Benz anthracenes protonation

In a recent comprehensive study with respect to the substituent effects of benz anthracene carbocations,280 exclusive protonation at C(7) (102) and C(12) (103, bay region protonation) in the C ring was shown to occur. The relative stability of the resulting carbocations, however, strongly depends on the substitution pattern. Substrates methyl-substituted in the A ring give mixtures of the two cations. Protonation of 5-, 6-, and 7-methyl- and 7-ethyl-substituted compounds, in turn, yields... 

In the case of benz[a]anthracene the positions 7 and 12 are approximately equivalent. Mackor and collaborators therefore discussed the effect of the position of methyl groups on the spectrum of the proton addition complex benz[a]anthracene in connection with the investigation of the basicity of methyl-benz[a]anthracenes (Mackor et al., 1956). The carbonium ions A and B are present in solution ... 

The piTj5-values of the methyl derivatives of benz[a]anthracene, summarized in Table 23, are particularly interesting. In the case of the unsubstituted compound, two positions of approximately equal proton affinity have to be taken into account. Thus two isomeric proton addition complexes A and B are present in solution (cf. IID, page 229). 

A series of 1- and 2-substituted acenaphthylenium ions has been generated by removing OH in strong acids from respective acenaphthenols The PMR spectra of the biphenylene and ancephthylene ions fail to reveal the spin-spin coupling of the CH3 protons with those of neighbouring carbons For the PMR spectra of the arenium ions formed by the protonation of 7-methyl-and 7,12-dimethylbenz[a]anthracene, pyrene, benz[a]pyrene, naphthacene and other polycyclic systems see... 

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