Chemistry 9701 · AS & A Level · Analytical techniques

Analytical techniques — practice question

Instrumental analysis is becoming more and more significant in modern chemistry. NMR spectroscopy and X-ray crystallography are two key techniques.
(a)[1]

Both techniques make use of a section of the electromagnetic spectrum. Which technique uses radiation with the longer wavelength, and where in the spectrum is that radiation found?

(b)[2]

NMR spectroscopy gives detailed information about protons, whereas X-ray crystallography cannot detect them. Explain these statements.

(c)[1]

The protein found in hair contains the amino acid cysteine, $\text{C}_3\text{H}_7\text{NO}_2\text{S}$. Crystalline cysteine was analysed by X-ray crystallography. State which atom gave the strongest reflection, and explain your answer.

(d(i))

Compound $P$ is an alcohol that can be changed into compound $Q$ by the following reaction sequence: $P \rightarrow \text{C}_4\text{H}_8\text{O} \rightarrow Q$. The mass spectrum of $P$ gives an $M : M+1$ peak ratio of $4.5 : 0.15$. Calculate how many carbon atoms are in $P$.

(d)

Compound $P$ is an alcohol that can be changed into compound $Q$ through the following reaction sequence: $P \rightarrow \text{C}_x\text{H}_6\text{O} \rightarrow Q$. Spectral analyses of $P$ and $Q$ were carried out.

(d(ii))

In the spectrum of $P$, mark the peak arising from the $-\text{OH}$ group with an $X$.

(d(iii))

State the number of different proton environments present in compound $Q$.

(d(iv))

What evidence in these spectra shows that $P$ is a primary rather than a secondary alcohol?

(d(v))[6]

Draw a structure for $Q$.

Worked solution & mark scheme

This 10-mark question has a full step-by-step worked solution and mark scheme. One marking point: NMR uses radiowaves in the VHF/UHF region.

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