O- Alkenes =)

Question 1

Explain why more 3-bromo-3-methylpentane is formed in electrophilic addition than 2-bromo-3-methylpentane. (2)

Answer 1

• 3-bromo-3-methylpentane is formed from 3° carbocation intermediate
• 3° carbocation ↑ stable than 2°
• ↑ +ve inductive effect ∵ 3 e- donating alkyl groups

Question 2

Explain why there is an attraction between a C=C double bond and Br2. (3)

Answer 2

• C=C is e- rich (/ area of high e- density)
• when Br-Br becomes polarised
• δ+ Br attracted to C=C

Question 3

State what you would observe if bromine water was added to poly(chloroethene).
Explain this observation. (2)

Answer 3

• x reaction
• polymer is saturated (x double bond)

Question 4

Explain how three isomeric products are formed when HBr reacts with but-1-ene. (3)

Answer 4

• major product exists as a pair of enantiomers
• 3rd isomer = 1-bromobutane (minor)
• formed from primary carbocation

Question 5

What does the term ‘addition’ mean in electrophilic addition ? (1)

Answer 5

reaction which increases no. of substituents/ converts double bond into single bond

Question 6

State the purpose of polymerisation in forming poly(ethene). (1)

Answer 6

molecules joined tgt –> long chain molecule

Question 7

Poly(propene) is not biodegradable because it is unreactive.
Explain why poly(propene) is unreactive. (1)

Answer 7

non-polar (x polar bonds in chain)

Question 8

Scientists are developing new polymers, including some that are biodegradable.
Suggest why it is beneficial for some polymers to be biodegradable. (1)

Answer 8

prevent build up of waste in landfill (✔broken down in natural processes)

Question 9

Explain how stereoisomerism arises. (1)

Answer 9

• C=C bond cannot rotate and
• Each carbon in the double bond has (2) different groups attached

Question 10

C20H42 –> C8H18 + 2 C3H6 + 3 C2H4
How do the products of the reaction show that it is an example of thermal cracking? (1)

Answer 10

mainly alkenes formed