Which of the following statements are correct? I. In nitrating mixture nitric acid participates as an acid.…
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.
II, III only
I, II only
I, III only
I, II, III
Solution
(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.
