Vibrational circular dichroism of 1,1′-binaphthyl derivatives:: Experimental and theoretical study

Absorption and vibrational circular dichroism (VCD) spectra of six 1, 1'-binaphthyl derivatives were measured and analyzed on the basis of ab initio modeling. The spectra of both enantiomers were recorded with a high signal-to-noise ratio. The BPW91/6-31G** density functional theory level and the gauge invariant atomic orbitals were used for the simulations of VCD intensities. The binaphthyl moiety behaves as a chiral chromophore with a strong VCD signal because the 1,1'-substitution hinders its rotation. Most of the VCD bands were assigned, and the contributions of the binaphthyl skeleton and the functional groups could be clearly distinguished. Distinct VCD characteristics were found for the compounds exhibiting C-2 and C-1 symmetry. A very good agreement between the calculated and experimental spectra was observed. Apart from indication of enantiomeric purity, the spectra contain readable information about molecular conformation. The dihedral angle between the naphthyls planes, equal to about 55 degrees when naphthyl residues were connected with PO4 covalent bridge, was found close to 90 degrees for all the other derivatives.