Advices For Studying Organic Chemistry

10.9 REDICAL ADDITION TO ALKENES: THE ANTI-MARKOVNIKOV

ADDITION OF HYDROGEN BROMIDE

1. Kharasch and Mayo (of the University of Chicago) found that when alkenes that
   contained peroxides or hydroperoxides reacted with HBr ⇒ anti-Markovnikov
   addition of HBr occurred.
   R OOR
   R

r

OOH

An organic peroxide An organic hydroperoxide

1) In the presence of peroxides, propene yields 1-bromopropane.

CH 3 CH=CH 2 + HB ROOR CH 3 CH 2 CH 2 Br Anti-Markovnikov addition

2) In the absence of peroxides, or in the presence of compounds that would “trap”

radicals, normal Markovnikov addition occurs.

no^

CH 3 CH=CH 2 + HBr (^) peroxides CH 3 CHBrCH 2 – H Markovnikov addition

2. HF, HCl, and HI do not give anti-Markovnikov addition even in the presence of
   peroxides.


3. Step 3 determines the final orientation of Br in the product because a more stable
   2° radical is produced and because attack at the 1° carbon is less hindered.

Br +H 2 CCHCH 3 CH 2 CH CH 3

x

x

Br

1) Attack at the 2° carbon atom would have been more hindered.