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Bromination and the Friedel–Crafts acetylation of monosubstituted pyrenes were examined. Acetylation of 1-acetyl- and 1-ethylpyrene occurred at the 8-, 6-, or 3-position, but the reaction of 1-methoxypyrene afforded only the 8- and 6-acetyl derivatives. By acetylation, 4-acetylpyrene yielded the 1- and 6-acetyl compounds, and 4-ethylpyrene gave the 6- and 8- derivatives. Also, 4-bromopyrene afforded the corresponding 8-, 6-, and 1-acetyl derivatives by the same reaction. Bromination of 1-ethyl- and 4-ethylpyrene yielded the 8- and 6-bromides, but the reaction of 1-nitro- and 1-bromopyrene took place at the 6-, 8-, or 3-position. The formation ratio of these regioisomers differs by the substituents. The regioselectivity on the acetylation accords in some degree with the prediction based on the 13C NMR chemical shift of each position. The relative rates of these electrophilic substitutions correlate to the substituent constant, σ+, of the substituent attached to the pyrene.

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One sesquifulvalene, 9-(cycloheptatrienylidene)fluorene, was found to be composed of a flat fluorenylidene part and a non-planar cycloheptatrienylidene moiety. 1-Substituted 9-(cycloheptatrienylidene)fluorene was not obtained because of a steric repulsion between the 1-substituent and the 7′-hydrogen of the seven-membered ring. Upon consideration of their 13C NMR spectra, the electronic properties of the seven-membered ring are slightly influenced by introducing a substituent (halogen, methoxy group, etc.) on the fluorenylidene part. The dissolution of 9-(cycloheptatrienylidene)fluorene in trifluoroacetic acid–chloroform afforded the (9-fluorenyl)tropylium cation. The substituent attached to the fluorene part also slightly influences the tropylium moiety.