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

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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.