Question

Write the structural formula for 1,2 -diiodobenzene (also known as ortho- diiodobenzene). Write the structural formulas for the meta and para isomers as well.

Short answer

Ortho-: adjacent iodines; Meta-: 1,3 positions; Para-: opposite positions (1,4).

Step-by-step solution

Understand the Structure of Benzene

Benzene is a six-carbon ring (aromatic) with alternating double and single bonds. Its chemical formula is C₆H₆, indicating it has six carbon atoms arranged in a ring, each bonded to one hydrogen atom.

Identify Iodo-Substituents

In 1,2-diiodobenzene, the '1,2' indicates the positions of the iodine groups. 'Ortho' means that the two iodine atoms are adjacent to each other on the benzene ring.

Draw the Ortho-Diiodobenzene

Start by drawing the benzene ring with alternating double bonds. Then, place iodine atoms on adjacent carbon atoms, specifically at positions 1 and 2 of the benzene ring.

Draw the Meta-Diiodobenzene

For the meta isomer, place the iodine atoms on the benzene ring so that they are separated by one carbon atom. Specifically, they should be on positions 1 and 3.

Draw the Para-Diiodobenzene

For the para isomer, place the iodine atoms on opposite ends of the benzene ring. Specifically, they should be on positions 1 and 4.

Key concepts

Benzene

Benzene is a fascinating molecule that serves as a fundamental building block in organic chemistry. It is best known for its distinctive ring structure composed of six carbon atoms. These carbon atoms form a perfect hexagonal shape, each bonded to one hydrogen atom, resulting in a chemical formula of \( C_6H_6 \).

One of the most intriguing aspects of benzene is its alternating double and single bonds. Rather than having fixed single and double bonds, these bonds resonate, making benzene exceptionally stable. This resonance also contributes to its classification as an aromatic compound.

In discussions involving benzene, such as the exercise about diiodobenzene, understanding this stability and aromatic nature is crucial. It impacts how benzene interacts with various substituents, further highlighting its importance in chemistry.

Aromatic Compounds

Aromatic compounds are a specific class of organic molecules hallmarked by their ring structure and delocalized bonding. The unique bonding arrangement in these compounds is similar to that of benzene, where electrons are shared across the structure, contributing to exceptional stability.

Characteristics of aromatic compounds include:

• A cyclic and planar structure, allowing for overlap of p-orbitals across the ring.
• Delocalized electrons, often leading to a lower reactivity compared to other unsaturated compounds.
• Adherence to Hückel's rule, which states that aromatic compounds must have a (4n + 2) number of π electrons. In benzene, this is satisfied with its 6 π electrons.

These properties make aromatic compounds essential in the field of chemistry. They are pivotal in synthesizing a variety of chemicals, dyes, and even medicines. Exploring aromaticity in benzene offers insights into why and how it can host different functional groups, such as iodine atoms in diiodobenzene.

Isomers

Isomers are molecules with the same molecular formula but different structural arrangements. This concept is fundamental when understanding variations of a compound, such as 1,2-diiodobenzene and its isomers.

For aromatic compounds like benzene, isomers can manifest as positional isomers. The placement of substituents, such as iodine atoms, on the benzene ring leads to different types of isomers including:

• **Ortho (1,2-isomer):** The substituents are adjacent to each other on the ring, like in 1,2-diiodobenzene.
• **Meta (1,3-isomer):** Here, there is a one-carbon gap between the substituents, offering a distinct configuration.
• **Para (1,4-isomer):** In this isomer, substituents are positioned directly opposite each other on the ring.

These variations aren't just structural trivia but offer different chemical and physical properties, influencing how the isomers behave in reactions. Understanding isomers in aromatic compounds reveals that small changes in structure can lead to significant differences in their chemical behavior and applications.