This chapter is central for Class 12 board as well as competitive exams because it links structure with key reaction pathways—ether formation/cleavage, acidity of phenols (resonance + substituent effects), and practical conversions between alcohols, ethers, and haloalkanes. Many JEE/NEET-style questions test mechanism-based regioselectivity and quantitative equilibrium ideas (especially using and dissociation).
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Questions
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Marking
Q1. A aqueous solution of phenol has . Using the approximation (where is the dissociated concentration), estimate the percent dissociation of phenol at equilibrium. (Use .)
Q2. When phenetole () is treated with excess , which organic halide is formed predominantly?
1-Phenylethyl bromide,
Benzyl bromide,
2-Phenylethyl bromide,
Ethyl bromide,
Q3. 2-Methoxypropane (isopropyl methyl ether, ) on reaction with excess at 298 K gives which alkyl bromide as the major product?
Methyl bromide,
Isopropyl bromide,
An approximately equal mixture of and
An approximately mixture of and (favoring )
Q4. Assertion (A): Williamson ether synthesis between sodium phenoxide () and methyl iodide () gives anisole () in good yield.
Reason (R): The reaction proceeds via formation of a methyl carbocation () which then reacts with phenoxide to give the ether.
Both A and R are true and R is the correct explanation of A.
Both A and R are true but R is not the correct explanation of A.
A is true but R is false.
A is false but R is true.
Q5. Two phenols are separately dissolved: (A) p-nitrophenol with and (B) p-methoxyphenol with , each at . Using and the approximation , estimate the ratio of phenoxide concentrations at equilibrium.
Q6. Among the following compounds, which has the highest boiling point?
(diethyl ether)
(2‑butanol)
(‑butanol)
(tert‑butanol)
Q7. Which of the following is the most acidic in aqueous solution? Consider resonance and intramolecular hydrogen‑bonding effects.
‑Nitrophenol (‑nitrophenol, ‑NO_2C_6H_4OH$)
‑Nitrophenol (‑nitrophenol, ‑NO_2C_6H_4OH$)
‑Nitrophenol (‑nitrophenol, ‑NO_2C_6H_4OH$)
Phenol ()
Q8. Treatment of ethoxyisopropane () with excess HI yields which major alkyl halide as product (consider mechanistic preference under acidic cleavage)?
Isopropyl iodide ()
A 1:1 mixture of isopropyl iodide and ethyl iodide
n-Propyl iodide () (major due to rearrangement)
Ethyl iodide ()
Q9. Which statement about the cleavage of ethers by HBr is correct?
Diethyl ether () is cleaved faster than methyl tert‑butyl ether () because SN2 on primary carbons always outcompetes SN1 on tertiary centers.
Methyl tert‑butyl ether () is cleaved faster than diethyl ether because protonation followed by formation of a stable tert‑butyl carbocation (SN1) lowers activation energy; major products include and .
Both ethers are cleaved by the same SN2 pathway at the methyl end, so their rates are nearly identical.
Diethyl ether gives + , whereas methyl tert‑butyl ether gives predominantly methyl bromide () under identical conditions.
Q10. Assertion (A): A tertiary alkyl halide cannot be converted to the corresponding tertiary ether by Williamson ether synthesis (SN2), but the same ether can be obtained by acid‑catalysed dehydration of a tertiary alcohol.
Reason (R): Williamson synthesis requires SN2 displacement at the alkyl carbon (which is sterically hindered in tertiary halides leading to elimination), whereas acid‑catalysed dehydration proceeds via a stable tertiary carbocation (SN1) that can be attacked by an alcohol to give the ether.
Both A and R are true and R is the correct explanation of A.
Both A and R are true but R is not the correct explanation of A.
A is true but R is false.
Both A and R are false.