Hydrohalogenation Section 9.3

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

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

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

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

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

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

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

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

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

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