CHM2210 Ch. 8 Alkenes

Alkene Mechanisms Learn!

Hydrohalogenations

adding HX X= Cl, Br, I

Markonikov Rule

Mixed Addition

Racemic + Rearrangement

Anti markonikov of Hydrohalogenation

HBR
ROOR (Nu)
hv (Light)

Stereochemistry: ❗Mixed (radical mechanism)
Anti-Markonikov Product

Acid Catalyzed Hydration

cat. H2SO4

H2O around

Mixed
Markonikov

Oxymercuration Demercuration

1. Hg(OAc)2 , H2O

2. NaBH4
   
   Skips Carbo Cation
   ==> No rearrangement
   

   Stereochemistry: ❗Mixed, but generally anti in the first step
   Markonikov Product of OH

Hydroboration Oxidation

1. BH3 * THF

2. NaOH, H2O2
   
   Forms Boron concerted 4-membered transition state
   Boron adds directly to the less substituted carbon — no carbocation involved
   Double bond attacks boron, H from BH3 attacks more substituted carbon
   No rearrangement
   Stereochemistry: ✅ Syn
   Anti Markonikov addition of OH

Hydrogenation

H2
Pd/Pt/Ni

syn addition of H2 to alkene carbons

Halogenation

X2 — > x = Cl, Br only
Non nucleophliic solvent: CCl4, CHCl3, etc
Anti addition

forms Br a three-membered halonium ion, no carbocation

Halohydrin Formation

X2 — > x = Cl, Br only
Nucleophilic solvent:
H2O, ROH, etc
OH at more substituted carbon, X at less substituted carbon
Anti Addition
forms Br a three-membered halonium ion, no carbocation

Anti Dihydroxylation

Anti Addition of 2 OH groups

Reagents: RCO₃H (peroxy acid, e.g., mCPBA)
Peroxy Acid solvent
Add H3O to add H to epoxide and OH attacks more subsitutded carbon

Forms 3 membered O ring (epoxide)

Syn Dihydroxylation

2 Methods:

A) KmNO4
NaOH cold

B) OsO4
NMO

Forms Syn diol

Oxidative Cleavage

11.1
Ozonlysis
1. O3
2. Zn/H2O or DMS
Forms Aldehyde/Ketone

11.2
KMnO4
Warm Condition
Forms Ketone/Carboxylic Acid