Alcohols, Phenols, and Ethers (JEE Chemistry)
1. Introduction
Alcohols, phenols, and ethers are oxygen-containing organic compounds.
They differ in the nature of the group attached to the oxygen atom.
| Compound | General Formula |
|---|---|
| Alcohol | $R–OH$ |
| Phenol | $Ar–OH$ |
| Ether | $R–O–R'$ |
2. Classification of Alcohols
(a) Based on Carbon Atom
| Type | Structure |
|---|---|
| Primary ($1^\circ$) | $R–CH_2OH$ |
| Secondary ($2^\circ$) | $R–CHOH–R'$ |
| Tertiary ($3^\circ$) | $R–C(OH)(R')(R'')$ |
(b) Based on Number of –OH Groups
- Monohydric alcohols
- Dihydric alcohols (glycols)
- Trihydric alcohols (glycerol)
3. Nomenclature
IUPAC naming of alcohols:
- Select longest carbon chain containing –OH
- Replace “-e” with “-ol”
- Give lowest locant to –OH
4. Preparation of Alcohols
(a) From Alkenes (Hydration)
$CH_2=CH_2 + H_2O \xrightarrow{H^+} CH_3CH_2OH$
(b) From Alkyl Halides
$R–X + OH^- \rightarrow R–OH + X^-$
(c) Reduction of Aldehydes & Ketones
$R–CHO \xrightarrow{NaBH_4} R–CH_2OH$
5. Physical Properties of Alcohols
- High boiling point due to hydrogen bonding
- Lower alcohols are water soluble
- Solubility decreases with increasing alkyl chain
6. Chemical Reactions of Alcohols
(a) Reaction with Sodium
$2ROH + 2Na \rightarrow 2RONa + H_2$
(b) Dehydration
$CH_3CH_2OH \xrightarrow{conc.\ H_2SO_4} CH_2=CH_2 + H_2O$
(c) Oxidation
| Alcohol | Product |
|---|---|
| Primary | Aldehyde → Acid |
| Secondary | Ketone |
| Tertiary | No oxidation |
7. Phenols
Phenols have –OH group directly attached to aromatic ring.
They are more acidic than alcohols.
Acidity of Phenol
$C_6H_5OH \rightleftharpoons C_6H_5O^- + H^+$
Resonance stabilizes phenoxide ion → increased acidity.
8. Preparation of Phenol
(a) From Chlorobenzene (Dow Process)
$C_6H_5Cl + NaOH \xrightarrow{623K,300atm} C_6H_5ONa \rightarrow C_6H_5OH$
(b) From Cumene
Cumene $\rightarrow$ Cumene hydroperoxide $\rightarrow$ Phenol + Acetone
9. Reactions of Phenol
(a) Kolbe’s Reaction
$C_6H_5ONa + CO_2 \rightarrow o$-hydroxybenzoic acid
(b) Reimer–Tiemann Reaction
Phenol + $CHCl_3 + NaOH \rightarrow o$-hydroxybenzaldehyde
10. Ethers
Ethers contain oxygen atom between two alkyl or aryl groups.
They are relatively inert compounds.
11. Preparation of Ethers
(a) Williamson Ether Synthesis
$R–ONa + R'–X \rightarrow R–O–R' + NaX$
Best for primary alkyl halides.
12. Physical Properties of Ethers
- Lower boiling points than alcohols
- Slightly soluble in water
- Used as solvents
13. Chemical Reactions of Ethers
Cleavage by Acids
$R–O–R' + HI \rightarrow R–I + R'–OH$
14. Comparison Table
| Property | Alcohol | Phenol | Ether |
|---|---|---|---|
| Acidity | Low | High | Very low |
| Hydrogen Bonding | Yes | Yes | No |
15. Important JEE Points & Traps
- Phenol does not give Lucas test
- Tertiary alcohols do not oxidize
- Ethers form peroxides on standing
- Williamson synthesis fails for tertiary halides
16. Final Revision Checklist
You have mastered this chapter if you can:
- Differentiate alcohol, phenol, ether reactions
- Predict products correctly
- Explain acidity order
- Apply named reactions confidently