Chapter 7 Alcohols Phenols and Ethers Intext Questions NCERT Solutions Class 12 Chemistry- PDF Download

Page No. 195

7.1. Classify the following as primary, secondary and tertiary alcohols:

Solution

Primary alcohol → (i), (ii), (iii)

Secondary alcohol → (iv), (v)

Tertiary alcohol → (vi)

7.2. Identify allylic alcohols in the above examples.

Solution

The alcohols given in (ii) and (vi) are allylic alcohols.

Page No. 198

7.3. Name the following compound according to IUPAC system.

Solution

(i) 3-Chloromethyl-2-isopropylpentan-1-ol

(ii) 2, 5-Dimethylhexane-1, 3-diol

(iii) 3-Bromocyclohexanol

(iv) Hex-1-en-3-ol

(v) 2-Bromo-3-methylbut-2-en-1-ol

Page No. 203

7.4. Show how are the following alcohols prepared by the reaction of a suitable Grignard reagent on methanal?

Solution

(i)

(ii)

7.5. Write structures of the products of the following reaction:

Solution

(i) Propene to Propene-2-ol

(ii) Methyl (2-oxocyclohexyl) ethanoate to Methyl (2-hydroxycyclohexyl) ethanoate

(iii) 2-Methylbutanal to 2-Methylbutan-1-ol

Page No. 213

7.6. Give structures of the products you would expect when each of the following alcohol reacts with (a) HCl-ZnCl₂ (b) HBr and (c) SOCl₂

(i) Butan-1-ol

(ii) 2-Methylbutan-2-ol

Solution

(a) Reaction with HCl-ZnCl₂:

(i) Primary alcohols do not react appreciably with Lucas’ reagent (HCl-ZnCl₂) at room temperature.

(ii) Tertiary alcohols react immediately with Lucas’ reagent.

(b) Reaction with HBr :

(i)

(ii)

(c) Reaction with SOCl₂:

(i)

(ii)

7.7. Predict the major product of acid catalysed dehydration of:

(i) 1-Methylcyclohexanol

(ii) Butan-1-ol

Solution

(i) 1-Methylcyclohexanol

(ii) Butan-1-ol

7.8. Ortho and para nitrophenols are more acidic than phenol. Draw the resonance structures of the corresponding phenoxide ions.

Solution

Resonance structure of the phenoxide ion

Resonance structures of p-nitrophenoxide ion

Resonance structures of o-nitrophenoxide ion

It can be observed that the presence of nitro groups increases the stability of phenoxide ion.

7.9. Write the equations involved in the following reactions:

(i) Reimer-Tiemann reaction

(ii) Kolbe’s reaction

Solution

(i) Reimer-Tiemann reaction: When phenol is treated with chloroform (CHCl₃) in the presence of sodium hydroxide, a −CHO group is introduced at the ortho position of the benzene ring.

This reaction is known as the Reimer-Tiemann reaction.

The intermediate is hydrolyzed in the presence of alkalis to produce salicyclaldehyde.

(ii) Kolbe’s reaction: When phenol is treated with sodium hydroxide, sodium phenoxide is produced. This sodium phenoxide when treated with carbon dioxide, followed by acidification, undergoes electrophilic substitution to give ortho-hydroxybenzoic acid as the main product. This reaction is known as Kolbe’s reaction.

7.10. Write the reactions of Williamson synthesis of 2-ethoxy-3-methylpentane starting from ethanol and 3-methylpentan-2-ol.

Solution

In Williamson synthesis, an alkyl halide reacts with an alkoxide ion. Also, it is an S_N2 reaction. In the reaction, alkyl halides should be primary having the least steric hindrance. Hence, an alkyl halide is obtained from ethanol and alkoxide ion from 3-methylpentan-2-ol.

7.11. Which of the following is an appropriate set of reactants for the preparation of 1-methoxy-4-nitrobenzene and why?

Solution

Set (ii) is an appropriate set of reactants for the preparation of 1-methoxy-4-nitrobenzene.

In set (i), sodium methoxide (CH₃ONa) is a strong nucleophile as well as a strong base. Hence, an elimination reaction predominates over a substitution reaction.

7.12. Predict the products of the following reactions:

(i) CH₃ −CH₂ −CH₂ −O – CH₃ +HBr →