 The strain energy in 1,8-dimethylnaphthalene was calculated to be 7.6 kcalmol−1 and around 12-15 kcalmol−1 for 4,5-dimethylphenanthrene.Allylic strain tends to be greater for cyclic molecules compared to olefins as strain energy increases with increasing rigidity of the system.An in depth summary of allylic strain in six membered rings has been presented in a review by Johnson, F.
Several factors influence the energy penalty associated with the allylic strain.