IUPAC name for isobutyric acid is___________.

Options

A. 2-methylpropanoic acid
B. butanoic acid
C. butanol
D. dimethylethanoic acid

Answer

To determine the IUPAC name for isobutyric acid, we can follow these steps:

### Step 1: Understand the Structure
Isobutyric acid is a branched-chain carboxylic acid. The structure can be represented as:
```
CH3
|
CH3-C-COOH
```
This indicates that there is a carboxylic acid group (-COOH) attached to a carbon that is also bonded to two other methyl groups (CH3).

### Step 2: Count the Carbon Atoms
In the structure, we can see that there are a total of 4 carbon atoms:
- 3 from the three methyl groups (CH3)
- 1 from the carboxylic acid group (COOH)

### Step 3: Identify the Longest Carbon Chain
The longest continuous carbon chain contains 3 carbon atoms (the carbon in the carboxylic acid and the two adjacent carbons). Therefore, the base name of the acid is derived from propane, which is a 3-carbon chain.

### Step 4: Identify the Substituents
The isobutyric acid has a methyl group (CH3) attached to the second carbon of the propane chain.

### Step 5: Name the Compound
According to IUPAC nomenclature:
- The base name is "propanoic acid" (from the 3-carbon chain).
- Since there is a methyl group on the second carbon, we name it as "2-methylpropanoic acid".

### Final Answer
The IUPAC name for isobutyric acid is **2-methylpropanoic acid**.

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