Question: Why is $\alpha$-hydrogen of carbonyl group acidic in nature?

Step 1 (Conceptual Basis): [1 Mark]

The acidity of the $\alpha$-hydrogen is primarily due to the strong electron-withdrawing effect of the carbonyl group ($C=O$). The carbonyl carbon is $sp^2$ hybridized and highly electronegative, which exerts an inductive effect ($-I$ effect), pulling electron density away from the $\alpha$-carbon.

Step 2 (Mechanism and Stabilization): [1.5 Marks]

When an $\alpha$-hydrogen is removed by a base, the resulting conjugate base is a carbanion. This carbanion is stabilized by resonance, where the negative charge is delocalized onto the electronegative oxygen atom of the carbonyl group. The resonance structures are represented as follows:

$$CH_3-C(=O)-CH_3 \xrightarrow{-H^+} [CH_3-C(=O)-CH_2]^- \longleftrightarrow [CH_3-C(O^-)=CH_2]$$

The resonance stabilization of the enolate ion makes the release of the proton energetically favorable, thereby increasing the acidity of the $\alpha$-hydrogen.

Step 3 (Final Conclusion): [0.5 Mark]

Therefore, the $\alpha$-hydrogen is acidic because the conjugate base (enolate ion) formed after the loss of a proton is highly stabilized through resonance delocalization of the negative charge onto the oxygen atom.

💡 EL10 Concept Insight: Think of the carbonyl group as a "magnet" that pulls electrons toward itself; when the $\alpha$-hydrogen leaves, the leftover negative charge is spread out (delocalized) across the oxygen atom, making the whole molecule much more stable and happy to let that hydrogen go.