Question

In this given reaction sequence Red ppt. cannot be obtained by reaction of \(\mathrm{NH}_{4} \mathrm{OH} / \mathrm{Cu}_{2} \mathrm{Cl}_{2}\) with (A) X (B) \(\mathrm{P}\) (C) Ethene (D) Ethyne

Short answer

The red precipitate cannot be obtained by the reaction of ammonium hydroxide (NH4OH) and copper(II) chloride (Cu2Cl2) with Ethene (C2H4). Ethene is an unsaturated hydrocarbon that cannot effectively react with these reagents to produce a red precipitate.

Step-by-step solution

Analyzing compound A: X

Since X is an unknown compound, we cannot predict its reaction with NH4OH / Cu2Cl2. Hence, we cannot draw any conclusions regarding the formation of a red precipitate in this case.

Analyzing compound B: P

In this option, P is mentioned. Like in option A, we cannot predict how compound P would react with NH4OH / Cu2Cl2 since this compound is not properly defined. Thus, we cannot determine whether a red precipitate will form or not.

Analyzing compound C: Ethene (C2H4)

Ethene is an unsaturated hydrocarbon with a C=C double bond. Ammonium hydroxide (NH4OH) and copper(II) chloride (Cu2Cl2) can't effectively react with ethene in such a way to produce a red precipitate. Copper (I) chloride (CuCl) is needed to form the red precipitate. The reaction sequence would be \(C_2H_4 + H_2O + CuCl \rightarrow CH_2ClCH_2Cl + 2NH_3\). Hence, ethene will not form a red precipitate with NH4OH / Cu2Cl2.

Analyzing compound D: Ethyne (C2H2)

Ethyne (C2H2) is an unsaturated hydrocarbon with a carbon-carbon triple bond. It is known to react with ammonium hydroxide (NH4OH) in the presence of copper(II) chloride (Cu2Cl2) to produce a red precipitate of copper(I) acetylide (Cu2C2). The reaction can be represented as \(C_2H_2 + NH_4OH + Cu_2Cl_2 \rightarrow Cu_2C_2 \downarrow (red) + 2NH_3 + 2H_2O\). Ethyne will form a red precipitate with NH4OH / Cu2Cl2. From the analysis of the given options, the correct answer is: (C) Ethene

Key concepts

IIT JEE Organic Chemistry

The Indian Institutes of Technology Joint Entrance Examination (IIT JEE) is a highly competitive test that challenges students on various topics, including Organic Chemistry. This branch of science examines the structure, properties, composition, reactions, and synthesis of carbon-containing compounds. In Organic Chemistry for the IIT JEE, mastering the basics such as nomenclature, stereochemistry, and functional groups is just as important as understanding complex synthesis problems and reaction mechanisms.

For a student preparing for IIT JEE, being proficient in reaction mechanisms and being able to predict the products of reactions in organic syntheses are crucial skills. It is essential not just to memorize reactions but also to comprehend the underlying principles governing these reactions. Moreover, a deep knowledge of organic chemistry principles helps in reasoning out solutions for complex problems, such as predicting whether a certain reagent will give a specific reaction product, as in the textbook exercise mentioned.

Organic Reaction Mechanisms

Organic reaction mechanisms are the step-by-step descriptions of the processes by which chemical reactions occur. In solving IIT JEE organic chemistry problems, understanding these mechanisms is a vital part of predicting the outcome of chemical reactions. They involve the movement of electrons, breaking and forming of bonds, and the rearrangement of atoms.

For instance, in the exercise regarding ethene and ethyne, the ability to anticipate whether a red precipitate will form when treated with a specific reagent duo hinges on the knowledge of the mechanisms. Ethene, with its double bond, and ethyne, with its triple bond, will behave differently under similar conditions due to the disparities in bond energies and stabilities. Students are expected to know that ethyne's triple bond is more reactive in the presence of NH4OH/Cu2Cl2, leading to the formation of copper(I) acetylide, as showcased in the exercise solution. Knowing the mechanistic pathway helps in visualizing what happens at each stage of the reaction, leading to a more concrete understanding of the expected products.

Chemical Reagents

Chemical reagents are substances or compounds that are used to bring about a chemical reaction. They are important tools in the world of chemistry, especially in organic synthesis, as they can determine the course of a reaction. In the context of IIT JEE, students are required not only to recognize common reagents but also to understand how they can influence different substrates.

In the context of the exercise, ammonium hydroxide (NH4OH) and copper(II) chloride (Cu2Cl2) are the reagents in question. Their role is to react with organic substrates, such as ethyne, to produce specific reaction products like the red precipitate of copper(I) acetylide. Understanding the reactivity of such reagents can also help in predicting whether they will engage in substitution, addition, elimination, or rearrangement reactions with given organic compounds. A thorough understanding of the reactivity and specificity of different reagents is a formidable skill for cracking tough organic chemistry problems in competitive exams like the IIT JEE.