HS 2 Chemistry Unit 7: Alcohols, Phenols and Ethers

 

🔷 1. Introduction to Alcohols, Phenols, and Ethers

Q1. What are alcohols, phenols, and ethers?
Ans:

• Alcohols: Organic compounds where –OH group is attached to an aliphatic carbon (e.g., CH₃OH).

• Phenols: Compounds where –OH is attached to aromatic carbon (e.g., C₆H₅OH).

• Ethers: Compounds where an alkoxy (–OR) or aryloxy (–OAr) group replaces a hydrogen atom in a hydrocarbon (e.g., CH₃OCH₃).

Key Words (with Bengali meaning):

• Hydrocarbon = হাইড্রোকার্বন

• Hydroxyl group = হাইড্রোক্সিল গ্রুপ

• Aliphatic = অ্যালিফ্যাটিক

• Aromatic = অ্যারোমেটিক

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🔷 2. Classification

Q2. How are alcohols classified based on the number of –OH groups?
Ans:

• Monohydric: One –OH group

• Dihydric: Two –OH groups

• Trihydric: Three –OH groups

• Polyhydric: More than three –OH groups

Q3. How are alcohols classified based on the type of carbon attached to –OH?
Ans:

• Primary (1°): –OH attached to a primary carbon

• Secondary (2°): –OH attached to a secondary carbon

• Tertiary (3°): –OH attached to a tertiary carbon

Key Words:

• Monohydric = এক-অ্যালকোহল

• Primary carbon = প্রাথমিক কার্বন

• Tertiary carbon = তৃতীয় কার্বন

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🔷 3. Nomenclature

Q4. What are the rules for naming alcohols in the IUPAC system?
Ans:

• Replace ‘e’ of the alkane with ‘ol’.

• Number the chain from the end closest to –OH.

• Use prefixes di-, tri- for polyhydric alcohols.

Key Words:

• IUPAC = আইইউপিএসি

• Suffix = প্রত্যয়

• Prefix = উপসর্গ

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🔷 4. Preparation of Alcohols

Q5. How are alcohols prepared from alkenes?
Ans:
(i) Acid-catalysed hydration
(ii) Hydroboration-oxidation

Q6. How are alcohols prepared from carbonyl compounds?
Ans:

• Aldehydes/ketones reduced by H₂/Ni or NaBH₄/LiAlH₄

• Carboxylic acids and esters reduced by LiAlH₄

Q7. What happens when a Grignard reagent reacts with an aldehyde/ketone?
Ans:

• It forms an alcohol after hydrolysis.

• With methanal → 1° alcohol

• With other aldehydes → 2° alcohol

• With ketones → 3° alcohol

Key Words:

• Hydration = জলায়ন

• Reduction = হ্রাস প্রক্রিয়া

• Grignard reagent = গ্রিগনার্ড বিকারক

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🔷 5. Preparation of Phenols

Q8. Mention methods of preparation of phenols.
Ans:

1. From haloarenes

2. From benzenesulphonic acid

3. From diazonium salts

4. From cumene

Key Words:

• Diazonium salt = ডায়াজোনিয়াম লবণ

• Sulphonation = সালফোনেশন

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🔷 6. Physical Properties

Q9. Why do alcohols have higher boiling points than ethers and hydrocarbons?
Ans:
Because of strong intermolecular hydrogen bonding in alcohols.

Q10. Why are lower alcohols soluble in water?
Ans:
Due to their ability to form hydrogen bonds with water.

Key Words:

• Boiling point = স্ফুটনাঙ্ক

• Solubility = দ্রাব্যতা

• Hydrogen bonding = হাইড্রোজেন বন্ধন

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🔷 7. Chemical Reactions

(a) Reactions of Alcohols

Q11. How do alcohols show acidic nature?
Ans:
They react with active metals (like Na) to form alkoxides and H₂.

Q12. What is esterification?
Ans:
Alcohols + Carboxylic acids → Esters + Water (in presence of H₂SO₄)

Q13. How do alcohols form alkenes?
Ans:
By acid-catalysed dehydration at high temperature.

