Functional Isomerism
Structural Isomerism | Organic Chemistry Class 11
1. Definition
Functional Isomerism: It is a type of structural isomerism where compounds have the same molecular formula but different functional groups.
This difference in functional groups leads to significantly different physical and chemical properties.
2. Common Functional Isomer Pairs
Certain functional groups typically form pairs of functional isomers for a specific general formula.
| General Formula | Functional Group Pair | Example ($C_2H_6O$) |
|---|---|---|
| $C_nH_{2n+2}O$ | Alcohol ($-OH$) & Ether ($-O-$) | Ethanol vs Dimethyl Ether |
| $C_nH_{2n}O$ | Aldehyde ($-CHO$) & Ketone ($>C=O$) | Propanal vs Propanone |
| $C_nH_{2n}O_2$ | Carboxylic Acid ($-COOH$) & Ester ($-COOR$) | Ethanoic Acid vs Methyl Methanoate |
| $C_nH_{2n-2}$ | Dienes ($C=C-C=C$) & Alkynes ($C \equiv C$) | Butadiene vs Butyne |
| $C_nH_{2n+1}NO_2$ | Nitro ($-NO_2$) & Nitrite ($-ONO$) | Nitroethane vs Ethyl Nitrite |
3. Detailed Examples
A. Alcohols and Ethers ($C_2H_6O$)
- Ethanol: CH3-CH2-OH (Liquid, reacts with Na)
- Dimethyl Ether: CH3-O-CH3 (Gas, does not react with Na)
B. Aldehydes and Ketones ($C_3H_6O$)
- Propanal: CH3-CH2-CHO
- Propanone (Acetone): CH3-CO-CH3
C. Acids and Esters ($C_2H_4O_2$)
- Ethanoic Acid: CH3-COOH (Sour taste, acidic)
- Methyl Methanoate: H-COO-CH3 (Sweet smell, neutral)
4. Special Cases
- Primary, Secondary, Tertiary Amines: $1^\circ, 2^\circ, 3^\circ$ amines having the same molecular formula are functional isomers (e.g., $C_3H_9N$).
- Cyanides and Isocyanides: $R-CN$ vs $R-NC$.
- Keto-Enol Tautomerism: A specific type of functional isomerism where isomers exist in dynamic equilibrium.
Practice Quiz
Identify the functional isomers correctly.
Best explanation.
ReplyDelete