Chapter 11 Alcohols Phenols and Ethers Solutions
Question - 41 : - Explain the fact that in aryl alkyl ethers
Answer - 41 : -
(i) The alkoxy group activates the benzene ring towards electrophilic substitution and
(ii) It directs the incoming substituents to ortho and para positions in benzene ring.
Answer
(i)
In aryl alkyl ethers, due to the +R effect of the alkoxygroup, the electron density in the benzene ring increases as shown in thefollowing resonance structure.
Thus, benzene is activated towards electrophilicsubstitution by the alkoxy group.
(ii) Itcan also be observed from the resonance structures that the electron densityincreases more at the ortho and para positions than at the meta position. As aresult, the incoming substituents are directed to the ortho and para positionsin the benzene ring.
Question - 42 : - Write the mechanism of the reaction of HI withmethoxymethane.
Answer - 42 : -
The mechanism of the reaction of HI with methoxymethaneinvolves the following steps:
Step1: Protonationof methoxymethane:
Step2: Nucleophilic attack of I−:
Step3:
When HI is in excess and the reaction is carried out at ahigh temperature, the methanol formed in the second step reacts with another HImolecule and gets converted to methyl iodide
Question - 43 : - Write equations of the following reactions:
Answer - 43 : -
(i) Friedel-Crafts reaction−alkylation of anisole.
(ii) Nitration of anisole.
(iii) Bromination of anisole in ethanoic acid medium.
(iv) Friedel-Craft’s acetylation of anisole.
Answer
(i)
(ii)
(iii)
(iv)
Question - 44 : - Show how would you synthesise the following alcohols fromappropriate alkenes?
Answer - 44 : -
(i)
(ii)
(iii)
(iv)
Answer
The given alcohols can be synthesized by applying Markovnikov’srule of acid-catalyzed hydration of appropriate alkenes.
(i)
(ii)
(iii)
Acid-catalyzed hydration of pent-2-ene also producespentan-2-ol but along with pentan-3-ol.
Thus, the first reaction is preferred over the second oneto get pentan-2-ol.
(iv)
Question - 45 : - When 3-methylbutan-2-ol is treated with HBr, the followingreaction takes place:
Answer - 45 : - 
Give a mechanism for this reaction.
(Hint : The secondary carbocation formed in step IIrearranges to a more
stable tertiary carbocation by a hydri
Answer
The mechanism of the given reaction involves the followingsteps:
Step 1: Protonation
Step 2: Formationof 2° carbocation by the elimination of a water molecule
Step 3: Re-arrangement by the hydride-ion shift
Step 4: Nucleophilic attack
