X-RAY STRUCTURAL INVESTIGATION OF 3 4-ARYL-SUBSTITUTED [2.2]PARACYCLOPHANES

The low-temperature crystal structures of 4-methylphenyl[2.2]paracyclo phane (1), C23H22, orthorhombic, Pbca,a = 12.880(2), b = 7.4234(12), c = 34.425(6) Angstrom, Z= 8; 2,6-dimethylphenyl[2.2]-paracyclophane (2) , C24H24, orthorhombic, P2(1)2(1)2(1), a = 8.593(3), b = 12.550(4), c = 15.745(4) Angstrom, Z = 4, and 2,4,5-trimethylphenyl[2.2]paracycloph ane (3), C25H26, monoclinic, P2(1)/c, a = 13.737(2), b = 17.883(2), c = 15.230(2) Angstrom, beta = 103.423(8)degrees, Z= 8 (two independent molecules) have been determined. Surprisingly, only small differences from the normal paracyclophane structure were found in the three steri cally hindered species; the paracyclophane rings are mutually rotated and twisted by a few degrees, and the torsion angle between paracyclop hane and aryl rings is slightly increased in 2 and 3 compared to 1.