Alkenes

Question 1

What is a Stereoisomerism?

Answer 1

Molecules with the same molecular and structural formula but a different array in space.

Question 2

E isomer

Answer 2

• Two higher priority groups are attatched to the carbon on OPPOSITE sides of the double bond.

Question 3

Z isomer

Answer 3

• Two higher priority groups are attatched to the carbon on the SAME side of the double bond.

Question 4

Each carbon must..

Answer 4

• Be bonded to 2 different atoms or groups
• two identical groups cant be joined to the same carbon

Question 5

Which atom takes priority?

Answer 5

atom attached to the carbon with the higher atomic number.

Question 6

What is an Electrophile?

Answer 6

An electron pair acceptor

Question 7

Electrophiles that react with alkanes have..

Answer 7

an atom with a partially positive charge

Question 8

What causes the carbon double bond to break?

Answer 8

When a pair of electrons from the double bind are donated to the electrophile.

Question 9

What happens when the C=C bond breaks?

Answer 9

Alkenes undergo addition reactions and form a single bond.

Question 10

What happens in electrophilic addition?

Answer 10

• pair of electrons from the C=C bond form a covalent bond with delta positive X atom
• X-Y bond breaks forming :Y- ion
• lone pair on :Y- form covalent bond with +ve carbon

Question 11

How are alkyl hydrogensulphates formed?

Answer 11

Alkenes are absorbed by cold, concentrated sulfuric acid (H2SO4) which is an electrophille

Question 12

What happened when you add hydrogensulfate to water?

Answer 12

Causes hydrolysis and ethanol is produced.

Question 13

Adding HBR/H2SO4 to an unsymmetrical alkene forms..

Answer 13

a major and minor product.

Question 14

What is a major product?

Answer 14

Product formed from the most stable carbocation.

Question 15

What is the equation for Direct Hydration?

Answer 15

ethene + water—————> ethanol
(conc. H2SO4)

Question 16

What role does sulfuric acid have in direct rehydration?

Answer 16

Catalyst

Question 17

What is a Primary (1°) Carbocation?

Answer 17

1 carbon is bonded to the positively charged carbon atom.

Question 18

What is a Secondary (2°) Carbocation?

Answer 18

2 carbons bonded to the positively charged carbon atom.

Question 19

What is a Tertiary (3°) Carbocation?

Answer 19

3 carbons bonded to the positively charged carbon atom.

Question 20

What is the electron releasing property of an alkyl group called?

Answer 20

Positive inductive effect ( electron pushing )

Question 21

Number of alkyl groups around positively charged carbon increases with..

Answer 21

stability of carbocation

Question 22

What forms a minor product?

Answer 22

The less stable carbocation

Question 23

What is a polymerisation recation?

Answer 23

Reaction that joins together many small molecules(alkenes) to form a very large molecule (polymer).
They form a polyalkene which are unreactive.

Question 24

How are polyalkekes represented?

Answer 24

Using a repeating unit.

Question 25

Describe poly(chloroethene)

Answer 25

• hard and rigid
• due to permanent dipole-dipole forces between chains.
• this is due to delta positive C and delta negative Cl

Question 26

How are Plasticisers used?

Answer 26

• added to poly(chloroethene) to reduce effectiveness of the attractions
• this makes plastic more flexible

Question 27

Why cant plastics be broken down?

Answer 27

• non biodegradable due to strong covalent non polar bonds between atoms in polymer molecules

Question 28

Why dies plastic take do long to decompose?

Answer 28

It cant be broken down by nucleophiles.

Question 29

How can polymers be remoulded?

Answer 29

by heating the polymer
• this breaks the weak van der waals forces between polymer molecules