Resolution and Enantiomerization Barrier of Tetramesitylethylene

The ¹H NMR spectrum of tetramesitylethylene (2) was analyzed, and the signals were assigned by means of a 2D NOESY spectrum. Attempts to observe anisochrony of the enantiotopic groups of a racemic mixture of 2 in a chiral solvent by ¹H NMR were unsuccessful. Molecular mechanics and MNDO calculations satisfactorily reproduce the ground-state conformation. The calculated barrier for the enantiomerization process is 21.8 (MM2) and 28.2 (MNDO) kcal mol⁻¹. 2 was chromatographically resolved on a (+)-poly(triphenylmethyl)methacrylate (PTrMA) column. Its specific rotation is [α]²⁵ = −12100° at 365 nm and −2300° at 589 nm (d line). The activation parameters for the enantiomerization of 2 in perhydrofluorene are ΔG^‡ = ΔH^‡ = 39.6 kcal mol^‒1 and ΔS^‡ = 0 cal mol⁻¹ K⁻¹. The barrier for 2 is the highest determined experimentally for a correlated rotation.