Quiz Tweek

Preparing your workspace...

Aldehydes, Ketones and Carboxylic Acids Set-5 MCQ Online Practice Test | Class 12 | Quiz Tweek

Aldehydes, Ketones and Carboxylic Acids Set-5

Practice Important MCQs for Aldehydes, Ketones and Carboxylic Acids — Chemistry, Class 12.

This chapter is crucial for board and competitive exams because it builds the core understanding of carbonyl reactivity—how aldehydes/ketones undergo oxidation, reduction, hydration, nucleophilic addition, and base-promoted rearrangements (like aldol/Claisen–Schmidt and Cannizzaro). It also links electronic effects (resonance/inductive) to reaction rates and product outcomes, and frequently appears in mechanism-based and reasoning-based MCQs across CBSE and entrance exams.

Minutes

Questions

1 / -0

Marking

Question Bank Preview

Q1. 0.10 mol of propanal ( $CH_3CH_2CHO$ ) is completely combusted in excess oxygen. The number of moles of $O_2$ required is:

(A)

$0.20\ \text{mol}$

(B)

$0.30\ \text{mol}$

(C)

$0.40\ \text{mol}$

(D)

$0.50\ \text{mol}$

Q2. When equimolar benzaldehyde ( $C_6H_5CHO$ ) and cyclohexanone ( $C_6H_{10}O$ ) are treated with catalytic $NaOH$ at room temperature, the major product formed is:

(A)

$2\text{-(phenylmethylene)cyclohexanone}$ (benzylidene cyclohexanone)

(B)

Equal moles of benzoic acid ( $C_6H_5CO_2H$ ) and benzyl alcohol ( $C_6H_5CH_2OH$ ) by Cannizzaro reaction

(C)

Self‑condensation product of cyclohexanone (cyclohexanone dimer/aldol type product)

(D)

Benzyl alcohol ( $C_6H_5CH_2OH$ ) as the sole major product

Q3. Arrange the following compounds in increasing order of rate of base‑catalysed α‑halogenation (i.e., ease of enolization): (i) $C_6H_5CHO$ (benzaldehyde), (ii) $CH_3COOCH_2CH_3$ (ethyl acetate), (iii) $CH_3COCH_3$ (acetone), (iv) $CH_3CHO$ (acetaldehyde). Which order is correct?

(A)

(ii) < (iv) < (iii) < (i)

(B)

(i) < (iii) < (ii) < (iv)

(C)

(ii) < (i) < (iii) < (iv)

(D)

(i) < (ii) < (iii) < (iv)

Q4. Consider base‑catalysed hydrolysis (saponification) of the following esters: methyl $p$ ‑methoxybenzoate, methyl benzoate, methyl $p$ ‑nitrobenzoate. Predict their relative rates of saponification under identical alkaline conditions. Which order (fastest → slowest) is correct?

(A)

methyl $p$ ‑methoxybenzoate > methyl benzoate > methyl $p$ ‑nitrobenzoate

(B)

methyl $p$ ‑nitrobenzoate > methyl benzoate > methyl $p$ ‑methoxybenzoate

(C)

methyl benzoate > methyl $p$ ‑methoxybenzoate > methyl $p$ ‑nitrobenzoate

(D)

methyl $p$ ‑methoxybenzoate > methyl $p$ ‑nitrobenzoate > methyl benzoate

Q5. Baeyer–Villiger oxidation of $2$ ‑butanone ( $CH_3COCH_2CH_3$ ) with a peroxyacid proceeds via migration of one alkyl group. Which ester will be formed predominantly?

(A)

methyl propanoate ( $CH_3CH_2COOCH_3$ )

(B)

methyl butanoate ( $CH_3CH_2CH_2COOCH_3$ )

(C)

ethyl acetate ( $CH_3COOCH_2CH_3$ )

(D)

2‑butanol ( $CH_3CH(OH)CH_2CH_3$ )

Q6. When equimolar amounts of acetaldehyde ( $CH_3CHO$ ) and acetone ( $CH_3COCH_3$ ) are separately treated with aqueous HCN under identical conditions, which gives the higher yield of cyanohydrin and why?

