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Bimodal Reaction Sequences Occurring through the Active Intermediates
Published in Robert Bakhtchadjian, Bimodal Oxidation: Coupling of Heterogeneous and Homogeneous Reactions, 2019
Unlike multistep (stepwise) reactions, in concerted reactions, the breaking of old chemical bonds and the formation of new bonds occur simultaneously, involving only a transition state complex but not other active intermediates, which can exist as individual chemical entities. In other words, the concerted reaction is a single-step chemical transformation.
Reactive atomistic simulations of Diels-Alder-type reactions: conformational and dynamic effects in the polar cycloaddition of 2,3-dibromobutadiene radical ions with maleic anhydride
Published in Molecular Physics, 2021
Uxía Rivero, Haydar Taylan Turan, Markus Meuwly, Stefan Willitsch
The cationic Diels-Alder reaction of maleic anhydride with 2,3-dibromobutadiene ions has been studied using reactive molecular dynamics. Trajectories were initiated in configurations with the two reactant molecules approaching each other mimicking a collision experiment. A competition of concerted and stepwise reaction pathways was found and both, the s-cis and s-trans conformers of the diene proved to be reactive. These findings are in contrast with the usual paradigm assumed for neutral Diels-Alder reactions as concerted processes in which only the s-cis conformer of the diene can react. The analysis of the minimum dynamic path of the reaction indicates that both, rotations and vibrations are important to drive the system towards the transition state, whereas for the neutral reaction [27] only rotations were found to play an important role in promoting the reaction. This may be rationalised by the fact that the transition state of the cationic concerted reaction pathway is asymmetric, whereas the one of the neutral variant is symmetric. Because for the ionic reaction the reactant molecules are symmetric, deformations of the molecular structures along the reaction path are more pronounced and vibrations are more highly excited along the MDP. This analysis of the minimum dynamic path clarified the role of rotational and vibrational degrees of freedom which provides valuable information for the design of future experiments.