 The three basic isotoluenes are "ortho"-isotoluene or "5-methylene-1,3-cyclohexadiene" (here labelled 1); "para"-isotoluene (2); and "meta"-isotoluene (3).Another structural isomer is the bicyclic compound "5-methylenebicyclo[2.2.0] hexene" (4).The "o"- and "p"-isotoluenes isomerise to toluene, a reaction driven by aromatic stabilisation.