Absolute configurational assignment of alpha-hydroxy acids and alpha-hydroxy esters from their Cupra A circular dichroism spectra

The in situ formed complexes of cuprammonium solution (Cupra A) with optica lly active alpha-hydroxy acids and alpha-hydroxy esters show circular dichr oism spectra suitable for determination of the absolute configuration of bo th groups of compounds. In the long wavelength spectral region, compounds o f R configuration at the ct carbon atom display a positive Cotton effect of around 600 nm and a negative one at ca. 720 nm, whereas (S)-alpha-hydroxy acids and esters exhibit negative and positive Cotton effects, respectively , in the same spectral range. (C) 1999 Elsevier Science Ltd. All rights res erved.