Unit 4: NMR Topical Chemistry A level P4

Unit 4: NMR

 O/N 07/P4/Q9

D Explain with reference to energy states how 1H NMR can supply information about the
structure of molecules.

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......................................................................................................................................[3]

E Nuclear magnetic resonance is used in magnetic resonance imaging scanners. These

scanners are increasingly used in hospitals to detect tumours. Suggest why magnetic
resonance techniques are better than X-rays.

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..........................................................................................................................................

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......................................................................................................................................[2]

Tabriaz Anwer 0333-8151689

Unit 4: NMR Topical Chemistry A level P4

F The NMR spectrum shown below was obtained from a simple organic molecule,
*, CxHyO2. When a sample of * was placed in a mass spectrometer, the ratio of the
M : M+1 peaks for the molecule was 14.5 : 0.66.

3
absorbance

11 10 9 8 7 4 3 2 1 0
chemical shift, ␦

L Calculate how many carbon atoms there are in the molecule.

LL Use the NMR spectrum and the Data Booklet to work out the structure of *.

[5]

Tabriaz Anwer 0333-8151689

Unit 4: NMR Topical Chemistry A level P4

2 M/J 08/P4/Q9,b

E Nuclear magnetic resonance (NMR) spectroscopy and mass spectrometry are also used
in the detection of certain molecules, particularly those containing hydrogen atoms.

L Explain how and why the NMR spectrum of propanal, CH3CH2CHO, would be
different from that of propanone, CH3COCH3, which contains the same atoms.

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LL Explain how and why the mass spectrum of the two compounds in L would be
different.

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[4]
3 O/N 08/P4/Q9,b

(b) NMR and X-ray crystallography have made significant contributions to our knowledge of
the structure of proteins and, in the pharmaceutical industry, how drugs react with target
proteins.

(i) Suggest an advantage of each technique in helping to determine protein structure.

..................................................................................................................................

..................................................................................................................................

..................................................................................................................................

(ii) MRI scanning is a medical technique based on NMR spectroscopy. It is particularly

useful for looking for tumours in healthy tissue.

Suggest how this technique can distinguish tumour tissue from healthy tissue.

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..................................................................................................................................
[3]

Tabriaz Anwer 0333-8151689

Unit 4: NMR Topical Chemistry A level P4

(c) A saturated molecule of formula CxHyNO was subjected to analysis by mass spectrometry
and NMR spectroscopy. In the mass spectrum of the compound, the M peak was at
m/e 73 and the ratio of the heights of the M:M+1 peak was 48 : 1.7.

(i) Using the data from the mass spectrum, determine the values of x and y in the
formula of the compound.

(ii) Use the data from (i) together with the NMR spectrum below to deduce a structure
for the compound, explaining how you arrive at your answer.

11 10 9 8 7 6 5 4 3
chemical shift,
/ ppm

[4]

Tabriaz Anwer 0333-8151689

Unit 4: NMR Topical Chemistry A level P4

4 O/N 09/P41/Q7,c

(c) NMR spectroscopy, in contrast to X-ray crystallography, is frequently used to examine

protons in organic molecules.
(i) What feature of protons enables their detection by NMR spectroscopy?

..................................................................................................................................

(ii) The NMR spectrum below was obtained from a compound X, CxHyOz. In the mass
spectrum of the compound, the M : M+1 ratio was found to be 25:2.

Determine the values of x, y and z in the formula of X and deduce a possible

structure for the compound, explaining how you arrive at your conclusion.

11 10 9 8 7 3 2
δ/ppm

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Possible structure of X

[6]

Tabriaz Anwer 0333-8151689

Unit 4: NMR Topical Chemistry A level P4

5 M/J 10/P41/Q9

A range of modern analytical techniques has made the identification of molecules, and atoms
in compounds, much more rapid than traditional laboratory analysis.

(a) One instrumental technique is NMR spectroscopy, which uses the fact that under certain
conditions protons can exist in two different energy states.
Explain how these different energy states arise.

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...................................................................................................................................... [2]

(b) When methanol, CH3OH, is examined using NMR spectroscopy, it absorbs at two
different frequencies. Explain why, and predict the relative areas of the two peaks.

..........................................................................................................................................

..........................................................................................................................................

...................................................................................................................................... [2]

(c) The NMR spectrum below is that of one of three possible isomers of molecular formula
C3H6O2.

A B

10 9 8 7 6 5 4 3 2 1 0
chemical shift, δ / ppm

Tabriaz Anwer 0333-8151689

Unit 4: NMR Topical Chemistry A level P4

The compound could be propanoic acid, methyl ethanoate or ethyl methanoate.

(i) In the boxes provided, draw the structures of the three compounds.

propanoic acid methyl ethanoate ethyl methanoate

(ii) Explain which compound produced the spectrum shown, indicating which protons
are responsible for each of the peaks A and B.

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..................................................................................................................................

