The kinetic order of an interfacial Diels-Alder reaction depends on the environment of the immobilized dienophile

Cyclic voltammetry has been used to study the kinetics of the Diels- Alder reaction of cyclopentadiene with quinone immobilized on a monolayer (see scheme). By monitoring the reduction in current as the redox-active quinone is converted into the redox-inactive adduct, the reaction was shown to proceed with a second-order rate constant when hydroxyl groups were incorporated into the monolayer (X = OH), but with a first-order rate constant when methyl groups were incorporated (X = CH₃).