Reactivities of Stable Rotamers. VI. Manifestation of Differential Reactivities of the Methyls in a t-Butyl Group in Radical Halogenations

Abstract
The methyls in a t-butyl group are shown to exhibit different reactivities in radical halogenations, if rotation about a (CH3)3C–CXY2 bond is frozen. Barriers to rotation of halogenated 9-t-butyl-1,2,3,4-tetrachlorotriptycenes are obtained as ΔH\eweq ca. 32 kcal/mol. The cause of the selectivity in chlorination with sulfuryl chloride was discussed by obtaining reactivity data with a variety of compounds and halogenating reagents. It is concluded that the neighboring group participation of the peri-halo substituent is responsible for the observed selectivity.

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