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Aldehydes, Ketones and Carboxylic Acids Set-1 MCQ Online Practice Test | Class 12 | Quiz Tweek

Aldehydes, Ketones and Carboxylic Acids Set-1

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

This chapter is crucial for CBSE and competitive exams because it builds the core understanding of carbonyl (C=O) chemistry—how aldehydes and ketones react with nucleophiles, how carboxylic acids form salts/esters, and how key named reactions (Cannizzaro, aldol, Michael addition, Rosenmund reduction/Grignard strategies, etc.) can be predicted from structure and conditions. Mastery here directly improves scoring in reaction-based MCQs and helps in organic synthesis reasoning required for board exams, JEE, and NEET.

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Q1. Which of the following compounds will undergo the Cannizzaro reaction on treatment with concentrated aqueous $NaOH$ ?

(A)

$CH_3CHO$ (ethanal)

(B)

$C_6H_5CHO$ (benzaldehyde)

(C)

$CH_3COCH_3$ (acetone)

(D)

$CH_3CH_2CHO$ (propanal)

Q2. Which of the following carboxylic acids undergoes facile thermal decarboxylation (loss of $CO_2$ on gentle heating) due to stabilization of the transition state by resonance/enol formation?

(A)

$CH_3CH_2COOH$ (propionic acid)

(B)

$C_6H_5COOH$ (benzoic acid)

(C)

$HOOCCH_2CH_2COOH$ (succinic acid)

(D)

$CH_3COCH_2COOH$ (acetoacetic acid, 3-oxobutanoic acid)

Q3. Which reagent converts an acyl chloride $RCOCl$ into the corresponding methyl ketone $RCOCH_3$ in a controlled way without over-addition to give a tertiary alcohol?

(A)

$(CH_3)_2CuLi$ (lithium dimethylcuprate)

(B)

$CH_3MgBr$ (methylmagnesium bromide)

(C)

$CH_3OH$ (methanol)

(D)

$CH_3Li$ (methyl lithium)

Q4. For the $\alpha,\beta$ -unsaturated ketone $CH_3CH=CHCOCH_3$ , which reagent will predominantly give 1,4-conjugate (Michael-type) addition rather than direct 1,2-addition to the carbonyl?

(A)

$LiAlH_4$

(B)

$NaBH_4$

(C)

$(CH_3)_2CuLi$ (lithium dimethylcuprate)

(D)

$CH_3Li$

Q5. Which of the following sequences will selectively furnish acetophenone ( $C_6H_5COCH_3$ ) from methyl benzoate ( $C_6H_5COOCH_3$ ) without producing the tertiary alcohol resulting from over-addition of $CH_3^-$ ?

(A)

Direct treatment of $C_6H_5COOCH_3$ with excess $CH_3MgBr$ , then acid work-up

(B)

Convert $C_6H_5COOCH_3$ to N‑methoxy‑N‑methylbenzamide (Weinreb amide, $C_6H_5CON(CH_3)OCH_3$ ), then treat with $CH_3MgBr$ and acid work-up

(C)

Convert $C_6H_5COOCH_3$ to $C_6H_5COCl$ and treat with $CH_3Li$

(D)

Treat $C_6H_5COOCH_3$ directly with excess $CH_3Li$ , then acid work-up

Q6. At pH $5.0$ , which of the following carboxylic acids will be more than $90\%$ dissociated? (Use Henderson–Hasselbalch; given $pK_a$ values.)
$\;$ {benzoic acid: } $pK_a=4.20$ ;,; ${acetic acid: }$ pK_a=4.76 $\;,\;$ {p $-$ nitrobenzoic acid: } $pK_a=3.47$ ;,; ${p$ - $methoxybenzoic acid: }$ pK_a=4.50$

(A)

Benzoic acid ( $pK_a=4.20$ )

(B)

Acetic acid ( $pK_a=4.76$ )

(C)

p-nitrobenzoic acid ( $pK_a=3.47$ )

(D)

p-methoxybenzoic acid ( $pK_a=4.50$ )

Q7. A mixture of benzaldehyde (2 mol) and acetone (1 mol) is treated with dilute $\mathrm{NaOH}$ at room temperature. The major organic product isolated is:

(A)

Dibenzalacetone, $\mathrm{PhCH{=}CHCOCH{=}CHPh}$

(B)

Benzoin, $\mathrm{PhCH(OH)COPh}$

(C)

Cannizzaro products: benzoic acid + benzyl alcohol

(D)

Benzylideneacetone (mono-condensation), $\mathrm{PhCH{=}CHCOCH_3}$

Q8. Alkylation of $2$ -methylcyclohexanone with excess $\mathrm{CH_3I}$ under two sets of conditions gives different major products. Which mapping is correct?
(i) Deprotonation with LDA in THF at $-78^\circ\mathrm{C}$ , then $\mathrm{CH_3I}$ ; (ii) Deprotonation with $\mathrm{NaOEt}$ in EtOH at $25^\circ\mathrm{C}$ , then $\mathrm{CH_3I}$ .

(A)

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

(B)

(i) same product as (ii) — mainly $2,6$ -Dimethylcyclohexanone

(C)

(i) $2,6$ -Dimethylcyclohexanone ; (ii) mixture of many polysubstituted products

(D)

(i) $2,6$ -Dimethylcyclohexanone (kinetic alkylation) ; (ii) $2,2$ -Dimethylcyclohexanone (thermodynamic alkylation)

Q9. A volatile compound $X$ with formula $C_3H_6O$ gives the following qualitative test results: bright orange/yellow precipitate with $2,4$ -DNP, no silver mirror with Tollen's reagent, and a positive iodoform test (yellow precipitate). Which compound is $X$ ?

