Notice that the phenyl and hexyl substituents may be either cis or trans to each other. The two prod-ucts are the cis and trans stereoisomers.17.30Cyclic hemiacetals are formed by intramolecular nucleophilic addition of a hydroxyl group to acarbonyl.The ring oxygen is derived from the hydroxyl group; the carbonyl oxygen becomes the hydroxyloxygen of the hemiacetal.(a)This compound is the cyclic hemiacetal of 5-hydroxypentanal.Indeed, 5-hydroxypentanal seems to exist entirely as the cyclic hemiacetal. Its infrared spec-trum lacks absorption in the carbonyl region.(b)The carbon connected to two oxygens is the one that is derived from the carbonyl group.Using retrosynthetic symbolism, disconnect the ring oxygen from this carbon.
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