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YISHUN INNOVA JUNIOR COLLEGE
2021 JC2 H2 CHEMISTRY
ARENES (FOUNDATION)
EJC/2020/I/24
1
Cumene is an important intermediate in the industrial production of phenol.
A student synthesised cumene successfully by reacting benzene with C
3
H
7
C
l
in the
presence of aluminium chloride.
Which of the following statements are correct?
1
Cumene does not decolourise aqueous bromine at room temperature.
2
Aluminium chloride is acting as a Lewis acid in the synthesis of cumene.
3
The electrophile which reacted with benzene in the synthesis of cumene
was CH
3
CH
2
CH
2
+
.
A
1 only
B
1 and 2
C
2 and 3
D
1, 2 and 3
TJC/2020/I/28
2
Use of the Data Booklet is relevant to this question
.
Which of the following routes is most suitable to synthesise 3-amino-5-bromobenzoic acid
from phenylamine?
A
reduction
bromination
alkylation
oxidation
neutralisation
B
neutralisation
bromination
alkylation
oxidation
neutralisation
C
reduction
alkylation
bromination
oxidation
neutralisation
D
neutralisation
alkylation
oxidation
bromination
neutralisation
ASRJC/2020/I/17
3
Compound
G
reacts with acidified KMnO
4
under suitable condition.
Compound
G
What is the most likely organic products formed from this reaction?
A
CO
2
H
CO
2
H
HO
2
C
HO
2
C
B
CO
2
H
CO
2
H
HO
2
C
HO
2
C
C
D
RI/2020/I/26
4
When heated with concentrated nitric acid in the presence of a catalyst, chlorobenzene
undergoes a reaction to form 4-chloronitrobenzene.
Which statement about the above reaction is correct?
A
FeC
l
3
is a suitable catalyst for the reaction.
B
One of the intermediates is
.
C
The reaction requires a lower temperature compared to benzene.
D
The reaction involves the electrophilic attack of NO
2
+
on the benzene ring.
RI/2020/III/5c
5
Hydrocarbons undergo reactions with chlorine under different conditions. Compare and
account for the differences in conditions used in the chlorination of cyclohexene and
benzene.
[3]
DHS/2020/III/2a
6
The Gattermann
–
Koch reaction is used to produce benzaldehyde. An example is provided
below in Fig. 2.1.
+
CO
+
HC
l
CHO
A
l
C
l
3
Fig. 2.1
(a)
(i)
Suggest an alternative reagent to replace A
l
C
l
3
in the Gattermann
–
Koch
reaction.
[1]
(ii)
The mechanism of the reaction involves an acylium ion,
+
CHO, as an
electrophile and tetrachloroaluminate ion, A
l
C
l
4
–
. Draw the mechanism of the
reaction. You need not show the formation of the acylium ion.
[3]
(iii)
The synthesis of compound
W
involves the Gattermann-Koch reaction.
CH
3
X
Y
Z
CH
2
C
l
HOOC
CHO
CH
3
Br
A
l
Br
3
C
l
2
uv
CO,HC
l
A
l
C
l
3
Step 1
compound
W
State the reagents and conditions required of Step 1 and draw the structures of
X
,
Y
and
Z
.
[4]
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ASRJC/2020/III/3d
7 (a)
(i)
Benzene rings are commonly found in many naturally occurring organic
compounds.
Explain why benzene tends to undergo substitution reactions instead of
addition reactions like alkenes.
[2]
(ii)
The position of substitution in the electrophilic substitution of arenes can be
explained based on the stability of the intermediate carbocation formed.
Fig. 3.5 shows the possible carbocation intermediates that can be formed from
the bromination of methylbenzene.
CH
3
CH
3
Br
H
methylbenzene
CH
3
H
Br
2-position
3-position
4-position
Br
H
CH
3
Fig. 3.5
Use the information and your knowledge about the stability of carbocations to
suggest why the CH
3
group directs incoming electrophiles to the 2
–
and 4
–
positions in preference to the 3
–
position.
[2]
(iii)
Suggest a synthesis of 2
–
bromobenzoic acid starting from methylbenzene
according to the scheme in Fig. 3.6.
CH
3
CO
2
H
Br
more than
one step
3-bromobenzoic acid
Fig. 3.6
[3]
YISHUN INNOVA JUNIOR COLLEGE
2021 JC2 H2 CHEMISTRY
ARENES (ADVANCED)
DHS/2020/I/20
8
The diagram below shows the epoxidation of carbon
–
carbon double bonds. Epoxidation of
an alkene occurs much more readily than epoxidation of benzene.
Which statement helps to explain this?
A
The extent of delocalisation of
electrons of benzene will be decreased and the
product will no longer be aromatic if benzene undergoes epoxidation.
B
The carbon
–
carbon double bond of alkene is stronger and hence, it is more reactive
towards epoxidation.
C
Benzene is a stronger nucleophile than alkenes as it is more electron rich.
D
Benzene lacks a directing group that is needed to form the three
–
membered ring in
epoxide.
ACJC/2020/I/23
9
Which of the following is the best method to prepare 2-bromophenylamine from
benzene?
