OCHEM Mechanisms Alkenes

HBR

Hydrohalogenation, Markovnikov, low T

Carbocation

Triganal Planar, sp2 hybridized C with +, stabilized by hyperconj.

H₂O₂

Peroxide= radical initiator, anit-markov addition, hyper conj radical

Racemic Mixture

Addition rxn produce chirality centre

Methyl Shift

methyl shifts to (C+), increase conj in carbocat

Hydride shift

H shifts to (C+) 

X₂

Halogenation, anti add. attack top and bottom

1. Cl₂ or Br₂

2. H₂O

Halohydrin, bond forms with halogen, water attacks more sterically hindered side

1. Acid

2. H₂O

Hydration, Markov, OH + H to dbbl bond

1. Hg(OAc)₂, H₂O

2. NaBH₄

Oxymercuration-demercuration, markov. hydration. alkene attacks mercury, water cleaves a bond,NaBH4 cleaves

1. BH₃;THF 

2. H₂O₂, NaOH

Hydroboration Oxidation, anti-markov. hydration, SYN add (formed same time). Trialkyl borane carbo cat. 

1. H₂

2. Pt (Homogeneous metal)

SYN add. H₂ to dbbl bond

1. RCO₃H 

2. H₃O⁺

Epoxidation, make epoxide, acid and water open epoxide. ANTI add. of 2 OH groups.

Protonated Epoxide

Epoxidation

Bromonium ion 

Halohydrin

Mercurinium ion

Oxymercuration-demercuration

1. OsO₄

2. NaHSO₃/H₂O

Dihydroxylation, one step SYN add., Cyclic osmate ester carbo cat.

1. KMnO₄, NaOH

2. Cold

Dihydroxylation, but only in cold conditions

1. O₃

2. DMS or Zn, acetic acid

Ozonolysis, oxidative cleavage