26.22(a)There are no direct methods for the reduction of a carboxylic acid to an alkane. A number ofindirect methods that may be used, however, involve first converting the carboxylic acid to analkyl bromide via the corresponding alcohol.Once the alkyl bromide is in hand, it may be converted to an alkane by conversion to a Grignardreagent followed by addition of water.Other routes are also possible. For example, E2 elimination from 1-bromooctadecanefollowed by hydrogenation of the resulting alkene will also yield octadecane.(b)Retrosynthetic analysis reveals that the 18-carbon chain of the starting material must be attachedto a benzene ring.The desired sequence may be carried out by a Friedel–Crafts acylation, followed by Clemmensenor Wolff–Kishner reduction of the ketone.(c)First examine the structure of the target molecule 3-ethylicosane.
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