Non—primitive basic single coronoid

It is also needed to consider corona hole benzenoids which cannot be circumscribed. Such corona holes are associated with the non-primitive basic single coronoids (Vol. 1-8, especially 1-8.3). The well known smallest non-primitive basic coronoid (I-8.2.2 and I—Fig. 8.2) has h = 12. Its corona hole (benzo[c]phenanthrene) has ho = 4, 71 0 = 0. Here again h = h, where h is defined in (2), but n-= 1. The next-smallest non-primitive basic coronoid, which has h = 13, is also well known (references as above). Its corona hole (pentahelicene) has ho = 5, nfl = 0. In this case h = h — 1 and n = 0. The two smallest non—primitive basic coronoids are depicted in the following (cf. also the top row of I-Fig.8.1). 

These two cases exemplify corona hole benzenoids with a cove and a fjord, respectively. They are representative for all the non—primitive basic single coronoids with h = 12, 13 and 14 (I-Fig. 8.2), which are those of the prime interest in this section. For the sake of clarity we repeat the relevant rules in strict formulations. For 12 < h < 14 the non-primitive basic single coronoids are of two kinds, (a) The corona hole benzenoid possesses exactly one cove then h = h n = 1. (b) The corona hole possesses exactly one fjord then h = h — 1, = 0. 

The situation is not so simple for the non—primitive basic single coronoids with h > 15. Already for h = 15 there is one instance not covered by the cases (a) and (b) above. It is depicted below (left-hand drawing). 

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