Question

How many dichloronitrobenzene isomers will be obtained by introducing an additional chloro-substituent into the benzene ring of \(p\)-chloronitrobenzene? (A) 1 (B) 2 (C) 3 (D) 4

Short answer

The correct answer to the question is (B) 2. There are two possible dichloronitrobenzene isomers that can be obtained by introducing an additional chloro-substituent into the benzene ring of p-chloronitrobenzene. These isomers are the ortho-isomer (2,4-dichloronitrobenzene) and the meta-isomer (3,4-dichloronitrobenzene).

Step-by-step solution

Draw p-chloronitrobenzene molecule

Draw the structure of the p-chloronitrobenzene. The benzene ring has 6 carbon atoms, with a nitro group (NO2) at the first position and a chloro group (Cl) at the fourth position. \( p- \text{chloronitrobenzene} : \) NO₂ | C₂═C₃ | | C₁═C₆ | | Cl -C₄ | C₅

Identify possible positions for an additional chloro group

Study the benzene ring and identify the carbon positions where the additional chloro group can be introduced. There are 2 possible positions for the second chlorine atom: adjacent to the nitro group (ortho position), and adjacent to the chloro group (meta position).

Sketch the isomers

Draw the isomers for each of the two positions: Ortho-Isomer: 2,4-dichloronitrobenzene (with the second chlorine at position 2) NO₂ | C₂-Cl | | C₁═C₆ | | Cl -C₄ | C₅ Meta-Isomer: 3,4-dichloronitrobenzene (with the second chlorine at position 3) NO₂ | C₂═C₃ | | C₁═C₆═Cl | Cl -C₄ |

Count the number of isomers and choose the correct answer

Count the number of isomers (ortho and meta) and compare with the given options: There are 2 isomers in total (ortho and meta), which correspond to answer choice (B). So, the correct answer is (B) 2.

Key concepts

p-chloronitrobenzene

In organic chemistry, particularly when studying aromatic compounds, you may come across the term **p-chloronitrobenzene**. This compound is derived from benzene by replacing hydrogen atoms with a nitro group (NO₂) and a chlorine atom (Cl). The prefix 'p-' refers to the para position, which means that the substituents are located across from each other on the benzene ring. For p-chloronitrobenzene, the NO₂ group is at position 1, and the Cl is at position 4.

Understanding how substituents are positioned on the benzene ring helps you visualize different chemical reactions. The arrangement of the substituents influences the compound's chemical properties and behavior in reactions. When preparing molecules for further chemical reactions, recognizing these positions is crucial for predicting and controlling the chemical path.

ortho and meta positions

The terms ortho and meta are spatial descriptors for substituents on a benzene ring in organic chemistry. When a new substituent, like an additional chlorine atom, is added to a benzene ring like in p-chloronitrobenzene, it can occupy different positions relative to existing groups.

• **Ortho position** refers to carbon positions adjacent to an existing substituent. For p-chloronitrobenzene, if a chloro group is added at the 2nd carbon (adjacent to the nitro group), it's in the ortho position.
• **Meta position** indicates a carbon separated by one other carbon from an existing group. Thus, adding a chloro group at the 3rd carbon (between the nitro and chloro group) forms a meta isomer.

These positions are crucial as the chemical properties and reactivity of the isomers can vary depending on the positioning of the substituents.

substitution reactions

In organic chemistry, substitution reactions are a type of reaction where one or more hydrogen atoms in a molecule are replaced with a different atom or group. In the context of dichloronitrobenzene isomers, adding a chloro substituent to p-chloronitrobenzene is an example of such a reaction.

The induction of a new substituent at a specific position is significant because it changes the geometry and potentially the reactivity of the molecule. In this case, additional chlorine is introduced into a benzene ring, creating a new structural isomer at either ortho or meta positions to form 2,4-dichloronitrobenzene and 3,4-dichloronitrobenzene, respectively.

These types of reactions are common in synthetic organic chemistry, where chemists aim to modify molecules to alter their properties for various applications.

organic chemistry

Organic chemistry is the branch of chemistry that deals with the structure, properties, composition, reactions, and synthesis of compounds primarily made of carbon and hydrogen. It also involves other elements such as nitrogen, oxygen, halogens, phosphorus, silicon, and sulfur.

Understanding the basics of organic chemistry is essential for grasping more complex concepts like isomerism seen in dichloronitrobenzene. Isomerism refers to the phenomenon where compounds have the same molecular formula but different structures. Knowledge of bonds and molecular geometry helps predict how substances like p-chloronitrobenzene behave in chemical reactions by knowing possible structural variations.

The reactions and processes within organic chemistry are foundational for practical applications ranging from pharmaceuticals to the development of new materials.