electrocyclic reaction

Also contains definitions of: conrotatory, disrotatory
https://doi.org/10.1351/goldbook.E01948
A @M03997@ that involves the formation of a σ-bond between the termini of a fully @C01267@ linear π-electron system (or a linear fragment of a π-electron system) and a decrease by one in the number of π-bonds, or the reverse of that process. For example:
E01948-1.png
The stereochemistry of such a process is termed 'conrotatory' or @A00377-1@ if the substituents at the interacting termini of the conjugated system both rotate in the same sense, e.g.
E01948-2.png
or 'disrotatory' (or @A00377-2@) if one terminus rotates in a clockwise and the other in a counter-clockwise sense, e.g.
E01948-3.png
See also:
pericyclic reaction
Source:
PAC, 1994, 66, 1077. (Glossary of terms used in physical organic chemistry (IUPAC Recommendations 1994)) on page 1108 [Terms] [Paper]