DETERMINATION OF THE ENANTIOMERIC EXCESSES OF CHIRAL ACIDS BY F-19 NMR-STUDIES OF THEIR ESTERS DERIVING FROM (R)-(+)-2-(TRIFLUOROMETHYL)BENZHYDROL

15 Chiral acids were esterified with optically pure (R)-(+)-2-(trifluoromethyl)benzhydrol (R)-(+)-1, a readily available reagent. With respect to the carboxy group, the stereogenic centre is in the beta position in the case of the acids 5a-10a and 12a-16a, and in the alpha position in the case of the acids 17a-20a. The diastereomeric excesses of the corresponding esters 5b-10b and 12b-20b, respectively, were easily determined by means of F-19 NMR. These d.e. values were in very good agreement with the e.e. values of the corresponding acids when the latter were known compounds.