chapter  Chapter 17
11 Pages

Fries Structure

WithMarina A. Tudoran, Mihai V. Putz

A Fries structure is defined as a Kekule structure with maximum numbers of double bonds, with the property that most double bonds are common to two rings. In other words, these types of structures can be obtained in the same manner as Clar structures, with the difference that in the Fries structure case the circles can share an edge. Fries structures have an interesting characteristic: one may obtain few Clar structures with the maximum number of separated sextets, by respecting additional rules, such as the separation between the isolated formal double bonds. Due to the fact that for larger benzenoid hydrocarbon with low symmetry is difficult to determine the Clar structure with the maximum number of isolated sextets, Fries structures can be used as an initial step in this type of studies.