Concerted and stepwise mechanisms in cycloaddition reactions: potential surfaces and isotope effects

Abstract

CASSCF/6-31G* calculations have been performed on concerted and stepwise Diels–Alder reactions of butadiene with ethene, the dimerization of butadiene and the dimerization of cyclobutadiene. The relative energies of concerted and stepwise mechanisms are compared, and the factors influencing these “energies of concert” are discussed. The comparison of calculated isotope effects to experimental data provides support for theoretical results.