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7. (d) : Cyclopropane is under severe strain. Therefore,
it is always ready to undergo ring opening
reactions.
∴ Option (d) is correct.
Remember, when a carbanionic centre attached
with two chlorine atoms, substitution reaction
takes place. Also remember, in presence of sunlight
ring opening and substitution takes place via free
radical path.
8. (a) : Under vigorous conditions, Ni/H 2
will destroy
the double bonds of benzene.
∴ Option (a) will be the correct option.
9. (b): System is not conjugated. So, it is nonaromatic.
∴ Option (b) is correct.
10. (a) : Nitration will take place at o- or p-positions
of the aromatic ring if +I-effect group is attached
to the benzene ring. Hence, option (a) is correct.
Lower temperature prevents polynitration.
11. (a) : While electrophilic substitution reaction takes
place in naphthalene there are two positions where
it can take place, α and β.
H E
H
+
III
E +
-attack
60°C–70°C
E
I
H
II
+
E
+
+
E
E + H
-attack
160°C
VI
E
E
H
H
+
+
VIII
VII
E
+
E
H
H
+
IX
X
So, intermediates for α-attack are more stable than
that for β-attack. So, α-product must be kinetically
controlled product and at low temperature this
becomes irreversible in nature and the exclusive
product. α-product is thermodynamically less stable
than β-product due to steric reason.
No steric
interaction
H
-product
SO H 3
Steric
interaction
H
-product
SO H 3
This is why at higher temperature reaction occurs
to give thermodynamically more stable β-product.
At higher temperature reaction is also reversible in
nature. At higher temperature the readily formed
α-product desulfonates and gives β-product.
SO 3
H
-product
H +
H 2
SO 4
H + H 2
SO 4
SO 3 H
+
H
E
H
E
-product
+
IV
V
Now, understand a very simple thing, for α-attack
there are two structures whereas for β-attack there
is only one structure which is aromatic. For α-attack
the aromatic structures are I and II and for β-attack
the aromatic structure is VI.
P.E
E act (I)
E act
(II)
-product
Naphthalene +
conc. H 2
SO -product
4
Reaction co-ordinate
-zone product -zone product
68 CHEMISTRY TODAY | APRIL ‘17