Theoretical study on the mechanochemical reactivity in Diels-Alder reactions

Mechanochemical reactions sometimes give different yields from those under solvent conditions, and such mechanochemical reactivities depend on the reactions. This study theoretically elucidates what governs mechanochemical reactivities, taking the Diels-Alder reactions as an example. Applying mechanical force can be regarded as the deformation of molecules, and the deformation in an orthogonal direction to a reaction mode can lower the reaction barrier. Here, we introduce a dimensionless cubic force constant, a mechanochemical reaction constant. It tells us how easily the deformation can lower a reaction barrier and enables us to compare the mechanochemical reactivities of different reactions. The constants correlate positively with the yields of the mechanochemical Diels-Alder reactions.