Electrophilic aromatic substitution. Part III. The effect of strain on the electrophilic reactivity of fluorene, dibenzofuran, dibenzothiophen, and carbazole

Abstract

Application of a theory recently advanced to explain the Mills–Nixon effect and since extended by us to account for the reduced reactivity of the 1-position of triptycene, benzcyclobutene, and biphenylene, is found to account for the previously puzzling difference in reactivity between the positions ortho and para to the bridging group in fluorene, dibenzofuran, dibenzothiophen, and carbazole and its derivatives. It is shown that the greater the strain in the bridging ring, the greater the difference in reactivity between these positions relative to the corresponding positions in the related non-bridged compounds.