Question

Identify the structural formula of phloroglucinol.

• A. Benzene ring with -OH groups at 1, 3, 5 positions
• B. Benzene ring with -OH groups at 1, 2, 3 positions
• C. Benzene ring with -OH groups at 1, 2, 4 positions
• D. Benzene ring with -OH groups at 1, 3 positions

Hint:

Phloroglucinol is perfectly symmetrical. Think of a benzene ring where you skip one carbon between every -OH group.

Answer 1

The Correct Option is A

Step 1: Understanding the Concept:
Phloroglucinol is the widely accepted common or trivial name for a specific positional isomer of benzenetriol. Knowing the IUPAC names that correspond to these common historical names is essential for identifying their correct chemical structures.
Step 2: Key Formula or Approach:
Approach: Match the given common name "phloroglucinol" to its systematic IUPAC nomenclature to deduce its exact substitution pattern on the central benzene ring.
Step 3: Detailed Explanation:
Benzenetriol (a benzene ring with three hydroxyl groups) exists as three distinct positional isomers based on the relative placement of the $-\text{OH}$ groups: 1. 1,2,3-benzenetriol: Also commonly known as pyrogallol. In this isomer, all three $-\text{OH}$ groups are situated adjacent to one another. 2. 1,2,4-benzenetriol: Also commonly known as hydroxyquinol. Here, two $-\text{OH}$ groups are adjacent, and the third is separated by one unsubstituted carbon. 3. 1,3,5-benzenetriol: Also commonly known as phloroglucinol. In this highly symmetric isomer, the three $-\text{OH}$ groups are distributed evenly around the ring, occupying alternating carbon positions. Based on the visual structures provided in the original options: - Option (A) clearly shows a benzene ring with hydroxyl groups attached at the 1, 3, and 5 positions. This represents 1,3,5-benzenetriol, which is definitively phloroglucinol. - Option (B) shows a benzene ring with hydroxyl groups at the 1, 2, and 3 positions, representing pyrogallol. - Option (C) shows a benzene ring with hydroxyl groups at the 1, 2, and 4 positions, representing hydroxyquinol. - Option (D) shows a benzene ring with only two hydroxyl groups located at the 1 and 3 positions, representing a diol known as resorcinol.
Step 4: Final Answer:
The correct structural formula for phloroglucinol is a benzene ring with $-\text{OH}$ groups at the 1, 3, and 5 positions.