Alkenes

Question 1

Why are alkenes vulnerable to attacks by electrophiles?

Answer 1

The double bond has a high electron density so species that want to gain electrons are attracted to it.

Question 2

What are electrophiles?

Answer 2

electron pair acceptors

Question 3

What is the name of the mechanism for the reaction of an alkene and a hydrogen halide to form a halogenoalkene?

Answer 3

electrophilic addition

Question 4

Name and outline the mechanism for the reaction of ethene and hydrogen bromide.

Question 5

Why can more than two different halogenoalkanes be formed if the alkene is unsymmetrical?

Answer 5

The halogen will be more likely to bind to the more stable carbonation because they have more alkyl groups that can distribute the charge on the carbon.

Question 6

Name and outline the mechanism for the reaction of propene and hydrogen bromide. Draw the two products that could form in this reaction.

Question 7

What is the name of the mechanism for the reaction of an alkene and a bromine to form a dibromoalkane?

Answer 7

electrophilic addition

Question 8

Name and outline the mechanism for the reaction of ethene and bromine to form a dibromoalkane.

Question 9

What is the name of the mechanism for the reaction of an alkene and sulfuric acid to form an alcohol?

Answer 9

electrophilic addition and hydrolysis

Question 10

Name and outline the mechanism for the reaction of ethene and sulfuric acid to form an alcohol.

Question 11

What is the test for unsaturation?

Answer 11

Add bromine water and if the solution decolorises then an alkene is present.

Question 12

What do alkenes need to have for E-Z isomerism to arise?

Answer 12

1. The restricted rotation around the double bond.
2. Two groups are attached to each end of the double bond.

Question 13

Why does but-1-ene not show E-Z isomerism?

Answer 13

Because on one side of the double bond, there are two identical groups.

Question 14

What are polymers?

Answer 14

Large complex molecules made up of many monomers joined together.

Question 15

What is addition polymerisation?

Answer 15

When many of the same monomers are bonded together by condensation reactions.

Question 16

Why are addition polymers not very reactive?

Answer 16

They are non-polar.

Question 17

Why do additional polymers with longer chains and little branches have higher melting and boiling points?

Answer 17

The bigger the chain is and the closer the molecules are to each other the stronger the van der Waals forces are so more energy is needed to break those forces.

Question 18

What does PVC stand for?

Answer 18

Poly(chloroethene)

Question 19

What is the repeating unit for PVC?

Question 20

Why is PVC a hard material?

Answer 20

The chlorine atoms are more electronegative compared to the carbon and that means it has a slightly negative charge and the carbon has a positive one. This means that permanent dipole-dipole bonds can form between the PVC molecules. These forces need a lot of energy to break.

Question 21

How do plasticisers make PVC softer?

Answer 21

They weaken the van der Waals forces between the PVC molecules by forcing them apart and that means less energy is needed to break those bonds and change the shape of the PVC

Question 22

What is hard PVC used for?

Answer 22

drain pipes and window frames

Question 23

What is soft PVC used for?

Answer 23

electrical cable insulation