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-(trifluo romethyl)benzhydrol (R)-(+)-1, a readily available reagent. With respe ct to the carboxy group, the stereogenic centre is in the beta positio n in the case of the acids 5a-10a and 12a-16a, and in the alpha positi on in the case of the acids 17a-20a. The diastereomeric excesses of th e corresponding esters 5b-10b and 12b-20b, respectively, were easily d etermined by means of F-19 NMR. These d.e. values were in very good ag reement with the e.e. values of the corresponding acids when the latte r were known compounds.