A series of 9-(2-alkylphenyl) fluorene derivatives are prepared and their internal rotation about the C 9–C ar bond is examined. Those which have a methyl, an ethyl, or an isopropyl group in 2′ position exist as a mixture of sp and ap forms, showing coalescence phenomena in the NMR spectra at high temperatures. The barriers to rotation of these compounds are obtained by the usual DNMR method. 9-(2-t-Butylphenyl) fluorene, in ...
