Question

IUPAC name of \( CH_3-CH_2-CH(OH)-CH_3 \) is —

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

Hint:

Four carbons give the root but-; the OH sits on carbon 2 when numbered for the lowest locant.

Answer 1

The Correct Option is A

Step 1: Count the longest carbon chain. \( CH_3-CH_2-CH(OH)-CH_3 \) has four carbon atoms, so the parent alkane is butane.
Step 2: The functional group is \(-OH\) (alcohol), so the suffix -e of butane is replaced by -ol, giving butanol.
Step 3: Number the chain from the end that gives the \(-OH\) the lowest locant. The \(-OH\) is on the third carbon counting from the left, but on the second carbon counting from the right. The lower number (2) is chosen.
Step 4: The name is therefore butan-2-ol.
Why the others are wrong: Butan-1-ol would need \(-OH\) on a terminal carbon; propan-2-ol and propan-1-ol have only three carbons.
Correct answer: (i) Butan-2-ol.