CBSE 2022 · Region 5 · Set 3 · Q4 · 3 marks
Account for the following :(i)$\displaystyle \mathrm{pk}_{\mathrm{b}}$ of aniline is more than that of methylamine.(ii)Aniline does not undergo Friedel-Crafts reaction.(iii)Primary amines have higher boiling points than tertiary amines.(b)Arrange the following compounds in the increasing order of their basic strength in aqueous solution :$\displaystyle \mathrm{CH}_{3} \mathrm{NH}_{2},\left(\mathrm{CH}_{3}\right)_{3} \mathrm{~N},\left(\mathrm{CH}_{3}\right)_{2} \mathrm{NH}$(ii)What is Hinsberg's reagent ?(iii)What is the role of pyridine in the acylation reaction of amines?
Account for the following :
(i)
$\displaystyle \mathrm{pk}_{\mathrm{b}}$ of aniline is more than that of methylamine.
(ii)
Aniline does not undergo Friedel-Crafts reaction.
(iii)
Primary amines have higher boiling points than tertiary amines.
(b)
Arrange the following compounds in the increasing order of their basic strength in aqueous solution :$\displaystyle \mathrm{CH}_{3} \mathrm{NH}_{2},\left(\mathrm{CH}_{3}\right)_{3} \mathrm{~N},\left(\mathrm{CH}_{3}\right)_{2} \mathrm{NH}$
(ii)
What is Hinsberg's reagent ?
(iii)
What is the role of pyridine in the acylation reaction of amines?
Marking-scheme solution
(a) (i) lone pair of electrons are delocalised over benzene ring due to resonance, electron density decreases and hence less available for protonation / Due to electron withdrawing nature of the aryl group in aniline while electron donating nature of methyl group in methyl amine /Aniline is a weaker base than methylamine.
(ii) Aniline is a Lewis base and it reacts with \(\displaystyle \mathrm{AlCl}_{3}\) to form a salt / N of aniline acquires positive charge with \(\displaystyle \mathrm{AlCl}_{3}\) and hence is a deactivating group.
(iii) Presence of intermolecular hydrogen bonding in primary amines which is absent in tertiary amines.
OR
(b) (i) \(\displaystyle \left(\mathrm{CH}_{3}\right)_{3} \mathrm{~N}<\mathrm{CH}_{3} \mathrm{NH}_{2}<\left(\mathrm{CH}_{3}\right)_{2} \mathrm{NH}\)
(ii) \(\displaystyle \mathrm{C}_{6} \mathrm{H}_{5} \mathrm{SO}_{2} \mathrm{Cl}\) / Benzenesulphonyl chloride
(iii) Pyridine is used to remove HCl from the reaction mixture.
AminesPhysical Properties of AminesUnderstandshort_answermedium
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CBSE Class 12 Chemistry past-paper question from the 2022board exam, with the answer as CBSE’s own marking scheme gives it. Where our answers come from.