Question

Which of the following is not a homocyclic compound? (A) Phenol (B) Aniline (C) Ethylene epoxide (D) Benzene

Short answer

Ethylene epoxide (C) is not a homocyclic compound because its ring is composed of two carbon atoms and one oxygen atom, unlike the other compounds where the rings consist of only carbon atoms.

Step-by-step solution

Draw the structures of the given compounds

Let's draw the structures of the given compounds to analyze their rings: (A) Phenol: Phenol contains a benzene ring with an -OH (hydroxyl) group attached to one of the carbon atoms. \[ \text{Phenol:}\hspace{1cm}\chemfig{*6(=-=-(-\text{OH})-=)} \] (B) Aniline: Aniline contains a benzene ring with an -NH2 (amino) group attached to one of the carbon atoms. \[ \text{Aniline:}\hspace{1cm}\chemfig{*6(=-=-(-\text{NH}_2)-=)} \] (C) Ethylene epoxide: Ethylene epoxide is a three-membered ring containing two carbon atoms and one oxygen atom. \[ \text{Ethylene epoxide:}\hspace{1cm}\chemfig{*3(-=(-)O)} \] (D) Benzene: Benzene is a six-membered ring containing only carbon atoms and each carbon atom has a hydrogen atom attached to it. \[ \text{Benzene:}\hspace{1cm}\chemfig{*6(=-=-=-)} \]

Identify the compound with a ring that is not composed of only carbon atoms

Now that we have drawn the structures of the given compounds, let's examine the rings: (A) Phenol: The ring is composed of carbon atoms only, so it is a homocyclic compound. (B) Aniline: The ring is composed of carbon atoms only, so it is a homocyclic compound. (C) Ethylene epoxide: The ring is composed of two carbon atoms and one oxygen atom. Since the ring is not composed of only carbon atoms, it is not a homocyclic compound. (D) Benzene: The ring is composed of carbon atoms only, so it is a homocyclic compound.

Conclusion

From the analysis above, we can conclude that the compound which is not a homocyclic compound is (C) Ethylene epoxide.

Key concepts

Homocyclic Compounds

In organic chemistry, understanding different types of compounds helps us comprehend how molecules are structured and how they work. Homocyclic compounds are a specific type of chemical compound where the molecular structure consists of a ring constructed entirely of carbon atoms. This makes them a form of a carbocyclic compound.

Homocyclic compounds like Benzene, Phenol, and Aniline all include rings made only from carbon atoms. For instance:

• **Benzene**: A classic example of a homocyclic compound. It is made up of a hexagonal ring consisting of six carbon atoms.
• **Phenol**: Similar to benzene but with an additional OH group attached, still maintains its carbon-only ring.
• **Aniline**: Comparable to phenol but with an attached NH₂ group, the core is a benzene ring.

Beneath this surface though, these functional groups (OH and NH₂) do not alter the basic homocyclic structure. These compounds reflect the importance of homocyclic rings in modern chemistry, forming the backbone for more complex structures.

Molecular Structures

The arrangement of atoms within a molecule plays a crucial role in defining the chemical properties and behavior of a compound. Molecular structures are the blueprint of a chemical compound, showing how each element is connected and arranged in space. It often determines if a compound is homocyclic or heterocyclic.

The key to understanding molecular structures is to visualize how atoms are linked through bonds to form rings and chains. For homocyclic compounds, these structures will pinpoint a clear all-carbon ring

• **Benzene**: Every carbon atom forms two bonds to adjacent carbons, creating a closed hexagonal ring.
• **Aniline and Phenol**: Follow this structure but deviate slightly due to their attached functional groups, which do not integrate into the homocyclic ring.

Ethylene epoxide, on the other hand, demonstrates what happens when non-carbon atoms are introduced into a ring:

• **Ethylene Epoxide**: Incorporates an oxygen atom into its three-membered ring, making it a heterocyclic compound.

Thus, molecular structures can be observed to determine whether a compound is homocyclic based on the composition of its ring system.

Functional Groups

Functional groups are specific atoms or groups of atoms within molecules that have certain characteristic properties. They essentially define the chemical reactions that a molecule can undergo. In the context of organic chemistry, they are attached to the carbon backbone of a compound and often dictate the type of compound we're dealing with.

Functional groups are the key to unlocking the behavior of compounds, such as:

• **Hydroxyl Group (-OH)**: Found in phenol; influences the acidity and solubility of the molecule without changing the homocyclic nature of phenol's benzene ring.
• **Amino Group (-NH₂)**: Present in aniline, impacting its basicity and reactivity with acids.

These groups are crucial when characterizing different organic compounds and understanding how molecules interact with each other.

While Ethylene epoxide involves the presence of an oxygen atom, its functional groups create a different context in which the compound operates, categorizing it separately from true homocyclic compounds due to its heterocyclic nature. Therefore, understanding these groups can assist in differentiating and predicting chemical behavior and interactions.