Chemistry of novel compounds with multifunctional carbon structure. Part 4. Steric and electronic influences on the diastereoisomeric chemical shift differences in 19F n.m.r. spectra by introduction of fluorine, phenyl, and heteroatom groups into acetates

Abstract

In order to develop reagents more efficient than MTPA for the determination of enantiomeric excess, several fluoroacetic esters (2b)–(7b) have been prepared which have various heteroatom-centred groups or bulky groups at the α position. These compounds have been converted into the corresponding s-butyl ester (8a)–(13a), α-phenylethyl ester (8b)–(13b), and α-phenylethylamide (8c)–(13c) diastereoisomers; the chemical shift differences between each pair of diastereoisomers (Δδ) have been obtained from the ¹H and ¹⁹F n.m.r. spectra for each derivative. The influence on Δδ values of steric and possible electronic effects which arise upon introduction of a phenyl or a heteroatom group into the fluoroacetate structure are discussed.