Definition of conjugated system, conjugation

1. In the original meaning a conjugated system is a molecular entity whose structure may be represented as a system of alternating single and multiple bonds: e.g.

   CH2=CH=CH=CH2 CH2=CH-CN

   In such systems, conjugation is the interaction of one p-orbital with another across an intervening sigma bond in such structures. (In appropriate molecular entities d-orbitals may be involved.) The term is also extended to the analogous interaction involving a p-orbital containing an unshared electron pair, e.g.

   :Cl-CH=CH2

   See also delocalization, homoconjugation, resonance.