13.3 - Reactions of Alkenes

Question 1

Why are alkenes for more reactive than alkanes?

Answer 1

Alkenes have the C=C bond, because of the pi bond.

• The electron density is more exposed than the electrons in a sigma bond
• Therefore the pi bond is more easily broken than the sigma bond due to its lower bond enthalpy, allowing it to undergo addition reactions

Question 2

What are the 4 alkene addition reactions with?

Answer 2

Hydrogen - Ni Catalyst (makes alkanes)

Halogens - (makes dihaloalkane)

Hydrogen Halides - (makes haloalkane)

Steam in the presence of acid catalyst - (makes alcohol)

Question 3

What occurs during alkene hydrogenation?

Answer 3

Alkene + H2 > Alkane (Nickel catalyst, 150 degrees C0

- Hydrogen added across double bond

Question 4

What occurs during alkene halogenation?

Answer 4

Conditions: RTP
Alkene + Halide > dihaloalkane
- Test for unsaturation, orange bromine water adds across double bond making it colourless.

Question 5

What occurs during alkene + hydrogen halide?

Answer 5

Alkene + hydrogen halide
Conditions: RT
- If the reactants are gases, the 2 gases will mix
- If the alkene is a liquid, the haloalkane is bubbled through.

Question 6

What occures during alkene + hydrogen halide if the alkene is unsymmetrical?

Answer 6

Unsymmetrical - 2 possible products (Markownikoff’s Rule)

Symmetrical - 1 possible product

Question 7

What occurs during alkene hydration?

Answer 7

Conditions: Steam + phosphoric acid

Alkene + steam > alcohol