Write a mechanism for light-initiated reaction of cyclobutene with chlorine to give chlorocyclobutane. Label the initiation and propagation steps.

An atom or group of atoms containing odd or unpaired electron is known as the free radical. The unpaired electron is represented by a single unpaired dot in the formula. Free radicals are electrically neutral. They are highly reactive species formed by homolytic fission of a covalent bond.

In a free-radical chain reaction, free radicals are generally created in the initiation steps. A free radical and a reactant is combined to yield a product and another free radical in the propagation steps. Lastly, the number of free radicals generally decrease in the termination steps.

The mechanism consists of three parts which are initiation step, propagation step I and propagation step II.

Mechanism for free-radical chlorination of cyclobutane