Isomers

Rucete ✏ Chemistry In a Nutshell

1. What Are Isomers?

• Isomers are compounds that have the same molecular formula but different structures or arrangements of atoms.

2. Structural Isomers

• Differ in the connectivity of atoms.
• Types of structural isomerism:

a) Chain Isomerism

• Same molecular formula but different carbon chain arrangements.
• Example with C₅H₁₂ (pentane):
  • n-pentane (straight chain)
  • 2-methylbutane (branched)
  • 2,2-dimethylpropane (neo-pentane) (highly branched)

b) Positional Isomerism

• Same carbon skeleton and functional group, but different positions of the functional group.
• Example:
  • 1-butanol vs 2-butanol

c) Functional Group Isomerism

• Same molecular formula but different functional groups.
• Examples:
  • Alcohols vs Ethers → Ethanol vs Methoxymethane
  • Aldehydes vs Ketones → Propanal vs Propanone
  • Carboxylic acids vs Esters

3. Stereoisomers

• Same molecular formula and atom connectivity, but different spatial arrangement.

a) Geometric Isomerism (Cis-Trans)

• Occurs in alkenes with restricted rotation.
• Example:
  • Cis-2-butene vs Trans-2-butene

b) Optical Isomerism

• Involves chiral (asymmetric) carbon atoms bonded to four different groups.
• Isomers are non-superimposable mirror images (enantiomers).
• Important in biological systems and drug activity.