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The question is to find the product of the reaction of Styrene Oxide with Hydrogen Iodide.

According to me, this should be the mechanism- enter image description here

As the benzylic carbocation will be more stable, therefore the product made from A should be major and the other one should be minor. But, in my book the answer to this question is the opposite of mine. Where did I go wrong?

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  • $\begingroup$ Did your book mention cyclodextrin? In its presence iodide opening at the primary site. $\endgroup$ – user55119 Jul 29 at 22:26
  • $\begingroup$ No, only the structure of the two reactants was given. $\endgroup$ – Robin Singh Jul 30 at 2:48
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Your answer is the correct one. Acid-catalysed hydrolysis of epoxides proceeds exactly as shown. In the specific case of styrene oxide, nucleophiles attach themselves to the benzylic carbon1,2, which means that A should be the major product. I'm attaching an image from (1) which gives the products of reaction of methanol with styrene oxide: styrene oxide with methanol

If you want to, you can try to drop a note to the authors of your book about this error.

References:

  1. Mohseni, Sharareh, et al. “Theoretical and Experimental Studies on the Regioselectivity of Epoxide Ring Opening by Nucleophiles in Nitromethane without Any Catalyst: Nucleophilic-Chain Attack Mechanism.” Progress in Reaction Kinetics and Mechanism, vol. 39, no. 1, 2014, pp. 89–102. doi:10.3184/97809059274714X13874723178403.
  2. Morrison, Robert Thornton, and Robert Neilson Boyd. Organic Chemistry. 5. ed, Allyn and Bacon, 1987, pp. 780-785.
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