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Q.33  When 3-methylbutan-2-ol is treated with HBr, the following reaction takes
          place:

         
        Give a mechanism for this reaction.
        (Hint : The secondary carbocation formed in step II rearranges to a more stable tertiary carbocation by a hydride ion shift from 3rd carbon atom.

Mechanism for the  reaction  3-methylbutan-2-ol is treated with HBr

 Q.32   Show how would you synthesise the following alcohols from appropriate alkenes?

  

(i) (ii) (iii) (iv)

Q.31 Write equations of the following reactions:  (iv) Friedel-Craft’s acetylation of anisole.

Friedel-Craft’s acetylation of anisole:

Q.31 Write equations of the following reactions:  (iii) Bromination of anisole in ethanoic acid medium.

Bromination of anisole in ethanoic acid medium:

Q.31  Write equations of the following reactions: (ii) Nitration of anisole.

Nitration of anisole:

Q.31 Write equations of the following reactions:
       (i) Friedel-Crafts reaction – alkylation of anisole.

Fridel Craft reaction(Alkylation):

Q.30. Write the mechanism of the reaction of HI with methoxymethane.

Following is the mechanism: 1. Protonation of methoxymethane 2. Nucleophilic attack of  3. If HI is in excess, then methanol formed in step 2 reacts with another HI molecule and gets converted to methyl iodide at a high temperature.

 Q.29  Explain the fact that in aryl alkyl ethers  (ii) it directs the incoming substituents to ortho and para positions in benzene ring.

The above resonating structures shows that the electron density increases more at the ortho and para positions as compared to the meta positions. Hence, the alkoxy group directs the incoming substituents to ortho and para positions in the benzene ring.

Q.29 Explain the fact that in aryl alkyl ethers (i) the alkoxy group activates the benzene ring towards electrophilic substitution and

Due to the +R effect of the alkoxy group, it increases the electron density of the benzene ring pushing electrons into the ring making the benzene ring activated towards electrophilic substitution reactions.

 Q.28  Write the equation of the reaction of hydrogen iodide with: (iii) benzyl ethyl ether.

Benzyl ethyl ether reacts with HI to give benzyl iodide and ethanol.

 Q.28 Write the equation of the reaction of hydrogen iodide with: (ii) methoxybenzene

Methoxybenzene reacts with HI to give phenol and iodomethane.

 Q 28  Write the equation of the reaction of hydrogen iodide with:
(i) 1-propoxypropane

1-propoxypropane reacts with HI to give propan-1-ol and 1-iodopropane as the products.

Q.27   Preparation of ethers by acid dehydration of secondary or tertiary alcohols is not a suitable method. Give reason.

The formation of ethers by dehydration of a primary alcohol is an SN2 reaction. In case of secondary or tertiary alcohols, the alkyl group is hindered and hence elimination dominates substitution. Therefore alkenes are formed in place of ethers.

 Q.26  How is 1-propoxypropane synthesised from propan-1-ol? Write mechanism of this reaction.

Propan-1-ol on dehydration using protic acids such as sulphuric acid gives 1-propoxypropane. Mechanism of this reaction: Formation of protonated alcohol. Formation of carbocation: It is the slowest step and hence, the rate determining step of the reaction. Formation of ethene by the elimination of a proton.  

Q.25  Illustrate with examples the limitations of Williamson synthesis for the preparation of certain types of ethers.

Williamson synthesis involves attack by alkoxide ion on a primary alkyl halide. But if secondary or tertiary alkyl halides are taken then alkenes would be produced because elimination would take place. This is because alkoxides are nucleophiles as well as strong bases. 

Q.24 Write the names of reagents and equations for the preparation of the following ethers by Williamson’s synthesis:  (iv) 1-Methoxyethane

Names of reagents and equations for the preparation of the1-Methoxyethane ether by Williamson’s synthesis:-

Q24  Write the names of reagents and equations for the preparation of the following ethers by Williamson’s synthesis:
(iii) 2-Methoxy-2-methylpropane

Names of reagents and equations for the preparation of the2-Methoxy-2-methylpropane ether by Williamson’s synthesis:-

Q.24  Write the names of reagents and equations for the preparation of the following ethers by Williamson’s synthesis:
(ii) Ethoxybenzene

Names of reagents and equations for the preparation of the Ethoxybenzene ether by Williamson’s synthesis:-  with NaBr as side product.

 Q.24   Write the names of reagents and equations for the preparation of the following ethers by Williamson’s synthesis:
(i) 1-Propoxypropane

Names of reagents and equations for the preparation of the 1-Propoxypropane ether by Williamson’s synthesis:-

Q.23 Give IUPAC names of the following ethers:

IUPAC names of the given ether is Ethoxybenzene
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