Free Radical Substitution Mechanism

Initiation:

$$X_2 \xrightarrow{h\nu} 2X^\bullet$$

Propagation:

$$R-H + X^\bullet \rightarrow R^\bullet + HX$$
$$R^\bullet + X_2 \rightarrow R-X + X^\bullet$$

Termination:

$$X^\bullet + X^\bullet \rightarrow X_2$$
$$R^\bullet + X^\bullet \rightarrow R-X$$
$$R^\bullet + R^\bullet \rightarrow R-R$$