Organic Reaction Mechanisms

Question 1

What is homolytic fission?

Answer 1

Each bonding atom receives one electron from the bonded pair, forming 2 radicals

Question 2

Draw a diagram showing homolytic fission

Answer 2

See notes

Question 3

What is heterolytic fission?

Answer 3

One boding atom receives both electrons from the bonded pair, forming 2 ions

Question 4

Draw a diagram to show heterolytic fission

Answer 4

See notes

Question 5

What are the curly arrow rules?

Answer 5

A curly arrow starts from a bond, a lone pair or a negative charge, NEVER from a positive charge.
It represents the movement of a pair of electrons

Question 6

What is a radical?

Answer 6

Species (atom or molecule) with an unpaired electron

Question 7

What is a mechanism?

Answer 7

A sequence of steps showing the path taken by electrons in a reaction

Question 8

What is initiation?

Answer 8

The first step in a radical substitution in which free radicals are generated by ultraviolet light

Question 9

What is propagation?

Answer 9

The 2 repeated steps in radical substitution that build up products in a chain reaction

Question 10

What is termination?

Answer 10

The step at the end of radical substitution when 2 radicals combine to form a molecule

Question 11

Reactions of alkanes with halogens

Answer 11

• free radical substitution
• reaction initiated by presence of UV light
• substitution reaction that generates radicals

Question 12

Reaction of alkanes with halogens equation

Answer 12

CH4 + Cl2 -> CH3Cl + HCl

Question 13

Initiation step

Answer 13

Cl2 -> 2Cl*

Question 14

Propagation step 1

Answer 14

Cl* + CH4 -> HCl + CH3*

Question 15

Propagation step 2

Answer 15

CH3* + Cl2 -> Cl* + CH3Cl

Question 16

Termination step

Answer 16

Cl* + Cl* -> Cl2
CH3* + CH3* -> C2H6
Cl* + CH3* -> CH3Cl