3.3.4 Alkenes

Question 1

What are alkenes?

Answer 1

Unsaturated hydrocarbons.

Question 2

What is the general formula for an alkene?

Answer 2

CnH2n

Question 3

What shape is ethene and what are its bond angles?

Answer 3

Planar, 120 degrees.

Question 4

What are electrophiles?

Answer 4

+ ions or electron deficient atoms and act as e- pair acceptors.

Question 5

What does being an e- pair acceptor mean?

Answer 5

They seek e- rich sites.

Question 6

What state does HBr react with alkenes and what does it form?

Answer 6

Gas or concentrated aqueous solutions, to form bromoalkenes.

Question 7

Ethene + HBr ->

Answer 7

1-bromoethane

Question 8

What conditions in the HBr molecule make it suitable to react in an electrophillic addition reaction?

Answer 8

Br is > electroneg than H, makes HBr polar.

Question 9

What happens in the electrophilic addition reaction between H in the HBr and the C = C bond?

Answer 9

Electrons from the double bond move, forming a new C-H bond.

Question 10

What happens to the e-s in a electrophilic addition in the H-Br bond?

Answer 10

E-s shift towards Br making a bromide ion (tow dots Br -).

Question 11

What happens to the C = C bond in electrophilic addition with HBr?

Answer 11

Breaks, leaving a C to become an e- deficient carbocation.

Question 12

What is a carbocation?

Answer 12

Species which contains a carbon atom that has a+ charge.

Question 13

What does the Br- ion do in electrophilic substitution?

Answer 13

Acts as a nucleophile, attacks the carbocation, using its lone pairs to form a new bond between C and Br.

Question 14

Under what conditions do an alkene and sulphuric acid react, what does this form?

Answer 14

Alkene reacts with a cold, conc. sulphuric acid. Forms alkyl hydrogensulphates.

Question 15

What do two p orbitals produce when they overlap?

Answer 15

Pi orbitals.

Question 16

What can alkyl hydrogen sulphates be hydrolysed to, under what conditions?

Answer 16

Hydrolysed to an alcohol by reacting it with warm sulphuric acid.

Question 17

What is bromine water the test for, how does it change?

Answer 17

Alkenes, red/brown to colourless.

Question 18

Why don’t we use bromine water to test for alkanes?

Answer 18

Don’t react.

Question 19

If the alkene and the electrophile being added are both unsymmetrical what two possible products are formed?

Answer 19

Major and minor product.

Question 20

What is the major product formed by?

Answer 20

The more stable carbocation.

Question 21

What is the order of stability of the carbocations?

Answer 21

Tertiary > Secondary > Primary.

Question 22

Why does more alkyl groups around the carbocation do and what is more likely to happen?

Answer 22

Make it more stable, more likely to be formed.

Question 23

What is a tertiary carbocation bonded to?

Answer 23

3 C / 0 H.

Question 24

What is a secondary carbocation bonded to?

Answer 24

2 C / 1 H.

Question 25

What is a primary carbocation bonded to?

Answer 25

1 C / 1 H.

Question 26

Why can’t you produce major and minor products from a reaction with Br2?

Answer 26

Br2 is symmetrical.

Question 27

Explain the circumstances needed for a major and minor product to be formed in roughly equal amounts.

Answer 27

Both the same level of carbocation, electrophilic addition can occur on either carbon, no preference between the two.

Question 28

Can you draw the structure out when a question asks you for a balanced equation?

Answer 28

Yes.

Question 29

When identifying a product do you need to name it?

Answer 29

No you can just draw it instead.

Question 30

What are polymers formed from?

Answer 30

Monomers.

Question 31

What are monomers?

Answer 31

Tiny repeating units.

Question 32

What are polymers formed in the presence of?

Answer 32

A catalyst.

Question 33

How are polymers represented?

Answer 33

Using a repeating unit.

Question 34

What makes polyalkenes unreactive?

Answer 34

They are saturated.

Question 35

What are the strong bonds in a polyalkene?

Answer 35

C-H and C-C.

Question 36

Do polyalkenes biodegrade?

Answer 36

No, not attacked by biological agents (enzymes).

Question 37

What are plasticisers, what are they used for and why?

Answer 37

Small molecules that fill the gaps between the polymer chains, added to a polymer to modify them so chains can slide over eachother.

Question 38

Give an example of how a plastic changes with use of a plasticiser.

Answer 38

PVC, drainpipes and aprons.

Question 39

How are polymers written from the monomer?

Answer 39

A long C chain with whatever is attached to the monomer.

Question 40

How is a repeating unit written?

Answer 40

One part of the polymer is put in square brackets, the bonds on either side must go out of the brackets.

Question 41

What is the everyday name for polyethene and what is it used for?

Answer 41

Polythene, used for making plastic bags, packing film, squeezy bottles.

Question 42

What is the everyday name for polypropene and what is it used for?

Answer 42

Polypropylene, used for making ropes, plastic chairs and carpet.

Question 43

What is the everyday name of phenylethene?

Answer 43

Polystyrene.

Question 44

What is the everyday name of chloroethene?

Answer 44

PVC.

Question 45

What is the everyday name of tetrafluoroethene?

Answer 45

PTFE / Teflon.

Question 46

What is the everyday name of methyl 2-methylpropenoate?

Answer 46

PMMA, Perspex.