Extended Y-rule method for the characterization of the aromatic sextets in cata-condensed polycyclic aromatic hydrocarbons.

The location, number, and migrating behavior of the sextets in the cata-condensed benzenoid polycyclic aromatic hydrocarbons with available bay regions have been determined by a new proposed topological methodology called the extended Y-rule. The precursor of this rule is the well-known Y-rule method for determining sextets in peri-condensed polycyclic aromatic hydrocarbons. The new methodology has been successfully validated by means of literature information and by theoretical nucleus independent chemical shift (NICS) calculations. Even though the families of polycyclic aromatic hydrocarbons analyzed here comprise the C14H10, C18H12, C22H14, and C26H16 isomers, the procedure can practically be extended to the families C(10+4x)H(8+2x), where x = 1, ..., ∞. It is the first time that a straightforward procedure, easy to apply, has been proposed to obtain the sextets arrangement and behavior in the group of cata-condensed benzenoid polycyclic aromatic hydrocarbons.