Which one the following is an Z isomer ?

Options

A.
B.
C.
D.

Answer

To determine which of the given compounds is a Z isomer, we need to follow these steps:

### Step 1: Understand the Definition of Z and E Isomers
Z and E isomers are types of geometric isomers that arise due to the restricted rotation around a double bond.
- **Z isomer** (from the German word "zusammen," meaning together) has the highest priority substituents on the same side of the double bond.
- **E isomer** (from the German word "entgegen," meaning opposite) has the highest priority substituents on opposite sides of the double bond.

### Step 2: Assign Priorities to the Substituents
To determine whether a compound is a Z or E isomer, we need to assign priorities to the substituents attached to the double bond using the Cahn-Ingold-Prelog priority rules:
1. Compare the atomic numbers of the atoms directly attached to the double bond. The atom with the higher atomic number gets higher priority.
2. If the first atoms are the same, move to the next atoms in the substituent groups until a difference is found.

### Step 3: Analyze Each Compound
For each compound provided in the options:
1. Identify the substituents attached to the double bond.
2. Assign priorities based on the atomic numbers.
3. Check the position of the higher priority substituents.

### Step 4: Determine the Isomer Type
- If both higher priority substituents are on the same side of the double bond, the compound is a **Z isomer**.
- If they are on opposite sides, it is an **E isomer**.

### Conclusion
After analyzing the compounds, we find that:
- **Option A** has the two highest priority substituents on the same side, making it the Z isomer.

### Final Answer
**The Z isomer is Option A.**

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