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(iii) The NMR spectrum of another of the compounds has a peak at δ11.0.
State which compound this would be, and identify the proton(s) responsible for this
peak.

compound ..................................................

proton(s) ..................................................
[4]

(d) X-ray crystallography is a technique used to identify the relative positions of atoms in a
crystal of a compound.

(i) What further information about organic macromolecules can be deduced by the
use of X-ray crystallography?

..................................................................................................................................

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(ii) Which atoms cannot be located by X-ray crystallography?

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[2]

Tabriaz Anwer 0333-8151689

Unit 4: NMR Topical Chemistry A level P4

6 O/N 10/P41/Q8

(a) NMR spectroscopy and X-ray crystallography are two techniques that use
electromagnetic radiation to look at the structures of large molecules.

For each technique state the sub-atomic particle involved, and explain how this particle
interacts with the radiation.

NMR..................................................................................................................................

..........................................................................................................................................

X-ray .................................................................................................................................

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[4]

(b) The two NMR spectra 1 and 2 were obtained before and after an alcohol, Y, was oxidised
to give compound Z. The numbers of hydrogen atoms responsible for each peak have
not been shown. All the peaks have been shown.

11 10 9 8
δ / ppm

10 9 8 7 6 5 4 3 2 1 0
δ / ppm

Tabriaz Anwer 0333-8151689

Unit 4: NMR Topical Chemistry A level P4

(i) State which spectrum, 1 or 2, was produced by the alcohol, giving a reason for your
answer.

spectrum ....................................

reason .......................................................................................................................

..................................................................................................................................

(ii) The mass spectrum of Y showed an M : M + 1 peak ratio of 17.6:0.6.

Use this and other information in the question to suggest the identities of both Y
and Z.

(iii) Draw a displayed formula for Y in the box provided

Y is

(iv) Explain why the NMR spectrum of Z only shows one peak.

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[7]

Tabriaz Anwer 0333-8151689

Unit 4: NMR Topical Chemistry A level P4

7 O/N 10/P43/Q10,b

(b) NMR spectroscopy is a very important analytical technique for use with organic
compounds.

(i) Why is NMR spectroscopy particularly useful for organic compounds?

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(ii) Two molecules, propanal and propanone, have the same molecular formula,
C3H6O. Draw the displayed formula of each compound and explain briefly how
NMR spectroscopy can distinguish between the two structures.

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[4]

Tabriaz Anwer 0333-8151689

Unit 4: NMR Topical Chemistry A level P4

8 O/N 11/P43/Q7,c

(c) A combination of mass spectrometry and NMR spectroscopy is often enough to

determine the structure of a simple organic compound.
The organic compound N produced a mass spectrum in which the ratio of the M:M+1
peaks was 5.9:0.20, and which had an M+2 peak of similar height to the M peak.

(i) Calculate how many carbon atoms are present in one molecule of N.

(ii) Deduce which element, other than carbon and hydrogen, is present in N.

................................................................

(iii) Explain how many atoms of this element are present in one molecule of N.

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The NMR spectrum of N is shown.

6H doublet
absorption of energy

1H multiplet

10 9 8 7 6 3 2
chemical shift, ppm

(iv) State the empirical formula of N and, using the NMR data, suggest the structural
formula of N, explaining your reasons.

[6]

Tabriaz Anwer 0333-8151689

Unit 4: NMR Topical Chemistry A level P4

9 M/J 12/P42/Q7

NMR and X-ray crystallography are two important analytical techniques which can be used to
study the structure and function of molecules.

(a) Nuclear magnetic resonance, NMR, arises because protons possess spin which
generates a small magnetic moment. When an external magnetic field is applied the
protons can align with or against the external field. If they are given a small amount
of energy in the radio frequency range each can be ‘promoted’ so that their magnetic
moment opposes the external field.

Two factors can influence the energy required for this promotion. What are they?

(i) ....................................................................................................................................

(ii) ....................................................................................................................................
[2]

(b) A compound, J, has the formula C4H10O. The NMR spectrum of J is shown.

10 9 8 0
δ / ppm

(i) Indicate the groups responsible for each peak and hence deduce the structure of J.

peak at 1.26 δ ................................. peak at 2.0 δ .................................

structure of J

Tabriaz Anwer 0333-8151689

Unit 4: NMR Topical Chemistry A level P4

(ii) There are three other isomers of J containing the same functional group as J.
Draw the structures of two of these three isomers and indicate how many different
chemical shifts each would show in its NMR spectrum.

isomer 1 isomer 2

10 O/N 12/P41/Q7,c

(c) A sample of a liquid, P, was found at the scene of the crime and was analysed using
mass spectrometry and NMR spectroscopy.
number of groups of peaks .................... number of groups of peaks ....................
The mass spectrum has M and M+1 peaks in the ratio of 5.1: 0.22 with the M peak [6] at
m/e = 88.
The NMR spectrum is shown

11 10 9 8 0
δ / ppm

Use the data to suggest a structure for P, explaining your answer.

