There is one degree of unsaturation. The triplet at δ 1.06 and the quartet at δ 2.26 comprise an ethyl pattern (C₂H₅-). Clearly there must be a methyl singlet (δ 3.60 ). The remaining portion of the structure, C₂H₃O, can be arranged -O(C=O)CH₃ or -C(C=O)OCH₃. The first of these choices requires the methyl group to have a chemical shift at δ = ~ 2.0 - 2.6 and the quartet to be attached to a heteroatom near δ = 3.6 - 4.1. The second choice, -C(C=O)OCH₃, fits the chemical shift and integration data. Methyl propionate and ethyl acetate are structural isomers with the same peak patterns although the chemical shift differences are significant. It is an interesting example of the difference in chemical shift of the methylene carbon of the ethyl group and the carbon of the methyl group depending upon whether attachment is to carbon or oxygen. Compare the two spectra here.

The ¹³C spectrum displays a weak signal for the ester C=O at 174.1 ppm. The singlet at 50.7 ppm is attached to the oxygen. The two higher field carbons are the methylene carbon (26.7 ppm) and the remaining methyl group (8.4 ppm). Return to Menu.