Chemistry 9701 · AS & A Level · Analytical techniques

Analytical techniques — practice question

T is a saturated alcohol that was examined using mass spectroscopy and NMR spectroscopy. In its mass spectrum, the molecular ion peak, M, appeared at an m/e value of 74, and the height ratio of the M and M+1 peaks was $20.4 : 0.9$.
(a(i))

Use the ratio of the M and M+1 peaks to calculate how many carbon atoms are present in one molecule of T.

(a(ii))[3]

State the molecular formula of T.

(b(i))

The NMR spectrum of T shown below contains four absorptions. The absorption at $1.8\,\text{ppm}$ is a multiplet, whereas the one at $2.5\,\text{ppm}$ is a singlet. Use this information together with your answer to part (a)(ii) to deduce the structure of T.

(b(ii))

Describe and explain which proton type gives rise to each absorption.

(b(iii))

The absorption at $1.8\,\text{ppm}$ is a multiplet, while that at $2.5\,\text{ppm}$ is a singlet. State and explain the splitting patterns for the remaining absorptions at $0.9\,\text{ppm}$ and $3.4\,\text{ppm}$.

(b(iv))[9]

Describe and explain how the NMR spectrum of T in $\text{D}_2\text{O}$ would be different from the spectrum shown.

(ii)

Describe and explain which type of proton is responsible for each of the absorptions.

(iii)

The absorption at $1.8\,\text{ppm}$ is a multiplet and that at $2.5\,\text{ppm}$ is a singlet. State and explain the splitting patterns of the other absorptions, at $0.9\,\text{ppm}$ and $3.4\,\text{ppm}$.

(iv)

Describe and explain how the NMR spectrum of $T$ in $\text{D}_2\text{O}$ would be different from the spectrum shown.

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