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structure of P

[5]

Tabriaz Anwer 0333-8151689

Unit 4: NMR Topical Chemistry A level P4

11 O/N 12/P43/Q7

Although the chemical reactions of compounds remain important pointers to their functional
groups, instrumental techniques such as mass spectrometry and NMR spectroscopy are
increasingly used to determine molecular structures.

(a) Compound J was analysed using these two techniques with the following results.

The mass spectrum showed that

● the M peak was at m/e 86,
● the ratio of heights of the M and M+1 peaks was 23.5 : 1.3.

The NMR spectrum is shown below.

9 8
δ / ppm

(i) Use the data to determine the number of carbon and hydrogen atoms present in J,
showing your working.

(ii) Use the information given above and your answer to (i) to identify the other element
present in J.

........................................................................

(iii) Determine the structure of J, explaining how you reach your conclusion.

structure of J

explanation ................................................................................................................

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[5]

Tabriaz Anwer 0333-8151689

Unit 4: NMR Topical Chemistry A level P4

12 M/J 13/P42/Q7

The techniques of mass spectrometry and NMR spectroscopy are useful in determining the
structures of organic compounds.

(a) The three peaks of highest mass in the mass spectrum of organic compound L
correspond to masses of 142, 143 and 144.
The ratio of the heights of the M : M+1 peaks is 43.3 : 3.35, and the ratio of heights of
the M : M+2 peaks is 43.3 : 14.1.

(i) Use the data to calculate the number of carbon atoms present in L.

(ii) Explain what element is indicated by the M+2 peak.

....................................................................................................................................

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Compound L reacts with sodium metal. The NMR spectrum of compound L is given
below.

9 8
δ / ppm

(iii) What does the NMR spectrum tell you about the number of protons in L and their
chemical environments?

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Tabriaz Anwer 0333-8151689

Unit 4: NMR Topical Chemistry A level P4

(iv) Use the information given and your answers to (i), (ii) and (iii) to deduce a structure
for L.
Explain how you arrive at your answer.

structure of L

[7]

(b) The molecular formula C3H6 represents the compounds propene and cyclopropane.

H C H
H
CH3CH CH2 C C

H H
propene cyclopropane

(i) Suggest one difference in the fragmentation patterns of the mass spectra of these
compounds.

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(ii) Suggest two differences in the NMR spectra of these compounds.

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[3]

Tabriaz Anwer 0333-8151689

Unit 4: NMR Topical Chemistry A level P4

13 O/N 13/P43/Q8

Instrumental analysis plays an increasingly important role in modern chemistry. Two important
techniques are NMR spectroscopy and X-ray crystallography.

(a) Both techniques use part of the electromagnetic spectrum.

Which technique uses radiation with the longer wavelength, and in which part of the
spectrum is it found?

...........................................................................................................................................
[1]

(b) NMR spectroscopy provides detailed information about protons, but X-ray crystallography
is unable to detect them. Explain these facts.

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[2]

(c) The protein found in hair contains the amino acid cysteine, C3H7SNO2. Crystalline
cysteine was examined using X-ray crystallography. State which atom produced the
strongest reflection, explaining your answer.

...........................................................................................................................................

...........................................................................................................................................
[1]

(d) Compound P is an alcohol that can be converted into compound Q in the following
reaction sequence.

P → CxH6O → Q

Spectral analyses of P and Q were carried out.

(i) The mass spectrum of P shows an M : M+1 peak ratio of 4.5 : 0.15.
Calculate the number of carbon atoms in P.

Tabriaz Anwer 0333-8151689

Unit 4: NMR Topical Chemistry A level P4

The NMR spectra of P and Q are shown below.

11 10 9 8 7 6 5 4 3 2 1 0
δ / ppm

12 10 8 6 4 2 0
δ / ppm

(ii) In the spectrum of P, clearly label the peak due to the –OH group with an X.

(iii) State how many different proton environments are present in compound Q.

......................................

(iv) What evidence is there in these spectra that P is a primary rather than a secondary
alcohol?

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(v) Draw a structure for Q.

[6]

Tabriaz Anwer 0333-8151689

Unit 4: NMR Topical Chemistry A level P4

14 M/J 14/P41/Q7

The combination of mass spectroscopy and NMR spectroscopy provides a powerful method of
analysis for organic compounds.

(a) The mass spectrum of a compound G contains M and M+1 peaks in the ratio of their heights
of 74 : 2.5.
Use these data to calculate the number of carbon atoms present in G. Show your working.

[2]

(b) The NMR spectrum of compound G is shown.

12 10 8 6 4 2 0
δ / ppm

(i) Use the Data Booklet and your knowledge of NMR spectroscopy to identify the type of
proton responsible for each of the three absorptions.

 / ppm type of proton

1.1
2.2
11.8

(ii) The addition of D2O causes one of these absorptions to disappear.

Explain why this happens and state which absorption is affected.

.............................................................................................................................................

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Tabriaz Anwer 0333-8151689

Unit 4: NMR Topical Chemistry A level P4

(iii) Draw the structural formula of G.

