Pentadienyl
A CH2 group connected to two vinyl groups is said to be doubly allylic. The bond dissociation energy of C-H bonds on a doubly allylic centre is about 10% less than the bond dissociation energy of a C-H bond that is allylic. The weakened C-H bonds reflect the high stability of the resulting "pentadienyl" radicals. Compounds containing the C=C-CH2-C=C linkages, e.g. linoleic acid derivatives, are prone to autoxidation, which can lead to polymerization or form semisolids. This reactivity pattern is fundamental to the film-forming behavior of the "drying oils," which are components of oil paints and varnishes.