Conformational isomerism in 1,2-di-o-tolylnaphthalenes: selective rotation of the 2-aryl ring

Two derivatives (X=Cl, CN) of 1,2-ditolylnaphthalene were prepared as models to investigate their conformational behavior that could involve rotation of either of the tolyl rings. The existence of anti and syn atropisomers was evident from their 1H NMR spectra at room temperature indicating two pairs of well-resolved singlets for the methyl protons. Dynamic 1H NMR studies estimated the rotation barrier to be about 76–82 kJ mol−1, a value consistent with selective rotation of the 2-tolyl ring in the conformation inter-conversion.