[6]

(c) Several structural isomers of G exist.

(i) Draw the structural formula of an isomer of G with only two absorptions in its NMR
spectrum.

(ii) Use the Data Booklet to suggest where these absorptions would occur.

peak  / ppm
1
2
[3]

Tabriaz Anwer 0333-8151689

Unit 4: NMR Topical Chemistry A level P4

15 O/N 14/P41/Q8

T is a saturated alcohol. It was analysed by mass spectroscopy and NMR spectroscopy.

In the mass spectrum, the molecular ion peak, M, was at an m/e value of 74 and the ratio of the
heights of the M and M+1 peaks was 20.4 : 0.9.

(a)
a) Use the ratio of the heights of the M and M+1 peaks to calculate the number of carbon
atoms in a molecule of T.

(ii) What is the molecular formula of T?

molecular formula = .....................................

[3]

(b) The NMR spectrum of T given below shows four absorptions. The absorption at 1.8 ppm is a
multiplet and that at 2.5 ppm is a singlet.

11 10 9 8 7 6
δ / ppm

(i) Use this information and your answer to (a)(ii) to deduce the structure of T.

Tabriaz Anwer 0333-8151689

Unit 4: NMR Topical Chemistry A level P4

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

.............................................................................................................................................

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(iii) The absorption at 1.8 ppm is a multiplet and that at 2.5 is a singlet.
State and explain the splitting patterns of the other absorptions, at 0.9 and 3.4 ppm.

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(iv) Describe and explain how the NMR spectrum of T dissolved in D2O would differ from the
one shown.

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[9]

Tabriaz Anwer 0333-8151689

 Unit 4: NMR Topical Chemistry A level P4

16 O/N 14/P43/Q8,c

(c) There are four structural isomers with the molecular formula C5H10O that are aldehydes.

(i) Draw the structures of these aldehydes.

P Q

R S

(ii) The NMR spectrum of one of these isomers contains four absorptions.
Which isomer P, Q, R or S gives this spectrum?

isomer ...............................................

(iii) Predict the number of absorptions that would be given by each of the other three isomers.

isomer letter (P, Q, R or S) number of absorptions

[6]

Tabriaz Anwer 0333-8151689

Unit 4: NMR Topical Chemistry A level P4

17 M/J 15/P42/Q8,b

(b) The NMR spectrum below was obtained from an organic liquid, P, which contains five carbon
atoms per molecule.

10 9 8 7 6 5 4 3 2 1 0
δ / ppm

(i) How many protons are present in one molecule of P? Explain your answer.

number of protons ............................

.............................................................................................................................................

....................................................................................................................................... [1]

(ii) When a little D2O is added to P, the absorption at δ 2.0 disappears.

Explain what this tells you about the group responsible for this absorption and why.

.............................................................................................................................................

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....................................................................................................................................... [2]

(iii) What does the absorption at δ 0.9 tell you about the adjacent carbon atom?

.............................................................................................................................................

....................................................................................................................................... [1]

(iv) What group(s) is/are responsible for the absorption at δ 0.9?

....................................................................................................................................... [1]

(v) Suggest a structure for P.

[1]

Tabriaz Anwer 0333-8151689

Unit 4: NMR Topical Chemistry A level P4

18 O/N 15/P41/Q6,d,ii

(ii) In borazine, B3N3H6, the boron and nitrogen atoms alternate around the ring. Each ring
atom has a single hydrogen atom bonded to it.
All boron-nitrogen bonds in borazine are 0.144 nm in length, whereas in simple compounds
B–N and B=N bond lengths are 0.154 nm and 0.136 nm respectively.

Suggest and draw the structure of borazine.

[1]
19 O/N 15/P41/Q9,d

(d) The NMR spectrum of cysteine, H2NCH(CH2SH)CO2�������������

After shaking a solution of cysteine with a few drops of D2O, the NMR spectrum shows only
two absorptions, E and F, shown below.

E F

(i) Identify the two types of protons responsible for the absorptions E and F.

E .........................................................................................................................................

F ..........................................................................................................................................
[1]

(ii) State and explain the splitting patterns of the absorptions E and F.

E .........................................................................................................................................

.............................................................................................................................................

F .........................................................................................................................................

....................................................................................................................................... [2]

Tabriaz Anwer 0333-8151689

Unit 4: NMR Topical Chemistry A level P4

20 O/N 15/P43/Q8

(a) A mixture of volatile organic compounds X, Y and Z can be separated in a gas chromatograph.
Their identities can be �����by measuring their different retention times and comparing to
known values.
A gas chromatogram is shown.

X
absorption Z

5 10 15 20
time / mins

(i) Suggest what is meant by the term retention time.

.............................................................................................................................................

....................................................................................................................................... [1]

(ii) Give an example of a carrier gas used in gas chromatography.

....................................................................................................................................... [1]

(iii) Z spends the longest time in the chromatography column.

Suggest why this might be the case.

