Which of the following is the correct IUPAC name of the following compound? CH3CH2CH2OH a. hydroxypropylbenzene b. 2-propylphenol c. 2-propyl-1-hydroxybenzene d. 2-propylphenol
The Correct Answer and Explanation is:
The correct IUPAC name for the given compound is b. 2-propylphenol.
Here is a detailed explanation of how to arrive at this name:
1. Identify the Parent Compound
The first step in naming an organic compound is to identify the parent structure. The molecule consists of a benzene ring bonded to a hydroxyl group (-OH) and a propyl group (-CH2CH2CH3). According to the International Union of Pure and Applied Chemistry (IUPAC) nomenclature rules, a benzene ring with a hydroxyl group attached has a special, retained name: phenol. When possible, it is preferable to use these retained names as the parent structure because it simplifies the overall name. Therefore, the parent name for this molecule is phenol.
2. Number the Carbon Atoms
Once the parent compound is identified as phenol, the next step is to number the carbon atoms of the benzene ring. By definition, the carbon atom bonded to the hydroxyl group is always assigned position number 1 (C1). From there, you number the rest of the ring’s carbons in a way that gives the other substituents the lowest possible numbers. In this molecule, the only other substituent is the propyl group. Numbering in either the clockwise or counterclockwise direction from C1 will place the propyl group at position 2.
3. Name the Substituent and Assemble the Full Name
The substituent attached at position 2 is a three-carbon alkyl chain, -CH2CH2CH3, which is called a propyl group.
To form the final IUPAC name, you combine the position, the substituent name, and the parent name. The propyl group is at position 2, so the complete name is 2-propylphenol.
Why Other Options Are Incorrect
- a. 2-hydroxypropylbenzene: This name incorrectly suggests that the parent molecule is propylbenzene. The “2-hydroxy” prefix would indicate that the -OH group is on the second carbon of the propyl chain, not on the benzene ring.
- c. 2-propyl-1-hydroxybenzene: While this is a systematically correct name treating “benzene” as the parent, it is not the preferred IUPAC name. The name “phenol” for hydroxybenzene is retained and preferred for simplicity.
- d. 1-propylphenol: This name is incorrect because the hydroxyl group defines the number 1 position in a phenol. A substituent cannot also occupy the same position.
