On distribution of π-electrons in rhombus-shaped benzenoid hydrocarbons

Abstract

The distribution of π-electrons into rings of rhombus-shaped benzenoid hydrocarbons is reported here. In this class of benzenoid systems, the (unique) Clar formula represents only a minute fraction of the total number of Kekule structures, and therefore a breakdown of the Clar model could be expected. It is found that the π-electron distribution follows a pattern

different from what is predicted by the Clar model : the greatest π-electron content is in the two "full" peak hexagons (around 4.5 electrons). In the other boundary hexagons, the π-electrons are distributed almost uniformly (around 3 electrons per hexagon). In the internal hexagons, the π-electrons are also distributed in an almost uniform manner (around 2 electrons per hexagon), the π-electron content of the "full" hexagons insignificantly exceeding the π-electron contents of the "empty" hexagons.