Question

Peroxides are often added to free-radical reactions as initiators because the oxygen-oxygen bond cleaves homolytically rather easily. For example, the bond-dissociation enthalpy of O-Obond in hydrogen peroxide (H-O-O-H)is only 213 kJ/mol (51 kcal/mol). Give a mechanism for the hydrogen peroxide- initiated reaction of cyclopentane with chlorine. The BDE for HO-Clis 210 kJ/mol (50kcal/mol).

Short answer

mechanism for the hydrogen peroxide- initiated reaction of cyclopentane with chlorine

Step-by-step solution

Free radicals

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.

Steps involved in free radical chain reaction

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.

Bond dissociation enthalpy (BDE)

It may be defined as the amount of enthalpy required to break a bond homolytically in such a way that each bonded atom retains one of the bond’s two electrons.

Mathematically, ΔH^o= ∑ (BDE of bonds broken) - ∑(BDE of bonds formed)

Mechanism 

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

Initiation step

Propagation step I

Propagation step II

mechanism for the hydrogen peroxide- initiated reaction of cyclopentane with chlorine.