.............................................................................................................................................

....................................................................................................................................... [1]

(iv) Explain a possible limitation of gas / liquid chromatography in separating two esters such
as ethyl methanoate, HCO2CH2CH3, and methyl ethanoate, CH3CO2CH3.

.............................................................................................................................................

....................................................................................................................................... [1]

(v) A student works out the areas underneath the three peaks in the chromatogram.

peak X Y Z

area / mm2 22 38 16

Assuming the areas underneath the peaks are proportional to the masses of the respective
components, what percentage of the original mixture was made up of the organic
compound, X?

% of X = ........................ [1]

Tabriaz Anwer 0333-8151689

Unit 4: NMR Topical Chemistry A level P4

(b) The NMR spectrum of Y given below shows four absorptions.

absorption

4 3 2 1 0
δ / ppm

(i) What compound is responsible for the absorption at δ = 0?

....................................................................................................................................... [1]

(ii) Compound Y is an ester with the molecular formula C4H8O2.

Complete the table for the NMR spectrum of Y.

The actual chemical shifts for three absorptions in Y and the splitting pattern for the
resonance at δ = 3.7 ppm have been given for you.
Use of the Data Booklet may be helpful.

chemical shift
type of proton(s) number of protons splitting pattern
δ / ppm
1.0

2.3

3.7 singlet

[4]

(iii) Use your conclusions to suggest a structure for the ester Y.

[1]

Tabriaz Anwer 0333-8151689

Unit 4: NMR Topical Chemistry A level P4

21 M/J 16/P41/Q10,b

(b) Ethanedioic acid can be converted into ethanedioyl chloride:

HO2CCO2H → Cl OCCOCl

(i) State a suitable reagent for this reaction.

....................................................................................................................................... [1]

(ii) For the reactions of ethanedioyl chloride below, suggest the structures of compounds J
and K and draw them in the boxes.

CH3OH COCl H2NCH2CH2NH2

COCl

J (C4H6O4) K (C4H6N2O2)
[2]
(c) When ethanedioyl chloride is reacted with silver ethanedioate, AgO2CCO2Ag, in ethoxyethane
at –30 °C, an oxide of carbon, L, is formed. The molecule of L has no overall dipole and has
molecular formula C4O6.

The carbon-13 NMR spectrum of a solution of L in ethoxyethane, CH3CH2OCH2CH3, is shown

below.

150 100 50 0
δ (ppm)
(i) Use the Data Booklet to state in the boxes below the δ values for the peaks in the spectrum
which are due to the carbon atoms in ethoxyethane.

CH3 CH2 O CH2 CH3

δ values

[2]

(ii) Explain what the rest of the carbon-13 NMR spectrum indicates about the structure of L.

....................................................................................................................................... [1]

Tabriaz Anwer 0333-8151689

Unit 4: NMR Topical Chemistry A level P4

(d) When pure L is reacted with an excess of CH3OH, a mixture of three compounds is formed.

L an
and 3 OH → M and N and O
(C4O6) (C2H2O4) (C3H4O4) (C4H6O4)

M is formed as one of the products when either N or O is heated with aqueous acid.

The table gives information of the peaks recorded in the carbon-13 NMR spectra of M, N and O.

peaks recorded in
compound
carbon-13 NMR spectrum

M δ 162
N δ 53 δ 160 δ 162
O δ 53 δ 160

(i) Suggest the structures of M, N and O.

M, (C2H2O4) N, (C3H4O4)

O, (C4H6O4)
[3]

(ii) Suggest a structure for L����������������=

(c) and (d).

L, (C4O6)
[1]

Tabriaz Anwer 0333-8151689

Unit 4: NMR Topical Chemistry A level P4

22 M/J 16/P42/Q6,b

(b) Sample bottles of each of the isomers phenyl ethanoate and methyl benzoate have lost their
labels and so have been named isomer A and isomer B.

(i) The carbon-13 NMR spectra of isomers A and B contain the following peaks.

isomer A isomer B
δ 52 δ 26
δ 128 δ 122
δ 129 δ 126
δ 130 δ 129
δ 133 δ 151
δ 167 δ 169

The identity of the compound responsible for each spectrum can be deduced by studying
the chemical shifts (δ) of the peaks in the spectra.

Use the Data Booklet to assign the correct peaks to the labelled carbon atoms in the
structures of the isomers below. Write each value next to the relevant carbon atom and
hence deduce the identity of each isomer.

................... ...................
O
O CH3 C CH3
C O
O ................... ...................

phenyl ethanoate is isomer ............... methyl benzoate is isomer ...............

[2]

(ii) These two isomers are difficult to distinguish chemically.

Describe a method of converting them to suitable products in step 1 which can then be
tested in step 2.
You should state the reagents and conditions for each step, and any observations you
would make.

step 1 ..................................................................................................................................

.............................................................................................................................................

.............................................................................................................................................

step 2 ..................................................................................................................................

.............................................................................................................................................

