The determination of carbon-13 chemical shifts in esters by heteronuclear magnetic double resonance

Abstract

It is shown that there are linear correlations between ¹³C and ¹H chemical shifts of the methyl groups of esters and the pK_a values of the acids from which they are derived. The relationship between the two correlations is considered to show that both sets of chemical shifts are dominated by changes in the electron density at the oxygen atom adjacent to the methyl group, and that polarizability and neighbouring-group anisotropy effects are relatively unimportant. Relative signs of ¹³C–H coupling constants in methyl formate are also obtained.