Benzenoid isomers with greatest and smallest Kekulé structure counts

In families of benzenoid isomers, the species with the greatest and smallest value of the Kekulé structure count (K) possess, respectively, the greatest and smallest thermodynamic stability and, respectively, the smallest and greates reactivity. In this paper the structure of the isomers with extremal K-values for the benzenoid molecules A = A(a, b, c, d, e) (with the formula C4h+2H2h+4 )a ndB1 = B1(a, b, c, d )& B2 = B2(a, b, c, d) (with formula C 4h H 2h+2 ) were determined. The system A is obtained by attaching linear polyacene fragments of length a, b, c ,a ndd to a linear polyacene of length e +2 , so thath = a + b + c + d + e + 2, the number of hexagons of A, is constant. The systems B 1 and B 2 are obtained by attaching linear polyacene fragments of length a, b, c ,a ndd to pyrene, in two different ways, so that h = a + b + c + d + 4, the number of hexagons of B1 and B2 ,i s constant. The main conclusion is that K is maximal if the parameters a, b, c, d differ by at most one, and that K is minimal if b, c, d are equal to zero.