4B - Alkenes

Question 1

Test for a C=C double bond?

Answer 1

Add bromine water to the solution.

Colour change = Orange brown → Colourless if C=C bond is present.

If no C=C bond is present then solution remains orange brown.

Question 2

Name the mechanism for which you use an alkene to form a haloalkane by: Alkene + Halogen

Give the conditions required for the reaction

Answer 2

Mechanism = Electrophilic addition reaction

Condition = RTP, No UV light

Question 3

Draw the mechanism for the formation of 1,2-dibromoethane.

What is acting as the electrophile?

Answer 3

Electrophile in this reaction is the bromine.

Question 4

What type of bond fission is electrophilic addition?

Answer 4

Hetrolytic fission

Question 5

Draw the mechanism for the synthesis of 2-bromopropane.

Why is 2-bromopropane the preferred product in terms of relative stabilities of the possible organic intermediates (carbocations)?

Answer 5

The hydrogen atom will add onto the carbon that has the most number of hydrogens already.

2-bromopropane is the more stable carbocation as carbocation stability will increase as the number of hydrogens around the carbon atom increases.

Question 6

Name the reaction fo adding water to an alkene

Answer 6

Hydration reaction

Question 7

Name the reagents, mechanism name and the organic intermediate when you have: Alkene + Water

Waht do you get as a product?

Answer 7

Alkene + H₂O → Alcohol

Mechanism = Hydration reaction / electrophilic addition

Conditions = Heat + H₃PO₄ Catalyst

Reagents = Water (as steam), H₃PO₄ Catalyst

Organic intermediate = Alcohol

Question 8

Name the reaction of when you add H₂ to an alkene

Answer 8

Hydrogenation

Question 9

Conditions for hydogenation

Answer 9

Nickel catalyst

423K

Question 10

Why is 100% yield rarely achieved in organic reactions? (2)

Answer 10

• Transfer loss
• More byproduct is achieved than the desired product

Question 11

How can the atom economy for the synthesis of a substance be imporved?

Answer 11

Reduce the number of byproducts being formed and only have the desired product forming.

Question 12

How can percentage yield be improved?

Answer 12

Choose a reaction that doesn’t produce many byproducts

Question 13

Tetrafluoroethene

Common name + use

Answer 13

Common name = Teflon

Uses = Coating non-stick pans

Question 14

Phenylethene

Common name + use

Answer 14

Common name = Styrene

Uses = Packaging material

Question 15

Polypropene

Uses (2)

Answer 15

Used in the form of polypropene

Making children’s toys

Fibres for ropes

Question 16

Chloroethene

Use?

Answer 16

Used in the form of polychloroethene

Making PVC

Question 17

This is a section of a polymer. What is the monomer?

Answer 17

Propene

Question 18

Probems associated with the vast quantities of plastics that are used worldwide? (4)

Answer 18

• Takes a long time to biodegrade
• Animals can ingest it and choke as they can’t digest the plastics.
• Gets into water, pollutes the rivers/oceans
• Makes landscapes messy

Question 19

Name the 3 alternative ways of treating the vasts amount of plastic waste that we get in our world

Answer 19

• PVC recycling
• Producing Potodegradable and biodegradable polymers
• Reuse of material as a feedstock for the chemical industry

Question 20

How are addition polymers treated to allow them to be reused by the chemical industry?

Answer 20

They’re recycled.

They’re sorted into the various types of polymers and then copped into flakes, washed, dried and melted.

Recycled polymer is cut into pellets and used by manufacturers to repurpose into new products.

Question 21

Answer 21