Chemistry Class 12 NCERT Solutions: Chapter 11 Alcohols Phenols and Ethers Part 4

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Q: 6. What is meant by hydroboration-oxidation reaction? Illustrate it with an example.

Answer:

The addition of borane followed by oxidation is known as the hydroboration-oxidation reaction. For example, propan-1-ol is produced by the hydroboration-oxidation reaction of propene. In this reaction, propene reacts with diborane to form trialkyl borane as an addition product. This addition product is oxidized to alcohol by hydrogen peroxide in the presence of aqueous sodium hydroxide.

Q 6 The Presence of Aqueous Sodium hydroxide

Q 6 the Presence of Aqueous Sodium Hydroxide

Q 6 The Presence of Aqueous Sodium hydroxide

Q: 7. Give the structures and IUPAC names of monohydric phenols of molecular formula .

Answer:

Q 7 1 The Structure and IUPAC names of Monohydric Phenols of Molecular

Q 7 1 the Structure and IUPAC Names of Monohydric Phenols

Q 7 1 The Structure and IUPAC names of Monohydric Phenols of Molecular

Q: 8. While separating a mixture of ortho and para nitrophenols by steam distillation, name the isomer which will be steam volatile. Give reason.

Answer:

Intramolecular H-bonding is present in o-nitrophenol. In p-nitrophenol, the molecules are strongly associated due to the presence of intermolecular bonding. Hence, o-nitrophenol is steam volatile.

Q 8 O-Nitrophenol is Steam Volatile

Q 8 O-Nitrophenol is Steam Volatile

Q 8 O-Nitrophenol is Steam Volatile

Q: 9. Give the equations of reactions for the preparation of phenol from cumene.

Answer:

To prepare phenol, cumene is first oxidized in the presence of air of cumene hydro peroxide.

Q 9 1 The Presence of Air of Cumene Hydro Peroxide

Q 9 1 the Presence of Air of Cumene Hydro Peroxide

Q 9 1 The Presence of Air of Cumene Hydro Peroxide

Then, cumene hydroxide is treated with dilute acid to prepare phenol and acetone as by products.

Q 9 2 Cumene Hydroxide is Treated with Dilute Acid to Prepare Phenol and Acetone as by Products

Q 9 2 Cumene Hydroxide Treated with Dilute Acid

Q 9 2 Cumene Hydroxide is Treated with Dilute Acid to Prepare Phenol and Acetone as by Products

Q: 10. Write chemical reaction for the preparation of phenol from chlorobenzene.

Answer:

Chlorobenzene is fused with (at and atm pressure) to produce sodium phenoxide, which gives phenol on acidification.

Q 10 Chlorobenzene is Fused With NaOH to Produce Sodium Phenoxide, which gives Phenol on Acidification

Q 10 Chlorobenzene Fused with NaOH and Phenol on Acidification

Q 10 Chlorobenzene is Fused With NaOH to Produce Sodium Phenoxide, which gives Phenol on Acidification

Q: 11. Write the mechanism of hydration of ethene to yield ethanol.

Answer:

The mechanism of hydration of ethene to form ethanol involves three steps.

Step 1:-

Protonation of ethene to form carbocation by electrophilic attack of

Q 11 1 Protonation of ethene to form carbocation by Electrophilic attack

Q 11 1 Protonation of Ethene by Electrophilic Attack

Q 11 1 Protonation of ethene to form carbocation by Electrophilic attack

Step 2:

Nucleophilic attack of water on carbocation:

Q 11 2 Nucleophilic Attack of Water on Carbocation

Q 11 2 Nucleophilic Attack of Water on Carbocation

Q 11 2 Nucleophilic Attack of Water on Carbocation

Step 3:

Deprotonation to form ethanol:

Q 11 3 Deprotonation to form Ethanol

Q 11 3 Deprotonation to Form Ethanol

Q 11 3 Deprotonation to form Ethanol