How can I illustrate Markovnikov's rule by the reaction of propene with hydrobromic acid?

1 Answer
anor277
Sep 13, 2015

Treat the acid as #D-Br#, i.e. #D# = deuterium. Consider the intemediate after the olefin has reacted with #D^+#.

Explanation:

Markownikow addition:

#H_2C=CHCH_3 + D-Br rarr H_2DC-C^+HCH_3 + Br^-#

Anti-Markownikow addition:

#H_2C=CHCH_3 + D-Br rarr H_2C^+(-CHDCH_3) + Br^-#

As you know, the secondary carbocation is more stable than the primary carbocation. Because the carbocation intermediate is then going to react with the electrophile, #Br^-#, we should see more #H_2(D)C-CHBrCH_3# than the anti-Markownikow product, #H_2(Br)C-CHDCH_3#.

For further background see: Hughes, P. J. Chem. Ed. 2006 , 83 , 1152. Was Markovnikov's Rule an Inspired Guess? I can't get to this article, but your librarian should supply it. J. Chem. Ed. articles are generally very good.

Related questions
See all questions in Radical Halogenation of Alkenes (Antimarkovnikov)
Impact of this question
3577 views around the world
You can reuse this answer
Creative Commons License