Chemistry Class 12 NCERT Solutions: Chapter 11 Alcohols Phenols and Ethers Part 5

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Q: 12. You are given benzene, conc. and . Write the equations for the preparation of phenol using these reagents.

Answer:

Q 12 Benzene Is Fused With H2SO4 And NaOH To Produce Phenol.

Q 12 Benzene is Fused with H2SO4 and NaOH to Produce Phenol.

Q 12 Benzene Is Fused With H2SO4 And NaOH To Produce Phenol.

Q: 13. Show how will you synthesize:

(i) 1-phenylethanol from a suitable alkene

(ii) cyclohexylmethanol using an alkyl halide by an reaction.

(iii) pentan-1-ol using a suitable alkyl halide?

Answer:

(i) By acid-catalyzed hydration of ethylbenzene (styrene), 1-phenylethanol can be synthesized.

Q 13 (i) Phenylethanol

Q 13 (I) Phenylethanol

Q 13 (i) Phenylethanol

(ii) When chloromethylcyclohexane is treated with sodium hydroxide, cyclohexylmethanol is obtained.

Q 13 (ii) Chloromethylcyclohexane Is Fused With NaOH To Produce Cyclohexylmethanol.

Q 13 (Ii) Chloromethylcyclohexane Fused with NaOH

Q 13 (ii) Chloromethylcyclohexane Is Fused With NaOH To Produce Cyclohexylmethanol.

(iii) When 1-chloropentane is treated with , pentan-1-ol is produced.

Q: 14. Give two reactions that show the acidic nature of phenol. Compare acidity of phenol with that of ethanol.

Answer:

The acidic nature of phenol can be represented by the following two reactions:

(i) Phenol reacts with sodium to give sodium phenoxide, liberating .

Q 14 i Phenol and Sodium Phenoxide

Q 14 I Phenol and Sodium Phenoxide

Q 14 i Phenol and Sodium Phenoxide

(ii) Phenol reacts with sodium hydroxide to give sodium phenoxide and water as by- products

Q 14 ii Sodium Phenoxide

Q 14 Ii Sodium Phenoxide

Q 14 ii Sodium Phenoxide

The acidity of phenol is more than that of ethanol. This is because after losing a proton, the phenoxide ion undergoes resonance and gets stabilized whereas Ethoxide ion does not.

Q 14 ii 1 The Acidity of Phenol is more than that of Ethanol

Q 14 Ii 1 the Acidity of Phenol is More Than That of Ethanol

Q 14 ii 1 The Acidity of Phenol is more than that of Ethanol

Q: 15. Explain why is ortho nitrophenol more acidic than ortho methoxyphenol?

Answer:

Q 15 o-Nitrophenol and o-Methoxyphenol

Q 15 O-Nitrophenol and O-Methoxyphenol

Q 15 o-Nitrophenol and o-Methoxyphenol

The nitro-group is an electron-withdrawing group. The presence of this group in the ortho position decreases the electron density in the bond. As a result, it is easier to lose a proton. Also, the o-nitrophenoxide ion formed after the loss of protons is stabilized by resonance. Hence, ortho nitrophenol is a stronger acid.

On the other hand, Methoxy group is an electron-releasing group. Thus, it increases the electron density in the bond and hence, the proton cannot be given out easily. For this reason, ortho-nitrophenol is more acidic than ortho-methoxyphenol.

Q: 16. Explain how does the group attached to a carbon of benzene ring activate i towards electrophilic substitution?

Answer:

The −OH group is an electron-donating group. Thus, it increases the electron density i the benzene ring as shown in the given resonance structure of phenol.

Q 16 The Benzene Ring as shown in the given Resonance Structure of Phenol

Q 16 Resonance Structure of Phenol

Q 16 The Benzene Ring as shown in the given Resonance Structure of Phenol

As a result, the benzene ring is activated towards electrophilic substitution.