Problem 88 - A Complete Resource Book in Chemistry for JEE Main

Question

Alizarin dye obtained from the root of madder plant is an anthraquinone derivative. Its structure corresponds to (a) 2,3 -dihydroxy anthraquinone (b) 1,2 -dihydroxy anthraquinone (c) 1-hydroxy anthaquinone (d) 1,4 -dihydroxy anthraquinone

Step-by-Step Solution

Answer

(b) 1,2-dihydroxy anthraquinone

Step 1: Understanding the Structure of Alizarin

Alizarin is a derivative of anthraquinone, which is a compound composed of three fused benzene rings with ketone groups. Specifically, alizarin is identified by its hydroxyl groups on the anthraquinone structure.

Step 2: Identifying the Positions of Hydroxyl Groups

The defining feature of alizarin is that it has two hydroxyl (OH) groups attached. In the structure of anthraquinone, which has a numbering system, these hydroxyl groups are positioned at carbons 1 and 2.

Step 3: Comparing Given Options with Alizarin Structure

From the provided options, identify which option corresponds to the hydroxyl groups being at positions 1 and 2 on the anthraquinone head: (b) 1,2-dihydroxy anthraquinone.

Key Concepts

Anthraquinone Derivative

Alizarin, a vibrant red dye historically derived from the madder plant, is an example of an anthraquinone derivative. Anthraquinone itself is a chemical structure formed by three benzene rings fused together. This compound serves as the basic framework for a range of dyes and pigments. With two ketone groups located at specific positions, anthraquinones provide a backbone for further chemical modifications.
Alizarin's beauty arises from its functional groups, namely the hydroxyl (
F) groups, altering how it interacts with light and, consequently, the color it presents when observed. Understanding its nature as an anthraquinone derivative is key. It helps explain the dye's origin, properties, and the functionalities it exhibits. Alizarin holds a place in history not just because of its color but for how it helped define the chemistry of dyes.
Because of this stable structure, anthraquinone derivatives are widely used in applications ranging from dyes for textiles to indicators in various chemical processes.

Hydroxyl Group Positioning

One of the essential features of alizarin is the specific placement of hydroxyl groups. This positioning significantly influences alizarin’s chemical properties and its function as a dye. Within the molecular structure of anthraquinone, hydroxyl groups attach specifically to designated carbon numbers.

• For alizarin, these positions are at the first and second carbon atoms, leading to its categorization as a 1,2-dihydroxyanthraquinone.

Understanding this hydroxyl placement is not only critical for identifying alizarin but also for distinguishing it from other similar derivatives. The exact positions lead to differences in intermolecular interactions, solubility, as well as dyeing properties. These nuances highlight the importance of meticulous carbon numbering in organic chemistry.
Hydroxyl group positioning might seem minor, yet it fundamentally directs how this compound behaves, reacts, and its efficacy in particular uses, especially in the textile industry. This knowledge aids chemists in designing new compounds with desired traits by altering functional group placement.

Alizarin Identification

Identifying alizarin among other compounds involves recognizing its unique structural characteristics. As we've understood, the main differentiator is the location of the hydroxyl groups. In the case of alizarin, it is indispensable to spot the 1,2-dihydroxy arrangement on the anthraquinone backbone.
When tasked with identifying alizarin, comparing provided chemical structures with known markers such as these hydroxyl group positions is essential:

• Alizarin corresponds to option (b) 1,2-dihydroxy anthraquinone, from the multiple-choice format logging its uniqueness.

This method of identification is like giving alizarin its own chemical fingerprint, allowing professionals and students alike to verify its identity confidently. By learning to identify alizarin through these distinct group locations, students build a foundational understanding needed for broader organic chemistry studies.
Ultimately, these identification skills are practical and applicable in real-world laboratory settings, where correctly identifying substances can impact experimental outcomes and product formulations.