(A)

$CH_3COCH_3$ — greater yield because ketones have a more polar C=O than aldehydes

(B)

Both give comparable yields because $CN^-$ addition depends only on concentration of $CN^-$

(C)

$CH_3CHO$ — greater yield because aldehydes are less sterically hindered and their carbonyl carbon is more electrophilic than in ketones

(D)

$CH_3COCH_3$ — greater yield because the resulting cyanohydrins from ketones are less likely to revert to the carbonyl due to steric protection

Q7. Arrange the following benzaldehyde derivatives in decreasing reactivity toward nucleophilic addition of $CN^{-}$ (rate of cyanohydrin formation): $p$ -nitrobenzaldehyde ( $p$ - $NO_2$ - $C_6H_4$ CHO), benzaldehyde ( $C_6H_5$ CHO), $p$ -methoxybenzaldehyde ( $p$ - $OCH_3$ - $C_6H_4$ CHO).

(A)

$p$ - $NO_2$ - $C_6H_4$ CHO ;>; $C_6H_5$ CHO ;>; $p$ - $OCH_3$ - $C_6H_4$ CHO

(B)

$p$ - $OCH_3$ - $C_6H_4$ CHO ;>; $C_6H_5$ CHO ;>; $p$ - $NO_2$ - $C_6H_4$ CHO

(C)

$C_6H_5$ CHO ;>; $p$ - $NO_2$ - $C_6H_4$ CHO ;>; $p$ - $OCH_3$ - $C_6H_4$ CHO

(D)

$p$ - $NO_2$ - $C_6H_4$ CHO ;>; $p$ - $OCH_3$ - $C_6H_4$ CHO ;>; $C_6H_5$ CHO

Q8. Under strongly alkaline conditions (excess $OH^-$ ), which benzaldehyde derivative will undergo the Cannizzaro reaction most rapidly and why?

(A)

$C_6H_5$ CHO (benzaldehyde) — moderate rate because there are no strong substituent effects

(B)

$p$ - $OCH_3$ - $C_6H_4$ CHO (p-anisaldehyde) — fastest because $-OCH_3$ stabilizes intermediates by resonance donation

(C)

$p$ - $Cl$ - $C_6H_4$ CHO (p-chlorobenzaldehyde) — fastest because chlorine's weak $-I$ effect increases electrophilicity sufficiently

(D)

$p$ - $NO_2$ - $C_6H_4$ CHO (p-nitrobenzaldehyde) — fastest because the strong electron-withdrawing $-NO_2$ increases carbonyl electrophilicity and facilitates hydride transfer in the Cannizzaro step

Q9. When benzaldehyde ( $C_6H_5$ CHO) is treated with acetone ( $CH_3COCH_3$ ) in presence of dilute $NaOH$ , the major isolated product after dehydration is:

(A)

Self-condensation product of acetone (mesityl oxide, $CH_3COCH=C(CH_3)_2$ )

(B)

Cross-aldol condensation product $C_6H_5CH=CHCOCH_3$ (i.e., the $\alpha,\beta$ -unsaturated ketone from acetone enolate + benzaldehyde)

(C)

Benzoin ( $C_6H_5CH(OH)COC_6H_5$ ) formed by benzoin condensation

(D)

Cannizzaro products: benzoic acid and benzyl alcohol (from hydride transfer)

Q10. Alkylation of 2-methylcyclohexanone under different conditions gives different regioisomers. Predict the major methylation product (position of new $CH_3$ ) when 2-methylcyclohexanone is treated with $CH_3I$ after (i) deprotonation with LDA in THF at $-78^\circ C$ , and (ii) deprotonation with NaOEt in EtOH at room temperature.

