Restricted Rotation Involving the Tetrahedral Carbon. IL. Singly peri-Substituted 9-Isopropyltriptycenes Revisited

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Abstract
9-Isopropyltriptycene derivatives carrying a fluoro, chloro, bromo, or t-butyl substituent in a peri-position were synthesized and their dynamic NMR behavior was studied to see the dependence of the barrier to rotation of the bridgehead substituent upon the bulkiness of the peri-substituent. The data obtained in this work together with those reported earlier disclose that, among the derivatives in which the peri-substituent is not buttressed by the 2-substituent, the peri-methoxy compound has the highest barrier and the barrier decreases as the bulkiness of the peri-substituent increases. 1,2,3,4-Tetrachloro and tetrabromo derivatives show the slightly positive buttressing effect.

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