(f)The carboxylic acid function plays no part in this reaction; free-radical addition of hydrogenbromide to the carbon–carbon double bond occurs.Recall that hydrogen bromide adds to alkenes in the presence of peroxides with a regioselec-tivity opposite to that of Markovnikov’s rule.19.23(a)The desired product and the starting material have the same carbon skeleton, and so all that isrequired is a series of functional group transformations. Recall that, as seen in Problem 19.17,a carboxylic acid may be prepared by oxidation of the corresponding primary alcohol. Theneeded alcohol is available from the appropriate alkene.(b)The target molecule contains one more carbon than the starting material, and so a carbon–carbon bond-forming step is indicated. Two approaches are reasonable; one proceeds by wayof nitrile formation and hydrolysis, the other by carboxylation of a Grignard reagent. In eithercase the key intermediate is 1-bromo-2-methylpropane.
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