Biphenyl, Bibenzyl, and Cyclophane Derivatives

Biphenyl derivatives which have been examined include NNN N -UUm-methylbenzidine (TMBD), studied as the 2 1 molecular complex with chloranil. The crystal structure comprises distinct molecular groups, with one chloranil molecule sandwiched between two TMBD molecules, and situated over one benzene ring of each TMBD molecule. Despite the complex nature of the crystals, the TMBD molecules are non-planar, with a dihedral angle of 30.8 between the aromatic planes. Such non-planarity is a general feature of biphenyls, and has also been observed in (11) and in 16-bromomyricanol (12). The latter molecule is of additional interest. 

The dihedral angle in the biphenyl moiety of the dicarbonium ion (13) is 39.5°. Both carbonium ions in this molecule are planar, with the phenyl groups arranged in a propeller-like conformation [dihedral angles 26.7— 38.0°] with respect to the central trigonal planes. Yet another biphenyl derivative, bis-(2,2 -biphenylene)methane (14), in addition to only slightly 

6 -Hexamethyldiphenylsulphone (15) has been examined to investigate the molecular strain which results in chemical instability. The analysis reveals that steric interactions between the sulphone and methyl 

S-C bonds have lengths of 2.193(1) A, 1.428(1) A, and 1.753(1) A, respectively. Another compound containing sulphur-sulphur linkages, ben liden-imine tetrasulphide (17), shows alternating S-S bond lengths of 2.026(3) A 

088(3) A (central bond), and 2.031(3) A. The molecule folds back on itself, and the atoms of the four-sulphur chain form a spiral. 

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