WBJEE: Important Questions and Study Notes for Phenols and Ethers

In this article, we bring to you the notes of chapter Phenols and Ethers based on the latest pattern and syllabus of WBJEE 2018. About 2-3 questions have always been asked from this chapter in the examination. This is the perfect revision material which students can follow before appearing for the examination.

Students can learn the following topics here:

1. Preparation of Phenol,

(a) From haloarenes,

(b) From benzenesulphonic acid,

(c) From diazonium salts and

(d) From cumene

2. Physical properties of Phenol,

3. Chemical properties of Phenol,

(a) Electrophilic aromatic substitution,

(i) Nitration and

(ii) Halogenation

(b) Kolbe's reaction,

(c) Reimer-Tiemann reaction,

(d) Reaction of Phenol with zinc dust and

(e) Oxidation

4. Preparation of Ethers and

(a) By dehydration of alcohols and

(b) Williamson synthesis

5. Physical properties of Ether

About the notes:

1. These notes are prepared by Subject Experts of Chemistry after the detailed analysis of latest syllabus and pattern of the examination.

2. To make students understand the concepts, some solved questions are also included here.

3. It will provide you the complete overview of the chapter.

4. Students can refer these notes before the examination to save their precious time.

5. Students can easily understand the difficulty level of the questions which can be asked in coming examination with the help of the solved questions given here.

About the Exam:

West Bengal Joint Entrance Examination (WBJEE) is a state level common entrance test organized by West Bengal Joint Entrance Examinations Board for admission to the Undergraduate Level Engineering and Medical Courses through a common entrance test in the State of West Bengal.

WBJEE: Important Questions and Preparation Tips – Atomic Structure

Important Concepts:

Phenols: Phenols are the chemical compounds that consist of hydroxyl group bonded directly to aromatic hydrocarbon group. They are also called Phenolics.

Classification of alcohols:

The various reactions involving the preparation of Phenols are given below:

Physical Properties of Phenol:

• Simplest phenols are liquid or low melting solid.
• Phenols have high boiling points.
• Solubility decreases with increase in size of aryl group.
• They are colourless, but they are easily oxidized by atmospheric air and become coloured compounds.

Ethers: Ethers are organic compounds in which an oxygen atom is bonded to two alkyl groups or aryl groups. Therefore, ethers can be represented as R–O–R’ where R and R' may be alkyl or aryl groups.

When the two substituent groups (R and R’) are identical, then the ether is called a symmetrical ether, otherwise if these two groups are different, then the ether is known as an unsymmetrical ether.

Preparation of Ether:

• By dehydration of alcohols
• Williamson synthesis

By dehydration of alcohols                          

• On dehydration of alcohols in the presence of protic acid H₂SO₄. H₃PO₄ alkene or ether is formed depending on the reaction conditions

Williamson synthesis

• This is used for the synthesis of ether.
• Alkyl halide reacts with sodium alkoxide to produce ether.
• The reaction involves S_N2 mechanism.
• Primary alkyl halide gives best result.
• In case of tertiary halides elimination competes over substitution and no ether is formed

Physical Properties of ether:

• Ethers are more water-soluble than alkanes, because water molecules have H-bond with them.
• The boiling point of ether are high comparable to the alkanes.

Chemical Bonding: Hybridisation – Important Questions & Preparation Tips

Some important solved questions with solutions are given below:

Question 1:

(I) 1,2-dihydroxy benzene

(II) 1, 3-dihydroxy benzene

(III) 1, 4-dihydroxy benzene

(IV) Hydroxy benzene

The increasing order or boiIing points of above mentioned alcohols is

(a) I<II<III<IV

(b) I<II<IV<III

(c) IV<I<II< III

(d) IV<II<I<III

Solution 1:

All dihydroxy benzene will have higher boiling points than monohydroxy benzene. Also, among dihydroxy benzenes, 1, 2 -di-hydroxy benzene has lowest boiling point due to intramolecular H-bonding.

That means monohydroxy benzene has lowest boiling point out of the given compounds.

Hence, the correct option is (c).

Question 2:

Which of the following alkyl halides is least reactive in the Williamson synthesis of ether?

(a) CH₃CH₂CH₂Br                              

(b) CH₃CH₂CH₂Cl                              

(c) (CH₃)₃CCH₂Br                              

(d) CH₂= CH - CH₂Cl

Solution 2:

(CH₃)₃CCH₂Br is less reactive in the Williamson synthesis of ether.

Hence, the correct option is (c).

Question 3:

Hydrogen bonding is maximum in

(a) Ethanol                       

(b) Diethyl ether              

(c) Ethyl chloride            

(d) Ethyl amine

Solution 3:

Ethers and halides do not form H-bonding whereas oxygen being more electronegative forms excessive H-bonding

Hence, the correct option is (a).

Question 4:

The acidic hydrolysis of ether (X) shown below is fastest when

(a) One phenyl group is replaced by a methyl group

(b) One phenyl group is replaced by a para-methoxylphenyl group

(c) Two phenyl groups are replaced by two para-methoxylphenyl groups

(d) No structural change is made to X

Solution 4:

The more stable is carbocation formed during S_N1 reaction faster is the reaction.

Para-methoxylphenyl group is electron donating which stablises the carbocation.

Hence, the correct option is (c).

Conclusion:

The content given here is presented in a very systematic manner which makes it easier to study. These notes are based on the latest syllabus and pattern of the examination. With the help of solved questions given here aspirants can get familiar with the difficulty level of the question paper.

WBJEE 2018: Notification, Application, Dates, Eligibility, Exam Pattern, Syllabus

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