Illustrated Glossary of Organic Chemistry

Pi electron (π electron): An electron which resides in the pi bond(s) of a double bond or a triple bond, or in a conjugated p orbital.


   

The allyl carbanion has four pi electrons. In this resonance contributor, two pi electrons are assigned to the pi bond portion of the carbon-carbon double bond, and the other pi electron pair is assigned as a lone pair in a conjugated p orbital.