CONCERNING STERICAL HINDRANCE TO DEPROTONATION OF GASEOUS POLYALKYLBENZENIUM IONS

A "late" steric effect is discussed which hinders the gas-phase deprotonation of crowded arenium ions owing to the steric compression which occurs when bulky ortho substituents are forced into coplanarity by the deprotonation process. The results of experiments involving alkylation of toluene by gaseous t-C4H9+ ions demonstrate that such a late effect occurs even in cases where the "early" steric effect, which hinders the approach of a gaseous base to the proton to be removed, has been found inoperative.