Chemistry 9701 · AS & A Level · Analytical techniques

Analytical techniques — practice question

This question is about analysing compound $X$, $\text{C}_5\text{H}_{10}\text{O}_2$.
(a(i))[1]

In the mass spectrum of compound $X$, $\text{C}_5\text{H}_{10}\text{O}_2$, the peak heights are 22.65 for the M peak and 1.25 for the M+1 peak. Use these readings to demonstrate that one molecule of $X$ contains five carbon atoms. Show your working.

(a(ii))[2]

The mass spectrum shows a peak at $m/e = 57$. Finish the equation to show how $X$ fragments to give this peak: $[\text{C}_5\text{H}_{10}\text{O}_2]^+ \rightarrow$ ... + ...

(b)[1]

State the function of TMS and $\text{CDCl}_3$ in NMR spectroscopy.

(c(i))[3]

The proton NMR spectrum of compound $X$, $\text{C}_5\text{H}_{10}\text{O}_2$, is shown. By considering both the relative peak areas and their $\delta$ values, use the Data Booklet to deduce: the part of the molecule producing the peak at $\delta = 2.2$; the part of the molecule producing the peaks at $\delta = 1.2$ and $\delta = 3.5$; and the part of the molecule producing the peak at $\delta = 4.0$.

(c(ii))[1]

When $X$ is reacted with aqueous alkaline iodine, a yellow precipitate forms. Use this information together with your answers to (c)(i) to propose a structure for $X$.

(d)[1]

Compound $W$ is an ester with the molecular formula $\text{C}_5\text{H}_{10}\text{O}_2$. Its proton NMR spectrum shows just two peaks. The ratio of the areas of these peaks is $9 : 1$. Suggest a structure for this ester, $W$.

(e(i))[1]

Compound $V$ is a carboxylic acid containing a chiral centre. Its molecular formula is also $\text{C}_5\text{H}_{10}\text{O}_2$. Explain what is meant by the term chiral centre.

(e(ii))[1]

Suggest a structure for $V$.

Worked solution & mark scheme

This 11-mark question has a full step-by-step worked solution and mark scheme. One marking point: Thus, number of carbons $= 100 \times 1.25 / (22.65 \times 1.1) = 5.02$

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