W0012

The Pentamantanes; Nature's Diamonds. Marilyn Olmstead, Jeremy Dahl, Robert Carlson, Dept. of Chemistry, Univ. of California, Davis, CA 95616.

In collaboration with scientists at ChevronTexaco, four of the six possible geometric isomers of the higher diamondoid, C₂₆H₃₂, have been isolated from petroleum and their crystal structures determined. These naturally-occurring molecules are present in only trace quantities in hydrocarbon oils but may be recovered due to their thermodynamic stability. Their structures, called pentamantanes, are based on the face-fusing of five adamantane cages, forming a diamond-like carbon structure with all dangling carbon atoms terminated by hydrogen atoms. To date, only the diamond lattice segments adamantane, diamantane, and triamantane have been synthesized. Larger segments, termed higher diamondoids, have increasing numbers of isomers which has precluded their synthesis and separation. However, new isolation techniques from petroleum have raised the possibility that different sizes and shapes of these molecules may become available in larger quantities. The structures of these four members of the pentamantane series display fascinating variations in symmetry. As miniature diamonds, they mimic the structure of diamond better than had been previously predicted from theory.