Woodward–Hoffmann rules
The Woodward–Hoffmann rules can also explain bimolecular cycloaddition reactions through correlation diagrams. A [π"p" + π"q"] cycloaddition brings together two components, one with "p" π-electrons, and the other with "q" π-electrons. Cycloaddition reactions are further characterized as suprafacial (s) or antarafacial (a) with respect to each of the π components. ("See below "General formulation" for a detailed description of the generalization of WH notation to all pericyclic processes".)