STABILITIES OF CARBONIUM IONS IN SOLUTION .4. A LARGE BAKER-NATHAN EFFECT FOR ALKYLBENZENONIUM IONS

Heats of formation in SbF5-HSO3F at –62˚ are reported for a number of alkyl and polyalkyl benzenonium ions with methyl, ethyl, isopropyl, and f-butyl substituents and for two polycyclic systems. Large heats of formation are found which increase in size as a function of the number of groups in the benzene ring. Within experimental error, all results for a given series fall in the Baker-Nathan order (i.e., methyl > ethyl > isopropyl > r-butyl), the effects being many-fold larger than those observed previously for series of this type. It appears likely that the enthalpy and free energy differences in this series are equivalent and, hence, correspond to potential energy differences. If this possibility is supported by further studies, it may be taken as evidence that hyperconjugation is an important contributor to the Baker-Nathan order found in this system. © 1969, American Chemical Society. All rights reserved.