Alkenes

Question 1

Why are alkenes reactive?

Answer 1

They are attacked by electrophiles due to their double bond which has a high electron density

Question 2

What is an electrophile

Answer 2

An electron pair acceptor that is deficient in electrons and is attracted to the double bond

Question 3

Electrophile examples (4)

Answer 3

Positive charge ions : NO2+ and H+
Polar molecules: H-Br and H2SO4

Question 4

Addition of bromine (test for alkenes)
Colour change
Electrophile
Product

Answer 4

Orange brown to colourless
Electrophile: bromine
Product: dibromoalkane (colourless)

Question 5

The more ______ available, the more stable the intermediate is in the addition of hydrogen halides to alkenes

Answer 5

Alkyl groups

Question 6

Why do more alkyl groups bonded to the carbocation mean that it’s more stable?

Answer 6

Alkyl groups push electrons towards the positive carbocation stabilising it, and the more stable the carbocation the more likely it is to form

Question 7

Why does reacting hydrogen halides with unsymmetrical alkenes produce two products?

Answer 7

One is from a primary carbocation formed less often
The other is from a secondary carbocation formed more often (or other combinations of carbocations)

Question 8

Alkene to (alkylhydrogensulfate then alkyl hydrogensulfate to) alcohol catalyst

Answer 8

Cold, concentrated H3PO4

Question 9

Alkene and cold concentrated H2SO4 make…

Answer 9

Alkylhydrogensulphate

Question 10

Alkylhydrogensulphate to alcohol needs what other reactant?

Answer 10

cold water for a hydrolysis reaction reforming the H2SO4 from the alkene to alcohol reaction

Question 11

3 polymer examples

Answer 11

poly(ethane), nylon, Teflon

Question 12

2 types of polymers and 2 examples of each

Answer 12

Natural (proteins, and natural rubber)
Synthetic (poly(ethane) and poly(propene))

Question 13

Why are poly(alkenes) unreactive? What can this cause as an environmental consequence?

Answer 13

They are saturated molecules and normally non polar
This is why they don’t degrade well in landfill

Question 14

What does a repeating unit look like? 3 points

Answer 14

One single monomer
Trailing bonds outside brackets
n at bottom of right bracket

Question 15

Properties of poly(alkanes)

Answer 15

The longer and straighter the chains the stronger the Van der Waals
Shorter polymers with branching tend to be more flexible and weaker
Longer polymers with less branching tend to be stronger and more rigid
Some polyalkenes have halogens eg Chlorine (PVC - polyvinyl chloride) forming permanent dipole dipole

Question 16

What is a plasticiser for and what polymer do they usually get added to?

Answer 16

Adding to polymers to make them more flexible as they slide between the polymer chains pushing them apart and weakening intermolecular forces
This makes chains slide over each other more and easier to bend

PVC - poly(chloroethene)

Question 16

PVC uses before and after plasticisers

Answer 16

Before: long closely packed polymer chains that are hard and brittle, used in drain pipes
After: more flexible, used in electrical cable insulation and clothing