Introduction:

Understanding the nomenclature and structure of the carboxyl group is a crucial part of the Class 12 Chemistry syllabus. Carboxylic acids, which contain the carboxyl functional group (–COOH), play a vital role in organic chemistry and biological systems. This topic helps students master naming conventions, structural representation, and properties of carboxylic acids.

What is a Carboxyl Group?

The carboxyl group is a functional group consisting of a carbonyl (C=O) and a hydroxyl (–OH) group attached to the same carbon atom. It is represented as –COOH and is characteristic of carboxylic acids.

Structure of Carboxyl Group:

- The carboxyl group has a planar trigonal geometry.

- The central carbon forms:

- A double bond with oxygen (C=O).

- A single bond with the hydroxyl group (–OH).

- Bond angles are approximately 120° due to sp² hybridization.

Resonance in Carboxyl Group:

The carboxyl group shows resonance between the two oxygen atoms:

R–C–OH ⇌ R–C–O⁻

H⁺

This delocalization of electrons provides extra stability to carboxylic acids.

Nomenclature of Carboxylic Acids:

IUPAC Naming Rules:

1. Identify the longest carbon chain containing the –COOH group.

2. Replace the ‘e’ at the end of the alkane name with ‘oic acid’.

3. Numbering starts from the carbon of the carboxylic group, which is always carbon 1.

4. Name substituents as prefixes.

Examples:

- CH₃COOH → Ethanoic acid

- C₂H₅COOH → Propanoic acid

Common Names of Carboxylic Acids:

Some carboxylic acids have trivial names based on their sources:

- HCOOH – Formic Acid (from ants)

- CH₃COOH – Acetic Acid (from vinegar)

- C₆H₅COOH – Benzoic Acid

Functional Derivatives of Carboxylic Acids:

Carboxylic acids form several derivatives:

- Esters (R–COOR')

- Acid chlorides (R–COCl)

- Amides (R–CONH₂)

- Anhydrides (R–CO–O–CO–R')

Importance in Daily Life and Industry:

Examples in Real Life:

- Citric acid in fruits

- Lactic acid in sour milk

- Salicylic acid in skin treatments

Industrial Importance:

- Used in food preservation, plastic production, and medicines.

- Acetic acid is widely used in vinegar production.

Tips to Remember:

- Always count the carboxyl carbon as C-1.

- The presence of double bonds or substituents like halogens or alkyl groups are included with proper locants.

- Use resonance concepts to explain acidity and stability.

Conclusion:

The nomenclature and structure of the carboxyl group form the backbone of understanding carboxylic acids in organic chemistry. Mastering the IUPAC rules, structure, and real-life applications will not only help in board exams but also in competitive exams like NEET and JEE. Stay consistent with practice and examples to gain confidence in this fundamental topic.