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Aldehydes, Ketones and Carboxylic Acids Set-7 MCQ Online Practice Test | Class 12 | Quiz Tweek

Aldehydes, Ketones and Carboxylic Acids Set-7

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

This chapter is central for CBSE and competitive exams because it links key reaction patterns (Cannizzaro, aldol condensation, Michael addition, nucleophilic addition to carbonyls) with the underlying ideas of resonance, acidity, and soft–hard behavior. Mastery of these concepts allows you to predict major products quickly and solve both direct theory and application-based numerical/reasoning questions.

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Q1. Among the following benzoic acid derivatives, which is the strongest acid?

(A)

$p$ -Methoxybenzoic acid ( $p$ - $\mathrm{OCH_3C_6H_4COOH}$ )

(B)

$p$ -Nitrobenzoic acid ( $p$ - $\mathrm{NO_2C_6H_4COOH}$ )

(C)

Benzoic acid ( $\mathrm{C_6H_5COOH}$ )

(D)

$m$ -Nitrobenzoic acid ( $m$ - $\mathrm{NO_2C_6H_4COOH}$ )

Q2. Treatment of 2-cyclohexenone (an $\alpha,\beta$ -unsaturated ketone) with which reagent below will give predominantly the 1,4-conjugate (Michael) addition product (i.e., methyl at the $\beta$ -carbon) rather than 1,2-addition to the carbonyl?

(A)

$CH_3MgBr$ (Grignard reagent)

(B)

$LiAlH_4$

(C)

$NaBH_4$

(D)

$CH_3_2CuLi$ (Gilman reagent)

Q3. Assertion (A): When a mixture of benzaldehyde ( $\mathrm{C_6H_5CHO}$ ) and $p$ -nitrobenzaldehyde ( $p$ - $\mathrm{NO_2C_6H_4CHO}$ ) is treated with concentrated $NaOH$ , the crossed Cannizzaro reaction predominantly yields $p$ -nitrobenzyl alcohol ( $p$ - $\mathrm{NO_2C_6H_4CH_2OH}$ ) as the reduction product and benzoate as the oxidation product.
Reason (R): The $-NO_2$ group increases the electrophilicity of $p$ -nitrobenzaldehyde, making it the preferred hydride acceptor in the hydride-transfer step of the Cannizzaro mechanism.

(A)

Both A and R are true and R is the correct explanation for A.

(B)

Both A and R are true but R is not the correct explanation for A.

(C)

A is true but R is false.

(D)

A is false but R is true.

Q4. To obtain monoalkylation of acetone (giving predominantly 2-butanone) by reaction with $CH_3I$ , which of the following conditions will best minimize dialkylation and favour one‑time $\alpha$ -alkylation?

(A)

Aqueous $NaOH$ then $CH_3I$

(B)

$NaH$ (base) followed by $CH_3I$

(C)

Use of LDA at $-78^\circ\mathrm{C}$ to form the enolate, then addition of $CH_3I$

(D)

$K_2CO_3$ in acetone then $CH_3I$

Q5. Which reagent will selectively reduce the aldehyde group of $p$ -nitrobenzaldehyde ( $p$ - $\mathrm{NO_2C_6H_4CHO}$ ) to the corresponding alcohol without reducing the nitro group?

(A)

$H_2$ / Pd

(B)

$NaBH_4$

(C)

$LiAlH_4$

(D)

$Sn$ / HCl

Q6. Among the following carboxylic acids, which is the strongest acid (considering resonance and inductive effects)?

(A)

Acetic acid, $CH_3COOH$

(B)

Benzoic acid, $C_6H_5COOH$

(C)

p-nitrobenzoic acid, $p\text{-}NO_2\text{-}C_6H_4COOH$

(D)

p-methoxybenzoic acid, $p\text{-}OCH_3\text{-}C_6H_4COOH$

Q7. When benzaldehyde ( $C_6H_5CHO$ ) and acetaldehyde ( $CH_3CHO$ ) are treated with dilute NaOH at low temperature, the major organic product is:

(A)

Benzyl alcohol, $C_6H_5CH_2OH$

(B)

Cinnamaldehyde, $C_6H_5CH=CHCHO$

(C)

Benzoic acid, $C_6H_5COOH$

(D)

Dibenzalacetone, $C_6H_5CH=CHCOCH=CHC_6H_5$

Q8. Which of the following has the most acidic α-hydrogen (i.e., lowest pKa for the α-CH) and therefore forms the most stabilized enolate?

(A)

Acetylacetone, $CH_3COCH_2COCH_3$

(B)

Acetaldehyde, $CH_3CHO$

(C)

Acetone, $CH_3COCH_3$

(D)

Ethyl acetate, $CH_3COOCH_2CH_3$

Q9. A ketone on exhaustive oxidation with hot alkaline KMnO $_4$ yields acetic acid ( $CH_3COOH$ ) and propionic acid ( $CH_3CH_2COOH$ ) in equal amounts. Which ketone is most likely the starting compound?

