Give reason for the following:
Alpha (\(\alpha\)) hydrogens of aldehydes and ketones are acidic in nature.
Alpha (\(\alpha\)) hydrogens of aldehydes and ketones are acidic in nature.
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Solution and Explanation
Acidity of a hydrogen depends on how stable the anion (conjugate base) left behind is after the hydrogen is removed.
Step 1:
The alpha carbon is next to the carbonyl (C\(=\)O) group. When an alpha hydrogen is removed, a carbanion is formed on the alpha carbon.
Step 2:
This carbanion is stabilised by resonance with the carbonyl group: the negative charge can move onto the electronegative oxygen atom, forming a resonance-stabilised enolate ion.
Answer: Because the anion formed on removing an alpha hydrogen is stabilised by resonance with the adjacent carbonyl group (the charge is delocalised onto oxygen, giving a stable enolate ion), the alpha hydrogens of aldehydes and ketones are acidic in nature.
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