Past exam of the chemistry course of the year 1 of the natural sciences course of the University of Cambridge / 2024 / Paper 1 / 1 / c / i

Use the proton labels in the original drawing below. Let $a$ denote the three methyl hydrogens, $b$ the crotonyl beta-CH, $c$ the crotonyl alpha-CH, $d$ the O-bound vinyl CH, and $e,f$ the terminal vinyl hydrogens trans and cis to $d$, respectively.The integrals sum to eight hydrogens. Multiplet centres give the chemical shifts; a peak label at one edge of a multiplet is not its centre. The terminal vinyl hydrogens are chemically nonequivalent because one is cis and the other trans to the O-bound vinyl hydrogen. Each crotonyl CH couples to the other and to the methyl group; the resolved long-range interaction makes the methyl a doublet of doublets rather than a simple doublet.