Chapter 15 - Haloakanes

Question 1

What are haloalkanes?

Answer 1

Compounds containing hydrogen, carbon and at least one halogen atom

Question 2

When two or more halogens are present in a haloalkane, how do you name it?

Answer 2

Put the two halogens in alphabetical order

Question 3

How do you name haloalkanes?

Answer 3

Add the suitable prefix onto the name of the longest chain

Question 4

What is a nucleophile?

Answer 4

An electron pair donor

Question 5

Why are haloalkanes polar?

Answer 5

The carbon-halogen bond is polar. The halogen generally has a much higher electronegativity than carbon, so the electrons are pulled slightly towards the halogen and the carbon is left with a slight positive charge

Question 6

Give three examples of nucleophiles

Answer 6

Hydroxide ions, :OH-
Water molecules, H2O:
Ammonia molecules, :NH3

Question 7

What happens when a nucleophile is attracted to a carbon?

Answer 7

It donated electrons to form a new covalent bond

Question 8

Why are nucleophiles attracted to carbon?

Answer 8

The carbon-halogen bond is polar, so carbon is left with a slight positive charge

Question 9

What happens when a nucleophile reacts with a haloalkane?

Answer 9

The nucleophile replaces the halogen in a substitution reaction

Question 10

What is nucleophilic substitution?

Answer 10

When a nucleophile replaces a halogen in a haloalkane

Question 11

What happens when a haloalkane is hydrolysed?

Answer 11

An alcohol is formed

Question 12

Describe the nucleophilic substitution reaction to make an alcohol from a haloalkane

Answer 12

1) The nucleophile (OH- in this case) approaches the slightly positively charged carbon
2) The direction of the attack of this nucleophile reduces the repulsion between the negatively charged hydrogen atom and the OH- ion
3) The lone pair of electrons on the nucleophile is donated to the carbon atom
4) A new bond forms between the carbon and the oxygen of the OH- ion
5) The carbon-halogen bond breaks by heterolytic fission
6) An alcohol and halide ion are formed

Question 13

Why is the reaction different when water is used as a nucleophile?

Answer 13

It is much slower but will eventually get the same result

Question 14

Which bond in the haloalkane is broken during hydrolysis?

Answer 14

The carbon-halogen bond

Question 15

What does the rate of hydrolysis in haloalkanes rely upon?

Answer 15

The strength of the carbon-halogen bond

Question 16

Which haloalkanes have the weakest bonds and so react fastest?

Answer 16

Iodoalkanes

Question 17

Which haloalkanes have the strongest bonds and so react the slowest?

Answer 17

Fluoroalkanes

Question 18

Will primary, secondary or tertiary haloalkanes react fastest?

Answer 18

Tertiary

Question 19

Why do tertiary haloalkanes react fastest?

Answer 19

The tertiary haloalkane is much more stable than the primary one and reacts with a two-step mechanism

Question 20

What reaction would you conduct to measure the rate of hydrolysis of the haloalkanes?

Answer 20

1) 1 cm³ of ethanol + two drops of haloalkanes
2) stand in 60 C of water
3) place test tube with 0.1 moldm silver nitrate
4) add 1 cm³ of silver nitrate quickly to each of the test tubes
5) observe the test tubes for five minutes and record the time taken to form a precipitate

Question 21

Hydrolysis of 1-chlorobutane observation?

Answer 21

White precipitate forms very slowly

Question 22

Hydrolysis of 1-bromobutane observation?

Answer 22

A cream precipitate forms faster that 1-chlorobutane but slower than 1-iodobutane

Question 23

Hydrolysis of 1-iodobutane observation?

Answer 23

A yellow precipitate forms rapidly

Question 24

What is the conclusion of the hydrolysis of haloalkanes?

Answer 24

Rate of hydrolysis increase as the strength of the carbon-halogen bond decreases

Question 25

What are organohalogen compounds?

Answer 25

Molecules contain at least one halogen atom joined to a carbon chain

Question 26

What are organohalogen used for?

Answer 26

Many pesticides

Question 27

How are organohalogen found?

Answer 27

Rarely found in nature

Question 28

What is the ozone layer?

Answer 28

Found in the outer edge of the stratosphere