Alkenes

Question 1

What are the 2 types of geometric isomers?

Answer 1

Cis
Trans

Question 2

What is a trans geometric isomer?

Answer 2

Highest value Mr’s opposite.

Question 3

What is a cis geometric isomer?

Answer 3

Highest value Mr’s on same side.

Question 4

What symbol is used for a trans geometric isomer?

Answer 4

E

Question 5

What symbol is used for a cis geometric isomer?

Answer 5

Z

Question 6

How does the boiling point of alkenes change as the size of the molecule increase?

Answer 6

Shows increase.
Similar to alkanes with same number of C atoms.

Question 7

Which alkenes are gases at room temperature?

Answer 7

Ethene
Propene
Butene

Question 8

What intermolecular forces do alkenes contain?

Answer 8

Van der Waal’s forces.

Question 9

What is the solubility of alkenes?

Answer 9

Insoluble in water.
Soluble in organic solvents.

Question 10

What is the bonding in alkenes?

Answer 10

Two shared pairs of electrons.
Sigma bond and pi bond.

Question 11

What is the difference between the C=C and C-C bonds in an alkene?

Answer 11

C=C bond is stronger and shorter.

Question 12

What are the chemical properties of the alkenes?

Answer 12

Electrons in sigma bond closer to nucleus of atoms forming bond, therefore held more tightly in bond making difficult to break.

As result pi bond breaks more easily making alkenes more reactive than alkanes.

Question 13

What is bond energy?

Answer 13

Energy required to break one mole of a bond.

Question 14

What are the 3 addition reactions of the alkenes?

Answer 14

With hydrogen
With halogens
With hydrogen halides

Question 15

What is required for the addition reaction of alkenes with hydrogen to happen?

Answer 15

Finely divided metal catalyst (usually nickel).
High temperature and pressure.

Question 16

What is the addition reaction of the alkenes with hydrogen used for commercially?

Answer 16

Convert unsaturated oils into low-melting saturated fats for use in margarine.

Question 17

What is involved in the addition reaction of the alkenes with halogens?

Answer 17

Occurs at room temperature.
Electrophilic addition reaction.
Heterolytic fission.

Question 18

What is an electrophile?

Answer 18

An ion or molecule that attacks regions of high electron density.

Question 19

What is the process involved in the addition reaction of bromine with propene?

Answer 19

1. Propene has region of high electron density caused by pi electrons in double bond.
2. As bromine molecule approaches propene, becomes polarised by negative charge.
3. Loose association forms between propene and bromine molecules.
4. Negative charge moves from double bond towards delta + Br atom.
5. Simultaneously electron in Br-Br bond repelled by delta - Br atom.
6. Formation of C-Br bond and two ions, carbocation, and Br- ion.
7. Carbocation very unstable and reacts quickly with Br- to form 1,2 - dibromopropane.

Question 20

What is a sigma bond?

Answer 20

Covalent bond that results from the linear overlap of orbitals on neighbouring atoms.

Question 21

What is a pi bond?

Answer 21

Covalent bond that results from the sideways overlap of p-orbitals on neighbouring atoms.

Question 22

What is involved in the addition reaction of alkenes with hydrogen halides?

Answer 22

Alkene reacts with concentrated aqueous solutions of hydrogen halides in cold.
Hydrogen ion acts as electrophile.
Intermediate carbocation formed, reacts with halide ions to form product.

Question 23

What are the products of the addition reaction of hydrogen bromide with propene?

Answer 23

2-bromopropane (secondary) > Major product
1-bromopropane (primary) > Minor product

Question 24

Why is the major product of of the addition reaction of hydrogen bromide with propene 2-bromopropane and not 1-bromopropane?

Answer 24

Secondary carbonation more stable than primary.

Question 25

What is Markovnikov’s Rule?

Answer 25

When HX is added to an unsymmetrical Alkene, the halide attaches to the C with more alkyl groups attached to it.

Question 26

What is the process where some of the alkyl groups push electrons towards the carbocation in an addition reaction of alkenes with hydrogen halides called?

Answer 26

Positive inductive effect.

Question 27

What is polymerisation?

Answer 27

Joining together of many small molecules (monomers) to form large molecule (polymer).

Question 28

What are the 2 ways in which polymers are disposed of?

Answer 28

Landfill Incineration

Question 29

Why are landfill sites harmful to the environment?

Answer 29

Occupy land Eyesores Release harmful gases

Question 30

Why is the incineration of polymers harmful for the environment?

Answer 30

Releases GHG or harmful gases.

Question 31

What is the benefit of disposing of polymers by incineration?

Answer 31

Provides energy that can be used to generate electricity.

Question 32

What is the preferable way of dealing with used polymers?

Answer 32

Recycling or re-use.