Key Words:

• Ester = ইস্টার

• Alkene = অ্যালকিন

• Dehydration = জল অপসারণ

(b) Reactions of Phenols

Q14. Why are phenols more acidic than alcohols?
Ans:
Due to resonance stabilization of phenoxide ion and higher electronegativity of sp² carbon.

Q15. What is Kolbe’s Reaction?
Ans:
Phenol + NaOH → Sodium phenoxide → reacts with CO₂ → Salicylic acid

Q16. What is Reimer-Tiemann Reaction?
Ans:
Phenol + CHCl₃ + NaOH → Salicylaldehyde

Q17. Name some electrophilic substitution reactions of phenol.
Ans:

• Nitration

• Halogenation

• Sulphonation

Key Words:

• Phenoxide = ফিনোক্সাইড

• Resonance = অনুরণন

• Electrophile = ইলেক্ট্রোফাইল

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🔷 8. Preparation of Ethers

Q18. What are the two methods of preparing ethers?
Ans:

1. Dehydration of alcohols

2. Williamson synthesis (alkyl halide + sodium alkoxide)

Key Words:

• Ether = ইথার

• Dehydration = জল অপসারণ

• Williamson synthesis = উইলিয়ামসন সংশ্লেষণ

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🔷 9. Chemical Reactions of Ethers

Q19. How do ethers react with HI or HBr?
Ans:
They are cleaved into alcohol and alkyl halide via SN1 or SN2 mechanism.

Q20. What is the role of alkoxy group in aryl ethers?
Ans:
It activates the aromatic ring for electrophilic substitution (ortho-para directing).

Key Words:

• Cleavage = বিভাজন

• Alkyl halide = অ্যালকাইল হ্যালাইড

🧪 Worksheet: Alcohols, Phenols and Ethers

📘 Part A: Very Short Answer (1 mark each)

1. What is the IUPAC name of CH₃OH?

2. Write one example each of a primary, secondary, and tertiary alcohol.

3. What is the common name of C₆H₅OH?

4. What is meant by the term "esterification"?

5. Write the formula of cumene.

6. What happens when phenol is treated with zinc dust?

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📗 Part B: Short Answer (2–3 marks each)

7. Differentiate between alcohols and phenols based on structure and example.

8. Explain Kolbe’s reaction with an equation.

9. What are allylic and benzylic alcohols? Give one example each.

10. Why are phenols more acidic than alcohols?

11. Write the mechanism of acid-catalysed dehydration of ethanol.

12. What are the conditions required for the preparation of alcohol by hydroboration-oxidation?

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📙 Part C: Long Answer (5 marks each)

13. Write the chemical equations for preparation of alcohols from:
    a) Alkenes (any two methods)
    b) Carbonyl compounds
    c) Grignard reagents

14. How will you prepare phenol by the following methods?
    a) From haloarenes
    b) From diazonium salts
    c) From cumene

15. Compare the physical properties (boiling point and solubility) of alcohols, phenols and ethers. Explain the reason.

16. Describe the chemical reactions of alcohols involving:
    a) Reaction with metal
    b) Dehydration
    c) Oxidation (Primary and secondary alcohols)

17. Explain Reimer-Tiemann reaction with an example. What is the major product?

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📒 Part D: Fill in the Blanks (1 mark each)

18. Methanol is also called __________.

19. The IUPAC name of glycerol is __________.

20. In phenol, the –OH group is attached to __________ hybridised carbon.

21. In Williamson synthesis, ethers are formed by the reaction between __________ and __________.

22. Anisole is an example of __________ ether.

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📕 Part E: Match the Following (1 mark each)

A	B
23. Acidity of phenol	A. SN2 mechanism
24. Phenol + CHCl₃ + NaOH	B. 2,4,6-Tribromophenol
25. Phenol + Br₂ (in water)	C. Reimer-Tiemann Reaction
26. Alkyl halide + sodium alkoxide	D. Resonance stabilization
27. Preparation of ether	E. Williamson synthesis

📘 Part F: Key Word Matching (with Bengali meanings)

Match the English key terms with their Bengali meanings:

English Term	Bengali Meaning
28. Alcohol	A. ইথার
29. Phenol	B. ফিনল
30. Ester	C. অ্যালকোহল
31. Ether	D. ইস্টার
32. Dehydration	E. জল অপসারণ