(A)

3-Pentanone, $CH_3CH_2COCH_2CH_3$

(B)

2-Pentanone, $CH_3COCH_2CH_2CH_3$

(C)

Cyclohexanone, $C_6H_{10}O$

(D)

2-Butanone, $CH_3COCH_2CH_3$

Q10. Which reagent will preferentially give conjugate (1,4-) addition to the α,β-unsaturated ketone $CH_3CH=CHCOCH_3$ (adding to the β-carbon) while leaving the carbonyl largely intact?

(A)

Sodium borohydride, NaBH $_4$

(B)

Organocuprate (Gilman reagent), $R_2CuLi$

(C)

Lithium aluminium hydride, LiAlH $_4$

(D)

Hydrogen cyanide, HCN

Q11. Arrange the following carbonyl compounds in decreasing order of reactivity toward nucleophilic hydride addition by NaBH $_4$ at 0°C: benzaldehyde ( $\mathrm{C_6H_5CHO}$ ), cyclohexanone ( $\mathrm{C_6H_{10}O}$ ), 2,4,6-trimethylbenzaldehyde ( $2,4,6\text{-}(CH_3)_3C_6H_2CHO$ ), cinnamaldehyde ( $\mathrm{C_6H_5CH=CHCHO}$ ).

(A)

benzaldehyde $>$ cyclohexanone $>$ cinnamaldehyde $>$ 2,4,6-trimethylbenzaldehyde

(B)

benzaldehyde $>$ cinnamaldehyde $>$ cyclohexanone $>$ 2,4,6-trimethylbenzaldehyde

(C)

cyclohexanone $>$ benzaldehyde $>$ cinnamaldehyde $>$ 2,4,6-trimethylbenzaldehyde

(D)

2,4,6-trimethylbenzaldehyde $>$ benzaldehyde $>$ cinnamaldehyde $>$ cyclohexanone

Q12. Which of the following compounds will be effectively deprotonated by $NaOEt$ in ethanol to give the corresponding enolate (i.e., equilibrium strongly favours deprotonation)? (i) acetone ( $\mathrm{CH_3COCH_3}$ ), (ii) ethyl acetate ( $\mathrm{CH_3COOEt}$ ), (iii) ethyl acetoacetate ( $\mathrm{CH_3COCH_2COOEt}$ ), (iv) diethyl malonate ( $\mathrm{(EtOOC)CH_2COOEt}$ ).

(A)

(i) and (iii) only

(B)

(i) and (ii) only

(C)

(i) only

(D)

(iii) and (iv) only

Q13. Assertion (A): Enolates derived from stabilized 1,3-dicarbonyl compounds (e.g., diethyl malonate) preferentially undergo Michael (1,4-) addition to $\alpha,\beta$ -unsaturated carbonyl compounds rather than direct 1,2-addition to the carbonyl.
Reason (R): Stabilized enolates are resonance-delocalised and therefore "softer" nucleophiles; the $\beta$ -carbon of an $\alpha,\beta$ -unsaturated carbonyl is a softer electrophilic site than the carbonyl carbon, so soft–soft interaction favours 1,4-addition.

(A)

Both A and R are true, and R correctly explains A

(B)

Both A and R are true, but R does not correctly explain A

(C)

A is true but R is false

(D)

Both A and R are false

Q14. In an aldol condensation between benzaldehyde and acetone under basic conditions (NaOH), if two equivalents of benzaldehyde react with one equivalent of acetone, the major isolated product is:

(A)

benzyl alcohol (reduction product)

(B)

benzalacetone (mono-aldol condensation product, i.e., one benzaldehyde per acetone)

(C)

dibenzalacetone (the product from condensation of two benzaldehyde molecules with one acetone)

(D)

benzoin (product of benzaldehyde self-condensation via benzoin condensation)

Q15. Arrange the following benzoic acid derivatives in order of increasing acidity (least acidic → most acidic): $p$ -methoxybenzoic acid, benzoic acid, $p$ -nitrobenzoic acid, $o$ -nitrobenzoic acid.

(A)

$o$ -nitrobenzoic acid $<$ $p$ -nitrobenzoic acid $<$ benzoic acid $<$ $p$ -methoxybenzoic acid

(B)

$p$ -methoxybenzoic acid $<$ benzoic acid $<$ $p$ -nitrobenzoic acid $<$ $o$ -nitrobenzoic acid

(C)

benzoic acid $<$ $p$ -methoxybenzoic acid $<$ $o$ -nitrobenzoic acid $<$ $p$ -nitrobenzoic acid

(D)

$p$ -nitrobenzoic acid $<$ $o$ -nitrobenzoic acid $<$ benzoic acid $<$ $p$ -methoxybenzoic acid

...and 5 more challenging questions available in the interactive simulator.

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