Getting started: the three main classes of pericyclic reactions
Pericyclic is the name for the family of concerted reactions involving no charged intermediates with a single cyclic transition state. The word 'pericyclic' comes from how the electrons flow round the outside of the ring. Cycloadditions, sigmatropic rearrangements and electrocyclic reactions are the three main types.
Richard Windsor - Undergraduate Final Year Project 2008