The IUPAC name of `CH_3 - underset(CH_3) underset(|) CH - underset(O)underset(||) C - COOH ` is

Options

A. 3-Methyl-2-oxobutanecarboxylic acid
B. 2-Methyl-3-oxobutan-4-oic acid
C. 3-Methyl-2-oxobutanoic acid
D. 3-Methyl-1,2-dioxobutanoic acid

Explanation

To determine the IUPAC name of the compound `CH_3 - CH(CH_3) - CH(O) - C(COOH)`, we can follow these steps:

### Step 1: Identify the Functional Groups
The compound contains two functional groups: a carboxylic acid group (-COOH) and a ketone group (C=O). According to IUPAC nomenclature, the carboxylic acid group has higher priority over the ketone group.

### Step 2: Choose the Parent Carbon Chain
We need to select the longest continuous carbon chain that includes the functional groups. In this case, we can choose the following chain:
1. C1: COOH (carboxylic acid)
2. C2: CH
3. C3: CH (with a ketone group)
4. C4: CH3 (methyl group)

Thus, the parent chain consists of 4 carbon atoms.

### Step 3: Number the Carbon Atoms
We will number the carbon atoms in the parent chain starting from the end closest to the carboxylic acid group to give it the lowest possible number:
1. C1: COOH
2. C2: CH (with a ketone group)
3. C3: CH (with a methyl group)
4. C4: CH3

### Step 4: Identify Substituents and Their Positions
- The carboxylic acid group is at carbon 1.
- The ketone group (C=O) is at carbon 2.
- The methyl group (CH3) is at carbon 3.

### Step 5: Assign Prefixes and Suffixes
- The prefix for the ketone group is "oxo" since it is a substituent.
- The prefix for the methyl group is "methyl".
- The root name for a 4-carbon chain is "butane".
- The suffix for the carboxylic acid is "oic acid".

### Step 6: Combine the Information
Putting it all together, we have:
- The substituents are named in alphabetical order: "3-methyl" comes before "2-oxo".
- The full name is: 3-methyl-2-oxo-butanoic acid.

### Final Answer
The IUPAC name of the compound is **3-methyl-2-oxo-butanoic acid**.

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