Reactivity Of Alkanes

Question 1

Why do Alkanes have low reactivity with most reagents?

Answer 1

1. Sigma bonds are very strong
2. Bonds are non polar

Question 2

What is heterolytic bond fission?

Answer 2

The bond breaks unevenly with one of the bonded atoms receiving both electrons from the bonded pair

XY —> X+ + Y-

Question 3

What is homolytic bond fission?

Answer 3

The bond breaks evenly and each bonding atom receives one electron from the bonded pair

XY —> X. + Y.

Question 4

What happens as a result of halogenation of alkanes?

Answer 4

A hydrogen atom in the alkane is substituted by a halogen atom

Question 5

What are the conditions needed for halogenation of alkanes to take place?

Answer 5

• ultraviolet radiation
• 300 degrees

Question 6

Why happens during free radical substitution?

Answer 6

1. Covalent bonds are broken by homolytic fission forming radicals with an unpaired electron
2. Hydrogen atom in the alkane is substituted by a halogen atom

Question 7

Describe the mechanism that takes place during free radical substitution.

Answer 7

Step 1: Initiation
- free radicals are generated by UV radiation

Step 2 : Propagation
- occur rapid, and continue until no reactants remain

Step 3 : Termination
- removes radicals, stopping the reaction

Question 8

What are the three types of termination steps?

Answer 8

1. Reforming the halogen
2. Hydrocarbon chain
3. Haloalkane

Question 9

What are the limitations of radical substitution?

Answer 9

1. Lead to the formation of a mixture of products
2. Further reactions with the halogen radicals
3. Substitution at different points in the carbon chain