Quantitative characterization of the global electrophilicity power of common diene/dienophile pairs in Diels-Alder reactions

The global electrophilicity power, ω, of a series of dienes and dienophiles commonly used in Diels-Alder reactions may be conveniently classified within a unique relative scale. Useful information about the polarity of transition state structures expected for a given reaction may be obtained from the difference in the global electrophilicity power, Δω, of the diene/dienophile interacting pair. Thus the polarity of the process can be related with non-polar (Δω small, pericyclic processes) and polar (Δω big, ionic processes) mechanisms.