The IUPAC name of `CH_3 - CH = CH - overset(O)overset(||)C-OH` is

Options

A. But-1-en-4-oic acid
B. 1-hydroxybut-2-en-1-one
C. But-2-en-1-oic acid
D. But-2-en-4-oic acid

Explanation

To determine the IUPAC name of the compound `CH3 - CH = CH - C(=O)OH`, we can follow these steps:

### Step 1: Identify the Parent Carbon Chain
The first step is to identify the longest continuous carbon chain that includes the functional group. In this case, the longest chain consists of 4 carbon atoms.

**Hint:** Look for the longest chain that includes the functional group.

### Step 2: Number the Carbon Atoms
Next, we need to number the carbon atoms in the chain. We can start numbering from either end, but we must give priority to the functional group (which is a carboxylic acid, -COOH).

- If we number from the left:
- C1: CH3
- C2: CH
- C3: CH
- C4: C(=O)OH

- If we number from the right:
- C1: C(=O)OH
- C2: CH
- C3: CH
- C4: CH3

Since the functional group has higher priority, we start from the left, giving the functional group the lowest possible number (1).

**Hint:** Always give the functional group the lowest number when numbering the carbon chain.

### Step 3: Identify the Functional Group
The functional group present in this compound is a carboxylic acid (-COOH). The suffix for carboxylic acids is "-oic acid".

**Hint:** Recognize the functional group and its corresponding suffix.

### Step 4: Identify the Double Bond
There is a double bond between the second and third carbon atoms. In IUPAC nomenclature, we indicate the position of the double bond by using the number of the first carbon involved in the double bond. Here, the double bond starts at carbon 2.

**Hint:** Use the position of the double bond when naming the compound.

### Step 5: Combine the Information
Now, we can combine all the information:
- The root name for a 4-carbon chain is "but".
- The presence of a double bond at carbon 2 gives us "but-2-ene".
- The carboxylic acid functional group gives us the suffix "-oic acid".

Putting it all together, we get the IUPAC name: **but-2-enoic acid**.

### Final Answer
The IUPAC name of the compound `CH3 - CH = CH - C(=O)OH` is **but-2-enoic acid**.