Looking for classes? Ksquare Career Institute, Bengaluru →
Acidity of Alpha Hydrogen
Concepts tested here
- Acidity of alpha hydrogen of carbonyl compounds
All Questions
2008 AIPMT 1 question
-
A strong base can abstract an $\alpha$-hydrogen from:The hydrogen atoms on the carbon next to a carbonyl group ($\alpha$-hydrogens) are acidic.
The carbonyl group is strongly electron withdrawing, and the carbanion formed after the loss of the $\alpha$-hydrogen is stabilised by resonance with the $C=O$ group (enolate ion).
$R-CO-CH_3 + B^- \rightarrow R-CO-\overset{\ominus}{C}H_2 \leftrightarrow R-C(O^-)=CH_2 + BH$
So a strong base can abstract an $\alpha$-hydrogen from aldehydes and ketones to form a carbanion or the enolate ion. This is the first step of reactions like the aldol condensation.
In alkanes, alkenes and amines there is no such resonance stabilisation of the resulting carbanion, so their C-H hydrogens are not acidic enough to be removed in this way.
Hence the answer is ketone.