(A)

(i) $2,2$ -Dimethylcyclohexanone; (ii) $2,6$ -Dimethylcyclohexanone

(B)

(i) No reaction (kinetic enolate too unstable); (ii) Mixture of regioisomers

(C)

(i) $2,6$ -Dimethylcyclohexanone (kinetic alkylation at the less hindered $\alpha$ -carbon); (ii) $2,2$ -Dimethylcyclohexanone (thermodynamic alkylation at the more substituted $\alpha$ -carbon)

(D)

(i) $2,6$ -Dimethylcyclohexanone; (ii) $2,6$ -Dimethylcyclohexanone (both give same product due to ring constraints)

Q11. Among the following carbonyl compounds, which will exist predominantly as its geminal diol ( $RCH(OH)_2$ ) in aqueous solution? Consider the hydration equilibrium $RCHO + H_2O \rightleftharpoons RCH(OH)_2$ and factors such as resonance, steric hindrance and electron-withdrawing effects.

(A)

Acetone ( $CH_3COCH_3$ )

(B)

Formaldehyde ( $HCHO$ )

(C)

Benzaldehyde ( $C_6H_5CHO$ )

(D)

Acetaldehyde ( $CH_3CHO$ )

Q12. A mixture of benzaldehyde ( $C_6H_5CHO$ ) and acetone ( $CH_3COCH_3$ ) in molar ratio 2:1 is treated with $NaOH$ in ethanol and heated. Which is the major organic product formed under these conditions?

(A)

Benzoin ( $C_6H_5CH(OH)COC_6H_5$ )

(B)

Cannizzaro products: benzyl alcohol ( $C_6H_5CH_2OH$ ) and sodium benzoate ( $C_6H_5COONa$ )

(C)

Mesityl oxide ( $CH_3COCH=C(CH_3)_2$ ) from acetone self-condensation

(D)

Dibenzalacetone ( $C_6H_5CH=CHCOCH=CHC_6H_5$ )

Q13. Which of the following compounds has the most acidic $\alpha$ -hydrogen (lowest $pK_a$ ) and is therefore most easily enolized?

(A)

Ethyl acetate ( $CH_3COOEt$ )

(B)

Acetone ( $CH_3COCH_3$ )

(C)

Acetylacetone ( $CH_3COCH_2COCH_3$ )

(D)

Ethyl acetoacetate ( $CH_3COCH_2COOEt$ )

Q14. Assertion: On treatment of an $\alpha,\beta$ -unsaturated ketone such as $CH_2=CHCOCH_3$ with one equivalent of an organolithium reagent ( $RLi$ ), the predominant product is the 1,2-addition (attack at the carbonyl) rather than 1,4-conjugate addition.
Reason: Organolithium reagents are hard nucleophiles that preferentially attack the electrophilic carbonyl carbon, whereas organocuprates (Gilman reagents) are softer nucleophiles that favor 1,4-conjugate addition.

(A)

Both Assertion and Reason are true, and Reason correctly explains the Assertion.

(B)

Both Assertion and Reason are true, but Reason does not correctly explain the Assertion.

(C)

Assertion is true but Reason is false.

(D)

Assertion is false but Reason is true.

Q15. Ethyl acetoacetate ( $CH_3COCH_2COOEt$ ) is treated with $NaOEt$ followed by $CH_3I$ , then the ester is hydrolysed ( $H_3O^+$ ) and the resulting acid is heated to effect decarboxylation. The major organic product obtained after these steps is:

(A)

2-Butanone ( $CH_3COCH_2CH_3$ )

(B)

3-Methyl-2-butanone ( $CH_3COCH(CH_3)CH_3$ )

(C)

2-Methylpropanoic acid ( $(CH_3)_2CHCOOH$ )

(D)

2-Methyl-1-propanol ( $CH_3CH(CH_3)CH_2OH$ )

More Quizzes for Class 12

Explore other chapters and subjects, or view all quizzes for this class.

Quiz Tweek

Aldehydes, Ketones and Carboxylic Acids Set-5

Question Bank Preview

More Quizzes for Class 12

Chemistry

Mathematics

Physics