Imperfect extremal coronoid

An extremal coronoid which is not perfect, shall be referred to as an imperfect extremal coronoid. 

Furthermore, one should observe the termination of each row in the right-hand direction. This termination results in the staircase boundary. It is determined by the formulas situated at the extreme—right of each row, namely the formulas which pertain to the extremal polyhexes, as should be dear from the definition of these systems (Par. 3.3.4). When perfect extremal p-tuple coronoids are involved, then the corresponding staircase boundary reflects a part of the staircase boundary for benzenoids. It is specifically the part which corresponds to the benzenoids associated with the tuple coronoids in question. Thus, for instance, the staircase boundary for single coronoids has the same shape as the one for benzenoids when starting from C32H14 ovalene (cf. Table 5, where the start of this staircase boundary for benzenoids is indicated by thin lines). A staircase boundary of this kind, determined by perfect extremal coronoids or extremal benzenoids, shall be referred to as a perfect staircase (boundary). If imperfect extremal coronoids are involved we shall call it an imperfect staircase. 

Moreover, it was found that the catacondensed extremal tuple coronoids for p = 1 and 2 are perfect, while those for > 4 are all supposed to be imperfect. Therefore, in a sense, the unique case of y = 3, for which there is no catacondensed extremal coronoid (cf. Par. 3.5.5), marks a borderline between the perfect and imperfect catacondensed extremal coronoids. 

In the above diagrams the staircase boundaries are indicated by heavy lines. For the portions where they are imperfect they are augmented by stippled lines to the shapes which conform with perfect boundaries. Hence it should be understood that the parenthesized formulas actually do not exist for the coronoids in question. The heavy formulas pertain to perfect extremal coronoids. 

Figure 3 shows a dot diagram for the formulas of single coronoids as in Fig. 5.8. However, more detailed information about the extremal (A) systems is included formulas for ground forms and higher members, both perfect and imperfect, are indicated.

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