Functional Groups in Organic Chemistry

Table of Contents

• Introduction
• Common Functional Groups
• Importance of Functional Groups
• Classification of Organic Compounds
• Quiz Section
• Frequently Asked Questions

Introduction

In organic chemistry, a functional group is a specific group of atoms within a molecule that is responsible for the characteristic chemical reactions of that molecule. These groups behave in a predictable way during reactions, regardless of the molecule they are attached to.

Common Functional Groups

• Hydroxyl group (–OH): Found in alcohols.
• Carbonyl group (C=O): Found in aldehydes and ketones.
• Carboxyl group (–COOH): Found in carboxylic acids.
• Amino group (–NH₂): Found in amines.
• Alkyl halide group (–X): Halogens like Cl, Br, I, F replace hydrogen.
• Ester group (–COOR): Found in esters.
• Amide group (–CONH₂): Found in amides.
• Nitrile group (–C≡N): Found in nitriles.
• Ether group (R–O–R’): Found in ethers.

Functional Group Importance

• They determine the chemical reactivity and physical properties of organic molecules.
• They help in identifying homologous series of organic compounds.
• They are used in IUPAC nomenclature and classification.
• Compounds with multiple groups (e.g., amino acids) have unique properties.

Classification of Organic Compounds by Functional Group

Class	Functional Group	General Formula	Example
Alcohol	–OH	R–OH	Ethanol (CH₃CH₂OH)
Aldehyde	–CHO	R–CHO	Formaldehyde (HCHO)
Carboxylic Acid	–COOH	R–COOH	Acetic Acid (CH₃COOH)
Ester	–COOR	R–COOR’	Methyl acetate (CH₃COOCH₃)
Amine	–NH₂	R–NH₂	Methylamine (CH₃NH₂)

Quiz: Test Your Knowledge

MCQs

1. Which of the following contains a hydroxyl group?

• A. Acetic acid
• B. Ethanol ✅
• C. Ethanal
• D. Methylamine

Explanation: Ethanol contains –OH, the hydroxyl group.

2. The functional group –CHO belongs to which class?

• A. Alcohol
• B. Aldehyde ✅
• C. Ketone
• D. Acid

Explanation: –CHO is the aldehyde group.

True/False

1. Amino group is represented as –NH₂. ✅ True

Explanation: Amines contain the –NH₂ group.

2. Esters contain the –COOH group. ❌ False

Explanation: Esters contain –COOR, not –COOH.

Fill in the Blanks

1. The general formula of alcohol is R–OH.

2. The functional group of carboxylic acid is –COOH.

Matching

Functional Group	Example Compound
–OH	Ethanol
–CHO	Formaldehyde
–COOH	Acetic Acid
–NH₂	Methylamine

Frequently Asked Questions

Q1. What is a functional group?

A functional group is a specific group of atoms responsible for the chemical properties of a compound.

Q2. Why are functional groups important in organic chemistry?

They determine reactivity, classification, and naming of compounds.

Q3. Give an example of a molecule with multiple functional groups.

Amino acids contain both –NH₂ (amine) and –COOH (carboxyl).