Solution

ID: past-exam-of-the-chemistry-course-of-the-year-1-of-the-natural-sciences-course-of-the-university-of-cambridge/2022/paper-1/1/c/iv/solution

The vinyl ether has an important resonance contributor
Donation from oxygen into the conjugated system increases electron density at the terminal unsaturated carbon, helping explain its unusually shielded ppm and its terminal protons near 4.1–4.2 ppm. The directly oxygen-bound unsaturated carbon is strongly deshielded at ppm; its proton at ppm also experiences the oxygen substituent and alkene magnetic anisotropy. These trends are consistent with the whole delocalized electronic structure; a chemical shift is not simply a meter for an atom's partial atomic charge.
For the saturated part, the stronger local deshielding by oxygen places at , , while lies at and ppm. The two terminal vinylic protons have different geometrical relationships to the oxygen substituent and therefore different chemical shifts as well as different vicinal couplings.

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