Optically Active Amines. 36. Application of the Benzene Chirality Rule to Ring-Substituted Mandelic Acids

Article abstract of DOI:10.1021/jo00007a016

The positive sign of the ¹L_b Cotton effects (CEs) from about 250 to 270 nm in the circular dichroism (CD) spectrum of (R)-mandelic acid and its sodium salt is determined by vibronic borrowing from allowed transitions at shorter wavelength.On ring substitution, transition moments are induced in the benzene ring bonds adjacent to the attachment bond of the chiral group, resulting in enhanced coupling of the ¹L_b transition with the chiral group.The sign of the ¹L_b CEs for a ring-substituted (R)-mandelic acid may be the same or opposite to that of (R)-mandelic acid, but the sign of its ¹L_b CEs can often be correlated wit h its absolute configuration provided the ring position of the substituent and its spectroscopic moment is taken into account.