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

1 Answer
Sep 13, 2015

Answer:

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.