Easy method for the calculation of the algebraic structure count of phenylenes

Abstract

Each phenylene molecule (containing n six-membered and n–1 four-membered rings) is in a unique manner associated to a catacondensed benzenoid system (containing n six-membered rings). The algebraic structure count of the phenylene is equal to the number of Kekule structures of the corresponding benzenoid system. This latter quantity is easily computed.