Abstract
It has been hypothesised that steric congestion could play a key role in directing the 1,3-dipolar reaction mechanism in its shift from a concerted to a stepwise model. An example is given of the influence of steric congestion on the concertedness of a 1,3-dipolar reaction mechanism. Keeping other influences untouched, including the effects of electron-withdrawing or electron-donating groups, the nature of the dipole or dipolarophile, solvent, as well as the catalytic effects which have been kept fixed, this study focuses on the steric effect. At least in the case of the 1,3-dipolar cycloaddition of nitrile ylide and common olefins, when steric congestion serves as the only influence, it is unable to change the reaction mechanism from concerted into stepwise.
