31: Typical Reactions of Selected Functional Groups

Question 1

In the reaction of methane with halogens, what is the difference in reaction conditions with chlorine and bromine?

Answer 1

Chlorine is more reactive than bromine, so it requires less energy to activate the reaction. The reaction with chlorine can take place in diffused sunlight while that with bromine can only take place in direct sunlight.

Question 2

What is the reaction condition of the hydrogenation of alkenes?

Answer 2

Room temperature in the presence of a platinum catalyst,
or on heating at 150ºC in the presence of a nickel catalyst.

Question 3

What is the reaction condition of the chlorination of alkenes?

Answer 3

The reaction proceeds at room temperature and pressure.

Question 4

What is the reaction condition of the bromination of alkenes?

Answer 4

The reaction proceeds at room temperature and pressure.

Question 5

What is the chemical equation of the reaction when chlorine is mixed with water?

Answer 5

Cl₂ + H₂O <-> HCl + HOCl

Question 6

What is the chemical equation of the reaction when bromine is mixed with water?

Answer 6

Br₂ + H₂O <-> HBr + HOBr

Question 7

What is the word equation of the bromination of ethene?

Answer 7

Ethene + bromine (in 1,1,1-trichloroethane) -> 1,2-dibromoethane

Question 8

What is the word equation of the reaction when bromine water is added to ethene?

Answer 8

Ethene + bromine + water -> 2-bromoethan-1-ol + hydrogen bromide

Question 9

What is the word equation of the reaction when hydrogen bromide is added to ethene?

Answer 9

Ethene + hydrogen bromide -> bromoethane

Question 10

What is the reaction condition of the reaction between alkenes and gaseous hydrogen halides?

Answer 10

The reaction proceeds at room temperature and pressure.

Question 11

What is the condition for different isomers to be produced when an alkene reacts with a hydrogen halide?

Answer 11

Both the alkene and hydrogen halide are unsymmetrical molecules.

Question 12

What is the Markonikov’s Rule?

Answer 12

Markonikov’s rule states that when a molecule HX adds to an unsymmetrical alkene, the hydrogen atom attaches mainly to the carbon atom that already carries the greater number of hydrogen atoms.

Question 13

What are primary haloalkanes?

Answer 13

Primary haloalkanes are haloalkanes which have only one carbon atom bonded to the carbon atom bearing the halogen atom.

Question 14

What are secondary haloalkanes?

Answer 14

Secondary haloalkanes are haloalkanes which have two carbon atoms bonded to the carbon atom bearing the halogen atom.

Question 15

What are tertiary haloalkanes?

Answer 15

Tertiary haloalkanes are haloalkanes which have three carbon atoms bonded to the carbon atom bearing the halogen atom.

Question 16

What are the reaction conditions of the reaction of haloalkanes to form alcohols?

Answer 16

Sodium hydroxide solution is added and the reaction mixture is heated under reflux.

Question 17

What is an alternative name for the reaction of haloalkanes to form alcohols?

Answer 17

Hydrolysis

Question 18

What is heating under reflux?

Answer 18

Heating under reflux means heating with a condenser fitted vertically in the reaction flask.

Question 19

What is the importance of heating under reflux?

Answer 19

Heating under reflux ensures that the volatile reactants are condensed back into the reaction mixture, which prevents them from evaporating before they have a chance to react.

Question 20

What is the importance of using the correct direction of water flow in the condenser when heating under reflux?

Answer 20

The place where water enters should be lower than the place where water exits on the condenser column. This ensures that water can build up in the condenser column before flowing out, which provides a better cooling effect.

Question 21

What is the importance of adding anti-bumping granules when heating under reflux?

Answer 21

Anti-bumping granules provide a larger surface area for the formation of bubbles, so a lot of small bubbles will be formed instead of a big one. This prevents a big bubble from pushing the liquid up the condenser column, which may lead to spilling.

Question 22

What are primary alcohols?

Answer 22

Primary alcohols are alcohols which have only one carbon atom bonded to the carbon atom bearing the hydroxyl group.

Question 23

What are secondary alcohols?

Answer 23

Secondary alcohols are alcohols which have two carbon atoms bonded to the carbon atom bearing the hydroxyl group.

Question 24

What are tertiary alcohols?

Answer 24

Tertiary alcohols are haloalkanes which have three carbon atoms bonded to the carbon atom bearing the hydroxyl group.

Question 25

What are the reaction conditions of the reaction of tertiary alcohols with concentrated hydrochloric acid?

Answer 25

The reaction proceeds on shaking at room temperature.

Question 26

What are the reaction conditions of the reaction of secondary alcohols with concentrated hydrochloric acid?

Answer 26

Anhydrous zinc chloride is added as a catalyst, and the reaction mixture is heated under reflux.

Question 27

What are the reaction conditions of the reaction of secondary alcohols with dry hydrogen chloride gas?

Answer 27

Anhydrous zinc chloride is added as a catalyst.

Question 28

What are the reaction conditions of the reaction of alcohols with phosphorus pentachloride?

Answer 28

The reaction proceeds on shaking at room temperature.

Question 29

What are the reaction conditions of the reaction of alcohols with phosphorus trichloride?

Answer 29

The reaction mixture is heated under reflux.

Question 30

Explain the difference in reactivity of phosphorus pentachloride and phosphorus trichloride.

