“…This has been demonstrated by crystal structure analyses of two 1,1,2,2-tetraphenylethane-1,2- C---C bond length of 1.54 A, (Toda, Tanaka, Wang & Lee, 1986;Bourne, Nassimbeni &Toda, 1991). Angular strain in the cyclobutaarene fragment also contributes at least 0.04 A to the elongation of the saturated C--C bond (see above; Boese et al, 1994). The unique stereochemistry of these species thus accounts for a C--C stretching of ca 0.1 A.…”