HALOGENOALKANES

Question 1

Define primary halogenoalkane

Answer 1

One carbon attached to the at in atom adjoining the halogen

Question 2

Define secondary halogenoalkane

Answer 2

Two carbons attached to the carbon atom anointing the halogen

Question 3

Define tertiary halogenoalkane

Answer 3

Three carbons attached tot the carbon stoma joining the halogen

Question 4

What are the two reactions halogenoalkanes can undergo

Answer 4

Substitution

Elimination

Question 5

Define substitution

Answer 5

Swapping a halogen atom for another atom or groups of atoms

Question 6

Define nucleophile

Answer 6

Electron pair donor

Question 7

Give an example of a nucleophile

Answer 7

:OH-

:NH3

CN-

Question 8

Outline nucleophilic substitution

Answer 8

The nucleophile attack the (delta) positive carbon atom

The carbon has a small positive charge because of the electronegativity difference between carbon and the halogen

The nucleophile replaces the halogen on the alkane

Question 9

How is the rate of a substitution reaction affected by the strength of the carbon-halogen bond?

Answer 9

The weaker the bond
The easier it is to break
And the faster the reaction

Question 10

What is the trend in rate of a substitution reaction of halogenoalkanes?

Answer 10

Iodo alkanes substitute the fastest

Fluoroalkanes substitute the slowest

Because C-I bonds have the weakest bond enthalpy

And C-F bonds have the strongest bond enthalpy

Question 11

Define hydrolysis

Answer 11

Splitting a molecule by reaction with water

Question 12

Describe water as a nucleophile

Answer 12

Water is a POOR nucleophile

But reacts slowly with haloalkanes in a substitution reaction

Question 13

Describe the reaction between aqueous silver nitrate and haloalkanes

Answer 13

Halide group combined with silver ion to form a silver halide precipitate

I- + Ag+ -> AgI

Question 14

Describe the colour of silver ha life precipitates

Which form fastest?

Answer 14

AgI (yellow) forms fastest
AgBr (cream)
AgCl (white) forms slowest

Question 15

Describe the conditions of nucleophilic substitution with aqueous hydroxide ions

Answer 15

Potassium (or sodium) hydroxide reagent

Aqueous solution

Heat under reflux

Question 16

Describe the change in halogenoalkane when substituted in aqueous hydroxide ions

Answer 16

Forms an alcohol

Question 17

Why is the aqueous condition important in nucleophilic substitution with hydroxide ions

Answer 17

Ethanol would trigger an elimination reaction

Question 18

Outline tertiary halogenoalkane nucleophilic substitution

Answer 18

The halogen breaks away from haloalkane

To form a carbocations intermediate

The hydroxide nucleophile then attacks the positive carbon

Question 19

Describe the conditions of nucleophilic substitution with cyanide ions

Answer 19

KCN dissolved in ethanol/water mixture reagent

Heating under reflux

Question 20

Outline the change in rules for naming nitriles

Answer 20

Nitriles have to be at the end of a chain

Start numbering the chain from the c in CN

Include the e (butanenitrile not butannitrile)

Question 21

Describe the conditions of nucleophilic substitution with ammonia

Answer 21

NH3 dissolved in ethanol reagent

Heating under pressure

Question 22

Outline nucleophilic substitution with ammonia

Answer 22

The ammonia attack the (delta) positive carbon atom

The ammonia replaces the halogen on the alkane producing a halogen radical

Excess ammonia then reacts with the hydrogen on the positive charged nitrogen

Question 23

Why must excess ammonia be used in nucleophilic substitution

Answer 23

To minimise a lower yield due to further substitution reactions occurring

Question 24

Define elimination

Answer 24

Removal of small molecule (often water) from the organic molecule

Question 25

Outline the conditions for elimination with alcoholic hydroxide ions

Answer 25

Potassium (or sodium) hydroxide reagent In ethanol With heat

Question 26

Outline elimination with alcoholic hydroxide ions

Answer 26

The radical reacts with a hydrogen bonded to a neighbouring carbon to the halogen The bond between mentioned hydrogen and carbon breaks to form a double bond between carbon carbon atoms The halogen group forms a negative ion And H2O

Question 27

What types of reaction are likely to occur between primary and tertiary halogenoalkanes

Answer 27

Primary tends toward substitution Tertiary tends toward elimination

Question 28

What are some of the uses of halogenoalkanes

Answer 28

Chloroalkane a and chlorofluoroalkanes can be used as solvents in dry cleaning Refrigerants Pesticides Aerosol propellants

Question 29

Why have many uses of halogenoalkanes been stopped?

Answer 29

Toxic Detrimental effects on the atmosphere

Question 30

Why is the ozone layer benefitial

Answer 30

Filters out harmful UV radiation

Question 31

What does ozone in the lower atmosphere do

Answer 31

Pollutes Contributes toward smog formation

Question 32

Outline the conditions for nucleophilic substitution of halogenoalkanes with aqueous hydroxide ions

Answer 32

Potassium/Sodium hydroxide Aqueous solution heat under reflux Neucleophile OH-