Halogenoalkanes

Question 1

What order do the halogens go when naming halogenoalkanes?

Answer 1

Alphabetical order.

Question 2

What happens to the boiling point of halogenoalkanes as you go down the group?

Answer 2

Increases.

Question 3

Why doe boiling point of halogenoalkanes increase down the group?

Answer 3

*number of electrons increases
*more van der waals forces
*stronger forces
*require more energy to overcome

Question 4

Why are halogenoalkanes attacked by nucleophiles?

Answer 4

They have a polar bond.

Question 5

Why do halogenoalkanes have a polar bond?

Answer 5

The halogen is more electronegative that the carbon (pulls the electrons towards it).

Question 6

What is a nucelophile?

Answer 6

An electron pair donor.

Question 7

What are the three nucelophiles?

Answer 7

*ammonia
*cyanide
*hydroxide

Question 8

What is the name of the mechanism when a nucleophile attacks a halogenoalkane?

Answer 8

Nucleophilic substitution.

Question 9

What are the conditions of nucleophilic substitution with hydroxide?

Answer 9

*warm aqueous sodium hydroxide
*carried out under reflux

Question 10

What does nucleophilic substitution with hydroxide form?

Answer 10

Alcohols.

Question 11

What are the conditions of nucleophilic substitution with cyanide?

Answer 11

*warm ethanolic potassium cyanide
*carried out under reflux

Question 12

What does nucleophilic substitution with cyanide form?

Answer 12

Nitriles.

Question 13

What are the conditions of nucleophilic substitution with ammonia?

Answer 13

*heat with ethanolic ammonia
*excess ammonia

Question 14

What does nucleophilic substitution with ammonia form?

Answer 14

Amines (+ammonia ion).

Question 15

How do you know an amine has been formed?

Answer 15

They smell fishy.

Question 16

What happens to the reactivity of halogenoalkanes down the group?

Answer 16

Increases.

Question 17

What determines reactivity?

Answer 17

Bond strength/bond enthalpy.

Question 18

Why does reactivity of halogenoalkanes increase down the group?

Answer 18

*C–X bond strength/enthalpy decreases
*easier to break
*more reactive

Question 19

What are the conditions of elimination with hydroxide?

Answer 19

*warm ethanolic sodium hydroxide
*carried out under reflux

Question 20

What does elimination with hydroxide from?

Answer 20

Alkenes.

Question 21

How can you tell the reaction is substitution?

Answer 21

*aqueous sodium hydroxide
*solvent is water
*hydroxide ions acts as nucleophile
*forms alcohol

Question 22

How can you tell the reactions is elimination?

Answer 22

*ethanolic sodium hydroxide
*solvent is ethanol
*hydroxide ion acts as base
*forms alkene

Question 23

What is a base?

Answer 23

A proton acceptor.

Question 24

What happens if a mixture of water and ethanol as the solvent is used?

Answer 24

Both substitution and elimination occur, forming both alkenes and alcohols.

Question 25

What are the equations of chlorine radicals depleting the ozone?

Answer 25

*Cl° + O3 → O2 + ClO°
*ClO° + O3 → 2O2 + Cl°

Question 26

What does chlorine act as in ozone depletions?

Answer 26

A catalyst.

Question 27

Why is the C–Cl bond broken in the CFC?

Answer 27

It is weaker than the C–F bond.

Question 28

What is the overall reaction of ozone depletions?

Answer 28

2O3 → 2O2

Question 29

Why is ozone good?

Answer 29

It absorbs the harmful UV radiation.

Question 30

What is used now instead of CFCs?

Answer 30

HFCs (contain no chlorine).

Question 31

Draw the mechanism of bromoethane with a aqueous sodium hydroxide.

Question 32

Draw the mechanism of bromoethane with ammonia.

Question 33

Draw the mechanism of bromoethane with a cyanide ion.

Question 34

Draw the mechanism of bromopropane with ethanolic sodium hydroxide.