Question

The IUPAC name for the formula \[ CH_3 - C( CH_3 ) = C( H ) - COOH \] is

• A. 2-methyl 2-butanoic acid
• B. 3-methyl 3-butanoic acid
• C. 3-methyl-2-butanoic acid
• D. 2-methyl-3-butanoic acid

Hint:

Always give highest priority group (COOH) the lowest number.

Answer 1

The Correct Option is C

Step 1: Understanding the Concept:
For naming unsaturated carboxylic acids:
1. The carbon of the \( -\text{COOH} \) group is always C1.
2. Select the longest chain containing the \( -\text{COOH} \) group and the double bond.
3. Use the suffix "oic acid" and specify the position of the double bond with "en".
Step 2: Detailed Explanation:
1. Numbering: Start from the carboxyl carbon:
C1: \( \text{COOH} \)
C2: \( \text{CH} \)
C3: \( \text{C}(\text{CH}_{3}) \)
C4: \( \text{CH}_{3} \)
2. Parent chain: 4 carbons with a double bond at C2 \( \to \) but-2-enoic acid.
3. Substituent: There is a methyl group attached to C3.
4. Full name: 3-methylbut-2-enoic acid (or 3-methyl-2-butenoic acid).
Step 3: Final Answer:
The IUPAC name is 3-methyl-2-butenoic acid.