Proton (1H) NMR Spectroscopy | CIE A Level Chemistry Structured Questions 2025

1a2 marks

This question is about the NMR analysis of various organic compounds.

Name and draw the structure of the chemical that is commonly used as a standard in NMR spectroscopy.

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1b3 marks

Fig. 1.1 shows the structures of compounds A, B and C.

labelled-isomers-of-pentane

Fig. 1.1

Compound A is pentane, with the chemical formula C₅H₁₂. Compound B is 2-methylbutane and compound C is 2,2-dimethylpropane, which are both isomers of pentane.

State the number of hydrogen peaks that would be expected in low resolution ¹H-NMR spectrum of each isomer.

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1c3 marks

More structural details can be deduced using high resolution ¹H NMR.

Explain why the methyl groups in 2-methylbutane, compound B, give a doublet splitting pattern while the methyl groups in 2,2-dimethylpropane, compound C, give a singlet splitting pattern.

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1d3 marks

Carbon-13 NMR is also commonly used to distinguish chemicals.

Predict the number of peaks in the carbon-13 NMR spectra of compounds A, B and C.

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1a

3 marks

Compound P is a naturally occurring chemical found in strawberries, apples and Parmesan cheese.

The percentage by mass is carbon 58.82%, hydrogen 9.80% and oxygen 31.38%.

The mass spectrum of compound P is recorded in Fig. 1.1.

Fig. 1.1

Determine the molecular formula of compound P. Show your working.

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1b4 marks

Table 1.1 shows the results of qualitative tests performed on compound P.

Table 1.1

Test	Observation
Addition of H₂O	Forms separate layers
Na₂CO₃(aq)	No visible change
2,4-DNPH	No visible change
Tollens' reagent	No visible change

Analyse the potential functional groups in compound P. Explain your answers.

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1c3 marks

The carbon-13 (¹³C) NMR spectrum of compound P is shown in Fig. 1.2.

6-9-q1c-ocr-a-as--a-level-hard-sq

Fig. 1.2

Table 1.2

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

Identify the functional group(s) present in compound P using your answer in (b) and information from Fig. 1.2 and Table 1.2. Explain your answer.

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1d3 marks

The high-resolution proton NMR spectrum of compound P was recorded as shown in Fig. 1.3.

6-9_q1d-ocr-a-as--a-level-hard-sq

Fig. 1.3

Table 1.3

Environment of proton	Example	chemical shift range, δ / ppm
alkane	–CH₃, –CH₂–, >CH–	0.9 – 1.7
alkyl next to C=O	CH₃–C=O,–CH₂–C=O, >CH–C=O	2.2 – 3.0
alkyl next to aromatic ring	CH₃–Ar, –CH₂–Ar, >CH–Ar	2.3 – 3.0
alkyl next to electronegative atom	CH₃–O,–CH₂–O, –CH₂–Cl	3.2 – 4.0
attached to alkene	=CHR	4.5 – 6.0
attached to aromatic ring	H–Ar	6.0 – 9.0
aldehyde	HCOR	9.3 – 10.5
alcohol	ROH	0.5 – 6.0
phenol	Ar–OH	4.5 – 7.0
carboxylic acid	RCOOH	9.0 – 13.0
alkyl amine	R–NH–	1.0 – 5.0
aryl amine	Ar–NH₂	3.0 – 6.0
amide	RCONHR	5.0 – 12.0

Suggest the structure of compound P using your answers to (a), (b) and (c) and information from Fig. 1.3 and Table 1.3. Explain your answer.

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2a1 mark

A chemist prepares and analyses some esters.

The chemist prepares an ester by reacting propan-2-ol with ethanoic anhydride.

Using structural formulae, write an equation for the reaction of propan-2-ol and ethanoic anhydride.

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2b3 marks

A sample contains a mixture of two esters contaminated with an alkane and an alcohol.

The chemist attempts to separate the four organic compounds in the mixture using gas chromatography. The stationary phase in the gas chromatograph column is a liquid alkane.

i)

How does a liquid stationary phase separate the organic compounds in a mixture?

[1]

ii)

Predict the separation of these four compounds using the alkane stationary phase, including relative retention times. Explain your answer.

[2]

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2c8 marks

Gas chromatography is often used in conjunction with other techniques such as mass spectrometry and NMR spectroscopy.

An ester is isolated from a perfume by gas chromatography and then analysed.

The percentage by mass is carbon 66.63%, hydrogen 11.18% and oxygen 22.19%.

The mass spectrum and high-resolution proton NMR spectrum of the ester are recorded in Fig. 2.1 and Fig. 2.2 respectively.

cie-ial-8-1h-q6-mass-spectrum

Fig. 2.1

Fig. 2.2

Table 2.1

Environment of proton	Example	chemical shift range, δ / ppm
alkane	–CH₃, –CH₂–, >CH–	0.9 – 1.7
alkyl next to C=O	CH₃–C=O,–CH₂–C=O, >CH–C=O	2.2 – 3.0
alkyl next to aromatic ring	CH₃–Ar, –CH₂–Ar, >CH–Ar	2.3 – 3.0
alkyl next to electronegative atom	CH₃–O,–CH₂–O, –CH₂–Cl	3.2 – 4.0
attached to alkene	=CHR	4.5 – 6.0
attached to aromatic ring	H–Ar	6.0 – 9.0
aldehyde	HCOR	9.3 – 10.5
alcohol	ROH	0.5 – 6.0
phenol	Ar–OH	4.5 – 7.0
carboxylic acid	RCOOH	9.0 – 13.0
alkyl amine	R–NH–	1.0 – 5.0
aryl amine	Ar–NH₂	3.0 – 6.0
amide	RCONHR	5.0 – 12.0

Use all of the information to draw the structure of the ester. Explain your answer.