.............................................................................................................................................
[3]

Tabriaz Anwer 0333-8151689

Unit 4: NMR Topical Chemistry A level P4

23 O/N 16/P41/Q5,c

(c) F was dissolved in deuterated trichloromethane, CDCl 3, and the proton NMR spectrum of this
solution obtained.

14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
δ / ppm

(i) Use the Data Booklet and your answer to (a)(ii) to complete Table 1 for the proton NMR
spectrum of F.
The actual chemical shifts for the four absorptions in F have been added for you.

Table 1

δ / ppm type of proton relative peak area

1.4

3.9

4.7

12.9
[4]

(ii) Describe and explain the splitting pattern for the absorption at δ = 1.4.

.............................................................................................................................................

....................................................................................................................................... [1]

(iii) F was dissolved in D2O and the proton NMR spectrum of this new solution obtained.
Two of the absorptions in Table 1 were not present in this spectrum.

Which absorptions were not present?

......................................... and ......................................... [1]

(iv) Suggest the structure of F.

[1]

Tabriaz Anwer 0333-8151689

Unit 4: NMR Topical Chemistry A level P4

(d) Molecules of cycloheptadiene, C7H10, consist of a seven-membered ring with two

carbon-carbon double bonds.

(i) Complete the skeletal formulae of two isomers of cycloheptadiene.

P Q
[1]

The isomers P and Q were analysed using carbon-13 NMR spectroscopy.

(ii) Predict the number of peaks that will be seen in the carbon-13 NMR spectra of P and Q.

isomer number of peaks

P
Q
[2]

24 M/J 17/P41/Q6,d

(d) The proton NMR spectrum of a sample of 1-phenylethanol shows four peaks: a multiplet for
the C6H5 protons and three other peaks as shown in the table. When the sample is shaken with
D2O and the proton NMR spectrum recorded, fewer peaks are seen.

Complete the table for the proton NMR spectrum of 1-phenylethanol, C6H5CH(OH)CH3.
Use of the Data Booklet might be helpful.

number of 1H atoms group responsible result on shaking

δ / ppm splitting pattern
responsible for the peak for the peak with D2O

1.4

2.7

4.0

7.2-7.4 5 C 6H 5 multiplet peak remains

[4]

Tabriaz Anwer 0333-8151689

Unit 4: NMR Topical Chemistry A level P4

25 M/J 17/P41/Q2,d

(d) (i) Suggest the mechanism for the reaction of 2-chlorobutane with iodide ions. Draw out the
steps involved, including the following.

● all relevant lone pairs and dipoles

● curly arrows to show the movement of electron pairs
● the structure of any transition state or intermediate

[3]

(ii) This reaction was carried out using a single optical isomer of 2-chlorobutane.

Use your mechanism in (i) to predict whether the product will be a single optical isomer or
a mixture of two optical isomers. Explain your answer.

.............................................................................................................................................

....................................................................................................................................... [1]

(e) (i) State the number of peaks that would be seen in the carbon-13 NMR spectrum of
CH3CH2CHCl CH3.

....................................................................................................................................... [1]

(ii) There are two isomers of CH3CH2CHCl CH3 that have fewer peaks in their carbon-13
NMR spectra than CH3CH2CHCl CH3.

Draw the structures of the isomers and state the number of peaks for each isomer.

isomer 1 isomer 2

number of peaks = .............................. number of peaks = ..............................

[3]

Tabriaz Anwer 0333-8151689

Unit 4: NMR Topical Chemistry A level P4

26 O/N 17/P41/Q6,d

(d) A sample of benzocaine, shown below, was analysed by proton NMR and carbon-13 NMR
spectroscopy.

(i) Predict the number of peaks that would be seen in the carbon-13 NMR spectrum.

....................................................................................................................................... [1]

(ii) Benzocaine was dissolved in CDCl 3 and the proton NMR spectrum of this solution was
recorded.

CO2CH2CH3

NH2

benzocaine

8 7
δ / ppm

Suggest why CDCl 3 and not CHCl 3 is used as the solvent when obtaining a proton NMR
spectrum.

.............................................................................................................................................

....................................................................................................................................... [1]

(iii) Use the Data Booklet and the spectrum in (d)(ii) to complete the table for the proton
NMR spectrum of benzocaine. The actual chemical shifts, δ, for the four absorptions have
been added.

group responsible number of 1H atoms

δ / ppm splitting pattern
for the peak responsible for the peak

1.2

3.5

5.5

7.1–7.4 multiplet
[4]

(iv) Explain the splitting pattern for the absorption at δ1.2 ppm.

....................................................................................................................................... [1]

Tabriaz Anwer 0333-8151689

Unit 4: NMR Topical Chemistry A level P4

(v) The proton NMR spectrum of benzocaine dissolved in D2O was recorded.

Suggest how this spectrum would differ from the spectrum in (d)(ii).
Explain your answer.

.............................................................................................................................................

....................................................................................................................................... [1]

(e) Benzocaine can also be used to synthesise the dyestuff S by the following route.

