# Reactive Atomistic Simulations of Diels-Alder Reactions: the Importance of Molecular Rotations

## TL;DR

This study uses reactive atomistic simulations with neural networks to analyze Diels-Alder reactions, revealing that molecular rotations significantly influence reaction pathways and are enhanced by bromine substituents.

## Contribution

The paper introduces multisurface adiabatic reactive molecular dynamics combined with PhysNet neural networks to investigate Diels-Alder reactions, highlighting the role of molecular rotations.

## Key findings

- Rotational energy accounts for about 65% of the energy driving the reaction.
- Bromine substituents increase the importance of rotational excitation.
- Reactions at high energies are predominantly direct and synchronous.

## Abstract

The Diels-Alder reaction between 2,3-dibromo-1,3-butadiene and maleic anhydride has been studied by means of multisurface adiabatic reactive molecular dynamics and the PhysNet neural network architecture. This system is used as a prototype to explore the concertedness, synchronicity and possible ways of promotion of Diels-Alder reactions. Analysis of the minimum dynamic path indicates that rotational energy is crucial ($\sim$ 65 %) to drive the system towards the transition state in addition to collision energy ($\sim$ 20 %). Comparison with the reaction of butadiene and maleic anhydride shows that the presence of bromine substituents in the diene accentuates the importance of rotational excitation to promote the reaction. At the high total energies at which reactive events are recorded, the reaction is found to be direct and mostly synchronous.