Rotation in Biphenyls with a Single Ortho-Substituent

Abstract
Barriers to rotation in a range up to 15.4 kcal mol-1 were determined by dynamic NMR spectroscopy for a series of biphenyl compounds 1a − 1h and 2a − 2d with a single ortho-substituent. Ab initio calculations reproduce these barriers satisfactorily and indicate the ground-state conformation of these molecules. Results are discussed in terms of the contribution of individual substituents to the barrier and of the buttressing of adjacent positions in a benzene ring by substituents.

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