Large Hyperconjugation in Strained Systems

Carbocations can appear as transient species, for instance, in elimination reactions and various rearrangements. Hyperconjugation (or conjugation) can then stabilize the cationic character and form a partial pi bond. The effect of the electronic delocalization from strained substituents to a carbocation part was calculated. Very large hyperconjugation was found, sometimes more than 80 kcal mol(-1), which is much larger than typical conjugation effects (56 kcal mol(-1) for the allyl cation).