Chemistry Class 12 NCERT Solutions: Chapter 11 Alcohols Phenols and Ethers Part 7 (For CBSE, ICSE, IAS, NET, NRA 2023)

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Q: 19. Write the mechanism of acid-catalysed dehydration of ethanol to yield ethene.


The mechanism of acid dehydration of ethanol to yield ethene involves the following three steps:

Step 1:

Protonation of ethanol to form ethyl oxonium ion:

Q_19_1_Protonation of Ethanol to Form Ethyl Oxonium Ion

Step 2:

Formation of carbocation (rate determining step) :

Q_19_2_Formation of Carbocation

Step 3:

Elimination of a proton to form ethene:

Q_19_3_Elimination of a Proton to Form Ethene

The acid consumed in step 1 is released in Step 3. After the formation of ethene, it is removed to shift the equilibrium in a forward direction

Q: 20. How are the following conversions carried out?

(i) Propene ⇾ Propan-2-ol

(ii) Benzyl chloride ⇾ Benzyl alcohol

(iii) Ethyl magnesium chloride ⇾ Propan-1-ol

(iv) Methyl magnesium bromide ⇾ 2-Methylpropan-2-ol


(i) If propene is allowed to react with water in the presence of an acid as a catalyst then propan-2-ol is obtained.

Q_20_i_Propene ⇾ Propan-2-Ol

(ii) If benzyl chloride is treated with (followed by acidification) then benzyl alcohol is produced

Q_20_ii_Benzyl Chloride ⇾ Benzyl Alcohol

(iii) When ethyl magnesium chloride is treated with methanal, an adduct is the produced which gives propan-1-ol on hydrolysis.

Q_20_iii_Ethyl Magnesium Chloride ⇾ Propan-1-Ol

(iv) When methyl magnesium bromide is treated with propane, an adduct is the product which gives 2-methylpropane-2-ol on hydrolysis.

Q_20_iv_Methyl Magnesium Bromide ⇾ 2-Methylpropan-2-Ol

Q: 21. Name the reagents used in the following reactions:

(i) Oxidation of a primary alcohol to carboxylic acid

(ii) Oxidation of a primary alcohol to aldehyde

(iii) Bromination of phenol to 2,4, 6-tribromophenol.

(iv) Benzyl alcohol to benzoic acid.

(v) Dehydration of propan-2-ol to propene

(vi) Butan-2-one to butan-2-ol.


(i) Acidified potassium permanganate

(ii) Pyridinium chlorochromate (PCC)

(iii) Bromine water

(iv) Acidified potassium permanganate

(v) phosphoric acid