Reactions in Organic Chemistry - Addition Reaction

Question 1

Addition Reaction

Answer 1

One of which two or more molecules react together to form a single molecule

Question 2

Example of an addition reaction

Answer 2

addition of hydrogen to ethene to form ethane.

Involved hydrogen reacting w/ an unsaturated substance (hydrogenation reaction)

Question 3

Ethene

Answer 3

Prod. on an industrial scale, often referred to as ‘industry’s most important organic chemical’

Question 4

products of addition reactions of ethene

Answer 4

1, 2 - dibromoethane

1,2 - dichloroethane

chloroethane

ethanol

Question 5

Hydrogenation of vegetable oils

Answer 5

Hydrogenation of C=C double bonds used in manufacture of margarine

Question 6

polyunsatuated

Answer 6

Edible oils such as sunflower oil, palm oil, corn oil, are refered to as polyunsaturated

Question 7

saturated vs unsaturated

Answer 7

Unsaturated compounds are thought to be less damaging to our health than saturated fats found in dairy products.
Animal fats - usually saturated, veg. oils - unsaturated

Question 8

margarine

Answer 8

By controlling degree of hydrogenation, margerine can be made as hard or soft as needed

Question 9

Mechanism of the reaction between ethene + bromine

Answer 9

Reaction between ethene + bromine can occur in dark. Suggests mechanism is diff from that between methane + chlorine (free radical substitution)

Question 10

Mechanism of the reaction between ethene + bromine -

steps

Answer 10

1. Polarisation
2. Heterolytic fission
3. Carbon Ion Formation
4. Ionic Addition

Question 11

Mechanism of the reaction between ethene + bromine -

Step 1: polarisation

Answer 11

1. C=C double bond in ethene is a region of high concentration of negative charge
2. Br₂ molecule, as it approaches C=C double bond, becomes polarised as result of repulsion by electrons in double bond

Question 12

Mechanism of the reaction between ethene + bromine -

Step 2: Heterolytic fission

Answer 12

1. Induced polarisation becomes so great that the Br₂ molecule splits into Br⁺ and Br⁻ ions
2. This breaking of bond so that the two electrons end up on one atom is called heterolysis or heterolytic fission bc two diff species are formed

Question 13

Mechanism of the reaction between ethene + bromine -

Step 3: Carbonium Ion Formation

Answer 13

1. Br⁺ species attacks C₂H₄ molecule. (C₂H₄ molecule has the req. two electrons in its pi bond)
2. Br⁺ ions forms a covalent bond w/ one of the carbon atoms using these two electrons, one of which belonged to the other carbon atom
3. Leaves this w/ a positive charge
4. Positively charged carbon atom is called carbonium ion. Often referred to as an intermediate

Question 14

Mechanism of the reaction between ethene + bromine -

Evidence for carbonium ion has cyclic structure

Answer 14

• Evidence to suggest that carbonium ion intermediae has cyclic structure
• Called a cyclic bromium ion

Question 15

Mechanism of the reaction between ethene + bromine -

Step 4: Ionic Addition

Answer 15

1. Carbonium ion attacked by Br⁻ ion. Results in formation of 1, 2-dibromoethane
2. Mechanism of this reaction is referred to as ioni addition since ions add across the C=C double bond

Question 16

evidence for ionic addition

Answer 16

• 1,2-dibromoethane formed but two toher compounds also formed. One of these compounds is 1-bromo-2-chloroethane
• Formed when the carbonium ion attacked by the Cl⁻ ion

Evidence for the existence of the carbonium ion as an intermediate

Question 17

other compound formed

Answer 17

2-bromoethanol,

formed when carbonium ion attacked by water

Question 18

three products formed when ethene is added to bromine water containing dissolved sodium chlroide

Answer 18

1,2-dibromoethane CH₂BrCH₂Br

1-bromo-2-chloroethane CH₂BrCH₂Cl

2-bromoethanol CH₂BrCH₂OH

Question 19

Mechanism for addition of Cl2 / HCl to ethene

Answer 19

• Same mechanism

- no evidence for formation of a cyclic intermediate in cases of these

Question 20

Polymerisation reactions

Answer 20

Possible for molecules of ethene to link w/ each other to form long chain of carbon atoms

Question 21

Polythene / poly(ethene)

Answer 21

Compound formed from polymerisation, it is an example of a polymer

Question 22

Polymers

Answer 22

Long chain molecules made by joining together mainly small molecules
-consists of repeating structure + can have a relative molecular mass of several thousand

Question 23

Monomers

Answer 23

Small molecules from which polymer is made

Question 24

Use of polythene

Answer 24

Used in manufacture of plastic bags, bowls, lunch boxes, buckets

Question 25

Example of polymers

Answer 25

poly(chloroethene) and poly(propene)

Question 26

Poly(chloroethene)

Answer 26

commonly called polyvinyl chloride (PVC)

Made by reacting together cloroethene molecules

Question 27

Poly(propene)

Answer 27

made by polymerisation of propene

Question 28

Use of chloroethene

Answer 28

used for clothes

Question 29

Use of poly(propene)

Answer 29

manufacture of toys, jugs, plastic beakers

Question 30

Repeating unit

Answer 30

The repeating unit of a polymer is that part of the polymer whose repetition produces the complete polymer chain except for the end groups

Question 31

Addition polymers

Answer 31

Polymers like polythene and poly(propene) are categorised as addition polymers

Question 32

Crude oil

Answer 32

Raw material for the manufacture of polymers

Question 33

Examples of compounds manufactured by petrochemical industry

Answer 33

plastics
detergents
medicines
solvents
fabrics
paints

Question 34

1, 2 - dibromoethane

Answer 34

Formed by reaction between ethene + bromine, used as a fumigant

Question 35

1,2 - dichloroethane

Answer 35

Formed by a reaction between ethene + chlorine, used to manufacture chloroethene, used to make polyvinyl chloride (PVC), widely used plastic

Question 36

Chloroethane

Answer 36

Formed by reaction between ethene + hydrogen chloride, used in dentistry

Question 37

ethanol

Answer 37

Formed by reaction between ethene + water, used as an industrial solvent + as a fuel