Advices For Studying Organic Chemistry

CC CC

X

H

CC

H

H

X

X

HX HX

Haloalkene gem-Dihalide

2) The H atom of the HX becomes attached to the carbon atom that has the greater

number of H atom

s.

C 4 H 9 C CH 2

Br Br

2-

HBr C

4 H 9 CCH 3

Bromo-1-hexene 2,2-Dibromohexane

C HBr

4 H 9 CCH

2. The addition of HBr to an alkyne can be facilitated by using acetyl bromide
   (CH 3 COBr) and alumina instead of aqueous HBr.

1. CH 3 COBr acts as an HBr precursor by reacting with alumina to generate HBr.

Br

2) The alumina increases the rate of reaction.

CH 3 COBr/alumina

"HBr"

C

CCH 2

5 H 11

Br

CH 2 Cl (^2) (82%)
C 5 H 11 CCH

3. Anti-Markovnikov addition of HBr to alkynes occur when peroxides are present.
   
   
   1. These reactions take place through a free radical mechanism.
   
   
   
   

CH 3 CH 2 CH 2 CH 2 C CH peroxideHBr s CH 3 CH 2 CH 2 CH 2 CH CHBr

(74%)

8.14 OXIDATIVE CLEAVAGE OF ALKYNES

1. Treating alkynes with ozone or with basic potassium permanganate leads to