Animated Solution for Chemistry - Organic Chemistry: In the following sequence of reactions, the final product $D$ is

The beauty of organic synthesis lies in its logical progression. Each step is a carefully choreographed dance of electrons, transforming simple molecules into complex architectures. Let's embark on a thrilling journey through this multi-step synthesis problem, starting with propyne and ending with a seven-carbon ketone.

The Acid-Base Activation

Our journey begins with propyne (${\text{CH}}_3-\text{C}\equiv \text{C}-\text{H}$) and sodium amide (${\text{NaNH}}_2$). Sodium amide is a formidable base. When it encounters a terminal alkyne, it immediately recognizes the slightly acidic hydrogen attached to the $sp$-hybridized carbon.

The amide ion snatches this proton, generating the propynyl sodium or acetylide ion (Intermediate A). This ion is a fantastic, electron-rich nucleophile, perfectly primed for the next stage of our synthesis.

The $S_{N}2$ Coupling

Next, we introduce our electrophile: 4-bromobutan-2-ol. This molecule features a four-carbon chain with a bromine atom at one end and a hydroxyl group at the other.

Here is where the magic happens. The acetylide ion executes a classic $S_{N}2$ attack on the partially positive carbon attached to the bromine atom. The bromide ion is kicked out as a leaving group.

This crucial step couples the two chains together, forming a new carbon-carbon bond. Our product B is hept-5-yn-2-ol. We have successfully built a seven-carbon skeleton containing both an alkyne and an alcohol group!

The Catalytic Reduction

Moving forward, we treat intermediate B with hydrogen gas over a palladium-carbon catalyst (${\text{H}}_2/\text{Pd-C}$). This creates a strong reducing environment specifically targeted at $\pi$-bonds.

The triple bond is completely reduced all the way down to a single bond, transforming the alkyne into an alkane. Notice that the alcohol group remains completely unaffected by this catalytic hydrogenation. We have now formed heptan-2-ol (Intermediate C).

The Final Oxidation

Finally, we introduce chromium trioxide (${\text{CrO}}_3$), a well-known and powerful oxidizing agent. Its target? The secondary alcohol group in heptan-2-ol.

The hydroxyl group loses its hydrogen, and a carbon-oxygen double bond is formed. We arrive at our final product D, which is heptan-2-one.

Comparing our final structure with the given options, we can clearly see that it perfectly matches option (d). A beautiful sequence of reactions, flawlessly executed!