CBSE 2023 · Region 1 · Set 3 · Q29 · 3 marks
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.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 $\displaystyle \mathrm{Pd}-\mathrm{BaSO}_{4}$.
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.
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.
Aldehydes, Ketones and Carboxylic AcidsChemical Reactions of Aldehydes, Ketones and Carboxylic AcidsUnderstandshort_answermedium
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