Question

The correct IUPAC name of the compound \[ CH_3-CH(CH_3)-CH_2-CH(OH)-CH_3 \] is:

• A. 4-Methylpentan-2-ol
• B. 2-Methylpentan-4-ol
• C. 2-Methylpentan-2-ol
• D. 4-Methylpentan-4-ol

Hint:

For alcohols, always assign the lowest possible number to the carbon atom carrying the \(-OH\) group, even if this results in a higher locant for alkyl substituents.

Answer 1

The Correct Option is A

Concept: According to IUPAC nomenclature rules, the longest continuous carbon chain containing the principal functional group is selected as the parent chain. The chain is then numbered in such a way that the principal functional group receives the lowest possible locant. For alcohols, the hydroxyl group \((-OH)\) is the principal functional group and takes priority over alkyl substituents during numbering.

Step 1: Identify the longest carbon chain. The given structure is \[ CH_3-CH(CH_3)-CH_2-CH(OH)-CH_3 \] The longest continuous chain containing the hydroxyl group consists of five carbon atoms. Therefore, the parent hydrocarbon is \[ \boxed{\text{Pentane}} \] Since the compound contains an alcohol functional group, the suffix will be \[ \boxed{\text{-ol}} \]

Step 2: Number the carbon chain. Numbering must begin from the end nearest to the hydroxyl group. Numbering from the right: \[ CH_3-CH(OH)-CH_2-CH(CH_3)-CH_3 \] gives \[ OH \text{ at C-2} \] and \[ CH_3 \text{ substituent at C-4} \] Numbering from the left would place the hydroxyl group at carbon 4, which violates the lowest locant rule. Therefore, numbering from the right is correct.

Step 3: Identify substituents. A methyl group is attached at carbon number 4. Hence the substituent name is \[ \boxed{4\text{-methyl}} \]

Step 4: Write the complete IUPAC name. Combining the substituent name, parent chain and alcohol suffix: \[ 4\text{-Methyl} + Pentan + 2\text{-ol} \] \[ \boxed{\text{4-Methylpentan-2-ol}} \]

Final Answer \[ \boxed{\text{4-Methylpentan-2-ol}} \] Hence, the correct option is \[ \boxed{\text{(A)}} \]