Problem 21 - A Complete Resource Book in Chemistry for JEE Main

Question

Which of the following compounds will show metamerism? (a) \(\mathrm{CH}_{3}-\mathrm{O}-\mathrm{C}_{2} \mathrm{H}_{5}\) (b) \(\mathrm{CH}_{3}-\mathrm{O}-\mathrm{CH}_{3}\) (c) \(\mathrm{CH}_{3}-\mathrm{CO}-\mathrm{C}_{2} \mathrm{H}_{5}\) (d) \(\mathrm{C}_{2} \mathrm{H}_{5}-\mathrm{S}-\mathrm{C}_{2} \mathrm{H}_{5}\)

Step-by-Step Solution

Answer

Option (a) \( \mathrm{CH}_{3}-\mathrm{O}-\mathrm{C}_{2} \mathrm{H}_{5} \) shows metamerism.

Step 1: Understanding Metamerism

Metamerism is a type of isomerism where compounds have the same molecular formula but different arrangements of alkyl groups around a functional group such as oxygen, sulfur, or nitrogen. These compounds are called metamers.

Step 2: Analyzing Option (a)

In option (a), the compound is \( \mathrm{CH}_{3}-\mathrm{O}-\mathrm{C}_{2} \mathrm{H}_{5} \). This compound is an ether with an alkoxy group (\(-\mathrm{O}-\)) surrounded by two different alkyl groups (methyl and ethyl). This satisfies the criteria for metamerism.

Step 3: Analyzing Option (b)

For option (b), the compound is \( \mathrm{CH}_{3}-\mathrm{O}-\mathrm{CH}_{3} \). This is also an ether, but it has the same alkyl groups (methyl) on both sides, hence it will not show metamerism.

Step 4: Analyzing Option (c)

In option (c), the compound is \( \mathrm{CH}_{3}-\mathrm{CO}-\mathrm{C}_{2} \mathrm{H}_{5} \). This is a ketone, not an ether or sulfide, and therefore, does not typically display metamerism.

Step 5: Analyzing Option (d)

Option (d) is \( \mathrm{C}_{2} \mathrm{H}_{5}-\mathrm{S}-\mathrm{C}_{2} \mathrm{H}_{5} \). This compound is a sulfide with identical (ethyl) groups on either side of sulfur, thus, it will not display metamerism.

Step 6: Conclusion

By examining each compound, only option (a) exhibits metamerism because it has different alkyl groups around the ether functional group.

Key Concepts

Isomerism

In chemistry, isomerism refers to the occurrence of two or more compounds that share the same molecular formula but exhibit different structural arrangements or configurations. Isomers are distinguished by their varying atomic arrangements and often have distinct chemical and physical properties.

Isomerism can be categorized into two main types: structural isomerism and stereoisomerism. Structural isomerism occurs when the atoms are connected in different orders. Types of structural isomerism include chain isomerism, position isomerism, functional group isomerism, and metamerism, among others.

Metamerism, a subset of structural isomerism, is identified when compounds have identical molecular formulas but differ in the nature or positioning of their alkyl groups around a specific functional group. Understanding this form of isomerism helps in differentiating certain organic compounds based on their structural compositions.

Organic Chemistry

Organic chemistry is the branch of chemistry that focuses on the study of carbon-based compounds, encompassing a vast array of molecules that contain carbon atoms linked to hydrogen, oxygen, nitrogen, sulfur, and other elements.

Organic compounds are classified based on the presence of different functional groups, which are specific groups of atoms within molecules that have characteristic chemical behaviors. This field of chemistry is crucial for understanding a range of substances from simple molecules like methane, to complex structures like proteins and DNA.

Organic chemistry is foundational for developing pharmaceuticals, plastics, fuels, and many other materials. It deals with reactions that form and break bonds between carbon atoms, and it studies how these processes are influenced by the surrounding atoms and molecules.

Functional Groups

Functional groups are the core arrangement of atoms within a molecule that define its chemical properties and reactions. They are pivotal in the study of organic chemistry as they determine the character and functionality of organic compounds.

Common functional groups include:

• Hydroxyl group (-OH): found in alcohols and phenols.
• Carbonyl group (>C=O): found in aldehydes, ketones, and carboxylic acids.
• Carboxyl group (-COOH): present in carboxylic acids.
• Amine group (-NH2): found in amino acids and amines.
• Ether group (-O-): found in ethers such as the compound \( \mathrm{CH}_{3}-\mathrm{O}-\mathrm{C}_{2} \mathrm{H}_{5} \).

Functional groups are crucial in determining the types of reactions compounds will undergo, influencing properties like solubility and acidity. They aid chemists in categorizing organic compounds and predicting their behaviors in chemical reactions.

Alkyl Groups

Alkyl groups are hydrocarbons derived from alkanes that have had one hydrogen atom removed, allowing them to connect with other molecules or functional groups. They play an essential role in organic chemistry due to their capacity to modify the properties of molecules.

Alkyl groups are categorized by their carbon chain arrangement, such as:

• Methyl group (\(\mathrm{CH}_{3}-\)): a single carbon chain.
• Ethyl group (\(\mathrm{C}_{2}\mathrm{H}_{5}-\)): a two-carbon chain.
• Propyl group (\(\mathrm{C}_{3}\mathrm{H}_{7}-\)): a three-carbon chain.

These groups, when attached to functional groups, can alter the way a compound reacts by affecting its steric and electronic environments. For example, in metamerism, alkyl groups exchanged around a central atom or group result in differing compounds with the same molecular formula but distinct structures, as seen in the compound \( \mathrm{CH}_{3}-\mathrm{O}-\mathrm{C}_{2} \mathrm{H}_{5} \).