Alkenes

Question 1

Why are alkenes more reactive than alkanes?

Answer 1

-Alkenes are unsaturated compounds with a C=C double bond
- The high electron density of the double bond makes alkenes more reactive

Question 2

Explain the carbon - carbon double bond?

Answer 2

-There double bond consists of a sigma bond and a pi bond
-The pi bond is weaker than the sigma bond so thee sigma bond breaks first in reactions involving alkenes.
- The pi bond changes the shape around the carbon atom to a trigonal planar with a bond
angle of 120
- The planar double bond locks the molecule around the double bond
- This means that there is no free rotation about these bonds.

Question 3

What mechanism is use for Alkenes?

Answer 3

Electrophilic addition

Question 4

What are the electrophiles used in alkenes?

Answer 4

HBr, H2SO4 and Br2

Question 5

Condition of Bromine?

Answer 5

• Room temperatur

Question 6

How does the Br2 attack the alkene?

Answer 6

• As the Br2 molecule approaches the alkene,
  the pi bond electrons repel the electron pair in
  the Br2 bond.
  -This induces a dipole. Br2 becomes polar and
  electrophilic (Brδ+).
• The intermediate formed, which has a positive charge on a carbon atom is called a carbocation.

Question 7

Conditions of H-X (i.e Br, Cl)?

Answer 7

• Room temperature
  (reagent is HCl and HBr).
  The alkene produced from the reaction is unsymmetrical

Question 8

Stages of Electrophilic addition with H2S04?

Answer 8

Stage 1:
-Conditions – Room temperature
- Reagents = H2S04
- Role is a catalyst
Stage 2:
- Conditions: warm mixture
- Reagents: water

Question 9

Why are poly(alkenes) unreactive?

Answer 9

• strong C-C and C-H bonds