Which of the following represents an `E` isomer?

Options

A.
B.
C.
D.

Answer

To determine which of the given options represents an `E` isomer, we need to follow these steps:

### Step 1: Understand the definition of `E` isomer
`E` isomerism occurs when the higher priority substituents on each carbon of a double bond are located on opposite sides of the double bond.

### Step 2: Apply the Cahn-Ingold-Prelog (CIP) priority rules
According to the CIP rules, the priority of substituents is determined by their atomic number. The higher the atomic number, the higher the priority.

### Step 3: Analyze each option
1. **Option 1**: Identify the groups attached to the first and second carbon atoms.
- **Carbon 1**: Bromine (Br) and Iodine (I)
- **Carbon 2**: Methyl (CH3) and Chlorine (Cl)
- **Priority**: Iodine has a higher atomic number than Bromine, and Chlorine has a higher atomic number than Carbon.
- **Conclusion**: Both higher priority groups (I and Cl) are on the same side, indicating a `Z` isomer.

2. **Option 2**: Analyze the groups.
- **Carbon 1**: Bromine (Br) and Chlorine (Cl)
- **Carbon 2**: Methyl (CH3) and Iodine (I)
- **Priority**: Bromine has a higher atomic number than Chlorine, and Iodine has a higher atomic number than Carbon.
- **Conclusion**: The higher priority groups (Br and I) are on opposite sides, indicating an `E` isomer.

3. **Option 3**: Check the groups.
- **Carbon 1**: Methyl (CH3) and Hydrogen (H)
- **Carbon 2**: Chlorine (Cl) and Bromine (Br)
- **Priority**: CH3 has a higher priority than H, and Br has a higher priority than Cl.
- **Conclusion**: The higher priority groups (CH3 and Br) are on the same side, indicating a `Z` isomer.

### Step 4: Determine the answer
From the analysis, we find that the only option that represents an `E` isomer is **Option 2**.

### Final Answer:
**Option 2** represents an `E` isomer.

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