CBSE 2023 · Region 2 · Set 1 · Q31 · 4 marks
The carbon - oxygen double bond is polarised in aldehydes and ketones due to higher electronegativity of oxygen relative to carbon. Therefore they undergo nucleophilic addition reactions with a number of nucleophiles such as $\displaystyle \mathrm{HCN}, \mathrm{NaHSO}_{3}$, alcohols, ammonia derivatives and Grignard reagents. Aldehydes are easily oxidised by mild oxidising agents as compared to ketones. The carbonyl group of carboxylic acid does not give reactions of aldehydes and ketones. Carboxylic acids are considerably more acidic than alcohols and most of simple phenols. Answer the following :(a)Write the name of the product when an aldehyde reacts with excess alcohol in presence of dry $\displaystyle \mathrm{HC} l$.(b)Why carboxylic acid is a stronger acid than phenol ?(c)Arrange the following compounds in increasing order of their reactivity towards $\displaystyle \mathrm{CH}_{3} \mathrm{MgBr}$: 
(ii)Write a chemical test to distinguish between propanal and propanone.Write the main product in the following:(i)(ii)
The carbon - oxygen double bond is polarised in aldehydes and ketones due to higher electronegativity of oxygen relative to carbon. Therefore they undergo nucleophilic addition reactions with a number of nucleophiles such as $\displaystyle \mathrm{HCN}, \mathrm{NaHSO}_{3}$, alcohols, ammonia derivatives and Grignard reagents. Aldehydes are easily oxidised by mild oxidising agents as compared to ketones. The carbonyl group of carboxylic acid does not give reactions of aldehydes and ketones. Carboxylic acids are considerably more acidic than alcohols and most of simple phenols. Answer the following :
(a)
Write the name of the product when an aldehyde reacts with excess alcohol in presence of dry $\displaystyle \mathrm{HC} l$.
(b)
Why carboxylic acid is a stronger acid than phenol ?
(c)
Arrange the following compounds in increasing order of their reactivity towards $\displaystyle \mathrm{CH}_{3} \mathrm{MgBr}$:
(ii)
Write a chemical test to distinguish between propanal and propanone.
Write the main product in the following:
(i)
(ii)
Marking-scheme solution
(a) Acetal
(b) Because the carboxylate ion is more resonance stabilized than the phenoxide ion. (c) (i)
<smiles>CC(C)(C)C(=O)CCCC(=O)OCCC=O</smiles>
(ii) ($\displaystyle 1$) Add Iodine \(\displaystyle \left(\mathrm{I}_{2}\right), \mathrm{NaOH}\), and heat both the test tubes containing the given organic compounds. Propanone gives yellow precipitate \(\displaystyle \left(\mathrm{CH}_{3}\right)\) while propanal will not give yellow precipitate.
Aldehydes, Ketones and Carboxylic AcidsChemical Reactions of Aldehydes, Ketones and Carboxylic AcidsUnderstandcase_studymedium
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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.