What is the primary difference between homolytic and heterolytic fission?

The primary difference lies in how the shared pair of electrons is distributed. In homolytic fission, the electron pair is split equally, with each atom receiving one electron, forming free radicals. In heterolytic fission, the electron pair is transferred entirely to one of the atoms, resulting in the formation of ions (a cation and an anion). This fundamental difference dictates the nature of the reactive intermediates and the subsequent reaction mechanism.

Why are free radicals so reactive?

Free radicals are highly reactive because they possess an unpaired electron. According to the octet rule, most atoms strive to achieve a stable configuration with eight valence electrons. An unpaired electron makes the radical electron-deficient and unstable, driving it to quickly react with other molecules or radicals to achieve a stable electron pair, often by abstracting an atom or adding to a double bond.

How do reaction conditions influence the type of bond fission?

Reaction conditions play a critical role. High temperatures, UV light, or radical initiators (like peroxides) favor homolytic fission. These conditions provide the energy to break bonds symmetrically. Conversely, polar solvents, which can stabilize charged species, and the presence of good leaving groups or catalysts (acids/bases) promote heterolytic fission, leading to ion formation.

What factors stabilize carbocations and carbanions?

Carbocations are stabilized by electron-donating groups (like alkyl groups via inductive effect and hyperconjugation) and resonance. The order is $3^circ > 2^circ > 1^circ > ext{methyl}$. Carbanions are stabilized by electron-withdrawing groups (inductive effect), resonance, and increased s-character of the carbon orbital. For simple alkyl carbanions, the order is $ ext{methyl} > 1^circ > 2^circ > 3^circ$ (opposite to carbocations).

Can a bond undergo both homolytic and heterolytic fission?

Yes, in principle, any covalent bond *can* undergo both types of fission. However, the specific reaction conditions (temperature, solvent, presence of light or catalysts) will strongly favor one mode over the other. For example, a C-Cl bond might undergo heterolytic fission in a polar solvent to form a carbocation and chloride ion, but under UV light in a non-polar solvent, it could undergo homolytic fission to form free radicals.

Why is understanding bond fission important for NEET?

Understanding bond fission is foundational for organic chemistry. NEET questions frequently test your ability to predict reaction intermediates (carbocations, carbanions, free radicals), determine their relative stabilities, and deduce reaction mechanisms. Without a clear grasp of homolytic and heterolytic fission, it's challenging to comprehend substitution, elimination, addition, and rearrangement reactions, which are core topics in the syllabus.

← ALL TOPICS

Chemistry

NEXT TOPIC →

Nucleophiles and Electrophiles

Fission of Covalent Bond

Chemistry

NEET UG

Version 1Updated 22 Mar 2026

Explore This Topic

Definition Deep Explanation Core Principles NEET Importance Problem Strategy Practice Problems MCQ Practice Quick Revision

The fission of a covalent bond, a fundamental process in organic chemistry, refers to the breaking of the chemical bond between two atoms. This crucial step initiates virtually all chemical reactions, transforming reactants into products. Depending on how the shared pair of electrons in the covalent bond is distributed between the two separating atoms, bond fission can occur in two primary ways: h…

Quick Summary

Covalent bond fission is the breaking of a chemical bond, a prerequisite for any chemical reaction. It occurs in two main ways: homolytic and heterolytic. Homolytic fission involves the symmetrical breaking of a bond, where each atom retains one electron, forming highly reactive, electrically neutral species called free radicals.

This process is favored by high temperatures, UV light, or radical initiators and is depicted by fish-hook arrows. Heterolytic fission, on the other hand, involves the unsymmetrical breaking of a bond, where one atom takes both shared electrons, leading to the formation of charged species called ions (carbocations or carbanions).

This is favored by polar solvents and good leaving groups, and is depicted by curved arrows. The stability of these intermediates (carbocations, carbanions, free radicals) is crucial for predicting reaction pathways and is influenced by inductive effects, hyperconjugation, and resonance.

Carbocations and free radicals generally follow the stability order $3^circ > 2^circ > 1^circ > \text{methyl}$ , while simple alkyl carbanions follow the opposite trend.

Vyyuha

Your 6-Month Blueprint, Updated Nightly

AI analyses your progress every night. Wake up to a smarter plan. Every. Single.…

Key Concepts

Homolytic Fission and Free Radical Stability

Homolytic fission is the equal sharing of electrons during bond breaking, leading to free radicals. These…

Heterolytic Fission and Carbocation Stability

Heterolytic fission involves the unequal sharing of electrons, forming ions. When a carbon atom loses the…

Heterolytic Fission and Carbanion Stability

When a carbon atom gains the electron pair during heterolytic fission, it forms a carbanion (negatively…

Covalent Bond Fission: — Breaking of a covalent bond.

Homolytic Fission: — Symmetrical breaking, each atom gets one electron.

- Forms: Free radicals (e.g., $ext{R}cdot$ ) - Conditions: High T, UV light, peroxides. - Arrow: Fish-hook ( $curvearrowright$ ) - Stability: $3^circ > 2^circ > 1^circ > \text{methyl}$ (similar to carbocations)

Heterolytic Fission: — Unsymmetrical breaking, one atom gets both electrons.

- Forms: Ions (carbocations $ext{R}^+$ , carbanions $ext{R}^-$ ) - Conditions: Polar solvents, good leaving groups, acids/bases. - Arrow: Curved ( $curvearrowright$ ) - Carbocation Stability: $3^circ > 2^circ > 1^circ > \text{methyl}$ - Carbanion Stability: $ext{methyl} > 1^circ > 2^circ > 3^circ$

Key Factors: — Electronegativity, bond strength, solvent, temperature, light.

Homo Radicals UV Temp Peroxides, Hetero Ions Polar Leaving Groups.

Homo: Homolytic fission

Radicals: Forms Free Radicals

UV Temp Peroxides: Conditions (UV light, high Temperature, Peroxides)

Hetero: Heterolytic fission

Ions: Forms Ions (Carbocations, Carbanions)

Polar Leaving Groups: Conditions (Polar solvents, Good Leaving Groups)

For stability: Carbocations & Radicals are 321M (3° > 2° > 1° > Methyl). Carbanions are M123 (Methyl > 1° > 2° > 3°).

← ALL TOPICS

Chemistry

NEXT TOPIC →

Nucleophiles and Electrophiles