4.1.3 Alkenes

Question 1

What are alkenes?

Answer 1

Unsaturated hydrocarbons that contain at least one C=C bond made up of a π bond and a σ bond

Question 2

What is the general formula of alkenes?

Answer 2

CnH2n

Question 3

How is a π bond formed?

Answer 3

Electrons in adjacent p orbitals overlap above and below the carbon atoms.

They can only be made after a σ bond is formed.

Question 4

What is the general formula of alkenes?

Answer 4

CnH2n

Question 5

What is the angle and shape of a double bond?

Answer 5

Trigonal planar
120

Question 6

Are they more or less reactive than alkanes? Why?

Answer 6

More reactive due to high electron density of the double bond and the fact the pi bond is slightly easier to break.

Question 7

What intermolecular forces of attraction do they have?

Answer 7

Only London forces due non-polar bonds

Question 8

Are they soluble in water?
Why?

Answer 8

No, non-polar bonds

Question 9

What are the types of isomers that can be formed using alkenes?

Answer 9

E/Z isomers - due to the restricted rotation

Cis-Trans isomers - if two of the same substituents are attached to each carbon

Question 10

What is an electrophile?

Answer 10

Species that are electron pair acceptors

Question 11

What is the most stable type of carbocation intermediate? Why?

Answer 11

Alkyl groups have a positive inductive effect, so the most stable carbocation is the one bonded to the most other carbon atoms i.e. A tertiary carbocation

Question 12

Major products will be formed from which kinds of carbocations?

Answer 12

Tertiary (or the most stable available)

Question 13

What conditions are needed for the elctrophilic addition of H2O to an alkene?

What is this type of reaction called?

Answer 13

Steam in the presence of an acid catalyst, usually phosphoric acid

Reaction is called hydration

Question 14

What are the product(s) of the hydration reaction?

Answer 14

An alcohol

Question 15

What conditions are needed for the electrophilic addition of a hydrogen halide to an alkene?

Answer 15

Hydrogen halide gases must be at room temperature

Question 16

What is the reaction called when a halogen is added to an alkene?

Answer 16

Halogenation

Question 17

How does a molecule with a non-polar bond react as if it is an electrophile?

Answer 17

C=C double bond with a high electron density induces a temporary dipole in the halogen molecule —- δ+ atom attracted to double bond

Question 18

How can an alkene be converted in to an alkane?

What is the reaction called?

What are the conditions?

Answer 18

Alkene + Hydrogen = Alkane

This is called Hydrogenation

Conditions—150°C,nickel catalyst

Question 19

What is an addition polymer?

Answer 19

Many monomers bonded together via rearrangement of bonds without the loss of any atom or molecule

Question 20

What are monomers?

What form do they usually take?

Answer 20

Molecules that combine to form a polymer

Usually have a C=C bond that breaks to leave a repeating pattern

Question 21

In what ways can Plastics be disposed (6)?

Answer 21

Landfill
Combustion
Electricity generation
Reuse
Recycle
Organic feedstock

Question 22

How do Photodegradable polymers break down?

Answer 22

They are broken down chemically using energy with similar wavelengths to light.
Once initiated the process can not stop.