(A)

Propanal, $\mathrm{CH_3CH_2CHO}$

(B)

Acetone, $\mathrm{CH_3COCH_3}$

(C)

Allyl alcohol, $\mathrm{CH_2=CHCH_2OH}$

(D)

Cyclopropyl alcohol, $c$ - $\mathrm{C_3H_6O}$

Q10. For the conjugated enone (chalcone) $\mathrm{PhCOCH{=}CHPh}$ , which of the following reagents will predominantly give 1,4-conjugate (Michael-type) addition of a methyl group (i.e., conjugate addition) rather than direct 1,2-addition to the carbonyl?

(A)

$\mathrm{(CH_3)_2CuLi}$ (Gilman reagent)

(B)

$\mathrm{CH_3MgBr}$ (methyl Grignard)

(C)

$\mathrm{NaBH_4}$

(D)

$\mathrm{H_2}$ / Pd-C

Q11. For acetic acid ( $\mathrm{CH_3COOH}$ ) with $pK_a = 4.76$ , what is the pH of a solution in which 75% of acetic acid is dissociated?

(A)

$pH = 4.76$

(B)

$pH \approx 5.24$

(C)

$pH \approx 4.28$

(D)

$pH \approx 5.76$

Q12. Rank the following benzaldehydes by their rate of nucleophilic hydride addition with $\mathrm{NaBH_4}$ (fastest → slowest): $p$ -nitrobenzaldehyde ( $p$ -NO $_2$ - $\mathrm{C_6H_4CHO}$ ), benzaldehyde ( $\mathrm{C_6H_5CHO}$ ), $p$ -methoxybenzaldehyde ( $p$ -OCH $_3$ - $\mathrm{C_6H_4CHO}$ ).

(A)

$\mathrm{C_6H_5CHO} > p$ -NO $_2$ - $\mathrm{C_6H_4CHO} > p$ -OCH $_3$ - $\mathrm{C_6H_4CHO}$

(B)

$p$ -OCH $_3$ - $\mathrm{C_6H_4CHO} > \mathrm{C_6H_5CHO} > p$ -NO $_2$ - $\mathrm{C_6H_4CHO}$

(C)

$p$ -NO $_2$ - $\mathrm{C_6H_4CHO} > p$ -OCH $_3$ - $\mathrm{C_6H_4CHO} > \mathrm{C_6H_5CHO}$

(D)

$p$ -NO $_2$ - $\mathrm{C_6H_4CHO} > \mathrm{C_6H_5CHO} > p$ -OCH $_3$ - $\mathrm{C_6H_4CHO}$

Q13. An equimolar mixture of benzaldehyde ( $\mathrm{C_6H_5CHO}$ ) and $p$ -nitrobenzaldehyde ( $p$ -NO $_2$ - $\mathrm{C_6H_4CHO}$ ) is treated with concentrated NaOH (Cannizzaro reaction). Which pair of organic products will predominate?

(A)

$p$ -NO $_2$ -benzyl alcohol ( $p$ -NO $_2$ - $\mathrm{C_6H_4CH_2OH}$ ) and benzoic acid ( $\mathrm{C_6H_5COOH}$ )

(B)

benzyl alcohol ( $\mathrm{C_6H_5CH_2OH}$ ) and $p$ -nitrobenzoic acid ( $p$ -NO $_2$ - $\mathrm{C_6H_4COOH}$ )

(C)

both aldehydes are reduced to their alcohols (no acid formed)

(D)

an equal mixture of both alcohols and both acids

Q14. Arrange the following carbonyl compounds in order of decreasing extent of hydration (formation of geminal diol) in aqueous solution at 25°C: formaldehyde ( $\mathrm{HCHO}$ ), acetaldehyde ( $\mathrm{CH_3CHO}$ ), acetone ( $\mathrm{(CH_3)_2CO}$ ), benzaldehyde ( $\mathrm{C_6H_5CHO}$ ).

(A)

$\mathrm{HCHO} > \mathrm{CH_3CHO} > \mathrm{C_6H_5CHO} > \mathrm{(CH_3)_2CO}$

(B)

$\mathrm{CH_3CHO} > \mathrm{HCHO} > \mathrm{(CH_3)_2CO} > \mathrm{C_6H_5CHO}$

(C)

$\mathrm{HCHO} > \mathrm{CH_3CHO} > \mathrm{(CH_3)_2CO} > \mathrm{C_6H_5CHO}$

(D)

$\mathrm{(CH_3)_2CO} > \mathrm{CH_3CHO} > \mathrm{HCHO} > \mathrm{C_6H_5CHO}$

Q15. A compound X (molecular formula $C_8H_8O_2$ ) gives a positive iodoform test, a negative Tollens test, and on oxidation with acidified $\mathrm{KMnO_4}$ yields $p$ -hydroxybenzoic acid. Which of the following is X?

(A)

$p$ -Methoxybenzaldehyde, $p$ -OCH $_3$ – $\mathrm{C_6H_4CHO}$

(B)

$p$ -Hydroxyacetophenone, $p$ -HO– $\mathrm{C_6H_4COCH_3}$

(C)

$p$ -Methylbenzoic acid, $p$ -CH $_3$ – $\mathrm{C_6H_4COOH}$

(D)

$p$ -Methoxyacetophenone, $p$ -OCH $_3$ – $\mathrm{C_6H_4COCH_3}$

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