1. Alkenes and Alkynes II Addition Reactions
Chapter 8
Alkenes and Alkynes II
Addition Reactions

2. Introduction: Additions to Alkenes
An addition to a C-C double bond

3. Electrophilic Addition

4. Electrophilic Addition of Hydrogen Halides to Alkenes-Mechanism

5. Electrophilic Addition of Hydrogen Halides to Alkenes Markovnikov’s Rule

6. Example

7. The Rate Determining step
Step 1 is the rate determined step
Formation of carbocation

8. Theoretical Explanation of Markovnikov’s Rules

9. Theoretical Explanation of Markovnikov’s Rules

10. A mechanism for the reaction
Predict the products and show the full mechanism

11. Modern Statement of markovnikov’s Rule
In the ionic addition of an unsymmetrical reagent to a double bond, the positive portion of the adding reagent attaches itself to a carbon of the double bond so as to yield the more stable carbocation as intermediate

12. Regioselective Reactions
When a reaction that can potentially yield two or more constutional isomers actually produces only one (or a predominance of one), the reaction is said to be regioselective
HX + unsymetrical alkene  more than product

13. An exception of Markovnikov’s Rule
When alkenes are treated with HBr in presence of peroxide, an anti-Markovnikov addition

14. 8.3 Stereochemistry of the Ionic Addition to an Alkene
The carbocation is formed in the first step of the addition is trigonal planar
achiral

15. 8.4 Addition of Sulfuric Acid Alkenes
When alkenes are treated with cold concentrated sulfuric acid, they dissolve because they react with electrophilic addition to form alkyl hydrogen sulfate

16. Alcohols from Alkyl Hydrogen Sulfate
Alkyl hydrogen sulfates can be easily hydrolyzed to alcohols by heating them with water
Markovnikov addition of H- and -OH

17. example Provide mechanistic explanation for the following observation
The addition of hydrogen chloride to 3-methyl-1-butene produces two products: 2-chloro-3-methylbutane and 2-chloro-2-methylbutane
Give the structure and name of the product that would be obatained from ionic addition of IBr to propene

18. example
In one industrial synthesis of ethanol, ethene is first dissolved in 95% sulfuric acid. In a second step of water is added and the mixture is heated. Out the reaction involved

19. 8.5 Addition of Water to Alkene: Acid-Catalyzed Hydration
Method for preparation of low molecular weight alcohols
Usually regioselective

20. Mechanism

21. Rate determining step
However, formation of 1o carbocation does not take place

22. Rearrangement
The carbocation formed initially invariable rearranges to a more stable one if possible
Provide the full mechanism