- Learning Objectives
- Name alcohols, phenols, and ethers according to the IUPAC system of nomenclature.
- Discuss the reactions involved in the preparation of alcohols from alkenes, aldehydes, ketones, and carboxylic acids.
- Discuss the reactions involved in the preparation of phenols from haloarenes, benzene sulphonic acids, diazonium salts, and cumene.
- Discuss the reactions for the preparation of ethers from alcohols and alkyl halides.
- Correlate physical properties of alcohols, phenols, and ethers with their structures.
- Discuss chemical reactions of alcohols, phenols, and ethers on the basis of their functional groups.
Alcohols: Phenols and Ethers
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Learning Objectives
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Revision Notes & Summary
TopNotes on Alcohols, Phenols, and Ethers
Overview
Alcohols, phenols, and ethers are important organic compounds with various applications in industry and daily life. They are characterized by the presence of hydroxyl (-OH) groups.
IUPAC Nomenclature
- Ethers: Named by identifying the alkyl or aryl groups attached to the oxygen atom. For example:
- C₂H₅OCH₂−CH−CH₃: Ethyl isopropyl ether
- CH₃OCH₂CH₂Cl: Methoxyethyl chloride
Classification
Alcohols
- Monohydric: Contain one hydroxyl group (e.g., CH₃OH - Methanol)
- Dihydric: Contain two hydroxyl groups (e.g., C₂H₄(OH)₂ - Ethylene glycol)
- Trihydric: Contain three hydroxyl groups (e.g., C₃H₈O₃ - Glycerol)
Phenols
- Monohydric Phenols: Contain one hydroxyl group attached to a benzene ring (e.g., C₆H₅OH - Phenol)
- Dihydric and Trihydric Phenols: Contain two or three hydroxyl groups respectively.
Ethers
- Simple (Symmetrical): Same alkyl or aryl groups (e.g., C₂H₅OC₂H₅ - Diethyl ether)
- Mixed (Unsymmetrical): Different alkyl or aryl groups (e.g., C₂H₅OCH₃ - Ethyl methyl ether)
Reactions
Williamson Synthesis
- A method for preparing ethers by reacting an alkoxide with a primary alkyl halide.
- Example: 1-Propoxypropane can be synthesized from sodium propoxide and 1-bromopropane.
Acid Dehydration
- Not suitable for certain ethers due to the formation of carbocations that can rearrange.
Reactions with Hydrogen Iodide
- Ethers react with hydrogen iodide to yield alcohols and alkyl iodides.
- Example: CH₃OCH₃ + HI → CH₃I + CH₃OH
Physical Properties
- Boiling Points: Alcohols and phenols have higher boiling points than hydrocarbons due to hydrogen bonding.
- Solubility: Alcohols are generally more soluble in water than hydrocarbons of comparable molecular mass due to the presence of the hydroxyl group.
Limitations of Williamson Synthesis
- Not effective for secondary or tertiary alkyl halides due to steric hindrance.
Key Concepts
- Acidity of Phenols: Ortho and para nitrophenols are more acidic than phenol due to resonance stabilization of the phenoxide ion.
- Electrophilic Substitution: The -OH group in phenols activates the benzene ring towards electrophilic substitution, directing incoming substituents to ortho and para positions.
Summary of Key Reactions
| Reaction Type | Example | Products |
|---|---|---|
| Williamson Synthesis | Sodium propoxide + 1-bromopropane | 1-Propoxypropane |
| Acid Dehydration | Ethanol | Ethene |
| Reaction with HI | Methoxybenzene + HI | Methanol + Iodide |
Conclusion
Understanding the structure, classification, and reactions of alcohols, phenols, and ethers is crucial for their application in various chemical processes.
Practice Test – MCQs, True/False
TopMultiple Choice Questions
A.
Bromine in at 273 K
B.
Bromine water
C.
Bromine in the presence of
D.
Bromine in
Correct Answer: B
Solution:
Phenol reacts with bromine water to form 2,4,6-tribromophenol as a white precipitate due to the activating effect of the -OH group.
Chapter Concept:
Electrophilic Aromatic Substitution in Phenols
A.
Methanol
B.
Ethanol
C.
Propan-2-ol
D.
Butan-1-ol
Correct Answer: C
Solution:
Propan-2-ol is a secondary alcohol, and when its vapors are passed over heated copper at 573 K, it forms a ketone.
Chapter Concept:
Oxidation of Alcohols
A.
Hydrolysis of diazonium salts
B.
Fusion of haloarenes with
C.
Oxidation of cumene
D.
Sulphonation of benzene followed by fusion with
Correct Answer: C
Solution:
Phenol is industrially produced from cumene by oxidizing it to cumene hydroperoxide, which is then converted to phenol and acetone.
Chapter Concept:
Preparation of Phenols
A.
Kolbe's Reaction
B.
Reimer-Tiemann Reaction
C.
Friedel-Crafts Acylation
D.
