Animated Solution for Chemistry - Organic Chemistry: Match List-I with List-II. $\begin{array}{ll}\text{List-I (Chemicals)}& \text{List-II (Use / Preparation / Constituent)}\\ \text{(A) Alcoholic potassium hydroxide}& \text{(i) Electrodes in batteries}\\ {\text{(B) Pd/BaSO}}_4& \text{(ii) Obtained by addition reaction}\\ \text{(C) BHC (Benzene hexachloride)}& \text{(iii) Used for }\beta \text{-elimination reaction}\\ \text{(D) Polyacetylene}& \text{(iv) Lindlar catalyst}\end{array}$ Choose the most appropriate match

Welcome to a classic match-the-column challenge! These types of questions are fantastic because they test your breadth of knowledge across multiple chapters in a single go. Here, we are presented with four distinct chemical entities—ranging from standard organic reagents to advanced polymers—and we need to pair them with their specific uses, preparation methods, or constituent properties. Let's break them down one by one and uncover the chemistry behind each.

First on our list is Alcoholic Potassium Hydroxide (Alcoholic KOH). When you see this reagent, your mind should immediately jump to elimination reactions. Unlike aqueous KOH, which acts as a nucleophile and promotes substitution (yielding alcohols), alcoholic KOH is a formidable base.

It aggressively abstracts a proton from the $\beta$-carbon of an alkyl halide, simultaneously kicking out the halide ion from the $\alpha$-carbon. This process is known as a $\beta$-elimination reaction (or dehydrohalogenation), and it results in the formation of a double bond, giving us an alkene.

Therefore, we can confidently match (A) with (iii).

Next up is $Pd/BaS{\mathrm{O}}_4$, universally recognized as Lindlar's catalyst. Imagine you have an alkyne and you want to reduce it. If you use standard hydrogen gas with a palladium or platinum catalyst, the alkyne will be fully reduced all the way down to an alkane. But what if you want to stop halfway at the alkene stage?

This is where Lindlar's catalyst shines. The palladium is "poisoned" or partially deactivated using barium sulfate ($\mathrm{BaS}{\mathrm{O}}_4$) and often a touch of quinoline. This poisoning reduces the catalyst's activity, ensuring that the hydrogenation stops at the alkene. Furthermore, because the hydrogen atoms add to the same side of the triple bond on the catalyst surface, it specifically yields a $cis$-alkene.

Thus, (B) perfectly matches with (iv).

Breaking the Aromaticity

Moving on to (C), we have BHC, which stands for Benzene Hexachloride. The name can be slightly misleading because BHC is no longer an aromatic benzene ring!

When benzene is treated with excess chlorine gas ($\mathrm{C}{\mathrm{l}}_2$) in the presence of ultraviolet light ($h u$), a radical reaction occurs. The stable, delocalized $\pi$-electron cloud of the benzene ring is completely shattered. Chlorine atoms add to every single carbon atom in the ring, converting the flat, aromatic benzene into a puckered cyclohexane derivative (${\mathrm{C}}_6{\mathrm{H}}_6\mathrm{C}{\mathrm{l}}_6$).

Because atoms are added to the molecule without any being removed, this is a textbook example of an addition reaction.

Therefore, (C) matches with (ii).

The Plastic that Conducts

Finally, we arrive at Polyacetylene. When we think of polymers and plastics, we usually think of insulators—materials used to coat copper wires to prevent electrical shocks. However, polyacetylene breaks this stereotype.

If you look at the structure of polyacetylene, it consists of a long chain of carbon atoms with alternating single and double bonds. This alternating pattern creates a conjugated $\pi$-electron system along the entire backbone of the polymer. Under the right conditions (often through a process called doping), these electrons become highly mobile, allowing the polymer to conduct electricity!

Because it is lightweight and conductive, polyacetylene and its derivatives are incredibly valuable in modern technology, specifically for making electrodes in batteries.

So, (D) matches with (i).

Let's bring all our deductions together: (A) Alcoholic KOH $\to$ (iii) $\beta$-elimination reaction (B) $Pd/BaS{\mathrm{O}}_4$ $\to$ (iv) Lindlar catalyst (C) BHC $\to$ (ii) Obtained by addition reaction (D) Polyacetylene $\to$ (i) Electrodes in batteries

This gives us the sequence: (A)-(iii), (B)-(iv), (C)-(ii), (D)-(i).

Looking at our options, this perfectly aligns with option (b). A beautiful synthesis of organic reactions and polymer applications!