37.3 Carbon-13 NMR Spectroscopy | CIE A Level Chemistry Topic Questions 2025

1a1 mark

This question is about the spectroscopy of benzene and some of its methylated derivatives.

Benzene is analysed using carbon-13 NMR spectroscopy.

Suggest why benzene has only one peak in its spectrum.

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1b1 mark

The displayed formula of methylbenzene is shown in Fig. 1.1.

methylbenzene

Fig. 1.1

State the number of peaks that would appear in the low resolution ¹H NMR spectrum of methylbenzene.

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1c3 marks

There are three isomers of dimethylbenzene shown in Fig. 1.2:

1,2-dimethylbenzene
1,3-dimethylbenzene
1,4-dimethylbenzene

dimethylbenzene-isomers

Fig. 1.2

Complete Table 1.1 to show the number of expected peaks in the low resolution ¹H NMR and ¹³C NMR spectra of the three dimethylbenzene isomers.

Table 1.1

Isomer	Number of peaks in ¹H NMR spectrum	Number of peaks in ¹³C NMR spectrum
1,2-dimethylbenzene
1,3-dimethylbenzene
1,4-dimethylbenzene

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1a3 marks

Three hydrocarbons, L, M and N, have the molecular formula C₈H₁₀. Information about the number of peaks seen in the carbon-13 (¹³C) NMR spectrum of the three isomers is shown in Table 1.1.

Table 1.1

	Number of peaks
L	3
M	5
N	4

Suggest structures for compounds L, M and N.

L

M

N

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1b3 marks

Complete Table 1.1 to give details of the proton NMR spectra for isomers L, M and N.

Table 1.1

	Number of peaks	Relative Peak area
L
M
N

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1c2 marks

Explain which of the three isomers, L, M or N has the highest melting point.

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1a3 marks

During the production of an NMR spectrum, tetramethylsilane (TMS) is mixed with the sample.

i)

Give the structural formula of the standard reference chemical used for ¹H NMR spectroscopy.

[1]

ii)

Explain why tetramethylsilane is used as the standard reference chemical.

[2]

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1b1 mark

State the number of peaks in the C-13 NMR spectrum of 1,3-dichlorobenzene.

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1c2 marks

i)

Predict the number of peaks in the ¹³C NMR spectrum of ethylbenzene, shown in Fig. 1.1.

Fig. 1.1

[1]

ii)

The data in Table 1.1 should be used in answering this question.

One of the carbon atoms in the structure of ethylbenzene shown in Fig. 1.1 is labelled with an asterisk (*). Suggest a C-13 chemical shift range for this carbon environment.

Table 1.1

Hybridisation of the carbon atom	Environment of carbon atom	Example	Chemical shift range δ/ppm
sp³	alkyl	CH₃–, CH₂–, –CH<, >C<	0 – 50
sp³	next to alkene / arene	–C–C=C, –C–Ar	25 – 50
sp³	next to carbonyl / carboxyl	C–COR, C–O₂R	30 – 65
sp³	next to halogen	C–X	30 – 60
sp³	next to oxygen	C–O	50 – 70
sp²	alkene or arene	>C=C<,	110 – 160
sp²	carboxyl	R−COOH, R−COOR	160 – 185
sp²	carbonyl	R−CHO, R−CO−R	190 – 220
sp	nitrile	R−C≡N	100 – 125

[1]

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Test	Acidity	Na₂CO₃ (aq)	2,4-DNPH	Tollens' reagent
Observation	pH 5.0	No reaction	Orange precipitate	No reaction

Hybridisation of the carbon atom	Environment of carbon atom	Example	Chemical shift range δ / ppm
sp³	alkyl	CH₃–, CH₂–, –CH<, >C<	0 – 50
sp³	next to alkene / arene	–C–C=C, –C–Ar	25 – 50
sp³	next to carbonyl / carboxyl	C–COR, C–O₂R	30 – 65
sp³	next to halogen	C–X	30 – 60
sp³	next to oxygen	C–O	50 – 70
sp²	alkene or arene	>C=C<,	110 – 160
sp²	carboxyl	R−COOH, R−COOR	160 – 185
sp²	carbonyl	R−CHO, R−CO−R	190 – 220
sp	nitrile	R−C≡N	100 – 125

Carbon-13 NMR Spectroscopy (CIE A Level Chemistry)

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