Stereochemistry of Dimesityl-9-anthrylmethane and Bis(2,6-xylyl)-1-(2-methylnaphthyl)methane. Evidence for the Two-Ring Flip Mechanism in Triarylmethanes

The temperature-dependent ¹H-nmr spectra of the title compounds indicate that these molecules adopt a propeller conformation in the ground state, and that a variety of interconversions of stereoisomeric molecules on the nmr time scale occurs at elevated temperatures. These interconversions are all shown to proceed by the tworing flip mechanism. The associated free energies of activation are reported. Comparison of the present results with the results of earlier studies on triarylmethanes, triarylboranes, and cognates brings to light that the two-ring flip mechanism is the favored stereoisomerization pathway for all of these systems.