Classification of Isomers

Key Concepts

• Isomers have the same chemical formula but different structures.

Types of Isomers

1. Constitutional Isomers

   • Differ in connectivity of atoms.
   • Example: Alcohol attached to C2 in one molecule and to C3 in another.

2. Stereoisomers

   • Connected in the same way but differ in spatial arrangement.
   • Example: Bromine atom on the same carbon but different spatial orientation.

Stereoisomers Subcategories

Enantiomers

• Non-superimposable mirror images.
• All chiral centers change configuration.
• Lack of symmetry indicates enantiomers.

Diastereomers

• Some but not all chiral centers change.
• Example: RRR to RSR.
• Cis-trans isomers: A subtype of diastereomers where there is geometric isomerism.
  • Cis: Same side.
  • Trans: Opposite sides.

Meso Compounds

• Have a plane of symmetry.
• Chiral centers reversed but molecules are identical.

Examples and Identification

1. Example 1

   • Molecule with plane of symmetry: Meso compound.
   • All chiral centers reversed but identical due to symmetry.

2. Example 2

   • All chiral centers change without symmetry: Enantiomers.

3. Example 3

   • Some chiral centers change, others remain: Diastereomers.
   • Cis-trans as a subtype seen with geometric isomerism examples.

4. Constitutional Isomers Example

   • Connectivity difference: Different carbons for functional groups.

5. Identical Molecules

   • No chiral centers or differences in arrangement: Identical.

Conclusion

• Enantiomers: All chiral centers change, no symmetry.
• Diastereomers: Some chiral centers change.
• Meso Compounds: Symmetry present, identical.
• Constitutional Isomers: Different connectivity of atoms.
• Cis-Trans Isomers: Type of diastereomers based on geometry.