Problem 8.5 asked you to predict the major organic product for addition of HCl to each of...

Problem 8.5 asked you to predict the major organic product for addition of HCl to each of the following alkenes. Do the same for the addition of HBr to these alkenes, comparing the products formed in the absence of peroxides and in their presence.

(a) 2-Methyl-2-butene

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(b) cis-2-Butene

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(c) 2-Methyl-1-butene

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(d)

Sample Solution (a) The addition of hydrogen bromide in the absence of peroxides exhibits a regioselectivity just like that of hydrogen chloride addition in that Markovnikov’s rule is followed.

Under free-radical conditions in the presence of peroxides, however, addition takes place with a regioselectivity opposite to Markovnikov’s rule.