Sterically Hindered Alkanes , I Synthesis and Structure of l , 2 - Bis ( 2 , 4 , 6 - tri - fert - butylphenyl ) ethane

X-ray, Steric Hindrance, Hindered Ethanes The title compound 9, C38H62, was prepared by dehalogenation of 2,4,6-tri-£er£-butylbenzyl chloride (7a). It crystallizes in the monoclinic space group C2/c with Z = 4. a = 10.923(7), b = 17.910(3), c = 17.395(3) A and ß = 91.87(3)° (the cell constants refer to 173 K). The structure was solved by direct methods and refined by full-matrix least squares to 7? = 0.073 for all 3853 reflexions (|Fo| > 0). On account of steric repulsions, the central ethane bond, which lies on a twofold crystallographic axis, is stretched to 1.567(4) A. Close packing of the molecules in layers parallel the ac-plane leads to boat-deformations of the benzene rings. Room-temperature data sets of weakly diffracting crystals [a = 10.948(0), b= 17.97(1), c= 17.52(2) and ß = 91.9(1)°] do not give rise to an artificial shortening of the central ethane bond of 9. Evidently, poor data quality or lack of resolution have not to be considered as an explanation for the unusual short ethane bond [1.47(3) A] in the first undamped hexaphenylethane [Stein, Winter, and Rieker (1978)].