4: Alkenes

Question 1

What is the functional group of an alkene?

Answer 1

C=C

Question 2

What is the general formula for alkenes?

Answer 2

CnH2

Question 3

Are alkenes saturated or unsaturated?

Answer 3

Unsaturated, all carbons do not have 4 things bonded to them.

Question 4

What does high electron density mean?

Answer 4

There is a high number of electrons within a bond.

Question 5

What makes alkenes reactive?

Answer 5

High electron density in the C=C bond

Question 6

Name the mechanism alkenes use to add molecules to them.

Answer 6

Electrophilic addition

Question 7

What is an electrophile?

Answer 7

Electron pair acceptors

Question 8

Give 3 types of molecule involved in electrophilic addition.

Answer 8

H - Halogen
H - OSO2OH
Halogen - Halogen

Question 9

1. In electrophilic addition, how may a dipole in non polar molecules be induced?

Answer 9

Non polar molecules, such as Br-Br, as they move towards the region of negative electron density, a dipole is induced as electrons on the closest atom to the alkene move to the furthest region on the atom. This leaves the closest end slightly positive and the furthest end slightly negative.

Question 10

2. In electrophilic addition, where do electrons move from and to once the molecule containing the electrophile has developed a dipole?

Answer 10

Electrons move from the double bond on the alkene to the slightly positive atom, causing the double C=C bond to break. This causes the bond between the slightly positive and slightly negative atom to break.

Question 11

3. In electrophilic addition, where does the slightly positive atom move to?
   What type of molecule is now created?

Answer 11

The slightly positive atom bonds to that was once an alkene.
This creates a carbocation, as the unoccupied carbon is now positive.

Question 12

4. In electrophilic addition, how does the remaining ion bond to the carbocation?

Answer 12

The remaining ion is negative, therefore attracts to the positive carbon.
It donates it’s lone pair.

Question 13

How do you test for unsaturation?

Answer 13

Mix sample with orange bromine water.
Shake.
If alkenes are present then a colour change from orange to colourless occurs.

Question 14

What is a primary carbocation?

Answer 14

The positive carbon attaches to 1 other carbon.

Question 15

What is a secondary carbocation?

Answer 15

The positive carbon is attached to 2 other carbons.

Question 16

What is a tertiary carbocation?

Answer 16

The positive carbon attaches to 3 other carbons.

Question 17

Which type of carbocation is most stable?

Answer 17

Tertiary, because the remaining carbons feed electrons to the positive charge.

Question 18

In a reaction where a primary and secondary carbocation is produced, which will create the minor/major product?

Answer 18

The major product is always formed by the most stable carbocation.
This means the secondary carbocation will be the major product while the primary carbocation will be the minor product?

Question 19

How long does a carbon chain need to be before a minor and major product can be produced?

Answer 19

3