Q40E - Organic Chemistry (Mcmurry)

Question

Base treatment of the following α,β-unsaturated carbonyl compound yields an anion by removal of H⁺ from the $\mathit{\gamma }$ carbon. Why are hydrogens on the $\mathit{\gamma }$  carbon atom acidic?

Step-by-Step Solution

Answer

In this compound $\gamma$-carbon loses its hydrogen atom to reduce positive charge and increase stability, and make it more acidic.

Step 1: Resonance structure of the compound

The resonance structures of the yield compound are,

                        Resonance forms of the given compound

Step 2: Determination of hydrogens on the g carbon atom is acidic

In enolate, the α-carbon is deprotonated which is stabilized by the resonance structure. In that structure, the negative charge is localised on electronegative O-atom.

In this compound, α,β-unsaturated carbonyl compound is deprotonated on $\gamma$-carbon. The resonance of this compound localise the negative charge on the oxygen atom.

In this compound $\gamma$-carbon loses its hydrogen atom and make it more acidic.