Volumes of activation for catalysed Diels–Alder reactions

Abstract

The Diels–Alder reactions between isoprene and N-phenylmaleimide catalysed by Lewis acids, in particular by aluminium chloride and by lithium perchlorate, have volumes of activation more negative than does the uncatalysed reaction. That between anthracene-9-methanol and N-ethyl-maleimide is faster in water than in organic solvents, and has a slightly more negative volume of activation in the aqueous than in the organic medium. The significance of these measurements is discussed.