1. Hydrohalogenation
Section 9.3

2. 9.3 Hydrohalogenation
Note the temperature used in this addition reaction
Does it matter whether the Br adds to the right side of the C=C double bond or whether it adds to the left?
Copyright © 2015 John Wiley & Sons, Inc. All rights reserved.
Klein, Organic Chemistry 2e

3. 9.3 Hydrohalogenation
Regiochemistry becomes important for asymmetrical alkenes
In 1869, Markovnikov showed that in general, H atoms tend to add to the carbon already bearing more H atoms
Copyright © 2015 John Wiley & Sons, Inc. All rights reserved.
Klein, Organic Chemistry 2e

4. 9.3 Hydrohalogenation
Markovnikov’s rule could also be stated by saying that in general, halogen atoms tend to add to the carbon that is more substituted with other carbon groups
This is a regioselective reaction, because one constitutional isomer is formed in greater quantity than another
Copyright © 2015 John Wiley & Sons, Inc. All rights reserved.
Klein, Organic Chemistry 2e

5. 9.3 Hydrohalogenation
Anti-Markovnikov products are observed when reactions are performed in the presence of peroxides such as H2O2
Why would some reactions follow Markovnikov’s rule, while other reactions give Anti-Markovnikov products?
The answer must be found in the mechanism
Practice with conceptual checkpoint 9.1
Copyright © 2015 John Wiley & Sons, Inc. All rights reserved.
Klein, Organic Chemistry 2e

6. 9.3 Hydrohalogenation Mechanism
The mechanism is a two step process
Which step do you think is rate determining?
Write a rate law for the reaction
Copyright © 2015 John Wiley & Sons, Inc. All rights reserved.
Klein, Organic Chemistry 2e

7. 9.3 Hydrohalogenation Mechanism
Recall that there are two possible products, Markovnikov and anti-Markovnikiv
Which process looks more favorable? WHY?
Copyright © 2015 John Wiley & Sons, Inc. All rights reserved.
Klein, Organic Chemistry 2e

8. 9.3 Hydrohalogenation Mechanism
Practice with SkillBuilder 9.1
Copyright © 2015 John Wiley & Sons, Inc. All rights reserved.
Klein, Organic Chemistry 2e

9. 9.3 Stereochemical Aspects
In many addition reactions, chirality centers are formed
There are two possible Markovnikov products
Which step in the mechanism determines the stereochemistry of the product?
Copyright © 2015 John Wiley & Sons, Inc. All rights reserved.
Klein, Organic Chemistry 2e

10. 9.3 Stereochemical Aspects
Recall the geometry of the carbocation
Practice with conceptual checkpoint 9.6
Copyright © 2015 John Wiley & Sons, Inc. All rights reserved.
Klein, Organic Chemistry 2e

11. 9.3 Rearrangements Klein, Organic Chemistry 2e
Copyright © 2015 John Wiley & Sons, Inc. All rights reserved.
Klein, Organic Chemistry 2e