CRYSTAL AND MOLECULAR STRUCTURE OF 1,3,5,7-TETRAMETHYLCYCLOOCTA-CIS,CIS,CIS,CIS-1,3,5,7-TETRAENE

The crystal structure of the title compound has been determined : space group I41/a, a = b = 7.53 ± 0.03 Å, c = 18.54 ± 0.10 Å. The structural problem was solved by using the close-packing principle. The molecule has 84 symmetry. Carbon-carbon bond lengths in the ring are alternatively 1.33 and 1.48 Å; valence angles are 122°. These parameters are not significantly different from those of cyclooctatetraene and of most crystalline derivatives of cyclooctatetraene. The conformational parameters of the molecule are discussed in connection with its variable-temperature pmr behavior.