DETERMINATION OF ESSENTIAL SINGLE BONDS IN BENZENOID HYDROCARBONS

All sites (vertices), to each of which an essential single bond can be attached, in the outer boundary of P(m, n) are determined, where P(in , n) (parallelogram-shaped polyhex, pericondensed polycyclic hydrocarb on) having two pairs of equal opposite sides is made up of in x n hexa gons. P(m,n) with external edges (attached to such sites) can be regar ded as an essentially disconnected polyhex (e.d.p.) subgraph. How to r educe one e.d.p. subgraph to another and how to join an e.d.p. subgrap h and catacondensed polyhexes together are presented.