Advices For Studying Organic Chemistry

8.8 HALOHYDRIN FORMATION

Cl 4 ), the

major product is a halohydrin (halo alcohol).

1. When an alkene is reacted bromine in aqueous solution (rather than C

CC+ X 2 + H 2 O CC

X OH

CC

X X

++HX

X = Cl or Br Halohydrin vic-Dihalide

(major)(minor)

A Mechanism for the Reaction

Halohydrin formation from an Alkene
Step 1

This step is the same as for halogen addition to an alkene

X −

Halonium ion

CC

X

X

δ− X

δ+ +

CC +

Step 2 and 3

OH

H

+ CC

X

O

H

H O

H

+ H

CC

X

O

H

+ OH

H

H +

Protonated

halohydrin

Halohydrin

Here, however, a water molecule

acts as the nuclephile and attacks a

carbon of the ring, causing the

formation of a protonated halohydrin.

The protonated hallohydrin loses a

proton (it is transferred to a molecule

of water). This step produces the

halohydrin and hydronium ion.

Halonium ion

CC

X+

1) Water molecules far numbered halide ions because water is the solvent for the