Alkenes

Question 1

What’s the brief summary of alkenes?

Answer 1

• Contain a C=C double bond
• General formula is C(n)H(2n)
• End in -ene
• Simplest example is ethene
• Are unsaturated (more hydrogen atoms can be added to their molecules)

Question 2

How can cracking affect alkenes?

Answer 2

Cracking can change alkanes into alkenes

Question 3

What does the double bond mean in terms of reactivity?

Answer 3

That it is more reactive, so they are more reactive than alkanes

Question 4

What do all alkene reactions involve?

Answer 4

Splitting the double bond to allow place for other atoms

Question 5

What important when naming alkenes?

Answer 5

To always state the location of the double bond in between the prefix for carbons and the suffix
Eg, pent - 2 - ene

Question 6

What are the three main types of reactions?

Answer 6

Addition
Substitution
Oxidation

Question 7

Describe addition with H2 reactions

Answer 7

The double bond separates, allowing for the H2 to separate and join into the available spaces

Question 8

Describe addition with H2O reactions

Answer 8

The double bond separates, allowing to H and OH to join into the available spaces. OH belongs to the alcohol family so therefore all alkene reactions with H2O will produce an alcohol (-anol). When naming these alcohols, the OH must be put in the position with the lowest number and this must be included in the name.

Question 9

Describe addition with halogens

Answer 9

The double bond separates, allowing the halogens (Br2, Cl2, I2, F2) to join into the available spaces. If there are two halogens on the same carbon atom, the position number needs to be written twice.

Question 10

Describe addition with hydrogen halides

Answer 10

The double bond separates, allowing the hydrogen and halogen to join into the available spaces. When there are unsymmetrical reactants, two products will be formed.

Question 11

How are alkenes oxidised?

Answer 11

By oxygen gas (combustion) or other oxidants such as permanganate

Question 12

Describe reactions with permanganate

Answer 12

Alkenes can be easily oxidised by permanganates and the products formed depend on the reaction conditions. At cold temperatures with low conditions of oxidising reagents, alkenes tend to form diols (two OH’s). Where the double bond splits, two OH’s join in.