Clar Structures for Smaller Benzenoid Hydrocarbons

ILLUSTRATION OF k-CLAR STRUCTURES FOR SMALLER BENZENOID HYDROCARBONS 

There are number of smaller benzenoids in which the set of HH-Clar structures and the set of k-Clar structures almost coincide. For example, this is the case with dibenzo[bc,kl]coronene, one of smaller benzenoid with large number of CC double bond fixation in its leading (i.e., the proper) Clar structure. Its Clar structure has three re-sextets but six CC double bonds. In Fig. 18 we illustrated seven out of nine HH-Clar structures of dibenzo[bc,kl]-coronene. Of the nine HH structures one has three resextets, six have two re-sextets (see Fig. 18) and two have a single re-sextet (shown in Fig. 19). Interestingly, there are also nine k-Clar structures, seven of which coincide with the first seven HH-Clar structures of Fig. 18. However, instead of the last two HH-Clar structures having a single re- 

A coincidence between the number of HH-Clar structures and k-Clar structures is again evident. To each of the five HH-CIar structures of Fig. 21 corresponds a k-Clar structure having one jt-sextet less (shown in Fig. 22). We have indicated by asterisk sextets of HH Clar structures that have not survived more restrictive definition of k-Clar structures which 

In Fig. 23 we have illustrated several HH-Clar structures of smaller benzenoids and have indicated their vulnerable rings. Each of the Kekule valence structure having a single vulnerable ring will produce the corresponding O-Clar structure (i.e., a Kekule valence structure that qualifies as Clar structure). In Fig. 24 are shown additional HH-Clar structures having besides vulnerable ring additional ji-sextets. These structures will reduce to k-Clar structures when Ji-sextet of the vulnerable 

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