Investigating Diels-Alder Reactions Combining Density Functional Theory with Bonding Evolution Theory

Joseline Flore Kenmogne Tchidjo,1,3 Vincent Liégeois,1 Abel Idrice Adjieufack2,3, Ibrahim Mbouombouo Ndassa,3 and Benoît Champagne1

1 Unit of Theoretical and Structural Physical Chemistry (UCPTS), Namur Institute of Structured Matter (NISM), University of Namur, rue de Bruxelles, 61, 5000 Namur, Belgium
2 Radical Chemistry Institute, UMR 7273, F-13397, CNRS, Aix-Marseille, France.
3 Unit of Computational Chemistry, Higher Teacher Training College, University of Yaoundé I, Cameroon.
e-mail: joseline-flore.kenmogne@unamur.be

The Diels-Alder reaction is one of the key organic chemistry reactions, leading to a broad range of products. In our work, we have studied four types of Diels-Alder reactions, between a unique diene (buta-1,3-diene) and different dienophiles, [ethylene, acrylaldehyde, acrylonitrile, (4aS,8aR)-3,4,4a,5,8,8a-hexahydronapthalen-1(2H)-one], to unravel the role of the substituent borne by the dienophile on the reaction mechanism, i.e. how the bond formation and breaking processes occur along the reaction path. We study the prototypical Diels-Alder reaction (buta-1,3-diene + ethylene) in comparison to cases where the substituent activates the reaction.

In this poster, we analyzed the reorganization of electron pairing by means of the Bonding Evolution Theory (BET).1 This approach combines the topological analysis of the electron localization functions (ELFs)2 with Thom's catastrophe theory (CT).3 The study was performed at the Density Functional Theory (DFT) level, with the M06-2X exchange-correlation functional and the 6-311++G** basis set. In addition to the calculation of the ELFs, DFT was used to evaluate the thermodynamical state functions for the reactants, transition states, and products.

We observed that all reactions are exothermic, exergonic, and spontaneous. The study of the synchronicity and the concertedness revealed that, only the reaction between 1,3-butadiene and ethylene takes place according to a synchronous (and concerted) mechanism (the process leading to the formation of the two bonds occurs at the same time). The others take place according to an asynchronous but still concerted mechanism (the process leading to the formation of the bonds occurs at different positions along the intrinsic reaction coordinate).

References

1.         Krokidis, X., Noury, S., Silvi, B. J. Phys. Chem. A, 1997, 101, 7277-7282.
2.         Becke, A.D.; Edgecombe, K. E. J. Chem. Phys,1990, 92, 5397-5403.
3.         Thom, R. Inter editions. Paris, 1972.