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.

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