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Alcohols, Phenols and Ethers Set-2 MCQ Online Practice Test | Class 12 | Quiz Tweek

Alcohols, Phenols and Ethers Set-2

Practice Important MCQs for Alcohols, Phenols and Ethers — Chemistry, Class 12.

This chapter is central because it builds the core concepts behind acidity/basicity of alcohols and phenols, substitution mechanisms of alcohol derivatives, and the practical behavior of ethers (including cleavage and Williamson synthesis). These ideas repeatedly appear in board exams through reaction-based questions and in competitive exams through mechanism, stereochemistry, and equilibria (acid–base) problems.

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Q1. A solution contains equimolar amounts of phenol and ethanol. Given $pK_a(\text{phenol})=10$ and $pK_a(\text{ethanol})=16$ , the equilibrium constant $K$ for the proton-transfer reaction

\mathrm{C_6H_5OH}+\mathrm{CH_3CH_2O^-}\rightleftharpoons\mathrm{C_6H_5O^-}+\mathrm{CH_3CH_2OH}

is closest to:

(A)

$10^{-6}$

(B)

$1$

(C)

$10^{6}$

(D)

$10^{4}$

Q2. You have a mixture of phenol and anisole dissolved in hexane. Given $pK_a(\text{phenol})\approx 10$ and $pK_a(\mathrm{H_2CO_3})\approx 6.3$ , which aqueous wash will selectively extract phenol into the aqueous layer leaving anisole in the organic layer?

(A)

$5\%$ NaHCO $_3$ (aqueous)

(B)

$0.1\ \mathrm{M}$ NaOH (aqueous)

(C)

Dilute HCl (aqueous)

(D)

Water (aqueous)

Q3. An optically active sample of $(R)$ -2-butanol is treated separately under two sets of conditions to give 2-bromobutane: (i) excess conc. HBr and (ii) PBr $_3$ at low temperature. Which statement correctly describes the stereochemical outcome in the two cases?

(A)

HBr treatment gives inversion of configuration; PBr $_3$ gives racemic 2-bromobutane.

(B)

HBr treatment gives racemic 2-bromobutane; PBr $_3$ gives retention of configuration.

(C)

Both HBr and PBr $_3$ treatments give racemic 2-bromobutane.

(D)

HBr treatment gives racemic 2-bromobutane; PBr $_3$ gives 2-bromobutane with inversion of configuration.

Q4. Allyl phenyl ether ( $\mathrm{C_6H_5OCH_2CH=CH_2}$ ) on heating undergoes the Claisen rearrangement. The major product formed is:

(A)

o-Allylphenol (2-allylphenol), $\mathrm{C_6H_4(OH)(CH_2CH=CH_2)}$ (allyl at ortho position)

(B)

p-Allylphenol (4-allylphenol), $\mathrm{C_6H_4(OH)(CH_2CH=CH_2)}$ (allyl at para position)

(C)

Phenol + propene (cleavage products)

(D)

1-Propenyl phenyl ether (isomerization), $\mathrm{C_6H_5OCH=CHCH_3}$

Q5. Which of the following ethers cannot be prepared by a classical Williamson ether synthesis (alkoxide + alkyl halide under SN2 conditions)?

(A)

Diethyl ether, $\mathrm{CH_3CH_2OCH_2CH_3}$

(B)

Methyl tert-butyl ether, $\mathrm{CH_3OC(CH_3)_3}$

(C)

Anisole (methyl phenyl ether), $\mathrm{C_6H_5OCH_3}$

(D)

Methyl n-propyl ether, $\mathrm{CH_3OCH_2CH_2CH_3}$

Q6. Which of the following alcohols will undergo the fastest conversion to the corresponding alkyl bromide when treated with concentrated HBr under conditions where the reaction follows an SN1 pathway? (Consider carbocation stabilities.)

(A)

$CH_3CH_2CH_2CH_2OH$ ( $1$ -butanol)

(B)

$CH_3CH(OH)CH_2CH_3$ ( $2$ -butanol)

(C)

$(CH_3)_3C OH$ (tert-butanol)

(D)

$(CH_3)_2CHCH_2OH$ ( $2$ -methyl-1 $-$ propanol, isobutanol)

Q7. An ether A on treatment with excess hydroiodic acid ( $HI$ ) under reflux gives the major organic products $(CH_3)_3C I$ and $CH_3OH$ . Which ether A was used?

(A)

$CH_3OCH(CH_3)_2$ (methyl isopropyl ether)

(B)

$CH_3OC(CH_3)_3$ (methyl tert-butyl ether)

(C)

$CH_3OCH_2C_6H_5$ (methyl benzyl ether)

(D)

$C(CH_3)_3OC(CH_3)_3$ (di-tert-butyl ether)

Q8. Among the following phenols, which is the most acidic? Consider electronic (inductive and mesomeric) effects of the substituents.

(A)

$p$ -cresol ( $p$ - $CH_3$ -phenol)

(B)

phenol ( $C_6H_5OH$ )

(C)

$p$ -methoxyphenol ( $p$ - $OCH_3$ -phenol)

(D)

$p$ -nitrophenol ( $p$ - $NO_2$ -phenol)

Q9. Two phenols, $A$ (phenol) and $B$ ( $p$ -nitrophenol), are each treated under identical conditions with sodium hydride ( $NaH$ ) in dry acetone followed by excess methyl iodide ( $CH_3I$ ). Which statement best predicts which phenol is methylated faster and why?

(A)

Phenol is methylated faster because with $NaH$ deprotonation is rapid for both; the rate is governed by nucleophilicity of the phenoxide and the $p$ - $NO_2$ group on $B$ greatly reduces nucleophilicity.

(B)

$p$ -Nitrophenol is methylated faster because its greater acidity makes deprotonation (the rate-determining step) much easier than for phenol.

(C)

Both phenols are methylated at essentially the same rate because $NaH$ quantitatively forms the corresponding phenoxides before any methylation step.

(D)

Methylation fails for $p$ -nitrophenol because resonance stabilization of its phenoxide completely prevents nucleophilic attack on $CH_3I$ .

Q10. Which of the following ethers will be least susceptible to cleavage by concentrated HBr/HI under typical acid-mediated cleavage conditions (i.e., will resist C–O bond cleavage)?

(A)

$CH_3OC(CH_3)_3$ (methyl tert-butyl ether)

(B)

$CH_3OCH_2C_6H_5$ (methyl benzyl ether)

(C)

$CH_3OCH_2C(CH_3)_3$ (methyl neopentyl ether)

(D)

$CH_3CH_2OCH_3$ (ethyl methyl ether)

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