A mathematical tool for haadling the topolopcal problems of conjugated molecules is provided by gmph theory [17], which is becoming a powerful method among the various mathematical methods available to theoretical chemistry. The topology of a molecular system is reflected essentially in the connections, i.e. chemical bonds, which exist between the atoms in the molecule. Hence, a graph is a convement mathematical device for representing the topology of a ^ven molecule because in the construction of the molecular (chemical) graph [16], the only property considered is the existence or non-existence of a dhemical bond.