Cyclooctannelated Biphenylenes. Diagnosis of an Anomalous Bond Length by Analysis of Ring Current Geometric Factors

Article abstract of DOI:10.1021/jo00203a013

The syntheses and properties of the benzocyclobutene- and naphthocyclobutene-fused dicyclooctabiphenylenes 8 and 9 are described.These ? systems show paratropic 1H NMR effects with magnitudes between those of the parent hydrocarbon dicyclooctabiphenylene (7) and the cyclooctabiphenylenes 1,2,and 3.A complete 1H NMR spectral analysis was performed on a series of 14 polycyclic hydrocarbons related to biphenylene (10) including 1-3 and 7-9.A self-consistent Heuckel-McWeeny ring current model provided an excellent description of the 1H NMR spectra observed for these polycycles.Correlation of biphenylenic 1H NMR chemical shifts with calculated ring currents for the polycycles 1,2,3,7,8,9, and 10 afforded a semiempirical determination of ring current geometric factors for these systems.Deviations of certain observed geometric factors from theoretical "Biot-Savart" values were found to be diagnostic for an unusually long bond in the cyclobutene ring of the higher annelates 2,3,8, and 9.