Structural characterization of racemic 1,1′-bi-(2-naphthol) monopivalate and its 6-nitro derivative

Racemic forms of 1,1′-bi-(2-naphthol) (BINOL) monopivalate (rac-1) and its 6-nitro substitute (rac-2) were structurally characterized by X-ray crystallography. Molecules of opposite chirality form dimers in the crystalline state of rac-1 through OH⋯O hydrogen-bonds between the free hydroxy and the pivalate carbonyl group. In contrast, polymeric hydrogen-bonded homo chiral chains were encountered for rac-2. In both rac-1 and rac-2, the dihedral angle between the naphthyl systems shows a significant deviation compared to the approximate 90° angle of BINOL. As expected, compound rac-1 exhibits an increased angle (108.80(4)° and 102.09(4)°) as one of the hydroxy groups in BINOL is replaced by the sterically demanding pivaloyl ester. In contrast, the angle is decreased to 72.0(2)° in the nitro derivative rac-2.