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1a2 marks

Methyl cinnamate, C₁₀H₁₀O₂, is a white crystalline solid used in the perfume industry.

The proton NMR spectrum of methyl cinnamate in the solvent CDCl₃ is shown in Fig. 1.1.

methyl-cinnamate-high-res-proton-nmr

Fig. 1.1

i)

Explain why CDCl₃ is used as a solvent instead of CHCl₃.

[1]

ii)

Explain why TMS is added to give the small peak at chemical shift δ = 0.

[1]

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1b3 marks

The structure of methyl cinnamate is shown in Fig. 1.2.

methyl-cinnamate-skeletal

Fig. 1.2

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

Identify the proton environment that gives rise to the peak at a chemical shift of 3.8 ppm in Fig. 1.1. Explain your answer.

Table 1.1

Environment of proton	Example	chemcial shift range, δ / ppm
alkane	–CH₃, –CH₂–, >CH–	0.9 – 1.7
alkyl next to C=O	CH₃–C=O,–CH₂–C=O, >CH–C=O	2.2 – 3.0
alkyl next to aromatic ring	CH₃–Ar, –CH₂–Ar, >CH–Ar	2.3 – 3.0
alkyl next to electronegative atom	CH₃–O,–CH₂–O, –CH₂–Cl	3.2 – 4.0
attached to alkene	=CHR	4.5 – 6.0
attached to aromatic ring	H–Ar	6.0 – 9.0
aldehyde	HCOR	9.3 – 10.5
alcohol	ROH	0.5 – 6.0
phenol	Ar–OH	4.5 – 7.0
carboxylic acid	RCOOH	9.0 – 13.0
alkyl amine	R–NH–	1.0 – 5.0
aryl amine	Ar–NH₂	3.0 – 6.0
amide	RCONHR	5.0 – 12.0

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1c2 marks

Proton NMR spectroscopy can be used to distinguish between isomers of C₆H₁₂O₂.

Draw the two esters with formula C₆H₁₂O₂ that each have only two peaks, both singlets, in their ¹H NMR spectra. The relative peak areas are 3:1 for both esters.

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1d5 marks

The proton NMR spectrum of another isomer of C₆H₁₂O₂ is shown in Fig. 1.3.

Fig. 1.3

The integration values for the peaks in the proton NMR spectrum of this isomer are given in Table 1.2.

Table 1.2

Chemical shift, δ/ppm	3.8	3.5	2.6	2.2	1.2
Integration value	0.6	0.6	0.6	0.9	0.9
Splitting pattern	triplet	quartet	triplet	singlet	triplet

i)

Deduce the simplest ratio of the relative numbers of protons in each environment in the isomer.

[1]

ii)

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

Describe and explain the splitting patterns of the peaks at δ = 3.5 and δ = 1.2.

splitting pattern at δ = 3.5 ...................................................................................................

reason for splitting pattern at δ = 3.5 ..................................................................................

splitting pattern at δ = 1.2 ...................................................................................................

reason for splitting pattern at δ = 1.2 ..................................................................................

[4]

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1e1 mark

Four isomers of C₆H₁₂O₂, A, B, C and D, are shown in Fig. 6.4.

c6h12o2-abcd

Fig. 1.4

The C-13 NMR spectrum of one of the four isomers of C₆H₁₂O₂ is shown in Fig. 1.5.

c6h12o2-abcd-13c-nmr

Fig. 1.5

The data in Table 1.3 should be used in answering this question.

Identify which of the four isomers, A, B, C or D of C₆H₁₂O₂ produced the C-13 NMR spectrum shown in Fig 1.5.

Table 1.3

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

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Bond	Functional groups containing the bond	Characteristic infrared absorption range (in wavenumber) / cm^–1
C−O	hydroxy, ester	1040 – 1300
C=C	aromatic compound, alkene	1500 – 1680
C=O	amide carbonyl, carboxyl ester	1640 – 1690 1670 – 1740 1710 – 1750
C≡N	nitrile	2200 – 2250
C−H	alkane	2850 – 2950
N−H	amine, amide	3300 – 3500
O−H	carboxyl hydroxy	2500 – 3000 3200 – 3600

δ / ppm	environment of proton	number of ¹H atoms responsible for the peak	splitting pattern
1.2	terminal methyl groups next to CH₂	6	triplet
2.3
3.0
7.1 - 7.4	attached to the aromatic ring	3	overlapping peaks
9.0

Proton (1H) NMR Spectroscopy (CIE A Level Chemistry)

Topic Questions

Spectrum	Organic compound	Explanation
A
B

Spectrum	Organic compound	Explanation
C
D