Benzenoid Compounds monosubstituted

As a result of most of the early work on the homolytic arylation of monosubstituted benzenoid compounds it was concluded that the attacking radical was directed to the ortho and para positions in the benzene ring regardless of the nature of the substituent. Similarly,... 

Formation of substituted products by electrophilic reactions is one of the characteristics of benzenoid compounds. It has been shown that a few dehydro-[4/j + 2]annulenes afford substituted annulenes under strictly limited reaction conditions. Monodehydro[14]annulene, on treatment at room temperature with copper(ii) nitrate-acetic anhydride, oleum-dioxane and subsequent methylation and acetic anhydride-borontrifluoride etherate, yielded monosubstituted products, 169a, 169b and 169c, respectively. The electrophilic reactions must have resulted in substitution of one of the outer protons, but the exact point of attack has not been determined . 

The reactions in this group comprise ring substitution and dealkylation of benzenoid compounds and syntheses with 1,3-dimethoxy compounds in the bicyclic and polycyclic series. The monosubstitution of polyalkoxy benzenes is generally not facile. Monobromination of 1,3-dimethoxybenzene in carbon tetrachloride was effected at 30°C during 2 hours with N-bromosuccinimide in the presence of acidic silica gel (type microbead 3A) in 99% yield without formation of dibromo compounds (ref.141). The evolution of HBr is avoided. 

Fig. 38. The ranges of half-wave potentials in which the reductions of monosubstituted benzenoid compounds at pH 5-8 and in unbuffered solution take place, provided that the reduction follows the same mechanism as that for the parent compound.

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