CO2CH2CH3

step 1

NH2
R
benzocaine

step 2 NaOH(aq), OH

phenol

(i) Suggest the reagents used for step 1.

....................................................................................................................................... [1]

(ii) Suggest structures for compounds R and S and draw them in the boxes. [2]

Tabriaz Anwer 0333-8151689

Unit 4: NMR Topical Chemistry A level P4

27 O/N 17/P42/Q3,c,ii

(ii) The proton NMR spectrum of M dissolved in CDCl 3 shows eight peaks due to the eight
different types of proton present in the molecule.

The proton NMR spectrum of M dissolved in D2O was recorded.

Predict the number of peaks that would be seen in the proton NMR spectrum of M in D2O.
Explain your answer.

number of peaks .................................................................................................................

explanation .........................................................................................................................

.............................................................................................................................................
[2]

Tabriaz Anwer 0333-8151689

Unit 4: NMR Topical Chemistry A level P4

28 M/J 18/P42/Q8

Calcitriol is a steroid hormone found in human blood.

HO

HO OH

calcitriol

(a) Give the number of primary, secondary and tertiary alcohol groups in one molecule of calcitriol.

primary .................................. secondary .................................. tertiary ..................................

[1]

(b) Give the number of chiral carbon atoms in one molecule of calcitriol.

.............................................................................................................................................. [1]

(c) Calcitriol shows geometrical isomerism.

Give the number of geometrical isomers of calcitriol, including calcitriol.

.............................................................................................................................................. [1]

(d) A
sample of calcitriol is treated with an excess of hot, concentrated, acidified
potassium manganate(VII). There are three different carbon‑containing products of this
reaction.

One of these three products, X, is shown.

O
O

O O
X

(i) Predict the number of peaks in the carbon‑13 NMR spectrum of X.

....................................................................................................................................... [1]

Tabriaz Anwer 0333-8151689

Unit 4: NMR Topical Chemistry A level P4

(ii) For the carbon‑13 NMR spectrum of X, state the expected chemical shift ranges (δ) of the
peaks predicted in (i) and the number of peaks in each range.

.............................................................................................................................................

.............................................................................................................................................

.............................................................................................................................................

....................................................................................................................................... [3]

(iii) Predict the number of peaks this compound would show in its proton NMR spectrum.

....................................................................................................................................... [1]

(iv) or each of the peaks in the proton NMR spectrum you have identified in (iii) give the
F
expected splitting pattern. Explain your reasoning.

.............................................................................................................................................

.............................................................................................................................................

....................................................................................................................................... [2]

(e) In addition to the product shown in (d), two other carbon‑containing products are formed
when a sample of calcitriol is treated with an excess of hot, concentrated, acidified
potassium manganate(VII).

(i) Of these two other carbon‑containing products, identify the product with the smaller
molecular mass. Explain how this product is formed.

.............................................................................................................................................

.............................................................................................................................................

.............................................................................................................................................

....................................................................................................................................... [2]

(ii) Of these two other carbon‑containing products, identify the product with the larger
molecular mass by drawing its skeletal formula in the space below.

[1]

Tabriaz Anwer 0333-8151689

Unit 4: NMR Topical Chemistry A level P4

29 O/N 18/P42/Q5,f

(f) Nitrous acid is used in the preparation of diazonium salts. The –N2+ group in the diazonium ion
can be replaced with Cl, Br or CN as shown.

The reagent used is a copper(I) salt, CuX.

CuX
N2+ X

diazonium ion where X = Cl, Br or CN

This reaction can be used in the synthesis of compound Z as shown.

H 3C H3C

N2+ CN
reaction 1

H3C H3C
W

aq HCl,
reaction 2
heat

Z Y
an excess of
MnO4– / H+ heat

reaction 3

(i) Suggest the reagent used in reaction 1.

....................................................................................................................................... [1]

(ii) Suggest structures of compounds Y and Z and draw them in the boxes above. [2]

Compounds W and Z were analysed using carbon-13 NMR spectroscopy.

(g) Predict the number of peaks in the carbon-13 NMR spectra of W and Z.

number of peaks

Z
[2]

Tabriaz Anwer 0333-8151689

Unit 4: NMR Topical Chemistry A level P4

30 M/J 19/P41/Q8

(a) The mass spectrum of compound X, C5H10O2, is recorded.

The peak heights of the M and M+1 peaks are 22.65 and 1.25 respectively.

(i) Use these data to show that there are five carbon atoms present in one molecule of X.

Show your working.

[1]

(ii) The mass spectrum has a peak at m/e = 57.

Complete the equation to show the fragmentation of X to produce this peak.

[C5H10O2]+ ................................... + ...................................

[2]

(b) State the use of TMS and CDCl 3 in NMR spectroscopy.

● TMS ....................................................................................................................................

● CDCl 3 .................................................................................................................................
[1]

Tabriaz Anwer 0333-8151689

Unit 4: NMR Topical Chemistry A level P4

(c) The proton NMR spectrum of compound X, C5H10O2, is shown.

