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Which of the following statements are correct?
I. In nitrating mixture nitric acid participates as an acid.
II. $\sigma$ complex is the intermediate substance in electrophilic substitution of benzene.
III. Benzene on Friedel-Crafts alkylation with n-propyl chloride gives isopropyl benzene.
Options:
I. In nitrating mixture nitric acid participates as an acid.
II. $\sigma$ complex is the intermediate substance in electrophilic substitution of benzene.
III. Benzene on Friedel-Crafts alkylation with n-propyl chloride gives isopropyl benzene.
Solution:
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Verified Answer
The correct answer is:
II, III only
(I) In nitrating mixture, nitric acid $\left(\mathrm{HNO}_3\right)$ partcipates as an acid is not a correct statement, as $\mathrm{HNO}_3$ in nitrating mixture (with $\mathrm{H}_2 \mathrm{SO}_4$ ) behaves as a base.
(II) Sigma complex is the intermediate substance in electrophilic substitution of benzene is a correct statement as it forms arenium ion as intermediate when electrophile $\left(E^{+}\right)$attacks on benzene ring.
$E^{+}$attacks on the benzene ring to give sigma complex or arenium ion, in which one of the carbon is $s p^3$-hybridised.
(III) Benzene on Friedel-Craft's alkylation with $n$-propyl chloride gives isopropyl benzene is the correct statement, as $2^{\circ}$ carbocation is more stable than that of $1^{\circ}$ carbocation. The reaction occurs as follows :
Hence, statements (II) and (III) are correct and option (a) is the correct answer.
(II) Sigma complex is the intermediate substance in electrophilic substitution of benzene is a correct statement as it forms arenium ion as intermediate when electrophile $\left(E^{+}\right)$attacks on benzene ring.
$E^{+}$attacks on the benzene ring to give sigma complex or arenium ion, in which one of the carbon is $s p^3$-hybridised.
(III) Benzene on Friedel-Craft's alkylation with $n$-propyl chloride gives isopropyl benzene is the correct statement, as $2^{\circ}$ carbocation is more stable than that of $1^{\circ}$ carbocation. The reaction occurs as follows :
Hence, statements (II) and (III) are correct and option (a) is the correct answer.
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