Alkenes

Question 1

Alkene to alcohol: conditions & reagents
- what type of reaction is this

Answer 1

Reagents : Alkene, conc H3PO4 acid catalyst , steam
Conditions : 60atm , 300 degrees

Hydration

Question 2

Alkene to alkane : reagents and conditions - what type of reaction is this

Answer 2

Reagents : H2 , Ni catalyst
Conditions : 150 degrees

-reduction
- application : manufacture of margarine by catalytic hydrogenation if unsaturated vegetable oils

Question 3

Alkene to Diol : conditions and reagents
-what type of reaction is this

Answer 3

Reagents : Acidified KMnO4 + cold
Condition : 20 degrees (about room temp)
- oxidation

(If it’s warm further oxidation will occur)

Question 4

Alkene to Halogenoalkane : Reagents and conditions - what type of reaction is this

Answer 4

Reagents : HX (hydrogen halides) , bubble gas into alkene
Conditions : room temp (around 20 degrees)
- electrophilic addition

Question 5

Alkene to Dihalogenoalkane : reagents and conditions - what type of reaction is this

Answer 5

Reagents : Halogen (X2) , bubble gas into alkene
Conditions : room temp

• electrophilic addition

Question 6

Alkene to polyalkene : reagents
- what type of reaction is this

Answer 6

Reagents : Ziegler- Natta catalyst
- addition reaction
60 degrees

Question 7

How to test for C=C bond?

Answer 7

Alkenes turn Bromine water colourless

Question 8

Why do you get major and minor products during electrophilic addition?

Answer 8

-For asymmetrical alkenes
- During EA different carbocations form, depending on where first atom is added
-different carbocations have different stability —> markovninov’s rule —> inductive effect of alkyl groups
- most stable carbocations lasts in mixture longer and more products are derived from it

Question 9

Rank carbocations from least to most stable

Answer 9

(Methyl carbocations) primary < secondary < tertiary carbocations

Question 10

Explain why tertiary carbocations are the most stable

Answer 10

• positively charged carbon bonded to 3 alkyl groups
  -which each push electron density onto the positively charged carbon, reducing the charge of the overall molecule (inductive effect)
• making the molecule more stable

Question 11

Are alkyl groups electron donating or withdrawing ?

Answer 11

• electron donating
  -hence having more alkyl groups bonded to the C+ atom in the carbocation increases stability

Question 12

What two bond types are found in alkenes?

Answer 12

• sigma and pi bonds
• pi bond found within the C=C double bond and arises from p- orbital overlap

(pi bonds are weaker than sigma bonds —> less overlap)

Question 13

Why is there restricted rotation around the C=C bond?

Answer 13

• due to the presence of the pi bond, restriction is rotated to 180 degrees
• because if the pi bonds do not overlap the bond is broken
  ( pi bonds have to be on the same axis as one another)

Question 14

What is an electrophile?

Answer 14

• an “electron loving ” species
  -usually positively charged or have partial positive charge
• accept an electron pair from a nucleophile