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 pKa 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.

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