Alkenes

Question 1

What is the general formula for an alkene?

Answer 1

C_nH_2n

Question 2

What other thing has the general formula C_nH_2n

Answer 2

Cycloalkanes

Question 3

What makes alkenes very reactive?

Answer 3

They are unsaturated compounds, with regions of high electron density

Question 4

What is the hybridisation of carbon in alkenes?

Answer 4

sp² hybridised

Question 5

What is a symmetrical alkene?

Answer 5

This is an alkene with an equal number of carbons on either side of the C=C bond

Question 6

What is an asymmetrical alkene?

Answer 6

This is an alkene with an unequal number of carbons on either side of the C=C bond

This gives room for a mixture of products to be formed in chemical reactions

Question 7

What reactions do alkenes undergo?

Answer 7

1. Oxidation
2. Electrophilic addition

Question 8

What reagents commonly react with alkenes?

Answer 8

Halogen molecules or hydrogen halides

Question 9

What property of hydrogen halides makes them act as electrophiles?

Answer 9

The electronegativity difference in the H-X bond, giving the H a δ+ charge

Question 10

How are the neutral halogen molecules made polar?

Answer 10

A dipole is induced when the halogen molecule approaches the electron rich C=C bond.

e^- repulsion occurs, making the halide atom closer to the C=C bond have a δ+ charge

Question 11

Do alkenes decolourise bromine water?

Answer 11

Yes

Question 12

What rule is typically followed when determining the major product in the reaction of an alkene with a hydrogen halide?

Answer 12

Markovnikov’s rule

Question 13

What does Markovnikov’s rule basically imply?

Answer 13

The most stable carbocation is formed in the intermediate step

Question 14

State Markovnikov’s rule

as applies to the reaxn. with hydrogen halides

Answer 14

When an asymmetrical alkene reacts with a hydrogen halide, the hydrogen atom bonds with the carbon that has** the higher number** of carbon atoms

Question 15

What bond is broken when alkenes react?

Answer 15

The π bond; the second bond of the C=C double bond

Question 16

What is a polymer?

Answer 16

A large molecular compound made of repeating units of monomers

Question 17

What is a monomer?

Answer 17

A small molecular unit which combines with other (like or unlike) monomers to form a large molecule

Question 18

What quality differentiates a polymer from a monomer?

Answer 18

Polymers are saturated and monomers are not

Question 19

While monomers are typically volatile liquids or gases, polymers are…?

Answer 19

Solids

The Van der Waal’s forces are stronger in polymers due to the large molecular structure

Question 20

What are the two types of polymerisation you know?

Answer 20

1. Addition polymerisation
2. Condensation polymerisation

Question 21

How does condensation polymerisation differ from addition polymerisation?

Answer 21

There is the elimination of a small molecule in condensation polymerisation

Hence two products are formed as opposed to one in the latter

Question 22

What is peculiar about a polymer

Answer 22

It is formed from repeating units of something

Question 23

True or False?

Addition polymerisation occurs in alkenes only

Answer 23

True

Question 24

In what type of polymerisation do the monomers have to be the same?

Answer 24

Addition polymerisation

Question 25

In what type of polymerisation can the monomers afford to be different?

Answer 25

**Condensation polymerisation**

Question 26

# What are the reaction conditions (reagents, catalyst, reacting system) for the addition polymerisation of alkenes?

Answer 26

1. **REAGENTS:** The monomer (containg the C=C bond) 2. **CATALYST:** An organic peroxide 3. **REACTING SYSTEM CONDITIONS:** High temperature and pressure

Question 27

Why is an organic peroxide used as a catalyst? | for the addition polymerisation of alkenes?

Answer 27

They **readily break up** to form free radicals ## Footnote These free radicals are very reactive and form a bond with one carbon, **breaking the π bond and forming another electrophile**

Question 28

# **Yes** or **No** Is there free rotation about the C=C double bond?

Answer 28

**No**

Question 29

What two compounds can be found in bromine water?

Answer 29

HBr and HOBr

Question 31

What catalyses the hydration of an alkene to an alkane

Answer 31

Finely-divided Iron or Nickel

Question 32

What can be physically observed when an alkene is mixed with cold dilute acidified KMnO₄?

Answer 32

The solution turns from purple to colourless

Question 33

What **is formed** when an alkene is mixed with an aqueous solution of cold dilute acidified KMnO₄?

Answer 33

A **diol** ## Footnote Oxygen is added to either side of the C=C double bond when broken

Question 34

What **is formed** when an alkene is mixed with hot conc. acidified KMnO₄?

Answer 34

An **aldehyde/carboxylic acid/ketone** ## Footnote Oxygen is added to either side of the C=C double bond when broken

Question 35

Why is there a difference in the products depending on the concentration and temperature of the acidified KMnO₄?

Answer 35

A hot and concentrated mixture present **much harsher reaction conditions**