Halogenoalkanes

Question 1

Hydrolysis

Answer 1

The splitting of a molecule by a reaction with water

Question 2

Uses of halogenoalkanes

Answer 2

• chloroalkanes and chlorofluoroalkanes can be used as solvents
• CH3CCl3 was used as solvents in dry cleaning
• they can be used as refrigerants, pesticides and aerosol propellants

Question 3

Why is ozone layer good

Answer 3

It filters out much of the suns harmful UV radiation

Question 4

What did man-made CFCs cause

Answer 4

A hole to form in the ozone layer

Question 5

What are HFCs and why are the important

Answer 5

Hydrofluorocarbons
And they are now used instead of CFCs as they are safer as they don’t contain the C-Cl bond

-> the C-F bond is stronger than the C-Cl bond and isn’t affected by UV

Question 6

What reactions can halogenoalkanes go through

Answer 6

Substitution or elimination reactions

Question 7

What is a nucelophile

Answer 7

An electron pair donator
Eg. OH- NH3 CN-

Question 8

What are primary halogenoalkanes

Answer 8

One carbon attached to the carbon atom adjoining the halogen

And so on for secondary and tertiary

Question 9

What does Nu present

Answer 9

Any nucelophile -> they always have a lone pair and act as electron pair donators

Question 10

Why are iodoalkanes the fastest to substitute

Answer 10

Because they have the lowest bond enthalpy

Question 11

Nucleophilic substitution with aqueous hydroxide ions

Answer 11

Change in functional group:
Halogenoalkane-> alcohol

Reagent: potassium/sodium hydroxide
Conditions: in aqueous solution, warm
Mechanism: nucelophilic substitution
Type of reagent: nucelophile OH-

Question 12

Why are aqueous conditions needed for nucelophile substitution

Answer 12

If the solvent is changed to ethanol an elimination reaction occurs

Question 13

What is a nucelophile

Answer 13

Electron pair donator
Eg NH3 OH- CN-

Question 15

What is a primary halogenoalkane

Answer 15

One carbon attached to the carbon atom adjoining the halogen

And so on for secondary and tertiary

Question 16

What does Nu represent

Answer 16

Any nucelophile -> they always have a lone pair and act as electron pair donators

Question 17

Why are iodoalkanes faster to substitute

Answer 17

Because C-I bonds have a lower bond enthalpy

Question 18

Nucleophilic substitution with aqueous sodium hydroxide ions

Answer 18

Change in functional group:
Halogenoalkane -> alcohol

Reagent: potassium/sodium hydroxide

Conditions: aqueous solution, warm

Mechanism: Nucleophilic substitution

Type of reagent: nucelophile OH-

Question 19

Why do you need to state it’s aqueous conditions in Nucleophilic substitution with aqueous OH- ions

Answer 19

Because if the solvent changed to ethanol an elimination reaction occurs

Question 20

Nucleophilic substitiim with cyanide ions

Answer 20

Change in functional group:
Halogenoalkane -> nitrile

Reagent: KCN dissolved in ethanol

Conditions: heating under reflux

Mechanism: Nucleophilic substitution

Type of reagent: nucelophile CN-

Question 21

Nucleophilic substitution with ammonia

Answer 21

Change in functional group:
Halogenoalkanes -> amine

Reagent: NH3 dissolves in ethanol

Conditions: hearing under pressure

Mechanism: Nucleophilic substitution

Type of reagent: nucelophile NH3

Question 22

Why would you use excess ammonia in Nucleophilic substitution of ammonia

Answer 22

Further substitution reactions can occur between the halogenoalkane and the amines formed leading to a lower yield of the amine -> using excess helps to minimise this

Question 23

Elimination

Answer 23

The removal of small molecule (often water) from the organic molecule

Question 24

Elimination with alcoholic hydroxide ions

Answer 24

Change in functional group:
Halogenoalkane -> alkene

Reagents: potassium/sodium hydroxide

Conditions: in ethanol, heat

Mechanism: elimination

Type of reagent: base, OH-

Question 25

What type of solvents do each reaction have

Answer 25

Aqueous: substitution Alcoholic: elimination