Chemistry 9701 · AS & A Level · Analytical techniques

Analytical techniques — practice question

Combining mass spectroscopy with NMR spectroscopy gives a very effective analytical technique for organic compounds.
(a)[2]

The mass spectrum of compound G shows M and M+1 peaks with heights in the ratio $74:2.5$. Use these figures to work out the number of carbon atoms in G. Show your working.

(b(i))[3]

Use the Data Booklet together with your knowledge of NMR spectroscopy to identify the proton type responsible for each of the three absorptions at $\delta = 1.1\,\text{ppm}$, $2.2\,\text{ppm}$ and $11.8\,\text{ppm}$.

(b(ii))[2]

On adding $\text{D}_2\text{O}$, one of these absorptions vanishes. Explain the reason for this and state which absorption is affected.

(b(iii))[6]

Draw the structural formula of $G$.

(c(i))[3]

Draw the structural formula of an isomer of $G$ with only two absorptions in its NMR spectrum.

(c(ii))[3]

Use the Data Booklet to suggest where these absorptions would appear, giving values of $\delta$ in $\text{ppm}$.

Worked solution & mark scheme

This 19-mark question has a full step-by-step worked solution and mark scheme. One marking point: $n = \dfrac{100 \times 2.5}{1.1 \times 74}$ or equivalent

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