IUPAC name of the following compound
`CH_(3)-CH_(2)-underset(CH_(3))underset("| ")"CH"-CH_(2)-underset(C_(2)H_(5))underset("| ")"CH"-CH_(2)-CH_(3)`

Options

A. 3 - Ethyl -5-methylheptane
B. 5 - Ethyl -3-methylheptane
C. 2 - Ethyl -5-methylheptane
D. 4 - Ethyl -5-methylheptane

Answer

To determine the IUPAC name of the given compound, we will follow the systematic approach outlined in the video transcript. Here’s a step-by-step breakdown:

### Step 1: Identify the Longest Carbon Chain
We need to find the longest continuous chain of carbon atoms in the compound.

- In this case, the longest chain consists of **7 carbon atoms**.

### Step 2: Number the Carbon Chain
Next, we will number the carbon chain from one end to the other. The goal is to assign the lowest possible numbers to the substituents (side groups).

- If we number the chain from left to right, we get:
1. C1
2. C2
3. C3
4. C4
5. C5
6. C6
7. C7

### Step 3: Identify and Number the Substituents
Now we will identify the substituents attached to the main chain and their positions based on the numbering we assigned.

- There are two substituents:
- An **ethyl group (C2H5)** at position **3**.
- A **methyl group (CH3)** at position **5**.

### Step 4: Determine the Correct Numbering
We need to check if numbering from the other end gives lower numbers to the substituents.

- If we number from right to left:
1. C1
2. C2
3. C3
4. C4
5. C5
6. C6
7. C7

In this case, the substituents would still be at positions 3 (ethyl) and 5 (methyl).

### Step 5: Apply the Alphabetical Order Rule
When substituents are at the same position, we assign the lowest number based on alphabetical order.

- Ethyl (E) comes before Methyl (M) in alphabetical order. Therefore, the ethyl group will take precedence in numbering.

### Step 6: Write the IUPAC Name
Now that we have all the information, we can write the IUPAC name of the compound.

- The base name for a 7-carbon alkane is **heptane**.
- The substituents are:
- **3-ethyl** (from position 3)
- **5-methyl** (from position 5)

Putting it all together, the IUPAC name of the compound is:

**3-ethyl-5-methylheptane**

### Summary of Steps
1. Identify the longest carbon chain.
2. Number the chain to give the lowest numbers to substituents.
3. Identify the substituents and their positions.
4. Use alphabetical order to assign numbers if needed.
5. Write the IUPAC name using the substituents and the base name.