(Z)-2,2,5,5-Tetramethyl-3,4-diphenyl-3-hexene: a cofacial stilbene

C22H28 , M r = 292.47, orthorhombic, Pbca, a = 18.154 (2), b = 16.973 (2), c = 12.081 (1)A, V = 3722.7/~3, Z = 8, Dx = 1-04 g cm-3, Mo Ka radia- tion, a = 0.71073 A,/z = 0.5 cm-1, F(000) = 1280, T = 294 (1) K, 5499 unique reflections, R = 0.040, wR = 0-046, S = 1.34 for 920 observed unique reflec- tions. Steric repulsion of the vicinal tert-butyl groups forces them back into the geminal phenyl rings. In order to avoid further steric strain, the phenyl rings assume a cofacial or face-to-face relationship. The planes of both phenyl rings are perpendicular to the plane of the central double bond with a nearest point of contact at 2.65 A. The central double bond is normal.