β Scribed by Lutz Hecht; Anthony L. Phillips; Laurence D. Barron
No coin nor oath required. For personal study only.
A simple method for the determination of enantiomeric excess is described. It is based on depolarized Raman optical activity (ROA) measurements in rightβangle scattering employing the incident ciruclar polarization (ICP) modulation approach. The accuracy of this method was assessed utilizing Ξ±βpinene as a chiral test compound. The four Ξ±βpinene ICP ROA signals associated with the Raman bands observed at ca. 772, 787, 887 and 929 cm^β1^ were selected to establish a linear relationship between ROA signal strength and enantiomeric composition for a set of calibration mixtures containing both Ξ±βpinene enantiomers. Using this relationship, a (+)βΞ±βpinene sample content of 16.3% was determined for a blind mixture containing 83.6% (1__S__)β( β )βΞ±βpinene and 16.4% (1__R__)β(+)βΞ±βpinene. Similary, utilizing additional spectral subtraction procedures, a (+)βΞ±βpinene sample content of 1.5% was estimated for a test mixture consisting of 50.1% (1__S__)β( β )βΞ±βpinene and 49.9% (1__S__)β( β )βtransβpinane.
π SIMILAR VOLUMES
Oxazolidine derivatives of p-amino alcohols such as ephedrine have been resolved by -C NMR spedroscopy using Eu(hfc), as a chiral shift reagent. The method is quantitative in the determination of enantiomeric excess, and is advantageous where 'H NMR is of limited use owing, for example, to signitica