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Chemistry · 2023 · 4 marks
Aldehydes, Ketones and Carboxylic AcidsChemical Reactions of Aldehydes, Ketones and Carboxylic Acids4 marksUnderstandcase study
CBSE 2023 · Region 2 · Set 1 · Q31
The carbon - oxygen double bond is polarised in aldehydes and ketones due to higher electronegativity of oxygen relative to carbon. Therefore they…
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 ?
(i)
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)
(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.
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