Isomerism: Same Formula, Different Compounds!

When 2+ compounds share the same molecular formula but have different properties, they’re called isomers �. This phenomenon is isomerism.

Types of Isomerism

Isomerism →

  • Structural Isomerism (atoms connected differently)
  • Stereoisomerism (same bonds, different 3D arrangement)

Structural Isomerism Subtypes

  1. Chain Isomerism ⛓️
    Same formula, different carbon skeletons.
    Example: \(\text{C}_5\text{H}_{12}\) has 3 isomers:
    • Pentane: \(\text{CH}_3-\text{CH}_2-\text{CH}_2-\text{CH}_2-\text{CH}_3\)
    • Isopentane (2-Methylbutane): \(\text{CH}_3-\text{CH}(\text{CH}_3)-\text{CH}_2-\text{CH}_3\)
    • Neopentane (2,2-Dimethylpropane): \(\text{CH}_3-\text{C}(\text{CH}_3)_2-\text{CH}_3\)
  2. Position Isomerism 📍
    Same skeleton, different positions of functional groups/substituents.
    Example: \(\text{C}_3\text{H}_8\text{O}\) has 2 alcohols:
    • Propan-1-ol: \(\text{CH}_3\text{CH}_2\text{CH}_2\text{OH}\)
    • Propan-2-ol: \(\text{CH}_3\text{CH}(\text{OH})\text{CH}_3\)
  3. Functional Group Isomerism 🔄
    Same formula, different functional groups.
    Example: \(\text{C}_3\text{H}_6\text{O}\) represents:
    • Ketone: Propanone (\(\text{CH}_3\text{COCH}_3\))
    • Aldehyde: Propanal (\(\text{CH}_3\text{CH}_2\text{CHO}\))
  4. Metamerism ⚖️
    Different alkyl chains on either side of a functional group.
    Example: \(\text{C}_4\text{H}_{10}\text{O}\) represents:
    • Methoxypropane (\(\text{CH}_3\text{OC}_3\text{H}_7\))
    • Ethoxyethane (\(\text{C}_2\text{H}_5\text{OC}_2\text{H}_5\))

Organic Reaction Basics

In organic reactions:

  • Organic molecule = Substrate (supplies carbon for new bonds)
  • Other reactant = Reagent (attacks substrate)
  • Reaction Mechanism: Step-by-step story of bond breaking/forming, electron movement, and energy changes ⚡.

Bond Breaking (Fission)

  1. Heterolytic Cleavage:
    Bond breaks unevenly → one fragment keeps both electrons.
    Example: \(\text{CH}_3\text{Br} \rightarrow \text{CH}_3^+ + \text{Br}^-\)
    Produces ions! Like carbocations (\(\text{CH}_3^+\)).
  2. Homolytic Cleavage:
    Bond breaks evenly → each fragment gets one electron.
    Produces radicals (not covered in detail here).

Carbocations: The “+” Heroes!

A carbocation has a carbon with 6 electrons and a positive charge (e.g., \(\text{CH}_3^+\)).

  • Classification:
    • Primary (1°): 1 carbon attached to \(\text{C}^+\) (e.g., \(\text{CH}_3\text{CH}_2^+\))
    • Secondary (2°): 2 carbons attached (e.g., \((\text{CH}_3)_2\text{CH}^+\))
    • Tertiary (3°): 3 carbons attached (e.g., \((\text{CH}_3)_3\text{C}^+\))
  • Stability Order:
    \(\text{CH}_3^+ < 1^\circ < 2^\circ < 3^\circ\)
    Why? Alkyl groups stabilize \(\text{C}^+\) via hyperconjugation and inductive effects.
  • Shape: Trigonal planar (sp² hybridized carbon).

NEET Spotlight ✨

Top 3 High-Yield Concepts:

  1. Isomer Types: Chain, position, functional group, metamerism (define + give examples).
  2. Carbocation Stability: Order (3° > 2° > 1° > \(\text{CH}_3^+\)) + reasons (hyperconjugation/induction).
  3. Bond Fission: Heterolytic vs. homolytic cleavage (products: ions vs. radicals).

Keep practicing naming isomers and drawing carbocations—it’s key! 💪