Animated Solution for Chemistry - Organic Chemistry: Total number of hydroxyl groups present in a molecule of the major product P is ______.

Let's carefully analyze our starting molecule. We are presented with a fascinating hydrocarbon that contains three distinct sites of unsaturation.

On the left, we have a cyclopentene ring containing one carbon-carbon double bond. In the center, there is an alkyne chain featuring a carbon-carbon triple bond. Finally, on the right, we find a cyclohexene ring with another carbon-carbon double bond.

To solve this problem, we need to understand exactly how our two sequential reagents interact with these specific functional groups.

Lindlar's Catalyst

Our first reagent is hydrogen gas ($H_2$) in the presence of Palladium on Barium Sulfate ($Pd-BaS{O}_4$), poisoned with quinoline. This specific combination is famously known as Lindlar's catalyst.

What makes Lindlar's catalyst so special? It is a mild, "poisoned" reducing agent. Its primary function is the partial reduction of alkynes to alkenes. Because the catalyst surface is partially deactivated by the quinoline, it is not reactive enough to reduce the resulting alkene down to an alkane. Furthermore, it is completely unreactive towards isolated, stable double bonds like those found in our cyclopentene and cyclohexene rings.

When we apply Lindlar's catalyst to our starting material, the central $-C\equiv C-$ triple bond is hydrogenated. The two hydrogen atoms are delivered from the surface of the catalyst to the same face of the alkyne, resulting in a syn-addition. This stereospecific reaction yields a cis-alkene.

Our intermediate molecule now possesses three carbon-carbon double bonds: the original two in the rings, and the newly formed cis-double bond in the central chain.

Baeyer's Reagent

Now for the second step. We treat our intermediate with cold, dilute potassium permanganate ($KMn{O}_4$) at $273\text{ K}$. This is known as Baeyer's reagent, a classic qualitative test for unsaturation.

Baeyer's reagent acts as a mild oxidizing agent. It attacks carbon-carbon double bonds and adds two hydroxyl ($-OH$) groups across the pi bond in a syn-addition fashion. This process is called syn-dihydroxylation, and it converts an alkene into a vicinal diol (a molecule with $-OH$ groups on adjacent carbons).

Because we have an excess of the reagent, it will react with all three double bonds present in our intermediate molecule.

The permanganate will attack the pi bonds, converting each one into a diol: 1. The double bond in the cyclopentene ring becomes a cyclopentanediol, contributing 2 hydroxyl groups. 2. The newly formed cis-double bond in the chain becomes a vicinal diol, contributing another 2 hydroxyl groups. 3. The double bond in the cyclohexene ring becomes a cyclohexanediol, contributing the final 2 hydroxyl groups.

The question asks for the total number of hydroxyl groups in the final major product $P$.

Thus, the final molecule contains exactly 6 hydroxyl groups.