8. Halogen Derivatives - Student Copy
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YISHUN INNOVA JUNIOR COLLEGE
2021 JC2 H2 CHEMISTRY
HALOGEN DERIVATIVES (FOUNDATION)
ACJC/2020/I/18
1
When CH
3
CH
2
CBr
2
CH
2
CH
3
is heated with ethanolic KOH, which hydrocarbons could be
produced?
1
CH
3
CH
2
C
CCH
3
2
CH
3
CH=C=CHCH
3
3
CH
3
CH
2
CH=C=CH
2
A
2 only
C
2 and 3
B
1 and 2
D
1, 2 and 3
ACJC/2020/I/19
2
When (bromomethyl)benzene was heated with NaOH in dimethyl sulfoxide solvent, the
following reaction takes place.
C
6
H
5
CH
2
Br + OH
–
C
6
H
5
CH
2
OH + Br
–
The energy profile diagram for the reaction is shown below.
Which of the following represents the species at point
X
?
A
C
B
D
NJC/2020/I/21
3
When methylamine, CH
3
NH
2
is heated with excess chloromethane, CH
3
C
l
for a long
period, the final product obtained is a white solid that is very soluble in water.
What is the
M
r
of the final product?
[
A
r
:
C,12.0;
N,14.0;
H,1.0;
C
l
, 35.5]
A
45.0
B
74.0
C
109.5
D
182.5
ASRJC/2020/I/19
4
Which sequence shows the correct order of
decreasing
ease of hydrolysis?
A
CH
3
CH
2
C
l
>
CH
3
CH
2
Br
>
CH
3
CH
2
I
B
(CH
3
)
2
CHC
l
>
(CH
3
)
2
CH
I >
(CH
3
)
2
CHBr
C
D
VJC/2020/II/5d
5
When the compounds shown below were reacted with aqueous sodium hydroxide at
55 °C, the rate of reaction decreases in the following order.
C
6
H
5
CH
2
Br > (CH
3
)
3
CBr > C
6
H
5
Br
(i)
Both C
6
H
5
CH
2
Br and (CH
3
)
3
CBr undergo unimolecular nucleophilic substitution with
aqueous sodium hydroxide. Explain their relative rates of reaction.
[1]
(ii)
Explain why C
6
H
5
Br has almost no reaction with aqueous sodium hydroxide at 55 °C.
[1]
TMJC/2020/III/5ci
6
Amphetamine is prescribed to treat medical conditions such as Attention Deficit
Hyperactivity Disorder (ADHD).
NH
2
CH
3
Amphetamine
Suggest the type of mechanism involved in the reaction of amphetamine with (CH
3
)
3
CC
l
.
Give a reason to support your answer.
[2]
DHS/2020/III/5d
7
Compound
V
can be formed from compound
W
.
OH
CH
3
C
H
3
CH
3
C
Compound
V
W
is a mono
–
substituted chloroalkane and kinetics studies showed that the rate law can
be expressed as rate =
k
[
W
].
(i)
Suggest appropriate reagents and conditions for the conversion of
W
to
V
.
[1]
(ii)
Name the mechanism of the reaction in
(i)
and explain your answer.
[2]
(iii)
Hence describe the mechanism.
Show all charges and relevant lone pairs and show the movement of electron pairs
by using curly arrows.
NJC/2020/II/6a
8
Halogenoalkanes react with a number of different reagents in nucleophilic substitution
reactions.
A sample of potassium cyanide dissolved in ethanol is added to a sample of
1-bromobutane and heated under reflux. Compound
A
is formed.
(i)
What is meant by the term
nucleophile
?
[1]
(ii)
Draw the
skeletal formula
of
A
.
[1]
(iii)
State the reagents and conditions needed for 1-bromobutane to react to form
butylamine, CH
3
(CH
2
)
3
NH
2
.
[1]
(iv)
Draw the mechanism of the reaction between 1-bromobutane and your reagent in
(iii)
to form butylamine.
Show all charges and relevant lone pairs and show the movement of electron pairs
by using curly arrows.
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YISHUN INNOVA JUNIOR COLLEGE
2021 JC2 H2 CHEMISTRY
HALOGEN DERIVATIVES (ADVANCED)
VJC/2020/I/23
9
Epoxy resins are polymers which are used in adhesives. One monomer used in their
manufacture has the following structure.
This monomer is manufactured from propene in three stages:
Stage I :
Stage II :
Stage III :
Which statements are correct for the above synthesis?
