Reactions of alkanes

Bond fission is the breaking of a covalent bond.

What is bond fission?

* Homolytic fission
* Heterolytic fission

What are the two ways a bond can break?

* The uneven breaking of bonds.
* One of the bonded atom receives both electrons form the bonded pair.
* Two different substances are formed - a positively charged cation and and a negatively charged anion.

What is heterolytic fission?

* The even breaking of bond.
* Each atom receives one electron from the bonded pair.
* Two radicals are formed (radicals are particles that have an unpaired electron.)
* Because of the unpaired electron, radicals are very reactive.

What is homolytic fission?

Free-radical substitution with UV light

What reaction forms haloalkanes from alkanes?

Halogens

What do alkanes react with to form haloalkanes?

* Initiation
* Propagation
* Termination

What are the three steps to a free-radical substitution mechanism?

* Sunlight provides enough energy to break the bond in the halogen.
* Homolytic fission takes place and the atom becomes a highly reactive free radical because of its unpaired electron.

What happens in the initiation stage of the reaction?

Free radicals are used up and created in a chain reaction.

What happens in the propagation stage of the reaction?

Free radicals join together to make a stable molecule.

What happens in the termination stage of the reaction?

* You don’t only get the product you are trying to make you get a mixture of products.
* It can take place at any point along the carbon chain so a mixture of isomers can be formed.

What are two problems with free-radical substitution?