A
B
C
D
Sn, conc
HC
l
, heat
conc H
2
SO
4
warm
Excess aq Br
2
Sn, conc
HC
l
, heat
conc H
2
SO
4
warm
Sn, conc
HC
l
, heat
conc H
2
SO
4
heat
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TMJC/2020/I/24
10
Which synthetic route gives the highest yield of the product?
step 1
step 2
step 3
A
FeBr
3
, Br
2
KMnO
4
, H
2
SO
4
, heat
conc. H
2
SO
4
,
conc. HNO
3
, heat
B
KMnO
4
, H
2
SO
4
, heat
FeBr
3
, Br
2
conc. H
2
SO
4
,
conc. HNO
3
, heat
C
conc. H
2
SO
4
,
conc. HNO
3
, heat
KMnO
4
, H
2
SO
4
, heat
FeBr
3
, Br
2
D
conc. H
2
SO
4
,
conc. HNO
3
, heat
FeBr
3
, Br
2
KMnO
4
, H
2
SO
4
, heat
TMJC/2020/I/23
11
Benzene-1,2-dicarboxylic acid can be prepared from benzene in the following two-step
synthesis.
Which structures could be compound
J
?
1
3
2
4
A
1, 2, 3 and 4
B
1, 2 and 4 only
C
1 and 2 only
D
2 and 4 only
ASRJC/2020/II/6d
12
Both naphthalene and diphenylamine contain aromatic system that obey
Hückel’s rule.
This rule states that an aromatic molecule is a cyclic, planar molecule that contains (4n+2)
delocalised
electrons, where n is 0 or a positive integer (1, 2, 3 etc.). Benzene is an
example of an aromatic molecule as it contains 6 delocalised
electrons where n = 1.
The Kekulé structure of naphthalene is shown below.
napthalene
(a)
(i)
Use the information above to explain why naphthalene is an aromatic molecule.
[1]
Pyrrole is another aromatic compound that obeys
Hückel’s rule.
N
H
pyrrole
(ii)
Deduce the type of hybridisation present in the N atom in pyrrole. Explain your
answer.
[1]
HCI/2020/III/4c
13
A student suggested the synthesis in Fig. 4.1 for 4-aminosalicylic acid, a drug that was
widely used against tuberculosis.
Fig. 4.1
(a)
(i)
Explain why steps 1 to 4 are
not
ideal.
[4]
(ii)
Suggest reagents and conditions for step 5.
[1]
TMJC/2020/III/4b
14
Benzene is a very stable organic compound which does not undergo electrophilic addition
or reduction under normal condition.
(a)
(i)
Explain why the benzene structure is very stable.
[2]
(ii)
Birch reduction is an organic reaction that is used to reduce arenes to
cyclohexadienes. The position of the alkene groups formed depends on the type
of substituent group present in the benzene ring.
Two examples are given as shown:
Predict the products of Birch reduction for the following compounds.
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NYJC/2020/II/5a
15
Alkyl benzenesulfonic acid is a class of organic compounds used in detergent
formulations.
S
O
O
OH
alkyl benzenesulfonic acid
(a)
In the presence of sulfur trioxide, concentrated sulfuric acid and heat, benzene
undergoes sulfonation to produce benzenesulfonic acid.
+
SO
3
SO
3
H
conc H
2
SO
4
heat
benzene
benzenesulfonic acid
The mechanism of this reaction is similar to that of the nitration of benzene.
Concentrated sulfuric acid is used in an initial step to generate the electrophile.
(i)
State and explain the role of concentrated sulfuric acid in the initial step to
generate the electrophile.
[1]
(ii)
Suggest a mechanism for the reaction between benzene and sulfur trioxide.
Indicate clearly any intermediates that may be formed. Show all charges and
relevant lone pairs and the movement of electron pairs by using curly arrows.
[3]
(iii)
Describe how the structure and bonding of the six-membered ring intermediate
of the mechanism in
(ii)
differ from those in benzene. In your answer refer to
the hybridisation, the
bonding and the bond angles in the ring system.
[3]
(b)
In electrophilic substitution of
ortho
-,
para
-directors, a mixture of products slightly
favouring
para
over
ortho
with a 60: 40 ratio is usually obtained.
OH
Br
+
Br
OH
OH
Br
para
ortho
60
:
40
(i)
Suggest why the
ortho
- products are less favoured over the
para
- products.
[1]
One way to get the
ortho
-
products exclusively is to use the sulfonyl as a “blocking
group”. The
para
- position is first blocked with SO
3
H, followed by performing the
desired reaction at the
ortho
- position (e.g. bromination). As sulfonation is reversible,
heating with strong acid will remove SO
3
H, giving the
ortho
- substituted product.
OH
Br
OH
SO
3
H
OH
SO
3
H
SO
3
, conc H
2
SO
4
heat
Br
2
anhydrous FeBr
3
Br
OH
H
2
SO
4
heat
(ii)
2-(butan-2-yl)aniline can be formed via a 5-step synthesis with benzene as the
starting material. Draw the structures of the reaction intermediates and state the
reagents and conditions for each step. One of your steps should include the use
of
sulfonyl as a “blocking group”.
step 1
NH
2
A
step 2
B
step 3
C
step 4
D
step 5
benzene
2-(butan-2-yl)aniline
(iii)
2-(butan-2-yl)aniline exists as two stereoisomers.
Draw 3-dimensional diagrams to show the stereoisomers of 2-(butan-2-
yl)aniline and state the type of stereoisomerism shown.
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