What is the Difference Between Free Radical Substitution and Free Radical Addition?

The main difference between free radical substitution and free radical addition lies in the type of reaction that occurs. In free radical substitution, a free radical replaces a functional group or atom in a molecule, while in free radical addition, a new functional group is added to a molecule without the removal of any other group or atom.

  • Free Radical Substitution: This type of reaction involves the replacement of a functional group or atom in a molecule with a free radical. For example, in the chlorination of methane, a chlorine atom is substituted for one of the hydrogen atoms in the methane molecule.
  • Free Radical Addition: In this type of reaction, a new functional group is added to a molecule without the removal of any existing group or atom. For instance, in the addition of a hydrogen halide to an alkene, a hydrogen atom and a halogen atom are added to the double bond without removing any other atoms.

In summary, free radical substitution involves the replacement of a functional group or atom, while free radical addition involves the addition of a new functional group without removing any existing group or atom.

Comparative Table: Free Radical Substitution vs Free Radical Addition

Here is a table comparing free radical substitution and free radical addition:

Feature Free Radical Substitution Free Radical Addition
Definition A type of radical reaction where a functional group is replaced by another functional group or atom. A type of addition reaction where a functional group is added to a compound through a free radical reactive intermediate.
Involves Replacement of a functional group or atom. Addition of a new functional group to a molecule.
Reaction Type Substitution reaction. Addition reaction.
Mechanism Proceeds through three distinct stages: initiation, propagation, and termination. May involve different mechanisms depending on the specific reaction.
Examples Halogenation of alkanes, where a hydrogen atom is replaced by a halogen atom. Addition of H-Br to alkenes, leading to the formation of new hydrocarbons.

In summary, free radical substitution involves the replacement of a functional group or atom, while free radical addition involves the addition of a new functional group to a molecule. Both reactions involve free radicals as reactive intermediates, but they differ in the type of reaction they belong to and the overall outcome of the reaction.