reactions involving radicals

Question 1

what happens between an alkane and halogen in the dark and sunlight (UV)?

Answer 1

Dark: no reaction
UV: explosion

Question 2

whats the mechanism called when an alkane and a halogen react?

Answer 2

radical substitution

Question 3

what are the three stages of radical substitution called?

Answer 3

1. initiation
2. propagation
3. termination

Question 4

what happens in initiation?

Answer 4

this is the stage where radicals are first produced, the UV light provides enough energy to break the bond between the Cl-Cl bond in some Cl2 molecules (homolytic fission) this is photodissociation

Question 5

what happens in propagation?

Answer 5

steps where one radical reacts but a new one is given, that new radical will also react, so these steps continue the chain reaction
in the first stage the halogen radical will take a H atom from the methane molecule, leaving a alkane radical.
in the second stage the alkane radical produced is very reactive, it reacts by taking a halogen atom from one of the many halogen molecules around.
this regenerates the halogen radical, which will then attack another alkane molecule (Cl acts as a catalyst)

Question 6

what happens in termination?

Answer 6

termination is when two radicals react with each other, giving no new radicals. this step stops the chain reaction.

Question 6

what happens if the two stages of propagation just repeat over and over?

Answer 6

there would be an explosion due to the chain reaction continuing

Question 7

what’s the Ea like for termination?

Answer 7

very low since no bonds are breaking only bond making.

Question 8

what’s the reaction between a halogen and an alkane called?

Answer 8

radical substitution

Question 9

if methane and chlorine were reacting what would the overall equation be?

Answer 9

CH4 + Cl2 => CH3Cl + HCl

Question 10

what kind of arrows do you use when representing the movement of electrons in a radical substitution mechanism?

Answer 10

a half curly arrow

Question 11

describe homolytic fission

Answer 11

when the covalent bond breaks in such a way that each atom receives an electrons which forms two radicals

Question 12

describe heterolytic fission

Answer 12

when a covalent bond breaks in such a way that one atom ends up receiving both electrons, this produces a negative ion and a positive ion which are known as intermediates

Question 13

which types of arrows does a heterolytic reaction equation show?

Answer 13

full curly arrows, two ions, the negative ion with a lone pair of electrons

Question 14

which type of arrows does a homolytic reaction show?

Answer 14

half curly arrows, producing two radicals

Question 15

what is an electron donor?

Answer 15

a nucleophile