Pericyclic Reactions. 1. Definition.

A pericyclic reaction is one in which bonds are made or broken in a concerted cyclic transition state. A concerted reaction is one which involves no intermediates during the course of the reaction. A stepwise and therefore non-concerted and non-pericyclic reaction is shown on the right.


Pericyclic reactions have certain characteristic properties, although as usual it is not difficult to find exceptions to all these rules.