organic chem; halogenoalkanes

Question 1

Halogenoalkanes

Answer 1

Are alkanes with 1 or more halogens attached to it

Question 2

What is the boiling point trend for halogenoalkanes?

Answer 2

Increases down the group

Question 3

Explain the boiling point trend of halogenoalkanes

Answer 3

• The no.of e- down the group increases
• more e- means stronger VDWs forces between the molecules & so more energy is needed to overcome these forces
• leads to be increasing down the group

Question 4

Halogenoalkanes have a … bond and are attacked by …

Answer 4

…polar
…nucleophiles

Question 5

Why do halogenoalkanes have a polar bond?

Answer 5

As halogens are more electronegative than C so they pull the e- towards themselves

Question 6

Nucleophile

Answer 6

Is a substance that is an e- pair donor

Question 7

Examples of nucleophiles

Answer 7

• ammonia (NH3)
• hydroxide ions (OH-)
• cyanide ions (-CN)

Question 8

Curly arrows show…

Answer 8

…the movement of e- pairs

Question 9

Halogneoalkanes react with hydroxide ions through…

Answer 9

…nucleophilic substitution

Question 10

What are the conditions of a nucleophilic substitution with hydroxide ions?

Answer 10

Warm aqueous sodium hydroxide (source of OH- ions)
Carried out under reflux

Question 11

Halogenoalkanes reacts with cyanide ions to make…

Answer 11

…nitriles

Question 12

What are the conditions of nucleophilic substitution reaction with cyanide ions?

Answer 12

Warm ethanolic potassium cyanide (source of CN- ions)
Carried out under reflux

Question 13

Conditions of nucleophilic reaction with ammonia

Answer 13

Heat with ethanolic ammonia
Must have excess ammonia

Question 14

Products of nucleophilic substitution with ammonia

Answer 14

Amine and ammonium ions (NH4+)

Question 15

Halogenoalkanes become more … , … the group

Answer 15

…reactive
…down

Question 16

What determines reactivity?

Answer 16

The bond strength/bond enthalpy determines the reactivity of haloalkanes — not bond polarity

Question 17

Halogenoalkanes react with hydroxide ions through … using an …

Answer 17

…elimination
…ethanol solvent

Question 18

Conditions of elimination reaction with halogenoalkanes and hydroxide ions

Answer 18

Warm ethanolic sodium hydroxide (source of OH ions)
Carried out under reflux

Question 19

What is formed when reacting sodium hydroxide with a halogenoalkane when using ethanol as a solvent?

Answer 19

Alkene

Question 20

What is formed when reacting sodium hydroxide with a halogenoalkane when using water as a solvent?

Answer 20

Alcohol

Question 21

CFCs break down … in the atmosphere

Answer 21

…ozone (O3)

Question 22

What are CFCs

Answer 22

They are molecules that have had all their H’s replaced by Cl and F — are stable molecules but are broken down by UV

Question 23

What catalyses the break down of ozone?

Answer 23

Radicals

Question 24

Why are C—Cl bonds broken easily?

Answer 24

As they have the lowest bond enthalpy

Question 25

How do CFC’s break down the ozone layer?

Answer 25

CFC’s break down to form chlorine radicals that break down ozone

Question 26

What are the steps of a radical substitution reaction?

Answer 26

1. Initiation 2. Propagation 3. Termination

Question 27

Why is the replacement for CFC’s

Answer 27

HFC’s (hydrofluorocarbons) as they don’t contain Cl