On understanding the unique role of electrophilicity on C60 reactivity and strain on exothermicity in Diels-Alder and epoxidation reactions

Semiempirical AM1 calculations have revealed that the electrophilic character of C-60 causes the barrier for the Diels-Alder addition of butadiene to be lowered (relative to ethylene) whereas for the epoxidation reaction (with dimethyldioxirane) the barrier is raised (relative to ethylene). This is because the electronic factor appears to be relatively greater than the steric influence of fullerene during the reaction. The loss of aromaticity in the six-membered faces of C-60 as well as the strain relief in the cluster during adduct formation leads the reaction to a less exothermic path compared to the ethylene reaction. These estimations have led us to provide a common criterion for any kind of cycloaddition and oxygen-transfer reaction involving the 6-6 ring junction of fullerene. (C) 1998 Elsevier Science B.V. All rights reserved.