EFFECT OF HETEROATOMS ON PARTITIONING OF π-ELECTRONS IN RINGS OF CATAFUSENES

Using Clar sextets for two- and three-dimensional aromatic systems

After a brief history of the aromaticity concept, the use of Clar sextet circles is reviewed for explaining various aspects of planar aromatic systems (benzenoids, heterocycles) and of tridimensional carbon aggregates. When folding a graphene sheet for obtaining nanotubes, nanotori, or nanocones, the congruence of Clar sextet circles allows the classification of all such aggregates into two classes (congruent or incongruent) with marked differences in properties; this is in agreement with the well-known condition h - k ≡ 0 (mod 3), equivalent to congruence, in terms of the chiral vectors h and k for graphene sheets.

Partitioning of π-electrons in rings of diaza-derivatives of acenes

A few years ago, a method was proposed for assessing the ?-electron content (EC) of rings in heteroatom-containing benzenoid molecules. In this work, the effect of two nitrogen atoms at the opposite sides of a linear benzenoid molecule on the partitioning of its ?-electrons was investigated. The results obtained can be explained by means of resonance-theoretical arguments.