= Solution
\Image[/past-exam-of-the-chemistry-course-of-the-year-1-of-the-natural-sciences-course-of-the-university-of-cambridge/2021/paper-1-q1-coupling-map.png]
{title=Coupling partners and approximate coupling constants, with line separations converted using 300 Hz per ppm}
\b[A:] ethoxy CH$_2$ ↔ CH$_3$, $J\simeq7\,\mathrm{Hz}$; vinyl CH ↔ each <alkene> methyl, small $^4J\simeq1$–$1.5\,\mathrm{Hz}$.
\b[C:] ethoxy CH$_2$ ↔ CH$_3$, about $7\,\mathrm{Hz}$; the two OCH$_2$ <proton> types have a <geminal coupling> of about $9$–$10\,\mathrm{Hz}$; <acetal> CH ↔ C≡CH has $^4J\simeq2\,\mathrm{Hz}$.
\b[B:] internal vinyl CH ↔ trans terminal H, about $17\,\mathrm{Hz}$; ↔ cis terminal H, about $10\,\mathrm{Hz}$; terminal CH$_2$ <geminal coupling> about $1$–$2\,\mathrm{Hz}$. Vinyl CH ↔ OCH$_2$ is about $6\,\mathrm{Hz}$. Both vicinal links along the butanoate alkyl chain are about $7$–$8\,\mathrm{Hz}$.
Use $J=300\,\Delta\delta$ when a separation is measured in ppm. Thus $0.057\,\mathrm{ppm}$ corresponds to about $17\,\mathrm{Hz}$, whereas $0.023\,\mathrm{ppm}$ corresponds to about $7\,\mathrm{Hz}$. These are approximate readings, not a fitted <spin> simulation.
The small four-bond splittings illustrate <allylic scalar coupling> and <acetal-alkyne long-range coupling>.
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