Alkenes

Question 1

what is stereoisomerism

Answer 1

molecules with the same structural formula but the bonds and atoms are arranged differently in space

Question 2

why does geometric isomerism arise in alkenes

Answer 2

• it occurs as a result of restricted rotation about the double carbon bond

Question 3

what is an E-isomer

Answer 3

priority groups are on different sides

Question 3

what is a Z-isomer

Answer 3

priority groups are on the same side

Question 4

what carbocation are major products formed from

Answer 4

• the most stable carbocation

Question 4

what is around a double carbon bond

Answer 4

• a region of high electron density which is readily attacked by electron deficient species called electrophiles

Question 5

what is an electrophile

Answer 5

an electron pair acceptor

Question 6

different types of carbocations and their relative stability

Answer 6

primary carbocation - 1 alkyl group - least stable

secondary carbocation - 2 alkyl groups

tertiary carbocation - 3 alkyl groups - most stable

Question 7

why is a tertiary carbocation the most stable

Answer 7

• the stability of a carbocation is increased by the presence of alkyl groups.
• the alkyl groups are electron releasing relative to the hydrogen atoms which helps the stabilise the positive charge on the carbocation ( positive inducing effect )
• more alkyl = more positive inducing effect = more stable

Question 8

what is poly(ethene) used to create

Answer 8

washing up bowls, plastic bags

Question 9

what is poly(propene) used for

Answer 9

rope

Question 10

how is poly(chloroethene) (PVC) made less hard and rigid

Answer 10

• plasticisers are added to the poly(chloroethene) to reduce the effectiveness of these attractions making the plastics more flexible. more plasticiser = more flexible
• most common plasticisers for PVC are phthalates

Question 11

why is poly(chloroethene) (PVC) so hard and rigid

Answer 11

• hard and rigid due to the permanent dipole-dipole forces between chains due to the δ+ carbon and the δ− chlorine

Question 12

problems with plastics

Answer 12

• they’re non-biodegradable due to the strong covalent non-polar bonds between atoms in the polymer molecules
• buried plastics in landfills can take hundreds of years to decompose
• tons of plastic are found in the ocean killing wildlife + habitats

Question 13

How can polymers be recycled by melting and remoulding?

Answer 13

Polymers can be melted down and remoulded by heating the polymer and breaking the weak van der Waals forces between the polymer molecules.

Question 14

How is poly(propene) recycled to produce new plastics?

Answer 14

Poly(propene) is heated to a high temperature to break the polymer bonds and produce the monomers again for making new plastics.

Question 15

What is the process for recycling polyethene?

Answer 15

Polyethene is separated from other plastics, washed, melted, and remoulded to make something else.