Chapter 8 Alkenes and Alkynes II: Addition Reactions
Table of Contents 1. Addition Reactions of Alkenes 2. Electrophilic Addition of Hydrogen Halides to Alkenes: Mechanism & Markovnikov’s Rule 3. Stereochemistry of the Ionic Addition to an Alkene 4. Addition of Water to Alkenes: Acid-Catalyzed Hydration 5. Alcohols from Alkenes through Oxymercuration–Demercuration: Markovnikov Addition 6. Alcohols from Alkenes through Hydroboration–Oxidation: Anti- Markovnikov Syn Hydration 7. Hydroboration: Synthesis of Alkylboranes 8. Oxidation and Hydrolysis of Alkylboranes 9. Summary of Alkene Hydration Methods 10. Protonolysis of Alkylboranes 11. Electrophilic Addition of Bromine & Chlorine to Alkenes 12. Stereospecific Reactions 13. Halohydrin Formation 14. Divalent Carbon Compounds: Carbenes 15. Oxidation of Alkenes: Syn 1,2-Dihydroxylation 16. Oxidative Cleavage of Alkenes 17. Electrophilic Addition of Bromine & Chlorine to Alkynes 18. Addition of Hydrogen Halides to Alkynes 19. Oxidative Cleavage of Alkynes 20. How to Plan a Synthesis: Some Approaches & Examples
In this chapter we will consider: v The regio- and stereochemistry of addition reactions of alkenes v Processes that can add molecules of water, halogens, carbon, and other functionalities across alkenes v Events that cleave double bonds and provide more highly oxidized compounds v Alkyne reactions that are analogous to alkene reactions
C C E Nu E C C Nu + 1. Addition Reactions of Alkenes
1A. How To Understand Additions to Alkenes v This is an addition reaction: E – Nu added across the double bond C C E Nu E C C Nu + Bonds broken Bonds formed p -bond s -bond 2 s -bonds
v Since p bonds are formed from the overlapping of p orbitals, p electron clouds are above and below the plane of the double bond C C p electron clouds
v Electrophilic ● electron seeking ● C=C and C≡C p bonds are particularly susceptible to electrophilic reagents (electrophiles) v Common electrophiles ● H + , X + (X = Cl, Br, I), Hg 2+ , etc. we together µ arm a BM war t aww
v In an electrophilic addition, the p electrons seek an electrophile, breaking the p bond, forming a s bond and leaving a positive charge on the vacant p orbital on the adjacent carbon. v Addition of a nucleophile to form a s bond provides an addition product.
C C E Nu d + d - Nu C C E t e Wl AM from the c meaning a pontine mange on the C 2 step nm Tffum m m many the lot AN the otter will be fait
2. Electrophilic Addition of Hydrogen Halides to Alkenes: Mechanism & Markovnikov’s Rule v Mechanism fwm And pi bird brat w nucophilil end u carbocation timed Islow pep I
v Mechanism ● Sometimes do not go through a “free carbocation”, may go via
C C H H H H E Nu E C C H H H H E C C H H H H E C C H H H H Nu E C C H H H H Nu Nu same as same as v Markovnikov ’ s Rule ● For symmetrical substrates, no problem for regiochemistry
E Nu C C H H 3 C H H E C C H H CH 3 H E C C CH 3 H H H E C C CH 3 H H H Nu E C C H H CH 3 H Nu Nu Nu or different from v Markovnikov ’ s Rule ● But for unsymmetrical substrates, two regioisomers are possible
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