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Thin polycrystalline films of perylenetetracarboxylic dianyhydride ͑PTCDA͒, an organic molecular solid, exhibits substantial anisotropies in its electronic transport properties. Only electrons transport in the directions along molecular planes, while mainly holes transport in the direction normal to molecular planes. A series of measurements on both field effect transistors with PTCDA active layers and light emitting diodes with PTCDA transport layers documents the anisotropy seen in the electronic transport in thin films of PTCDA.

crux of the issue, the specific manner in which the trans double bonds are positioned within the taxane framework, was deduced through the combined adaptation of one-bond *H/13C COSY correlation and NOE experiments.13 Several of the more diagnostic measurements are given in the illustrations.Molecular mechanics calculations (MODEL version KS 2.96)14 provided indication that 9 might be as much as 3 kcal/mol more thermodynamically stable than 10. Indeed, heating 10 in C6D6 at 67 °C resulted in its unidirectional conversion to 9, k¡ = 2.58 X 10"4 s'1, / j ^2 = 45 min. The relative ease of this diastereomeric interconversion places 10 closer to franr-cyclononene (t[/2 = 4 min at 0 eC)3 23than to frans-cyclooctene (f1/2 = 122 h at 132.7 °C)lc in the intrinsic ability of these molecules to overcome their internal rotational barriers. The thermal stability of 10 is, however, more than adequate to allow for its individual utilization in synthesis, thus providing a new dimension to this area of chemistry.Both 9 and 10 undergo osmylation to give diols 11a (60%) and 12a (84%), respectively, by electrophilic attack from the only available direction external to the ring. Subsequent acetylation provided lib and 12b efficiently.In summary, this study has established the feasibility of controlling stereochemistry by means of rotationally restrictive nonbonded interactions and laid the groundwork for possible entry to various taxanes including 1 by this useful tactic. Our current efforts are focused on these applications.Acknowledgment. We are grateful to the Bristol-Myers Squibb Company for their financial support, to Dr. Dirk Friedrich for his assistance with the NMR experiments, and to Eugene Hickey for the molecular modeling studies. (12) (a) Chapman, O. L.