Which one of the following compounds will be most readily dehydrated?
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Answer
(3) [figure]
Solution
In (1), (2) and (4) the –OH group is on the α-carbon of the ketone.
In (3) the –OH group is on the β-carbon (a β-hydroxy ketone, i.e. an aldol-type product).
∵ As per NCERT, β-hydroxy carbonyl compounds lose water readily (even on gentle heating) to give α,β-unsaturated carbonyl compounds, which are stabilised by conjugation of C=C with C=O.
CH3COCH2CH(OH)CH2CH2CH3
-H2O CH3COCH=CHCH2CH2CH3
∴ Compound (3) is dehydrated most readily.
Answer: (3)