Perimeter ring currents in benzenoids from Pauling bond orders

摘要

It is shown that the ring currents in perimeter hexagonal rings of Kekulean benzenoids, as estimatedudwithin the Randić conjugated-circuit model, can be calculated directly without tedious pairwiseudcomparison of Kekulé structures or Kekulé counting for cycle-deleted subgraphs. Required are onlyudthe Pauling bond orders of perimeter bonds and the number of Kekulé structures of the benzenoid,udboth readily available from the adjacency matrix of the carbon skeleton. This approach provides easyudcalculation of complete current maps for benzenoids in which every face has at least one bond on theudperimeter (as in the example of cata-condensed benzenoids), and allows qualitative evaluation of theudmain ring-current contributions to 1H chemical shifts in general benzenoids. A combined Randić-udPauling model for correlation of ring current and bond length through bond order is derived and shownudto be consistent with resilience of current under bond alternation.ud