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  •  » Acid catalyzed opening of 1,2-epoxypropane (epoxide)

#1 2011-03-19 07:17:27

orgopete
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Acid catalyzed opening of 1,2-epoxypropane (epoxide)

I saw a question posted about the acid catalyzed opening of epoxides. The poster asked why a tertiary epoxide opened at the more substituted carbon and a secondary epoxide opened at the less substituted end in an SN2 reaction.

      http://www.curvedarrow.com/chem/ZZ4BD8CAAE.jpg

The poster also cited some data (which I have altered slightly). The difference between these two systems reflects the stability of the carbocations. If the potential carbocation is tertiary (I v III), then attack occurs at the tertiary carbon. If the potential carbocation is secondary, then the selectivity of I v II is lower and most of the product is from the opening at the primary carbon.

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