3.3.4 Alkenes

Question 1

what is the general formula of an alkene?

Answer 1

CnH2n

Question 2

What is an alkene?

Answer 2

Unsaturated hydrocarbon
C=C double bond

Question 3

Why is there no rotation around the C=C double bond?

Answer 3

Electron density above and below holds the carbon atoms in place

Question 4

Are alkenes more or less reactive than alkanes? Why?

Answer 4

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

Question 5

What intermolecular forces do alkenes have?

Answer 5

Only Van der Waals
(Non polar bonds)

Question 6

Are alkenes soluble in water? Why?

Answer 6

No
No polar bonds
Cannot form H bonds with water molecules, the hydrogen bonding within water is stronger

Question 7

Name the three types of isomer alkenes can form?

Answer 7

positional isomer
chain isomer
E/Z

Question 8

Write an equation for the complete combustion of pent-2-ene.

Answer 8

C5H10 + 7.5O2 —> 5CO2 + 5H2O

Question 9

What is an electrophile?

Answer 9

Electron deficient atoms/ions which accept a pair of electrons (here, from the C=C bond)

Question 10

What is the most stable type of carbocation intermediate?

Answer 10

The one bonded to the most other carbon atoms eg. Tertiary carbocation

Question 11

Major products will be formed from which kinds of carbocation?

Answer 11

Tertiary

Question 12

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

Answer 12

Acid catalyst

Question 13

What are the products of electrophilic addition of H2O to an alkene?

Answer 13

An alcohol

Question 14

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

Answer 14

Room temperature

Question 15

What conditions are needed for the electrophilic addition of a halogen molecule to an alkene?

Answer 15

Room temperature and organic solvent

Question 16

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

Answer 16

C=C double bond with a high electron density induces a temporary dipole in the halogen molecule

Question 17

What is an addition polymer?

Answer 17

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

Question 18

What are monomers? What form do they usually take?

Answer 18

Molecules which combine to form a polymer
Usually have a C=C double bond which breaks to leave a repeating pattern

Question 19

Give 3 uses of poly(chloroethene) / PVC?

Answer 19

Drainpipes
Vinyl
Aprons

Question 20

What are plasticisers?

Answer 20

Small molecules that get between polymer chains to force them apart so they can slide over each other.

Question 21

How does the physical properties of PVC change due to a plasticiser? What can this be used for?

Answer 21

Makes PVC more flexible
With plasticiser - aprons
Without plasticiser - drainpipes

Question 22

Why do molecules containing mainly C-C and C-H bonds not decompose easily?

Answer 22

Bonds are non-polar so are not attacked by enzymes

Question 23

Why is a lack of biodegradability in compounds with C-C or C-H bonds a problem?

Answer 23

Disposal is very problematic