Organic Compounds Containing Oxygen

Oxygen-containing organic compounds include alcohols, ethers, carbonyl compounds, and carboxylic acids.

Overview

graph TD
    A[Oxygen Compounds] --> B[Alcohols & Phenols]
    A --> C[Ethers]
    A --> D[Carbonyl Compounds]
    A --> E[Carboxylic Acids]
    D --> D1[Aldehydes]
    D --> D2[Ketones]

Alcohols (R-OH)

Classification

• Primary (1°): R-CH₂-OH
• Secondary (2°): R₂CH-OH
• Tertiary (3°): R₃C-OH

Preparation

1. Hydration of alkenes
2. Reduction of carbonyl compounds
3. Grignard reaction

Reactions

Dehydration: Forms alkenes (with H₂SO₄)

$$\text{R-CH}_2\text{-CH}_2\text{-OH} \xrightarrow{\text{H}_2\text{SO}_4, \Delta} \text{R-CH=CH}_2$$

Oxidation:

• 1° alcohol → Aldehyde → Carboxylic acid
• 2° alcohol → Ketone
• 3° alcohol → No oxidation (without C-C cleavage)

Identification Tests

Alcohol	Lucas Test	Victor Meyer Test
1°	Slow (hours)	Red color
2°	5-10 min	Blue color
3°	Immediate	Colorless

Phenols (Ar-OH)

Acidic Nature

More acidic than alcohols due to resonance stabilization of phenoxide ion.

pKa: Phenol (10) < Alcohol (16)

Effect of substituents:

• Electron-withdrawing (e.g., -NO₂): Increase acidity
• Electron-donating (e.g., -CH₃): Decrease acidity

Reactions

• Kolbe-Schmidt reaction (with CO₂/NaOH → salicylic acid)
• Reimer-Tiemann reaction (with CHCl₃/NaOH → salicylaldehyde)
• Bromination (forms 2,4,6-tribromophenol)

Ethers (R-O-R')

Preparation

Williamson Synthesis:

$$\text{R-X} + \text{R'-O}^-\text{Na}^+ \rightarrow \text{R-O-R'} + \text{NaX}$$

Reactions

• Cleavage by HI: Forms alcohol + alkyl iodide

Aldehydes and Ketones

Preparation

1. Oxidation of alcohols
2. Ozonolysis of alkenes
3. Friedel-Crafts acylation (ketones)

Reactions

Nucleophilic Addition:

General mechanism: Nu attacks carbonyl carbon.

Reaction	Reagent	Product
Aldol	Base	β-hydroxyaldehyde
Cannizzaro	Conc. NaOH	Alcohol + acid salt
Wittig	Ph₃P=CHR	Alkene

Oxidation:

• Aldehydes → Carboxylic acids
• Tollen’s test: Silver mirror
• Fehling’s test: Red precipitate (for aliphatic aldehydes)

Reduction:

• Clemmensen: Zn(Hg)/HCl → CH₂
• Wolff-Kishner: N₂H₄/KOH → CH₂

Carboxylic Acids

Acidity

pKa ≈ 4-5 (stronger than alcohols and phenols)

Factors affecting acidity:

• Electron-withdrawing groups increase acidity
• Inductive effect decreases with distance

Reactions

• Salt formation
• Ester formation (with alcohols)
• Acid chloride formation (with SOCl₂)
• Amide formation (with amines)
• Reduction (with LiAlH₄ → alcohol)
• Decarboxylation

Practice Problems

1. Arrange in order of acidity: CH₃COOH, CF₃COOH, CHCl₂COOH, CH₂ClCOOH

2. What products are formed when benzaldehyde is treated with concentrated NaOH?

3. How would you convert ethanol to ethanal?

Further Reading

• Halogen Compounds - Preparation from alcohols
• Nitrogen Compounds - Amines and amides