Atomistic simulations provide theoretical mechanism for Diels-Alder reaction

When it comes to making cyclic structures, the Diels-Alder reaction has been a mainstay for synthetic organic chemists for nearly a century. Its uses range from assembling types of rubber to producing Vitamin B6. Although many features of the reaction and its products have been characterized, a complete understanding of its mechanism remains elusive. One theoretical approach using reactive atomistic simulations looks to provide a picture of the dynamics within these reactions.

Rivero et al. report new findings from simulations for the reaction between gaseous dibromobutadiene and maleic anhydride, two prototypical reagents for Diels-Alder reactions. After establishing a model to study the reaction, the group also applied a neural network to explore its synchronicity.

The work marks one of the first attempts to describe the reactive molecular dynamics of the Diels-Alder reaction in the gas phase and provides new avenues to promote it.

“Think of a chemical reaction as exploring the energy landscape and taking the path of least resistance from the reactants to the products of the reaction. But dynamics is also important,” said author Stefan Willitsch.

Investigators used machine learning techniques to simulate the entire Diels-Alder reactive process and predict physical properties of more complicated molecules, such as dibromobutadiene and maleic anhydride. While molecular vibrations are often a predominant driver of related reactions, analysis of the minimum dynamic path showed that rotations are imperative to promote reactions to reach transition states.

These findings are the most comprehensive dynamical calculations on a realistic Diels-Alder reaction to date and point to the importance of rotational excitation. The researchers hope to explore more variants of the reaction using computer simulations and to study it experimentally.

Source: “Reactive atomistic simulations of Diels-Alder reactions: The importance of molecular rotations,” by Uxia Rivero, Oliver T. Unke, Markus Meuwly, and Stefan Willitsch, The Journal of Chemical Physics (2019). The article can be accessed at https://doi.org/10.1063/1.5114981 .