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cbse 12th Standard Chemistry Alcohols , Phenols and Ethers Important Questions And Answers Study Material - QB365 Set A

Published on: 25/10/2025

Question Set A

cbse 12th Standard Chemistry Alcohols , Phenols and Ethers Important Questions And Answers Study Material - QB365

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Std: 12th Standard CBSE - Chemistry

chapter: Alcohols , Phenols and Ethers - Important Questions And Answers

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Questions:

Generic 2

5 x 2 = 10

Explain the mechanism of following reaction:

What happens when benzene diazonium chloride is heated with water?

Arrange the following in decreasing order of their acidic character:

Write the chemical equation for the preparation of phenol from benzene using oleum and sodium hydroxide.

How would you convert ethanol to ethene?

Generic 5

4 x 5 = 20

Predict the products of the following reactions:

Give structures of the products you would expect when each of the following alcohol reacts with (a) \(HCl-Zn{ Cl }_{ 2 }\), (b) \(HBr\) and (c) \(SO{ Cl }_{ 2 }\) .
(i) Butan-1-o1
(ii) 2-Methylbutan-2-o1

A compound A (C₄H₁₀O) is found to be soluble in concentrated sulphuric acid. (A) does not react with sodium metal or potassium permanganate. When (A) is heated with excess of HI, it gives a single alkyl halide. Deduce the structure of compound (A) and explain all the reactions involved.

Write equations of the following reactions:
(i) Friedel-Crafts reaction - alkylation in anisole,
(ii) Nitration of anisole
(iii) Bromination of anisole in ethanoic acid medium,
(iv) Friedel- Crafts acetylation of anisole.

Generic 3

10 x 3 = 30

10.

(i) What happens when phenol reacts with
(a) conc. HNO₃ and
(b) CHCl₃ in presence of aqueous NaOH followed by acidification?
(ii) Why does the reaction of CH₃ONa with (CH₃)₃C - Br gives 2-methylpropene and not (CH₃)₃ C - O-O-OCH₃?

11.

Predict the products of the following reaction:
\(\text { (i) } \mathrm{CH}_{3}-\mathrm{CH}=\mathrm{CH}_{2} \frac{\left(\text { i) } \mathrm{B}_{2} \mathrm{H}_{6}\right.}{\text { (ii) } 3 \mathrm{H}_{2} \mathrm{O}_{2} / \mathrm{OH}^{-}} \text {? }\)
\(\text { (ii) } \mathrm{C}_{6} \mathrm{H}_{5}-\mathrm{OH} \stackrel{\mathrm{Br}_{2}(a q)}{\longrightarrow} \text { ? }\)
\(\text { (iii) } \mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{OH} \stackrel{\mathrm{Cu} / 573 \mathrm{~K}}{\longrightarrow} \text { ? }\)

12.

The following is not an appropriate reaction for the preparation of tert-butyl methyl ether:
\(\begin{equation} \mathrm{CH}_{3} \mathrm{ONa}+\left(\mathrm{CH}_{3}\right)_{3} \mathrm{C}-\mathrm{Cl} \longrightarrow\left(\mathrm{CH}_{3}\right)_{3} \mathrm{C}-\mathrm{OCH}_{3} \end{equation}\)
(i) What would be the major product of the given reaction?
(ii) Write a suitable reaction for the preparation of tert-butyl methyl ether, specifying the names of re agents used. Justify your answer in both cases.

13.

Compound A having molecular formula C₄H₁₀O , is found to be soluble in concentrated sulphuric acid. It does not react with sodium metal or potassium permanganate. On heating with excess of HI, it gives a single alkyl halide. Deduce the structure of compound A and explain all the reactions.

14.

Show how will you synthesise
(i) 1-phenyl ethanol from a suitable alkene?
(ii) cyclohexyl methanol using an alkyl halide by an S_N2 mechanism?
(iii) pentan-1-ol using an alkyl halide?

15.

How is tert-butyl alcohol obtained from acetone?

16.

How do you convert the following:
(i) Phenol to anisole
(ii) Propan-2-ol to 2-methylpropan-2-o1
(iii) Aniline to phenol

17.

Write the main products(s) in each of the following reactions:

18.

Write the structures of the major products expected from the following reactions:
(a) Mononitration of 3-methylphenol
(b) Dinitration of 3-methylphenol
(c) Mononitration of phenyl methanoate.

19.

Name the reagents used in the following reactions:
(i) Benzyl alcohol to benzoic acid.
(ii) Dehydration of propan-2-ol to propene.
(iii) Butan-2-one to butan-2-ol.

