Problem 52 - A Complete Resource Book in Chemistry for JEE Main

Question

The correct IUPAC name of the compound, is (a) p-phenyldiphenyl (b) \(\mathrm{p}, 1\)-diphenylbenzene (c) \(1,1^{\prime}, 4^{\prime} .1^{\prime \prime}\)-terphenyl (d) terphenyl

Step-by-Step Solution

Answer

The correct IUPAC name is (c) 1,1', 4', 1''-terphenyl.

Step 1: Identify the Structure of the Compound

To determine the IUPAC name, first identify the structure of the compound based on the options given. The term 'terphenyl' generally refers to a class of aromatic hydrocarbons consisting of three benzene rings connected linearly. Specifically, the connectivity pattern is usually presented as three benzene rings connected in a 1,4-pattern to each other, where one benzene ring is central, and the others are connected at the ortho-position.

Step 2: Assess the Options Given

Now, look at each option: - (a) _p-phenyldiphenyl_ is not a valid IUPAC name. - (b) _p,1-diphenylbenzene_ is not specific enough and not standardized. - (c) _1,1', 4', 1''-terphenyl_ correctly describes the three benzene rings connected in a 1,4 manner aligning with the general description of terphenyl. - (d) _terphenyl_ is a class name without specifying the connectivity pattern clearly.

Step 3: Select the Correct IUPAC Name

Based on the correct structural description, option (c) '1,1', 4',1''-terphenyl' accurately and correctly names the compound in accordance with IUPAC naming guidelines. It specifies the necessary connectivity between the benzene rings: this option gives a precise depiction of the structure compared to the general term 'terphenyl' used in option (d).

Key Concepts

Aromatic Hydrocarbons

Aromatic hydrocarbons are a fascinating class of compounds known for their distinctive, stable structures. These compounds include rings of carbon atoms with delocalized electrons, forming what is known as an "aromatic ring." Common examples include benzene and its derivatives, which possess a six-membered carbon ring with alternating double bonds.
Aromatic hydrocarbons are unique due to their resonance, a quantum mechanical feature that allows them to maintain stability despite the presence of double bonds that would typically induce reactivity.

• Characteristics: Often colorless and have a pleasant odor.
• Stability: More stable than they might appear due to electron delocalization.
• Reactions: Undergo substitution reactions, rather than addition reactions typical of alkenes.

Understanding these aspects is essential to mastering organic chemistry, as many compounds such as terphenyl belong to this group.

Terphenyl

Terphenyls are a subset of aromatic hydrocarbons consisting of three benzene rings. Each ring is interconnected in a specific linear arrangement called the "1,4-pattern," which is a fundamental feature of these compounds.
Their structure can be visualized as:

• The central benzene ring acts as a bridge.
• The two outer rings attach at the opposite ends of the central ring.

This arrangement results in the term "terphenyl," which specifies a three-ring system. Rotation around the single bonds connecting the benzene rings allows for

Applications of Terphenyl

Beyond their structural intrigue, terphenyls are utilized in practical applications ranging from heat-transfer fluids to intermediates in organic synthesis. Their crystalline nature and stability make them valuable in various industries. Understanding terphenyls helps in grasping key concepts related to multi-ring aromatic compounds. This understanding is further deepened by exploring how these compounds are named using systematic IUPAC rules.

IUPAC Nomenclature Rules

IUPAC nomenclature rules provide a standardized method for naming compounds, ensuring clarity and consistency in the chemical literature.
When dealing with aromatic compounds like terphenyl, it is crucial to adhere to these rules to accurately convey the specific structure.

Key Nomenclature Principles

• Systematic Naming: Ensures that each compound has a unique name identifying its distinct structure.
• Locants: Numbers or positions assigned to substituents or points of attachment in the compound. For terphenyl, this involves numbering the benzene rings and specifying connections.
• Substituents: Identified and numbered to indicate their position on the aromatic ring system.

The compound "1,1',4',1''-terphenyl" exemplifies how IUPAC naming specifies the precise connectivity of the benzene rings, ensuring there is no ambiguity. This detail and precision are why IUPAC names are vital in communicating chemical structures."