Stereoisomerism

Stereoisomerism is the occurrence of compounds with the same molecular formula but different spatial arrangements, affecting drug action and activity.

• Stereoisomerism is a form of isomerism in which molecules have:
• The same molecular formula
• The same sequence of bonded atoms (i.e., the same structural formula)
• But a different spatial arrangement of atoms or groups in 3D space
• So, unlike structural (constitutional) isomers, stereoisomers differ only in how atoms are oriented in space, not in how they’re connected.

Classification of Stereoisomerism

1. Geometrical Isomerism (cis-trans or E/Z)

   • Occurs due to restricted rotation (e.g., around double bonds or in cyclic systems)
   • Groups are arranged differently in space relative to a reference plane
   • Examples:
     • Cis-but-2-ene (same groups on the same side)
     • Trans-but-2-ene (same groups on opposite sides)
     • E/Z isomerism in alkenes with different substituents

2. Optical Isomerism

   • Arises due to the presence of chiral centers or asymmetry
   • Molecules that can rotate plane-polarized light
   • Based on the concept of chirality

Thank you for reading from Firsthope's notes, don't forget to check YouTube videos!