Semiempirical computation of the solid phase Diels–Alder reaction between anthracene derivatives and p-benzoquinone via molecular distortion

The present computational study deals with the Diels–Alder reaction between anthracene derivatives and p-benzoquinone under mechanical stressing using an AM1 semiempirical method. During the reaction between free molecules, the dihedral angle (DHA) of anthracene reduces with decreasing intermolecular distance down to 150° at the state of activated complex. This in mind, we try to mimic the solid state process by changing DHA. The highest occupied molecular orbital (HOMO)–lowest unoccupied molecular orbital (LUMO) energy gap (HLG) have been computed over DHA range between 180° and 150°. The HLGs and those with p-benzoquinone (intermolecular HLG) for anthracene, 9-methylanthracene, 9,10-dimethylanthracene, 9,10-bis(chloromethyl)anthracene and 9,10-bis(bromomethyl)anthracene decreased with decreasing the DHA. Thus, the decrease in the HLG favors the Diels–Alder reaction, in favor of the mechanochemical Diels–Alder reaction.