Conformational preference of cis-1-aryl-2-(2-benzo[C]phenanthryl)-and cis-1-aryl-2-(3-phenanthryl)-ethenes

NMR measurements under different conditions (temperature, solvents used, presence of a shift-reagent) of cis- and trans-1-aryl-2-(2-benzo[c]phenanthryl)-ethenes reveal that an overcrowded conformation predominates in cis isomers. In the analogous 1-aryl-2-(3-phenanthryl)ethenes no clear conformational preference is found.