Question

The IUPAC name of CH$_3$CH(OH)CH$_2$CH$_3$ is:

• A. Butan-1-ol
• B. Butan-2-ol
• C. Propan-2-ol
• D. 2-Methylpropan-1-ol

Hint:

When naming simple alcohols, always count the total number of carbon atoms in the longest continuous chain first.
Here, 4 carbons means "butan-".
Since the $-\text{OH}$ group is on a non-terminal carbon, it must be on position 2, as counting from the other end would give 3.
Thus, Butan-2-ol is the correct answer.

Answer 1

The Correct Option is B

Step 1: Understanding the Question:
This question is from "Organic Chemistry - Nomenclature of Organic Compounds."
We need to determine the official IUPAC name of the compound whose structural formula is $\text{CH}_3\text{CH(OH)CH}_2\text{CH}_3$.

Step 2: Key Formula or Approach:
The IUPAC rules for naming acyclic alcohols are:
1. Identify the longest carbon chain containing the functional carbon (the one bonded to $-\text{OH}$). This gives the parent alkane.
2. Number the carbon chain from the end closer to the hydroxyl group (lowest locant rule).
3. Replace the suffix "-e" of the parent alkane with the position locant and the suffix "-ol".

Step 3: Detailed Explanation:

• The given compound is:
\[ \text{CH}_3-\text{CH(OH)}-\text{CH}_2-\text{CH}_3 \]

• Let us trace the longest carbon chain:
There are four continuous carbon atoms in a straight line, so the parent hydrocarbon is butane.

• Let us number the carbon chain to locate the $-\text{OH}$ group:
- Numbering from left to right:
$\text{C}_1$ ($\text{CH}_3$) $\rightarrow$ $\text{C}_2$ (CH-OH) $\rightarrow$ $\text{C}_3$ ($\text{CH}_2$) $\rightarrow$ $\text{C}_4$ ($\text{CH}_3$).
The $-\text{OH}$ group is on Carbon-2.
- Numbering from right to left:
$\text{C}_1$ ($\text{CH}_3$) $\rightarrow$ $\text{C}_2$ ($\text{CH}_2$) $\rightarrow$ $\text{C}_3$ (CH-OH) $\rightarrow$ $\text{C}_4$ ($\text{CH}_3$).
The $-\text{OH}$ group is on Carbon-3.

• We choose the left-to-right numbering system because 2 is a smaller number than 3 (lowest locant rule).

• The parent name "butane" loses its ending "-e" and gains "-2-ol", yielding "butan-2-ol".



Step 4: Final Answer:
The IUPAC name of the compound is Butan-2-ol, which matches option (B).