Synthesis and structural study of 9-(alkylphenyl)-9-fluorenols, 9-(alkylphenyl)fluorenes, alkyl -9 -fluorenylsulfones, and <i>N</i>-(<i>o</i>-alkylphenyl)carbazoles
Several 9-(alkylphenyl)-9-fluorenols and 9-(alkylphenyl)fluorenes have been synthesized and their X-ray crystal structure determined. Their ap or sp rotamers have been studied in solution and the solid phases. In general, compounds that were found to have hydrogen bonds failed to re-solidify after they had melted. NMR was taken of the melts and showed no molecular decomposition had occurred.
A family of alkyl-9-fluorenylsulfones, whose pK a was previously studied by Bordwell, has been re-examined using X-ray crystallography and Gaussian calculations. Bordwell's theory of relief of steric strain was specifically investigated. The evidence found adds support to Bordwell's theory, and leads to a better understanding of the compounds pKa.
Carbazole is isoelectronic to the fluorenyl anion. N-( o-alkylphenyl)carbazoles were compared to the appropriate 9-( o-alkylphenyl)fluorenyl anion. X-ray crystallography and Gaussian calculations showed the compound to be geometrically similar. The rotational barrier about the nitrogen-phenyl bond was investigated. The first way was by adding an isopropyl group to the carbazole ring and looking at the methyl groups in the NMR. The methyl groups in the isopropyl group were diastereotopic suggesting hindered rotation or no rotation. Rotation was also investigated using an L-menthyl ester group and an α-methyl benzyl amide group. In both cases, the compound was found to be a pair of diastereomers, also suggesting hindered or no rotation. Many attempts were made to resolve the diastereomeric pairs, but all failed. The closest separation achieved was using a chiral HPLC column. Partial separation was achieved and showed that if rotation occurred it was on the minute scale.