Heptamethylcyclohexadienyl cation

What happens if another Friedel-Crafts reaction occurs The product is the heptamethylcyclohexadienyl cation tetrachloroaluminate salt, and this material is stable under the reaction conditions. Why The resonance forms contributing... 

There are some amazingly stable cations. 1,2-Dipropylcyclopropenyl cation (IV) and aryl-substituted cyclopropenyl cations (Breslow, 1957 Breslow and Yuan, 1958 Breslow and Hover, 1960 Breslow and Chang 1961), the cycloheptatrienyl cation (V) (Doering and Knox, 1954 Turner et al., 1960), and the heptamethylcyclohexadienyl cation (VI) (Doering et al., 1958) are half-formed from their alcohols and/or olefins in the very dilute acids of pH 1-4. Tricyclopropylmethyl cation (VII) (Deno et al., 1963c) is half-formed from its alcohol in 22% H2SO4. 

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