Mechanochemical Diels-Alder Reactions: Conceptual Density Functional Theory and Information-Theoretic Analyses

Mechanochemistry is considered an important field in chemistry that provides a green synthesis of organic compounds. Seven retro Diels-Alder reactions under mechanochemical conditions are considered in this work. These are the reactions of anthracene, 9-methyl anthracene, 9,10-dimethyl anthracene, 9,10-difluoro anthracene, 9,10-dichloro anthracene, and 9,10-dibromo anthracene with benzoquinone, and the reaction of diphenylfulvene with maleimide. The well-known 'Constrained Geometries Simulate External Force (CoGEF)' has been utilized to calculate the parameters of the Morse potential and the maximum force required to rupture the bond. Conceptual Density Functional Theory (CDFT) is a framework that uses the principles of DFT to interpret chemical concepts like electronegativity, hardness, etc., in terms of electron density. The global and local CDFT-based calculations are performed near the curvature in the plot of energy versus force. The sign of the force-dependent response of the ionization energy (I), electron affinity (A), electronegativity (χ), hardness (η), and electrophilicity (ω) are found to be negative. Further, the local descriptors based on the Fukui function and philicity are also determined. In addition, the force-dependent first-order response of information-theoretic (IT) descriptors, topological parameters, and various energy terms obtained from energy decomposition analysis are also calculated.