Theoretical investigation of 1,1′-bi-2-naphthol isomerization

The mechanism of the isomerization of 1,1′-bi-2-naphthol (BINOL) has been investigated by means of density functional theory (DFT). There exist three isomers for BINOL; each of them has two enantiomers. The relative stabilities to the most stable isomer (referred to as I1) are 0.18 eV (I2) and 0.33 eV (I3). Two pathways were found for the isomerization: OH rotations around each of the OC bond and ring-ring torsion around the C-C inter-ring bond. The first one is far less energetic than the second one. For the ring-ring torsion, two pathways are possible, the cis and the trans rotation around the C-C inter-ring bond. Except for the isomer I3, the enantiomer may or may not be reached, depending on the starting isomer for I1 or I2. The most probable isomerization/enantiomerization pathway from I1 to I3 is presented.