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Rotational behavior of known systems (spheres are methyls): the two-DOF 9-(2,6-dimethylbenzyl)triptycene 3a and 9-(9-anthracenylmethyl)-triptycene 3b, each exhibiting correlated gear rotation. In the three-DOF triarylmethanes, 4a exists as 32 slowly interconverting rotamers; inversion of the helicity in 4b proceeds via a conrotatory two-ring flip.