Answer 30

Phosphorus pentachloride is more reactive than phosphorus trichloride. This is because the bond angle of phosphorus pentachloride is smaller and the chlorine atoms are brought together to as close as 90º surrounding the central phosphorus atom. After reacting with the alcohol, phosphorus trichloride oxide is formed, which is more stable since the bond angles are larger than that in phosphorus pentachloride. Meanwhile, the bond angle of the phosphorus molecule is not changed after reaction of alcohol with phosphorus trichloride, so the reaction proceeds less readily.

Question 31

What are the products and chemical formulas of the reaction of alcohols with phosphorus pentachloride?

Answer 31

Chloroalkane (RCl), phosphorus trichloride oxide (POCl₃), and hydrogen chloride gas (HCl).

Question 32

What are the products and chemical formulas of the reaction of alcohols with phosphorus trichloride?

Answer 32

Chloroalkane (RCl) and phosphorous acid (H₃PO₃).

Question 33

What are the reaction conditions of the reaction of alcohols with sulphur dichloride oxide?

Answer 33

The reaction mixture is heated under reflux.

Question 34

What are the products and chemical formulas of the reaction of alcohols with sulphur dichloride oxide?

Answer 34

Chloroalkane (RX), sulphur dioxide gas (SO₂), and hydrogen chloride gas (HCl).

Question 35

Explain the choice of chlorinating method which is widely used in industry.

Answer 35

SOCl₂ substitution, since the side products are sulphur dioxide gas and hydrogen chloride gas, which will escape freely and leave behind the chloroalkane of high purity.

Question 36

What are the ways to brominate an alcohol using hydrogen bromide?

Answer 36

1. Add the alcohol to hydrogen bromide and heat under reflux
2. Add a mixture of *sodium bromide and concentrated sulphuric acid** to the alcohol and heat under reflux.

Question 37

Why does orange colour appear when brominating an alcohol with sodium bromide and concentrated sulphuric acid?

Answer 37

Hydrogen bromide is produced in the reaction between sodium bromide and concentrated sulphuric acid. It is oxidised by the concentrated sulphuric acid to form bromine liquid, causing orange colour to appear in the reaction mixture.

Question 38

What are the ways to iodinate an alcohol using hydrogen iodide?

Answer 38

1. Add the alcohol to hydrogen iodide and heat under reflux
2. Add a mixture of sodium iodide and concentrated phosphoric acid to the alcohol and heat under reflux.

Question 39

Explain the choice of acid when producing hydrogen iodide for the iodination of alcohols.

Answer 39

Concentrated phosphoric acid is used.
If oxidising acids like concentrated sulphuric acid are used, the hydrogen iodide produced will quickly be oxidised to iodine by the acid, since hydrogen iodide is a strong reducing agent. This leaves almost no hydrogen iodide left for reaction.
If volatile acids like ethanoic acid are used, the acid evaporates easily since a large amount of heat is produced when hydrogen iodide reduces the acid.

Question 40

What are the ways to brominate an alcohol using phosphorus tribromide?

Answer 40

1. Add the alcohol to phosphorus tribromide and heat under reflux
2. Add a mixture of red phosphorus and bromine liquid to the alcohol and heat under reflux.

Question 41

What are the products and chemical formulas of the reaction of alcohols with phosphorus tribromide?

Answer 41

Bromoalkane (RBr) and phosphorous acid (H₃PO₃)

Question 42

What are the ways to iodinate an alcohol using phosphorus triiodide?

Answer 42

1. Add the alcohol to phosphorus triiodide and heat under reflux
2. Add a mixture of red phosphorus and iodine solid to the alcohol and heat under reflux.

Question 43

What are the products and chemical formulas of the reaction of alcohols with phosphorus triiodide?

Answer 43

Iodoalkane (RI) and phosphorous acid (H₃PO₃)

Question 44

Explain whether PBr₅ and PI₅ substitutions are possible with alcohols.

Answer 44

No, because PBr₅and PI₅ are unstable. They have a large atomic size and experience large forces of repulsion, so they cannot be held close to each other that the bond angles between some pairs are 90º.

Question 45

List all chlorinating agents and their chemical formulas for alcohols.

Answer 45

Hydrogen chloride / hydrochloric acid (HCl) liquid or gas, phosphorus pentachloride (PCl₅) or phosphorus trichloride (PCl₃), sulphur dichloride oxide (SOCl₂).

Question 46

List all brominating agents and their chemical formulas for alcohols.

Answer 46

Hydrogen bromide gas (HBr) or in situ production of HBr by sodium bromide and concentrated sulphuric acid (NaBr + H₂SO₄), phosphorus tribromide (PBr₃) or in situ production of PBr₃ by red phosphorus and bromine liquid (red P + Br₂).

Question 47

List all iodinating agents and their chemical formulas for alcohols.

Answer 47

Hydrogen iodide gas (HI) or in situ production of HI by sodium iodide and concentrated phosphoric acid (NaI + H₃PO₄), phosphorus triiodide (PI₃) or in situ production of PI₃ by red phosphorus and iodine solid (red P + I₂).

Question 48

What is dehydration?

Answer 48

Dehydration is a reaction in which a water molecule is removed from a reactant molecule.

Question 49

Explain whether all alcohols can undergo dehydration.

Answer 49

No, dehydration removes the hydroxyl group and the hydrogen atom attached to the adjacent carbon atom. If the adjacent carbon atom(s) have no hydrogen atoms, then they cannot undergo dehydration.

Question 50

What is the systematic name of the alcohol with smallest molar mass that cannot be dehydrated?

Answer 50

2,2-dimethylpropan-1-ol / 2,2-dimethylpropanol

Question 51

What is an elimination reaction?

Answer 51

An elimination reaction is a reaction where a small molecule is removed from a reactant molecule.