3
2

3
2

5 4 2 1
δ / ppm

(i) By considering both the relative peak areas and their δ values, use the Data Booklet to

● deduce the part of the molecule that produces the peak at δ 2.2,

.............................................................................................................................................

● deduce the part of the molecule that produces the peaks at δ 1.2 and δ 3.5,

.............................................................................................................................................

● deduce the part of the molecule that produces the peak at δ 4.0.

.............................................................................................................................................
[3]

(ii) When reacted with aqueous alkaline iodine, X produces a yellow precipitate.

Use this information and your answers to (c)(i) to suggest a structure for X.

[1]

Tabriaz Anwer 0333-8151689

Unit 4: NMR Topical Chemistry A level P4

(d) Compound W is an ester with the molecular formula C5H10O2.

The proton NMR spectrum of W contains only two peaks.

The relative areas of these two peaks are in the ratio 9 : 1.

Suggest a structure for this ester, W.

[1]

(e) Compound V is a carboxylic acid which contains a chiral centre. It also has the molecular
formula C5H10O2.

(i) Explain what is meant by the term chiral centre.

.............................................................................................................................................

....................................................................................................................................... [1]

(ii) Suggest a structure for V.

[1]

Tabriaz Anwer 0333-8151689

Unit 4: NMR Topical Chemistry A level P4

31 M/J 19/P42/Q8

Compound R is shown.

R
CH3

HO Cl

CH3

(a) State the systematic name of compound R.

.............................................................................................................................................. [1]

(b) (i) R is dissolved in CDCl 3 and analysed using carbon-13 and proton NMR spectroscopy.

● Predict the number of peaks that are seen in the carbon-13 NMR spectrum of R.

.............................................................................................................................................

● Predict the number of peaks that are seen in the proton NMR spectrum of R.

.............................................................................................................................................
[2]

(ii) A separate sample of R is dissolved in D2O. The proton NMR spectrum of this solution
shows one less peak than is obtained in CDCl 3.

Explain why.

.............................................................................................................................................

....................................................................................................................................... [1]

Tabriaz Anwer 0333-8151689

Unit 4: NMR Topical Chemistry A level P4

(c) Compound R reacts separately with the four reagents shown in the table.

omplete the table by

C
● drawing the structures of the organic products formed,
● stating the type of reaction.

reagent organic product structure type of reaction

Na

CH3COCl

Br2(aq)

+
N N

Cl –

[6]

Tabriaz Anwer 0333-8151689

 Unit 4: NMR Topical Chemistry A level P4

32 O/N 19/P41/Q9,c

(c) The proton NMR spectrum of butamben in CDCl 3 contains one or more peaks that show a
triplet splitting pattern.

(i) State the number of peaks in the spectrum that show a triplet splitting pattern.

....................................................................................................................................... [1]

(ii) On the diagram of butamben below, circle the protons responsible for the peak or peaks
you identified in (c)(i).

H O H H
H H
H C C C
O C C H
H H
H H H
N H

H H
[1]

(iii) Describe and explain how the proton NMR spectrum of butamben in D2O would differ from
the proton NMR spectrum of butamben in CDCl 3.

.............................................................................................................................................

....................................................................................................................................... [2]

(d) The mass spectrum of butamben includes peaks at m/e 92 and 57.

Identify the fragments responsible for these peaks.

m/e 92 = .....................................................................................................................................

m/e 57 = .....................................................................................................................................
[1]

Tabriaz Anwer 0333-8151689

Unit 4: NMR Topical Chemistry A level P4

33 O/N 19/P41/Q8,g

(g) Methylpropanedioic acid is an isomer of butanedioic acid.

methylpropanedioic acid
CH3
O O
C C C
HO OH
H

The proton NMR spectrum of methylpropanedioic acid in CCl 4 is shown.

δ 1.1

δ 12.7
δ 3.3

14 12 10 8 6 4 2 0
δ / ppm

(i) Identify the protons in the methylpropanedioic acid molecule that are responsible for each
area of the proton NMR spectrum.

δ 12.7 ..................................................................................................................................

δ 3.3 ....................................................................................................................................

δ 1.1 ....................................................................................................................................
[2]

Tabriaz Anwer 0333-8151689

Unit 4: NMR Topical Chemistry A level P4

(ii) Name the splitting pattern shown at δ 3.3 and explain how it arises.

.............................................................................................................................................

....................................................................................................................................... [1]

The carbon‑13 NMR spectra of butanedioic acid, HO2CCH2CH2CO2H, and

methylpropanedioic acid, HO2CCH(CH3)CO2H are different.

(iii) State the number of peaks

● in the carbon‑13 NMR spectrum of butanedioic acid

.............................................................................................................................................

● in the carbon‑13 NMR spectrum of methylpropanedioic acid.

.............................................................................................................................................
[1]

Tabriaz Anwer 0333-8151689