Free Radical Substitution

Question 1

What is a free radical?

Answer 1

A free radical is an atom or molecule which consists of an unpaired electron

Question 2

What are the three phases in free radical substitution?

Answer 2

• initiation phase
• propagation
• termination

Question 3

Describe what happens during the initiation phase of chlorine

Answer 3

• covalent bond is broken to form two chlorine free radicals
• UV light is used as it provides energy
• this is known as homolytic fission

Cl2 ———> 2Cl ~
(UV light)

Question 4

Describe what happens during propagation of methane and chlorine free radical

Answer 4

• methane is attacked by the chlorine free radical, this breaks the covalent bond between the carbon and the hydrogen - to produce a methyl free radical and HCl
• the methyl free radical then attacks a chlorine molecule, where a chlorine molecule then bonds onto the methyl free radical
• this produces chloromethane and a chlorine free radical

Question 5

What are the two equations in the propagation phase of methane and the chlorine free radical?

Answer 5

CH4 + Cl ~ ——-> CH3 ~ + HCl
CH3 ~ + Cl2 —–> CH3Cl + Cl ~

Question 6

Describe what happens during termination

Answer 6

Termination is when two free radicals come together (forms no free radicals)

• 2Cl ~ —–> Cl2
• CH3 ~ + Cl ~ —-> CH3Cl
• CH3 ~ + CH3 ~ —–> CH3CH3

Question 7

Show the depletion of ozone

Answer 7

O3 + Cl ~ —-> O2 + ClO ~
ClO ~ + O3 —-> 2O2 + Cl ~

Anytime ozone reacts, you make oxygen
- the free radical in this case is chlorine