Aldehyde ketones & carboxylic Acid MCQs for NEET — Chemistry Questions with Answers

The organic compound X with molecular formula $C_5H_{10}O$ is described as yielding phenyl hydrazone and giving a negative response to both the iodoform test and Tollen's test. This means that it is not a methyl ketone or an aldehyde, as these would give positive results with iodoform and Tollen's tests, respectively. Additionally, the compound produces n-pentane on reduction, indicating that the keto group is in the middle of the chain. Therefore, the compound is most likely pentan-3-one.

When $CH_3CHCl_2$ (1,1-dichloroethane) is heated with aqueous KOH, it undergoes a hydrolysis reaction to form acetaldehyde ($CH_3CHO$). The reaction proceeds through the formation of a geminal diol intermediate, which then loses water to form the aldehyde.

The formation of cyanohydrin from a ketone is an example of nucleophilic addition. In this reaction, the nucleophile (cyanide ion, $CN^-$) attacks the electrophilic carbonyl carbon of the ketone, forming a new carbon-carbon bond and resulting in the formation of cyanohydrin.

The reagent $ NaOH I_2 /H^+ $ is used for the iodoform test, which specifically converts methyl ketones (or secondary alcohols adjacent to a methyl group) into carboxylic acids with one carbon less. In the case of butan-2-one, it will be converted into propanoic acid using this reagent.

Cross aldol condensation occurs between two different aldehydes and ketones. This type of reaction involves the formation of a carbon-carbon bond between the alpha carbon of one carbonyl compound and the carbonyl carbon of another, resulting in a β-hydroxy ketone or β-hydroxy aldehyde.

Fehling's solution is used to distinguish between aldehydes and ketones. $C_2H_5CHO$ (an aldehyde) will reduce Fehling's solution, forming a red precipitate of copper(I) oxide, while $(CH_3)_2CO$ (a ketone) will not react with Fehling's solution.

Hexane-2,4-dione has the most acidic hydrogen due to the presence of two carbonyl groups (C=O) that increase the acidity of the hydrogen atoms on the methylene group (CH_2) between them. The inductive and resonance effects of the carbonyl groups make the hydrogen atoms more acidic.

$CH_3CHO$ (acetaldehyde) reacts with HCN to form $CH_3CH(OH)CN$, which upon hydrolysis gives $CH_3CH(OH)COOH$ (lactic acid). The reaction involves the addition of HCN followed by hydrolysis.