Alkenes

Question 1

Type of hybridisation of C atoms in alkenes

Answer 1

sp2

Question 2

Addition of H2

Answer 2

Reagent: H2 (g)
Condition: platinum/nickel catalyst, heat
An alkane is produced

Question 3

Addition of HX

Answer 3

Reagent: HX (g)
Condition: Room temperature
Type of reaction: Electrophilic addition
A halogenoalkane is produced

Question 4

What is Markovnikov rule of addition of HX to an unsymmetrical alkene

Answer 4

When HX is added to an unsymmetrical alkene, the H attaches to the C already having the greatest number of H atoms

Question 5

Explanation for the markovnikov rule

Answer 5

A tertiary carbocation is most stable due to having 3 alkyl groups attached to the positive C. Alkyl groups have a positive inductive effect, thus they stabilise the carbocation

Question 5

Addition of H2O to alkenes

Answer 5

Reagents: H2O (g) / steam
Conditions: heat, H3PO4 catalyst
Type of reaction: Electrophilic addition
An alcohol is produced

Question 5

Addition of X2 to alkenes

Answer 5

Reagent: X2 (not aqueous)
Conditions: Room temperature
Type of reaction: Electrophilic addition
A dihalogenoalkane is formed

Question 6

Why in the addition of X2 to alkenes is the halogen not aqueous?

Answer 6

If X2(aq) is used, OH- can also enter the molecule.

Question 7

Mild oxidation of alkenes

Answer 7

Reagents: KMnO4(aq)/H+
Condition: cold, dilute
An alcohol is produced

Question 8

Strong oxidation of alkenes

Answer 8

Reagents: KMnO4(aq)/H+
Conditions: hot, concentrated
If the OH is attached to 0 C then CO2 and H2O is formed. 1C - carboxylic acid. 2C - ketone

Question 9

Reactions to produce alkenes (3)

Answer 9

1) Cracking of alkanes
2) Elimination reaction of halogenoalkanes
3) Dehydration of alcohols