3.3.4 Alkenes

Question 1

What are alkenes, what is their general formula?

Answer 1

• Unsaturated hydrocarbons
• CnH2n
• Involves a double covalent bond - a centre of high electron density

Question 2

What is the test for alkenes?

Answer 2

• Add bromine water
• Goes from orange to colourless in the presence of a double bond

Question 3

Name and outline the mechanism for the reaction of ethene + bromine.

Answer 3

Physical flashcards

Question 4

Name and outline the mechanism for the reaction of ethene + hydrogen bromide.

Answer 4

Physical flashcards

Question 5

Name and outline the mechanism for the reaction of ethene + sulfuric acid.

Answer 5

Physical flashcards

Question 6

How is the major product in the electrophilic addition of unsymmetrical alkenes determined?

Answer 6

• From the more stable carbocation intermediate
• Tertiary most stable > secondary > primary
• Due to greater positive inductive effect

Question 7

Draw the mechanism for the electrophilic addition of HBr to an unsymmetrical alkene (propene), showing the formation of both major and minor products.

Answer 7

Physical flashcards

Question 8

What is addition polymerisation?

Answer 8

• A reaction where small molecules (monomers, alkenes) join together
• To form a very large molecule called a polymer (poly(alkene))
• Which is unreactive - due to the strong C-C and C-H bonds

Question 9

Draw the monomer ethene and its polymer.

Answer 9

Physical flashcards

Question 10

Draw one repeating unit of poly(propene).

Answer 10

Physical flashcards

Question 11

What is poly(chloroethene) and its typical uses?

Answer 11

• PVC
• Hard and rigid - permanent dipole-dipole forces between chains due to the δ- Cl and δ+ C
• Doors, Window frame coverings and guttering

Question 12

What are the purpose of plasticisers in PVC and the uses of plasticised PVC?

Answer 12

• Added to reduce the effectiveness of intermolecular forces
• Making the plastic more flexible
• Cable insulation