1
Stage I requires the use of ultraviolet light.
2
Stage II is an electrophilic addition.
3
Stage III is a nucleophilic substitution.
A
1, 2 and 3
C
2 and 3
B
1 and 2
D
1 only
HCI/2020/I/25
10
Equal amounts of compounds W, X and Y are added separately to three test-tubes
containing equal concentrations of ethanolic silver nitrate solution in a heated water bath.
No precipitate forms in the test-tube containing W.
For the other two test-tubes, precipitate is formed faster for Y.
What could be the identities of W, X and Y?
W
X
Y
1
2
3
A
3 only
C
2 and 3
B
1 and 2
D
1, 2 and 3
TMJC/2020/II/6cii
11
Compound
F
can be converted to compound
G
, C
16
H
16
N
+
, by reaction with Compound
E
.
Suggest the structure of compound
G
.
EJC/2020/III/4ai
12
Nucleophilic substitution reactions can proceed via bimolecular or unimolecular
mechanisms, which is often dependent on whether the halogenoalkane is primary,
secondary, or tertiary.
Fig. 4.1 shows the experimental data for a kinetics study for the reaction between aqueous
sodium hydroxide and a solution of benzyl bromide, C
6
H
5
CH
2
Br, which is carried out at
constant temperature.
(i)
With reference to the graph shown in Fig 4.1, determine the orders of reaction with
respect to NaOH and C
6
H
5
CH
2
Br.
[2]
(ii)
Hence, construct a rate equation for the reaction between NaOH and C
6
H
5
CH
2
Br.
[1]
(iii)
State and explain the type of mechanism for the reaction. Suggest how the
structure of C
6
H
5
CH
2
Br favours the type of mechanism you have stated.
[2]
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(iv)
Suggest and explain how the rate of reaction would change if aqueous potassium
hydroxide of the same concentration was used in place of aqueous sodium
hydroxide.
[1]
HCI/2020/II/4c
13
In 2019, a group of researchers from Singapore published an article in
Science
, one of the
world’s top academic journals, about the discovery of an unusual nucleophilic substitution
reaction involving tertiary halogenoalkanes.
This new reaction, named halogenophilic nucleophilic substitution (S
N
2X), is an
unconventional method of synthesising a chiral product with a large excess of one
enantiomer over the other. A simplified overall scheme of the S
N
2X reaction, as well as the
conventional unimolecular nucleophilic substitution (S
N
1), are shown in Fig. 4.2.
Fig. 4.2
(i)
Suggest why tertiary halogenoalkanes typically do not undergo S
N
2 reactions.
[1]
(ii)
Instead, tertiary halogenoalkanes undergo S
N
1 reactions to produce racemic product
mixtures.
Explain why this is so.
[1]
Fig. 4.3 shows the mechanism of the S
N
2X reaction which involves the generation of a
carbanion intermediate and an uncharged Nu-X intermediate.
The carbanion intermediate and Nu-X interact with an enantiomerically-pure chiral cation
(shown by the dotted lines) in the second step before undergoing a reaction. This results
in a product mixture with a large excess of one enantiomer.
Fig. 4.3
(iii)
Suggest why a
chiral
cation is crucial in the S
N
2X reaction to obtain a product mixture
with a large excess of one enantiomer.
[1]
NJC/2020/II/6b
14
In another experiment, equal amounts of three different organohalogen compounds are
added to separate test-tubes. Equal amounts of aqueous silver nitrate and ethanol is
added to each test-tube and warmed. The time taken for a precipitate to form is recorded
for each compound.
halogenoalkane
time taken for precipitate to form / s
(CH
3
)
3
CC
l
460
(CH
3
)
3
CBr
?
(CH
3
)
2
C=CHC
l
No ppt
(i)
Explain the reactivity of (CH
3
)
2
C=CHC
l
shown in this experiment.
[1]
(ii)
Predict and explain the time taken for (CH
3
)
3
CBr to form a precipitate when subjected
to the same experimental conditions.
[2]
(iii)
1-bromobutane reacts with ammonia to form butylamine, CH
3
(CH
2
)
3
NH
2
.
When above reaction involving 1-bromobutane was replaced with (CH
3
)
3
CBr, a
reaction
with
a
different
overall
order
of
reaction
was
obtained.
State the overall order of reaction for the reaction involving (CH
3
)
3
CBr and account
for this different overall order of reaction.
[2]
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