CBSE 2023 · Region 4 · Set 1 · Q32 · 4 marks

Amines are usually formed from nitro compounds, halides, amides, imides, etc. They exhibit hydrogen bonding which influences their physical properties. In alkyl amines, a combination of electron releasing, steric and hydrogen bonding factors influence the stability of the substituted ammonium cations in protic polar solvents and thus affect the basic nature of amines. In aromatic amines, electron releasing and withdrawing groups, respectively increase and decrease their basic character. Influence of the number of hydrogen atoms at nitrogen atom on the type of reactions and nature of products is responsible for identification and distinction between primary, secondary and tertiary amines. Presence of amino group in aromatic ring enhances reactivity of the aromatic amines. Aryl diazonium salts provide advantageous methods for producing aryl halides, cyanides, phenols and arenes by reductive removal of the diazo group. Answer the following questions :

(i)

Arrange the following in the increasing order of their $\displaystyle \mathrm{pK}_{\mathrm{b}}$ values in aqueous solution : \[\mathrm{C}_{2} \mathrm{H}_{5} \mathrm{NH}_{2}, \quad\left(\mathrm{C}_{2} \mathrm{H}_{5}\right)_{2} \mathrm{NH}, \quad\left(\mathrm{C}_{2} \mathrm{H}_{5}\right)_{3} \mathrm{~N} \]

(ii)

Aniline on nitration gives a substantial amount of m-nitroaniline, though amino group is o/p directing. Why ?

(iii)OR(iii)

An aromatic compound 'A' of molecular formula $\displaystyle \mathrm{C}_{7} \mathrm{H}_{6} \mathrm{O}_{2}$ on treatment with aqueous ammonia and heating forms compound 'B'. Compound 'B' on heating with $\displaystyle \mathrm{Br}_{2}$ and aqueous KOH gives a compound 'C' of molecular formula $\displaystyle \mathrm{C}_{6} \mathrm{H}_{7} \mathrm{~N}$. Write the structures of A, B and C.

CBSE Class 12 Chemistry past-paper question from the 2023board exam, with the answer as CBSE’s own marking scheme gives it. Where our answers come from.