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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 3 · 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)
Give chemical equation for the following reactions:
(i)
Propanone is treated with dil. $\displaystyle \mathrm{Ba}(\mathrm{OH})_{2}$.
(ii)
Acetophenone is treated with Zn (Hg) /Conc. HCl.
(iii)
Benzoyl chloride is hydrogenated in presence of $\displaystyle \mathrm{Pd}-\mathrm{BaSO}_{4}$.
Marking-scheme solution
(i) Because it is an electron-withdrawing group / deactivating group / -R effect , electrophilic substitution takes place at the m-position.
(ii) Because aldehyde & ketones form addition compound with \(\displaystyle \mathrm{NaHSO}_{3}\) which on hydrolysis forms pure aldehyde & ketones.
(iii) Due to resonance, carboxylic carbon becomes less electrophilic.
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CBSE Class 12 Chemistry past-paper question from the 2023 board exam, with the answer as CBSE’s own marking scheme gives it. Where our answers come from.