Question

The total number of benzenoid isomer of molecular formula \(\mathrm{C}_{6} \mathrm{H}_{3} \mathrm{Cl}_{3}\) possible is (A) 1 (B) 2 (C) 3 (D) 4

Short answer

The total number of benzenoid isomers of molecular formula C₆H₃Cl₃ is 3. We determined this by considering the different ways in which the 3 Cl atoms can replace the 3 H atoms in the benzene ring, taking into account adjacent and non-adjacent positions of Cl atoms. The correct answer is (C) 3.

Step-by-step solution

Draw the benzene ring with H atoms attached

First, let's draw a benzene ring (C₆H₆) with 6 carbon atoms and 6 hydrogen atoms attached to each carbon atom. Keep in mind that one benzene ring has 6 carbons connected by alternating single and double bonds.

Determine the possible positions for Cl atoms

Now we have to find the different ways in which the 3 Cl atoms can replace 3 H atoms in the benzene ring. We consider that two Cl atoms will be adjacent if they are either at relative positions 1,2 or 1,3. They'll be non-adjacent if they're at positions 1,4.

Number of isomers when two Cl atoms are adjacent

To determine the number of isomers when two Cl atoms are adjacent, the possible positions for Cl atoms are: 1. 1st Cl atom at position 1, 2nd Cl atom at position 2, and 3rd Cl atom at position 3 or 4. 2. 1st Cl atom at position 1, 2nd Cl atom at position 2, and 3rd Cl atom at position 4 or 5. With these possible positions we get 2 isomers when the 2 Cl atoms are adjacent.

Number of isomers when two Cl atoms are non-adjacent

To determine the number of isomers when two Cl atoms are non-adjacent, the possible positions for Cl atoms are: 1. 1st Cl atom at position 1, 2nd Cl atom at position 4, and the 3rd Cl atom at position 3. With these possible positions we get 1 isomer when the 2 Cl atoms are non-adjacent.

Determine the total number of isomers

Now, we add the number of isomers from Steps 3 and 4: Total number of isomers = number of isomers when two Cl atoms are adjacent + number of isomers when two Cl atoms are non-adjacent Total Number of isomers = 2 + 1 = 3 So, the total number of benzenoid isomers of molecular formula C₆H₃Cl₃ is 3. Thus, the correct answer is (C) 3.

Key concepts

Benzene Ring

The benzene ring is a fundamental structure in organic chemistry and serves as a building block for many complex molecules. It is characterized by a hexagonal arrangement of six carbon atoms, with alternating single and double bonds between them. This configuration is often represented by a hexagon with a circle inside, signifying the delocalized electrons that contribute to the ring's stability.

The unique stability of the benzene ring is due to its delocalized pi electrons, which allow the ring to be more resistant to reactions that would break its structure. Each carbon atom in the benzene ring can bond to one other atom, such as hydrogen in the simplest form, benzene (C₆H₆). In the context of benzenoid isomers, substituents like chlorine (Cl) atoms can replace the hydrogen atoms attached to the benzene ring, giving rise to various isomeric forms.

Isomerism

Isomerism is the phenomenon wherein chemical compounds have the same molecular formula but different structural arrangements of atoms, leading to unique physical and chemical properties for each isomer. In organic chemistry, isomers are classified into two main types: structural isomers and stereoisomers.

In the exercise, we analyzed structural isomers, specifically focusing on the differing positions of chlorine atoms on a benzene ring.

Positional Isomerism

One form of structural isomerism is positional isomerism, where the location of a substituent on a parent structure, such as a benzene ring, varies. For example, chlorobenzene can have chlorine at different positions, leading to different positional isomers.

Understanding Isomer Count

When counting the total number of isomers, as exemplified by the exercise, we consider all possible arrangements that follow the rules of chemical bonding without creating identical compounds. This understanding aids in discerning between compounds that share similar structural features but have different properties.

Organic Chemistry

Organic chemistry is a branch of chemistry focused on the study of the structure, properties, composition, reactions, and synthesis of carbon-containing compounds. Carbon's unique ability to form stable bonds with many elements, including itself, allows for an immense variety of organic compounds.

Understanding organic chemistry is crucial for a wide range of scientific disciplines, including biochemistry, medicine, and materials science. It provides insights into the behavior of molecules in living organisms and the design of pharmaceuticals, plastics, and other synthetic materials. In the exercise provided, we delved into a particular aspect of organic chemistry—identifying isomers of a chlorinated benzene derivative, which combines principles of structural chemistry and organic nomenclature to understand the diversity of compounds possible with a single molecular formula.