2-FLUORO-2-PHENYLACETIC ACID .4. CONFIGURATION OF ITS ESTERS WITH SUBSTITUTED-PHENYL ALCOHOLS BY F-19 NMR

The use of 2-fluoro-2-phenylacetic acid as a chiral derivatizing agent allowed the distinction, by means of fluorine NMR spectroscopy, of enantiomers of alcohols L1CH(OH)L2 converted into the diastereoisomeric esters PhCHFCO2CHL1L2. The delta-F(RR) and delta-F(RS) fluorine chemical shifts of diastereoisomeric esters obtained from series of alcohols containing a substituted-phenyl group (L1 or L2 = ZPh), and the DELTA-delta-F chemical shift differences, were linearly related to the Hammet sigma parameter of Z. The DELTA-delta-F originates from the different electronic effects of L1 and L2 groups on the fluorine atom, through space, in a minor conformation. A classification of the ZPh effects on delta-F with respect to Ph is obtained. The configuration of substituted-phenyl secondary alcohols, ZPhCH(OH)L, can be determined with the aid of the delta-F values of esters formed with PhCHFCO2H if the configuration of the unsubstituted alcohol PhCH(OH)L is known.