Chemistry 9701 · AS & A Level · Analytical techniques

Analytical techniques — practice question

Modern analytical methods have greatly sped up the identification of molecules and the atoms present in compounds, compared with traditional laboratory analysis.
(a)[2]

NMR spectroscopy is one instrumental method that relies on the fact that, under suitable conditions, protons can occupy two different energy states. Explain how these energy states are produced.

(b)[2]

When methanol, $\text{CH}_3\text{OH}$, is studied by NMR spectroscopy, two absorption frequencies are seen. Explain why this happens, and give the relative areas of the two peaks.

(c)

The NMR spectrum shown below belongs to one of three isomers with molecular formula $\text{C}_8\text{H}_6\text{O}_2$.

(c(i))

In the spaces provided, draw the structures for propanoic acid, methyl ethanoate and ethyl methanoate.

(c(ii))

Explain which compound gave the spectrum shown, and identify which protons account for peaks A and B.

(c(iii))[4]

The NMR spectrum for another of the compounds shows a peak at $\delta = 11.0$. State which compound this must be, and identify the proton(s) responsible for the peak.

(d)

X-ray crystallography is a method used to determine the relative positions of the atoms in a crystal of a compound.

(d(i))

What extra information about organic macromolecules can be obtained by using X-ray crystallography?

(d(ii))[2]

Which atoms are not able to be located by X-ray crystallography?

Worked solution & mark scheme

This 10-mark question has a full step-by-step worked solution and mark scheme. One marking point: A spinning proton gives two spin states/magnetic moments

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