Rank the following compounds in order of DECREASING acidity.
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Expert Chegg Question Answer:
The order of decreasing acidity would be:
A > D > B > C
i.e, diketone > diester > ketone > ester
In the given compounds it is the alpha-hydrogen which contributes to the acidity. What is important here is the pka of the (alpha) hydrogens which are adjacent to the respective functional groups. Now, pka = -log (ka) where ka is the acid dissociation constant. Greater the pka, lower will be the ka and hence lower will be the acidity.
The approximate pka’s of the alpha hydrogens are as follows:
– ketone = 20
– ester = 25
– diketone = 9
– diester = 13
Hence, we have : A > D > B > C