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Answers Key:

Generic 2

5 x 2 = 10

(ii) > (ii) > (i)

Generic 5

4 x 5 = 20

(i)

(ii)

(iii)

(iv)

(i)
\(\begin{array}{c} \mathrm{CH}_{3}-\mathrm{CH}_{2}-\mathrm{CH}_{2}-\mathrm{CH}_{2}-\mathrm{OH} \frac{\mathrm{HCl} \cdot \mathrm{ZnCl}_{2}}{\longrightarrow} \text { No reaction } \\ \quad \text { Butan }-1-\mathrm{ol} \end{array}\)
Primary alcohols do not react appreciably with Lucas' reagent (HCl-ZnCl₂) at room temperature.
(ii)

Tertiary alcohols react immediately with Lucas' reagent.
(b)
(i)

(ii)

(c)
(i)

(ii)

(i) Since compound A (C₄H₁₀O) does not react with Na metal or KMnO₄, it cannot be an alcohol.
(ii) Since compound A dissolves in cone, H₂SO₄, it may be an ether.
(iii) Since ether A on heating with excess of HI gives a single alkyl halide, therefore, ether (A) must be symmetrical. Now the only symmetrical ether having M.F. C₄HIOO is diethyl ether (CH₃CH₂OCH₂CH₃).

(i)

(ii)

(iii)

(iv)

Generic 3

10 x 3 = 30

10.

11.

\(\text { (i) } \mathrm{CH}_{3}-\mathrm{CH}=\mathrm{CH}_{2} \frac{\left(\text { i) } \mathrm{B}_{2} \mathrm{H}_{6}\right.}{\text { (ii) } 3 \mathrm{H}_{2} \mathrm{O}_{2} / \mathrm{OH}^{-}}{\longrightarrow} \mathrm{CH}_{3}-\mathrm{CH}_{2}-\mathrm{CH}_{2} \mathrm{OH}\)
propene propane-1-ol

12.

As the given alkyl halide is tertiary in nature, therefore on reaction with sodium methoxide, elimination reaction takes place in place of substitution and hence, alkene is formed as a major product. Therefore, in the given reaction, 2-methyl propene is formed as a major product.

13.

(i) As compound A does not react with sodium metal or potassium permanganate, it cannot be an alcohol.
(ii) As compound A dissolves in conc. H₂SO₄, it may be an ether.
(iii) As compound A on heating with excess of ill, gives a single alkyl halide, therefore compound A must be a symmetrical ether.
(iv) The only symmetrical ether having molecular formula C₄H₁₀O is diethyl ether. Thus, compound A is diethyl ether,
\(\begin{equation} \mathrm{CH}_{3}-\mathrm{CH}_{2}-\mathrm{O}-\mathrm{CH}_{2}-\mathrm{CH}_{3} \end{equation}\)
\(\begin{equation} \mathrm{CH}_{3} \mathrm{CH}_{2}-\mathrm{O}-\mathrm{CH}_{2} \mathrm{CH}_{3} \stackrel{\text { Conc. } \mathrm{H}_{2} \mathrm{SO}_{4}}{\longrightarrow} \end{equation}\)

14.

(i) On adding H₂O to ethenyl benzene in the presence of dil. H₂SO₄, we get 1-phenyl ethanol.

(ii) Hydrolysis of cyclohexyl methyl bromide by aqueous NaOH gives cyclohexyl methanol.

(iii) Hydrolysis of 1-bromopentane by aqueous NaOH, gives pentan-1-ol.

15.

(a) This is because pcc is a mild oxidising agent and can oxide methanol to methanal only while KMnO₄ being strong oxidising agent oxidises it to methanoic acid.
(b) Because esterification rxn is reversible and presence of base (pyridine) neutralises HCl produced during reaction thus promoting forward reaction.

16.

17.

(i) \({ CH }_{ 3 }-\overset { \underset { | }{ { CH }_{ 3 } } }{ \underset { \overset { | }{ { CH }_{ 3 } } }{ C } } -O-{ CH }_{ 3 }+HI\longrightarrow { CH }_{ 3 }-\overset { \underset { | }{ { CH }_{ 3 } } }{ \underset { \overset { | }{ { CH }_{ 3 } } }{ C } } -I+\underset { Methanol }{ { CH }_{ 3 }OH } \)
(ii) \({ CH }_{ 3 }-CH={ CH }_{ 2 }\overset { (i){ B }_{ 2 }{ H }_{ 6 } }{ \underset { (ii)3{ H }_{ 2 }{ O }_{ 2 }/{ H }^{ - } }{ \longrightarrow } } { CH }_{ 3 }{ CH }_{ 2 }{ CH }_{ 2 }OH\)