XII Stereoisomerism and Its Types – Class XII Chemistry Notes with Examples

Learn what stereoisomerism is, its main types (geometrical and optical isomerism), and see clear examples for each. Perfect for Class XII Chemistry students preparing for board exams.

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In this post, we’ll understand one of the most interesting topics in organic chemistry — Stereoisomerism. You’ll learn what stereoisomers are, how they differ from structural isomers, and the two main types: geometrical and optical isomerism, explained with simple examples and diagrams.

What is Stereoisomerism?

Stereoisomerism occurs when compounds have the same molecular formula and same structural formula, but differ in the spatial arrangement of atoms or groups in space.

These differences lead to distinct physical and sometimes chemical properties.

🔹 Difference between Structural and Stereoisomerism

Basis	Structural Isomerism	Stereoisomerism
Definition	Atoms are connected in different ways.	Atoms are connected in the same way but arranged differently in space.
Example	Butane & Isobutane	cis-But-2-ene & trans-But-2-ene

🧪 Types of Stereoisomerism

There are two main types of stereoisomerism:

1. Geometrical (cis–trans) isomerism

2. Optical isomerism

🔸 1. Geometrical Isomerism (cis–trans Isomerism)

Found in alkenes and compounds with restricted rotation (like double bonds).
Caused by different spatial arrangements of groups around a double bond.

Example:

👉 cis-But-2-ene and trans-But-2-ene

Isomer	Structure	Property
cis-isomer	Similar groups on the same side of the double bond	Higher boiling point
trans-isomer	Similar groups on opposite sides of the double bond	More stable

🔸 2. Optical Isomerism

Found in compounds containing a chiral carbon atom (a carbon attached to four different groups).
These isomers are non-superimposable mirror images of each other.
They rotate plane-polarized light in opposite directions.