The structures of (acetyl)[2.3]paracyclophane, (diacetyl)[3.3]paracyclophane and [4.4]paracyclophane show a gradation of structural distortions that are typical of paracyclophane systems, the steric effects of the forced bridgehead proximity becoming less as the bridges become longer. For bridges of equal length, the rings are parallel but slightly rotated with respect to each other. Unequal bridges cause the rings to tilt. The central bond of the four-atom bridges is significantly shorter (ca. 1.52 .ANG.) than a std. C-C single bond.