Long-range shielding effects in the (1)H NMR spectra of Mosher-like ester derivatives.

The relative magnitudes of the chemical shift differences (Deltadeltas) in the two diastereomers of menthyl esters of known chiral derivatizing agents (CDAs) were compared to those of the alpha-methoxy-alpha-trifluoromethyl-1-naphthylacetyl (MTN((1))A) analogues I. Discrimination of the terminal diastereotopic methyl resonances in esters of the homologous, symmetrical carbinols II was evaluated. Remarkably, the methyls differed in the MTN((1))A esters III even when n = 15; an unexpected crossover in the sign of the Deltadelta values was also observed.