CAMBRIDGE INTERNATIONAL AS & A LEVEL CHEMISTRY: COURSEBOOK
Exam-style questions and sample answers have been written by the authors. In examinations, the way marks are awarded
may be different.
Coursebook answers
Chapter 25
Self-assessment questions
1
a
d
6
b
p (or 2p) orbitals
c
electrons that are free to move around
the molecule in the π bonding system
above and below the plane of the
carbon atoms in the benzene ring
d
e
Br
Br
In benzene the six electrons in the
π bonding system are no longer
associated with any particular carbon
atoms in the molecule, whereas in hex3-ene the two electrons in the π bond
in the centre of the molecule are only
found above or below the central two
carbon atoms.
i
CH3
Br
3
Br
e
The hydrogen atoms in the —CH3
side-chain would be all or partially
replaced by Br atoms.
f
free-radical substitution
a
i
C6H4(NO2)CH3 + H+
ii
C6H4(NO2)CH3 + H2O
iii
1-methyl-2-nitrobenzene and
1-methyl-4-nitrobenzene
iv
CH3
CH3
NO2
Br
Br
ii
Cl
O2N
i
ii
2
b
i
sulfur atom
2-methylphenol
ii
1-bromo-2,3-dichlorobenzene
C6H6 + SO3 → C6H5SO3H
4
C6H5CH2CH2CH3 + HCl
Cl
+ Cl2
AlCl3
b
+ HCl
H
stage 1
Cl+ ⎯⎯→
i
Cl
stage 2
⎯⎯⎯→
[AlCl4]–
i
ii
c
Cl
+
a
ii
electrophilic substitution
c
1
1-methyl-2,4,
6-trinitrobenzene
Cl
a
b
NO2
NO2
1-methyl-2,
4-dinitrobenzene
f
NO2
O2N
+ HCl
(+AlCl3)
C6H5COCH2CH2CH2CH3 + HCl
propylbenzene
(aryl) ketone
With hexylbenzene, the hexyl side
chain would be oxidised to form an
aryl carboxylic acid (and the purple
potassium manganate(VII) solution
would be decolourised), whereas no
reaction would occur with hexane.
Cambridge International AS & A Level Chemistry © Cambridge University Press 2020
CAMBRIDGE INTERNATIONAL AS & A LEVEL CHEMISTRY: COURSEBOOK
d
i
ii
5
HCl, CH3COOH, C6H5OH, H2O,
C3H7OH
b
Methanol is less acidic than phenol
because methanol has an electrondonating methyl group attached to
the oxygen atom in the methoxide ion
that is formed on dissociation. This
has the effect of concentrating more
negative charge on this oxygen atom,
which more readily accepts an H+ ion,
re-forming undissociated methanol.
On the other hand, the phenoxide
ion, C6H5O−(aq), has its negative
charge spread over the whole ion as
the benzene ring draws in electrons
from the oxygen atom, reducing the
attraction of this ion for H+ ions.
i
ii
i
O−K+
A
a
c
6
c
Heat / hydrogen / nickel or
platinum catalyst
Phenylamine, sodium nitrate(III) /
sodium nitrite and dilute
hydrochloric acid (water)
ii
O−Na+
iii
OH
OH
Br
or
Br
iv
OH
OH
NO2
or
NO2
ice / below 10 °C
a
C6H5OH, C6H5CH3, C6H6,
C6H5COOH (remember —COOH is a
deactivating group)
b
i
OH
OH
Cl
Cl
+ 3HCl
+ 3Cl2
Cl
ii
2
A catalyst of AlCl3 would be needed.
Cambridge International AS & A Level Chemistry © Cambridge University Press 2020