Large Hyperconjugation in Strained Systems

International audienceCarbocations 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 π 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)