The IUPAC name of `CH_3 - CH = CH - COOH` is

Options

A. But-2-ene-1-oic acid
B. But-1-ene-1-oic acid
C. But-2-ene-1-carboxylic acid
D. Propene-1-carboxylic acid

Explanation

To determine the IUPAC name of the compound `CH₃ - CH = CH - COOH`, we can follow these steps:

### Step 1: Identify the Longest Carbon Chain
- Count the number of carbon atoms in the longest continuous chain. In this case, there are 4 carbon atoms in the chain: `CH₃ - CH = CH - COOH`.
- The longest chain is therefore butane, which corresponds to 4 carbon atoms.

**Hint:** Look for the longest unbroken chain of carbon atoms to determine the base name.

### Step 2: Number the Carbon Atoms
- We need to number the carbon atoms in the chain. There are two ways to number them:
1. Starting from the left (carboxylic acid end): 1 (COOH), 2 (C=C), 3 (CH), 4 (CH₃).
2. Starting from the right: 1 (CH₃), 2 (C=C), 3 (CH), 4 (COOH).

- According to IUPAC nomenclature, the functional group (carboxylic acid, COOH) takes precedence in numbering. Therefore, we start numbering from the end nearest to the carboxylic acid.

**Hint:** Always give priority to functional groups when numbering the carbon chain.

### Step 3: Identify the Functional Groups and Unsaturation
- From the numbering, we see:
- The carboxylic acid (COOH) is at position 1.
- The double bond (C=C) is at position 2.

- The presence of a double bond indicates that the compound is an alkene, and since there are 4 carbon atoms, we use "but" as the root name. The "ene" suffix indicates the presence of a double bond.

**Hint:** Identify the types of bonds and functional groups present in the compound.

### Step 4: Combine the Information
- The base name is "but" for 4 carbons, with "ene" for the double bond at position 2, and "oic acid" for the carboxylic acid at position 1.
- Therefore, the IUPAC name can be constructed as follows:
- The name is "but-2-enoic acid".

### Final Answer
The IUPAC name of `CH₃ - CH = CH - COOH` is **but-2-enoic acid**.

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