Which one of 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 Z and E Isomerism
Z isomers occur when the highest priority substituents on each carbon of a double bond are on the same side. E isomers occur when the highest priority substituents are on opposite sides.

### Step 2: Assign Priority to Substituents
To assign priority, we use the Cahn-Ingold-Prelog priority rules, which state that the atom with the higher atomic number gets higher priority.

### Step 3: Analyze Each Option
1. **Option 1**:
- Substituents: CH3 and H on one carbon; Br and Cl on the other.
- Priority:
- For the first carbon: CH3 (C) > H.
- For the second carbon: Br > Cl.
- Both high priority groups (Br and CH3) are on the same side → **Z isomer**.

2. **Option 2**:
- Substituents: CH3 and H on one carbon; Br and Cl on the other.
- Priority:
- For the first carbon: CH3 (C) > H.
- For the second carbon: Br > Cl.
- High priority groups (Br and CH3) are on opposite sides → **E isomer**.

3. **Option 3**:
- Substituents: CH3 and H on one carbon; Br and Cl on the other.
- Priority:
- For the first carbon: Br > CH3.
- For the second carbon: Cl > H.
- High priority groups (Br and Cl) are on opposite sides → **E isomer**.

4. **Option 4**:
- Substituents: CH3 and H on one carbon; CH3 and H on the other.
- Priority:
- Both carbons have the same substituents (C > H).
- High priority groups are on opposite sides → **E isomer**.

### Conclusion
The only option that is a Z isomer is **Option 1**.

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