Chapter 6: 6.4 Halogenation

Question 1

List:

Characteristics of Halogenation Reactions

Answer 1

1. Occur in multiple steps
2. Proceed via a three-membered ring intermediate
3. Have neither Markovnikov addition or anti-Markovnikov addition for a regiochemical outcome
4. The addition of the two X groups is anti (i.e. on the opposite side) for the stereochemical outcome

Question 2

What are the halogens that are the most commonly used in halogenation reactions?

Answer 2

• Bromine (Br2, liquid at room temperature)
• Chlorine (Cl2, gas at room temperature)

Question 3

Why are chlorine and bromine the only halogens commonly used in halogenation reactions?

Answer 3

They are:
* Reactive enough to do chemistry
* Not so reactive that they will lead to many undesired side-products

Question 4

Halogenation reactions are done in very unreactive solvents, why?

Answer 4

To avoid side reactions with the halogen and solvent

Question 5

What solvents are used in halogenation reactions?

Answer 5

• Benzene (C6H6)
• Carbon tetrachloride (CCl4)

Question 6

State:

Steps of a Halogenation Reaction

Answer 6

1. Nucleophilic and electrophilic attack of the halogen on the alkene for a reactive three-membered ring
2. Nucleophilic attack of the halogen anion onto the three-membered ring
3. Opening up of the three-membered ring

Question 7

Halogenation reactions are stereospecific, what does that mean?

Answer 7

They maintain the geometry of the reagent
* Cis double bonds stay cis
* Trans double bonds stay trans