Wurtz Reaction
Correct Answer: B
Solution:
The Reimer-Tiemann reaction involves treating phenol with chloroform in the presence of sodium hydroxide to introduce a -CHO group at the ortho position, forming salicylaldehyde.
Chapter Concept:
Special Reactions of Phenols
A.
Catalytic hydrogenation
B.
Heating with concentrated at 443 K
C.
Reaction with
D.
Hydroboration-oxidation
Correct Answer: B
Solution:
Ethanol undergoes dehydration to form ethene when heated with concentrated at 443 K.
Chapter Concept:
Preparation of Alcohols
A.
B.
C.
D.
Correct Answer: C
Solution:
is a strong reducing agent used to reduce carboxylic acids to primary alcohols.
Chapter Concept:
Preparation of Alcohols
A.
Primary alcohol
B.
Secondary alcohol
C.
Tertiary alcohol
D.
Phenol
Correct Answer: A
Solution:
The reaction of a Grignard reagent with methanal produces a primary alcohol.
Chapter Concept:
Preparation of Alcohols
A.
o-Nitrophenol
B.
p-Nitrophenol
C.
2,4,6-Trinitrophenol (Picric acid)
D.
3-Nitrophenol
Correct Answer: C
Solution:
When phenol is treated with concentrated , 2,4,6-trinitrophenol, commonly known as picric acid, is formed as the major product.
Chapter Concept:
Electrophilic Aromatic Substitution in Phenols
A.
Tertiary alcohols are readily oxidized to ketones.
B.
Tertiary alcohols are oxidized to aldehydes.
C.
Tertiary alcohols do not undergo oxidation under mild conditions.
D.
Tertiary alcohols are oxidized to carboxylic acids.
Correct Answer: C
Solution:
Tertiary alcohols do not undergo oxidation under mild conditions because they lack a hydrogen atom on the carbon bearing the hydroxyl group, which is necessary for oxidation.
Chapter Concept:
Oxidation of Alcohols
A.
Carboxylic acid
B.
Aldehyde
C.
Ketone
D.
No reaction
Correct Answer: B
Solution:
Pyridinium chlorochromate (PCC) is used to oxidize primary alcohols to aldehydes.
Chapter Concept:
Oxidation of Alcohols
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Alcohols: Phenols and Ethers
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Locked • AI Weakness TrackerTrue or False
Correct Answer: True
Solution:
According to the IUPAC system, the name of an alcohol is derived from the name of the alkane from which the alcohol is derived, by substituting 'e' of alkane with the suffix 'ol'.
Chapter Concept :
Nomenclature of Alcohols, Phenols, and Ethers
Correct Answer: True
Solution:
Grignard reagents react with aldehydes and ketones to form adducts, which upon hydrolysis yield alcohols. This method is widely used to synthesize primary, secondary, and tertiary alcohols depending on the carbonyl compound used.
Chapter Concept :
Preparation of Alcohols
Correct Answer: True
Solution:
In the Reimer-Tiemann reaction, phenol reacts with chloroform () and sodium hydroxide () to introduce a group at the ortho position, forming salicylaldehyde.
Chapter Concept :
Special Reactions of Phenols
Correct Answer: True
Solution:
Phenol, when treated with dilute , yields a mixture of ortho and para nitrophenols due to the activating effect of the -OH group, which directs electrophiles to the ortho and para positions.
Chapter Concept :
Electrophilic Aromatic Substitution in Phenols
Correct Answer: True
Solution:
Tertiary alcohols are generally resistant to oxidation due to the lack of a hydrogen atom on the carbon bearing the hydroxyl group. However, under strong oxidative conditions, they can undergo cleavage of C–C bonds to yield smaller carboxylic acids.
Chapter Concept :
Oxidation of Alcohols
Correct Answer: True
Solution:
The industrial preparation of phenol involves the oxidation of cumene to cumene hydroperoxide, which is then converted to phenol and acetone upon treatment with dilute acid.
Chapter Concept :
Preparation of Phenols
Correct Answer: True
Solution:
Phenols have the -OH group attached to an hybridised carbon of an aromatic ring, leading to a shorter C–O bond due to resonance, which imparts a partial double bond character.
Chapter Concept :
Structures of Functional Groups in Alcohols, Phenols and Ethers
Correct Answer: True
Solution:
The -OH group in phenols is attached to an hybridised carbon of an aromatic ring, and the partial double bond character due to resonance shortens the C-O bond compared to alcohols where the C is hybridised.
Chapter Concept :
Structures of Functional Groups in Alcohols, Phenols and Ethers
Correct Answer: True
Solution:
This statement describes the Reimer-Tiemann reaction, where phenol reacts with chloroform () and sodium hydroxide () to form salicylaldehyde with a -CHO group at the ortho position.
Chapter Concept :
Special Reactions of Phenols
Correct Answer: False
Solution:
The Williamson synthesis involves the reaction of sodium alkoxide/phenoxide with alkyl halide by the mechanism and works best with primary alkyl halides. Secondary and tertiary alkyl halides favor elimination reactions instead.
Chapter Concept :
Preparation of Ethers
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