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Chemistry · 2023 · 3 marks
Aldehydes, Ketones and Carboxylic AcidsChemical Reactions of Aldehydes, Ketones and Carboxylic Acids3 marksUnderstandshort answer
CBSE 2023 · Region 1 · Set 1 · Q29
(a) Explain why: (i) Carboxyl group in benzoic acid is meta directing. (ii) Sodium bisulphite is used for the purification of aldehydes and ketones.…
(a)
Explain why:
(i)
Carboxyl group in benzoic acid is meta directing.
(ii)
Sodium bisulphite is used for the purification of aldehydes and ketones.
(iii)
Carboxylic acids do not give characteristic reactions of carbonyl group.
OR
(b)
An organic compound'A', having the molecular formula $\displaystyle \mathrm{C}_{3} \mathrm{H}_{8} \mathrm{O}$ on treatment with Cu at $\displaystyle 573$ K, gives'B'. 'B'does not reduce Fehling's solution but gives a yellow precipitate of the compound'C'with $\displaystyle \mathrm{I}_{2} / \mathrm{NaOH}$. Deduce the structures of A, B and C.
Marking-scheme solution
(a)(i)
Because it is an electron-withdrawing group / deactivating group / -R effect , electrophilic substitution takes place at the m-position.
(ii)
Because aldehydes & ketones form addition compound with \(\displaystyle \mathrm{NaHSO}_{3}\) which on hydrolysis forms pure aldehydes & ketones.
(iii)
Due to resonance, carboxylic carbon becomes less electrophilic.
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