Download SPECTRA Q - the British School of Bahrain

1.
This question is about compounds X, C4H10O, and Y, C4H8O.
(a)
Compound X, C4H10O, can be oxidized to compound Y, C4H8O. The infrared spectrum
of X is given below.
Infrared Spectrum of X
What can be deduced about the structures of X and Y using all this information and the
data booklet? Justify your answer.
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(4)
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(b)
Below are the nmr spectra of X and Y.
nmr spectrum of X
nmr spectrum of Y
Use these nmr spectra and your answer to (a) to deduce the structural formulae of X and
Y. Justify your answer and explain why both nmr spectra are consistent with these
structures.
(6)
(Total 10 marks)
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2.
The spectra of the compounds with the formulae CH3CH(OH)CH3 and CH3CH2CH2OH can be
distinguished by
A
the value of m/e of the molecular ion in the mass spectrum.
B
the presence of a fragment with m/e = 15 in the mass spectrum.
C
the presence of an absorption peak due to O–H in the infrared spectrum.
D
the number of peaks in the nmr spectrum.
(Total 1 mark)
3.
Not all molecules will absorb infrared radiation. Those that do
A
change their dipole moment when their bonds stretch or bend.
B
undergo homolytic fission.
C
must be polar.
D
are always organic substances.
(Total 1 mark)
4.
This question concerns the three isomers A, B and C, each of which has a relative molecular
mass of 134.
O
C
O
CH 2
CH 3
CH 2
CH 2
C
H
A
B
CH
CH
CH 2 OH
C
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(a)
The mass spectrum of substance A is shown below. Identify the species responsible for
the peaks labelled 1, 2 and 3.
Peak 1 .........................................................................................................................
Peak 2 .........................................................................................................................
Peak 3 .........................................................................................................................
(3)
(b)
The infra-red spectra of two of these substances were also measured.
(i)
Use the table and the spectra below to identify which spectrum is that of
substance C.
Wavenumber
/ cm–1
Bond
Wavenumber
/ cm–1
C—H (arenes)
3000-3100
O––H (hydrogen bonded)
3200-3570
C—H (alkanes)
2850-3000
O––H (not hydrogen
bonded)
3580-3650
C==O
1680-1750
C==C (arenes)
1450-1600
Bond
The spectrum of substance C is spectrum number ..........................................
(1)
(ii)
Give one reason for your choice.
......................................................................................................................
(1)
(iii)
Give one other reason why the other spectrum could not be that of substance C.
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(1)
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4
100
2
Relative intensity
80
60
1
40
20
3
0
25
50
75
100
125
m/e
Transmittance
100
50
0
4000
3000
2000
1500
Wavenumber/cm–1
1000
3000
2000
1500
Wavenumber/cm–1
1000
Transmittance
100
50
0
4000
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(c)
State which of the substances A, B and C will react with the following reagents and state
what would be observed.
(i)
Bromine dissolved in hexane.
Substance(s) .....................................................................................................
Observation ......................................................................................................
(2)
(ii)
A warm ammoniacal solution of silver nitrate.
Substance(s) .....................................................................................................
Observation ......................................................................................................
(2)
(iii)
2,4-dinitrophenylhydrazine solution.
Substance(s) .....................................................................................................
Observation ......................................................................................................
(3)
(iv)
Give the structural formula of the organic product(s) obtained in (c)(i).
(1)
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(v)
Give the structural formula of the organic product(s) obtained in (c)(ii).
(1)
(Total 18 marks)
5.
The pain-relieving drug ibuprofen has the formula
CH 3
H
C
CH 3
CH 2
C
CH 3
(a)
H
CO 2 H
A molecule of this compound is chiral. Explain, with the aid of diagrams, how two
optical isomers result from chiral a centre. Identify the chiral centre in such a molecule
and explain how these isomers could be distinguished from each other.
(4)
(b)
Compounds A and B, shown below, are used as intermediates in the manufacture of
ibuprofen.
CH 3
H
C
CH 3
CH 2
C
CH 3
O
H
C
CH 3
CH 2
C
CH 3
A
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CH 3
H
OH
B
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(i)
Suggest how infra-red spectroscopy could be used to identify an impurity in a
sample of ibuprofen which is known to be one of these two compounds.
A table of infra-red absorbencies is given below.
Bond
C-H
Assignment
Wavenumbers/cm–1
alkanes
alkenes, arenes
2850 - 2950
3000 - 3100
arenes
1450 - 1650
C=O
aldehydes, ketones, esters,
carboxylic acids
1680 - 1750
O-H
free
hydrogen bonded in alcohols or phenols
hydrogen bonded in carboxylic acids
3580 - 3670
3230 - 3550
2500 - 3300
benzene ring
(3)
(ii)
Suggest a simple chemical test which would distinguish between A and B.
(2)
(iii)
Treatment of either A or B if heated with a mixture of aqueous sodium hydroxide
and potassium manganate(VII) solution would produce the same compound.
Suggest the structure of this compound.
(2)
(c)
A tablet of ibuprofen contains a very small quantity of the drug and the remainder of the
tablet material is unreactive.
In an analysis 50 tablets were reacted with 100.0 cm3 of 1.00 mol dm–3 aqueous sodium
hydroxide, an excess. The ibuprofen reacted as a weak acid. When the reaction was
complete, the remaining aqueous sodium hydroxide was titrated with 2.00 mol dm–3
hydrochloric acid. 25.75 cm3 of the acid were required for neutralisation.
(i)
Calculate the mass, in mg, of ibuprofen in each tablet.
(Mr for ibuprofen = 206)
(5)
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(ii)
Calculate the number of molecules of ibuprofen that this tablet represents.
(Avogadro constant h = 6.023 × 1023 mol–1)
(2)
(d)
Ibuprofen is almost insoluble in aqueous solutions at pH 3 but if the pH is raised to 8 then
the ibuprofen becomes reasonably soluble. Account for these observations.
(4)
(e)
Under the appropriate conditions ibuprofen reacts with ethanol to produce a substance
with a characteristic odour. Identify the functional group in ibuprofen that would react
with the ethanol. Suggest the conditions needed for the reaction to take place and identify
the product.
(3)
(Total 25 marks)
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