory provides deeper insights into chemical phenomena than simplified models.