Important Questions for Class 12 Chapter 11 - Alcohols, Phenols and Ethers

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Important questions based on NCERT syllabus for Chapter 11 - Alcohols, Phenols and Ethers:

Question-1: Give reasons for the following statement: ortho-nitrophenol is more acidic than ortho methoxy phenol.

Solution:
The nitro – group is an electron-withdrawing group. The existence of this group in the ortho position decreases the electron density in the O – H bond. Consequently, it is easier to give away a proton. Furthermore, the o -nitrophenoxide ion formed after the loss of protons is stabilized by resonance. Therefore, ortho nitrophenol is a stronger acid. In contrast, methoxy group is an electron – releasing group. Hence, it increases the electron density in the O – H bond & thus, losing proton is not possible easily. Therefore, ortho – nitrophenol is more acidic than ortho – methoxyphenol.

Question-2: List out the the reagents used in the reactions given below :
(i) Butan – 2 – one to butan – 2 – ol.
(ii) Dehydration of propan – 2 – ol to propene.
(iii) Benzyl alcohol to benzoic acid
(iv) Bromination of phenol to 2 , 4 , 6 – tribromophenol.
(v) Oxidation of a primary alcohol to aldehyde.
(vi) Oxidation of a primary alcohol to carboxylic acid.

Solution:
(i) NaBH4 or LiAlH4
(ii) 85 % phosphoric acid
(iii) Acidified potassium permanganate
(iv) Bromine water
(v) Pyridinium chlorochromate ( PCC )
(vi) Acidified potassium permanganate

Question-3: Reason the following statement : Acid dehydration of tertiary or secondary alcohols is not a suitable technique for synthesis of ethers.

Solution:
The synthesis of ethers with dehydration of alcohol is a bimolecular reaction (SN2) which involves the attack of an alcohol molecule on a protonated alcohol molecule. In the method, the alkyl group should be unhindered. In case of secondary or tertiary alcohols, the alkyl group is hindered. As a result, elimination dominates substitution. Hence, in place of ethers, alkenes are formed.