non-Kekulé molecules

https://doi.org/10.1351/goldbook.NT07085
Molecules that are fully conjugated, but each of whose Kekulé structures contains at least two atoms that are not π-bonded. Examples of non-Kekule @[email protected] are trimethylenemethane (2-methylidenepropane-1,3-diyl) 1, m-benzodiquinomethane (benzene-1,2-diyldimethyl) 2, and 1,2,4,5 - tetramethylenebenzene (benzene-1,2,4,5-tetrayltetramethyl) 3.
NT07085.png
Source:
PAC, 1999, 71, 1919. (Glossary of terms used in theoretical organic chemistry) on page 1955 [Terms] [Paper]