Substitution Reactions

Question 1

What are the two types of bond fission?

Answer 1

Homolytic and heterolytic fission.

Question 2

What is bond fission?

Answer 2

Breaking a covalent bond.

Question 3

What is heterolytic fission?

Answer 3

The breaking of a covalent bond with both of the bonded electrons going to one of the atoms, forming a cation (+ ion) and an anion (– ion).

Question 4

What is homolytic fission?

Answer 4

The breaking of a covalent bond with one of the bonded electrons going to each atom, forming two radicals.

Question 5

Reaction mechanism stages?

Answer 5

Initiation
Propagation
Termination

Question 6

Initiation…

Answer 6

1) UV provides enough energy to break the Cl-Cl bond- photodissociation.
2) The bond splits equally and each atom gets to keep one electron- homolytic fission.
The atom becomes a highly reactive free radical, Cl. because of its unpaired electrons.

Question 7

Propagation…

Answer 7

1) Cl. attacks a methane molecule: Cl. + CH4 -> .CH3 + HCl
2) The new methyl free radical, .CH3 can attack another Cl2 molecule: .CH3 + Cl2 -> CH3Cl + Cl.
3) The new Cl. can attack another CH4 molecule, and so on, until all the Cl2 or CH4 molecules are wiped out.

Question 8

Termination…

Answer 8

If two free radicals join together, they make a stable molecule.

Question 9

How are halogenoalkanes formed?

Answer 9

Halogens react with alkanes in photochemical reactions.

A hydrogen is substituted (replaced) by chlorine or bromine- FREE RADICAL SUBSTITUTION.

Question 10

What is the big problem with free radical substitution?

Answer 10

You don’t only get chloromethane but a mixture of products