© Prentice Hall 2001Chapter 31 Addition of Halogens The remaining halide ion is a good nucleophile which attacks the positively charged halonium ion

© Prentice Hall 2001Chapter 32 Addition of Halogens If the reaction is carried out in water a different product is obtained

© Prentice Hall 2001Chapter 33 Oxymercuration- Demercuration In oxymercuration-demercuration, an alkene is treated first with mercuric acetate in aqueous tetrahydrofuran The product is treated with sodium borohydride in the presence of hydroxide The result is Markovnikov addition of water to the double bond, yielding an alcohol

© Prentice Hall 2001Chapter 34 Oxymercuration- Demercuration Advantages over addition of H 2 O using H 2 SO 4 Oxymercuration-demercuration doesn’t require the presence of a strong acid is not subject to carbocation rearrangement

© Prentice Hall 2001Chapter 35 Oxymercuration- Demercuration

© Prentice Hall 2001Chapter 36 Oxymercuration and Alkoxymercuration Why does the nucleophile attack at the middle carbon and not at the end carbon? The transition state at the left is more stable than the one at the right.

© Prentice Hall 2001Chapter 37 Markovnikov’s Rule & Oxymercuration- Demercuration Recall the modern version, i.e. the electrophile adds to the carbon bonded to the greatest number of hydrogens In this case the electrophile is the mercuric acetate

© Prentice Hall 2001Chapter 38 Hydroboration-Oxidation Hydroboration-oxidation is a convenient way to add water to a double bond, forming an alcohol

© Prentice Hall 2001Chapter 39 Hydroboration-Oxidation Viewed in the classical sense, the addition appears to be in the anti-Markovnikov direction The hydroxyl group bonds to the carbon with the most hydrogens

© Prentice Hall 2001Chapter 310 Hydroboration-Oxidation As we consider the mechanism, we see that the electrophile bonds to the carbon with the most hydrogens (obeying the modern version of Markovnikov’s rule)

© Prentice Hall 2001Chapter 311 Hydroboration

© Prentice Hall 2001Chapter 312 Oxidation

© Prentice Hall 2001Chapter 313 Hydroboration-Oxidation In addition to the electronic effect, steric effects may be important Recall that three alkene molecules eventually surround each boron The structure on the left is less hindered than the structure on the right

© Prentice Hall 2001Chapter 314 Addition of Radicals Markovnikov Addition Anti-Markovnikov Addition Source of Confusion regarding addition of HBr for years

© Prentice Hall 2001Chapter 315 Heterolysis & Homolysis Heterolytic bond cleavage or heterolysis Homolytic bond cleavage or homolysis Homolysis produces radicals, which are very reactive species

© Prentice Hall 2001Chapter 316 Radicals are unpaired electron spins tend to perpetuate unpaired spin participate in chain reactions

© Prentice Hall 2001Chapter 317 Radicals Sources include: Hydrogen peroxide Alkyl peroxides Light causes homolysis of the weak O-O bond

© Prentice Hall 2001Chapter 318 Radicals Stability of alkyl radicals is similar to stability of carbocations

© Prentice Hall 2001Chapter 319 Radical Chain Reactions

© Prentice Hall 2001Chapter 320 Radical Chain Reactions

© Prentice Hall 2001Chapter 321 Radical Chain Reactions

© Prentice Hall 2001Chapter 322 Radical Addition is Unique to Hydrogen Bromide Why?

© Prentice Hall 2001Chapter 323 Radical Addition is Unique to Hydrogen Bromide

© Prentice Hall 2001Chapter 324 Addition of Hydrogen and Relative Stabilities of Alkenes

© Prentice Hall 2001Chapter 325 Addition of Hydrogen and Relative Stabilities of Alkenes

© Prentice Hall 2001Chapter 326 Relative Stabilities of Alkenes

© Prentice Hall 2001Chapter 327 Relative Stabilities of Alkenes

© Prentice Hall 2001Chapter 328 Relative Stabilities of Alkenes

© Prentice Hall 2001Chapter 329 Relative Stabilities of Alkenes