13.3- ELIMINATION REACTIONS IN HALOGENOALKANES

Question 1

How do halogenoalkanes typically react by?

Answer 1

nucleophilic substitution

Question 2

Under different conditions what can halogenoalkanes react by?

Answer 2

elimination

Question 3

What happens in an elimination reaction of a halogenoalkane?

Answer 3

hydrogen halide is eliminated from the molecule, leaving a double bond in its place so alkene formed

Question 4

Under different conditions what can the OH- ion act as?

Answer 4

base

Question 5

When the OH- ion is acting as a base what will it do to the halogenoalkane?

Answer 5

remove a H+ ion from the halogenoalkane

Question 6

What sort of reaction is it when a H+ ion is removed from the halogenoalkane?

Answer 6

elimination

Question 7

What are the conditions for the elimination reaction for halogenoalkanes? (3)

Answer 7

sodium (or potassium) hydroxide dissolved in ethanol
no water present
mixture heated

Question 8

What is the elimination reaction of halogenoalkanes useful for?

Answer 8

making molecules with carbon-carbon double bonds

Question 9

As the hydroxide ion can act as a nucleophile or base what is there between elimination and substitution?

Answer 9

competition

Question 10

As there is competition between elimination and substitution with hydroxide ions, what is generally produced?

Answer 10

a mixture of an alcohol and an alkene is produced

Question 11

What factors determine which reaction predominates between elimination and substitution with hydroxide ions? (2)

Answer 11

reaction conditions (aqueous or alcoholic)

type of halogenoalkane (primary, secondary, tertiary)

Question 12

What conditions would favour substitution ?

Answer 12

hydroxide ion at room temperature, dissolved in water

Question 13

What conditions would favour elimination?

Answer 13

hydroxide ions at high temperature, dissolved in ethanol

Question 14

What types of halogenoalkanes tend to react by substitution?

Answer 14

primary and secondary

Question 15

What type of halogenoalkanes tend to react by elimination?

Answer 15

secondary and tertiary

Question 16

Is a mixture of isomeric elimination products possible?

Answer 16

yes

Question 17

What are chlorofluorocarbons?

Answer 17

halogenoalkanes containing both chlorine and fluorine atoms but no hydrogen

Question 18

Name CCl3F

Answer 18

trichlorofluoromethane

Question 19

What are chlorofluorocarbons also called?

Answer 19

CFCs

Question 20

How reactive are CFCs under normal conditions?

Answer 20

very reactive

Question 21

What state are short chain CFCs in?

Answer 21

gas

Question 22

Examples of uses of short chain CFCs? (3)

Answer 22

aerosol propellants
refrigerants
blowing agents for foams like expanded polystyrene

Question 23

What are longer chain CFCs used in?

Answer 23

dry cleaning and de-greasing solvents

Question 24

Where do CFCs eventually end up?

Answer 24

in the atmosphere

Question 25

What do CFCs do in the atmosphere?

Answer 25

decompose to give chlorine atoms

Question 26

What do chlorine atoms decompose in the stratosphere?

Answer 26

decompose ozone, O3

Question 27

What has been caused as the chlorine atoms have decomposed ozone?

Answer 27

a hole in the Earth’s ozone layer

Question 28

An example of what CFCs replaced by?

Answer 28

hydrochlorofluorocarbons