Carbon Compounds and Functional Groups: A Complete Organic Guide

From ethanol in hand sanitisers to acetic acid in vinegar, organic compounds touch every aspect of our daily lives. This chapter is one of the highest-scoring sections in Class 10 board exams and provides the foundation for the much larger organic chemistry syllabus in Classes 11 and 12.

STEMBridge Learning thumbnail on carbon compounds and functional groups, featuring organic chemistry structures, functional groups, and carbon compounds in a clean educational layout without any person.

What Are Functional Groups?

A functional group is an atom or group of atoms within a molecule that decides the chemical properties of the entire compound. Two molecules with the same functional group behave similarly, no matter how long their carbon chain is.

Common Functional Groups

Alcohol (–OH): e.g., ethanol (C₂H₅OH).
Aldehyde (–CHO): e.g., methanal (HCHO).
Ketone (>C=O): e.g., propanone (CH₃COCH₃).
Carboxylic acid (–COOH): e.g., ethanoic acid (CH₃COOH).
Ester (–COOR): e.g., ethyl ethanoate.
Halide (–X): e.g., chloromethane (CH₃Cl).
Amine (–NH₂): e.g., methylamine (CH₃NH₂).

Homologous Series

A series of organic compounds with the same functional group and similar chemical properties, where each member differs from the next by a –CH₂– unit. They share a general formula and show a gradual change in physical properties.

Alcohols

Alcohols contain the –OH group attached to a carbon atom.

Preparation: By hydration of alkenes or fermentation of sugars.
Reactions: With sodium to form sodium ethoxide and hydrogen; with carboxylic acids to form esters (esterification).

Ethanol — A Key Example

Ethanol (C₂H₅OH) is used in alcoholic drinks, hand sanitisers, fuels, and as a solvent. Long-term consumption damages the liver, and methanol (CH₃OH) consumption can cause blindness or death.

Aldehydes and Ketones

Both contain the carbonyl group (>C=O), but they differ in location:

Aldehydes have the carbonyl at the end of the chain (R–CHO).
Ketones have it in the middle (R–CO–R′).

Important examples: formaldehyde (used as preservative), acetone (a common nail-polish remover).

Carboxylic Acids

Carboxylic acids contain –COOH and are weakly acidic. Examples include formic acid (in ant stings) and acetic acid (in vinegar). They react with:

Bases to form salt and water (e.g., CH₃COOH + NaOH → CH₃COONa + H₂O).
Carbonates to release CO₂.
Alcohols to form esters in the presence of concentrated H₂SO₄.

Esters and Esterification

Esters are formed when a carboxylic acid reacts with an alcohol:

CH₃COOH + C₂H₅OH ⇌ CH₃COOC₂H₅ + H₂O

Esters have pleasant, fruity smells and are used in perfumes, food flavourings, and synthetic essences.

Soaps and Detergents

Soaps

Sodium or potassium salts of long-chain fatty acids. They are made by saponification — heating a fat or oil with NaOH.

Limitation: Soaps do not lather well in hard water because Ca²⁺ and Mg²⁺ form insoluble scum.

Detergents

Sodium salts of long-chain sulphonic acids or alkyl hydrogen sulphates. Detergents work in both soft and hard water but are often non-biodegradable, contributing to water pollution.

Cleansing Action of Soap

Each soap molecule has a hydrophilic head (water-attracting) and a hydrophobic tail (water-repelling). The tails surround grease droplets, while the heads point outward into water, forming structures called micelles that lift dirt off clothes and skin.

Reactions Recap

Combustion of ethanol: C₂H₅OH + 3O₂ → 2CO₂ + 3H₂O.
Oxidation of ethanol to ethanoic acid: Using alkaline KMnO₄ or acidified K₂Cr₂O₇.
Dehydration of ethanol: To ethene using conc. H₂SO₄ at 170°C.

Worked Example

Identify the functional group in CH₃COOH and write its reaction with NaOH.

Solution: Functional group = –COOH (carboxylic acid).
CH₃COOH + NaOH → CH₃COONa + H₂O

Common Mistakes Students Make

Confusing alcohols and aldehydes during oxidation problems.
Forgetting that esterification is reversible.
Mixing up soaps and detergents in cleansing-action questions.

Frequently Asked Questions

Q1. Why is ethanol used as a sanitiser?
Because it denatures the proteins of bacteria and viruses, killing them on contact.

Q2. Why does soap not work well in hard water?
Because calcium and magnesium ions react with soap to form insoluble scum instead of lather.

Q3. Why are esters used in perfumes?
Because of their pleasant, fruity smells and their ability to evaporate slowly.

Q4. What is the difference between aldehyde and ketone?
The carbonyl group in aldehydes is at the terminal carbon, while in ketones it is between two carbon atoms.

Q5. Is acetic acid a strong acid?
No. Acetic acid is a weak acid that ionises only partially in water.

Key Takeaways

Functional groups are the heart of organic chemistry. Recognising them helps you predict reactions, write structures, and understand everyday materials. Alcohols, acids, esters, soaps, and detergents are not just exam topics — they are the chemistry of our food, fuel, and hygiene.