Chemistry 9701 · AS & A Level · Analytical techniques

Analytical techniques — practice question

Combining mass spectroscopy with NMR spectroscopy gives a very effective approach for analysing 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 values to calculate how many carbon atoms are present 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 $\delta = 1.1$, $2.2$ and $11.8\ \text{ppm}$.

(b(ii))[1]

The addition of $\text{D}_2\text{O}$ makes one of these absorptions vanish. Explain why this occurs and identify which absorption is removed.

(b)

The NMR spectrum for compound G is shown.

(b(iii))[6]

Draw a structural formula for G.

(c)

There are several structural isomers of G.

(c(i))

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

(c(ii))[3]

Use the Data Booklet to indicate where these absorptions would appear.

Worked solution & mark scheme

This 15-mark question has a full step-by-step worked solution and mark scheme. One marking point: $n = \frac{100 \times 2.5}{1.1 \times 74}$

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