OCTAMETHYLCUNEANE AND OCTAMETHYLCUBANE - THE FIRST X-RAY CRYSTAL-STRUCTURE OF A CUNEANE

In the crystal of octamethylcuneane (1,2,3,4,5,6,7,8-octamethylpentacy clo [3.3.0.0(2,4).0(3,7).0(6,8)]octane), C16H24, there are two indepen dent molecules in the asymmetric unit. 1,2,3,4,5,6,7,8-octamethylpenta cyclo[4.2.0.0(2,5). 0(3,8).0(4,7)]octane), C16H24, exhibits crystallog raphic (3) over bar m symmetry. Due to the eclipsed orientation of the methyl groups in octamethylcubane, the average bond length is extende d to 1.563(3) Angstrom compared with cubane itself. In the cuneane der ivative, the Sage bond lengths vary between 1.517(2) and 1.573(2) Angs trom in accordance with their bicyclic character and the repulsive for ces between the methyl groups. The exocyclic bonds to the methyl C ato ms in both molecules are shortened due to the increased s character of the cage C atoms.