Which does not have conjugate system?

Options

A. `CH_(2)=CHCl`
B. `CH_(2)=CHCHO`
C. `CH_(3)CH=CH_(2)`
D.

Explanation

To determine which of the given options does not have a conjugate system, we will analyze each option step by step.

### Step 1: Analyze Option A - CH2=CH-Cl
- In this molecule, we have a double bond between the two carbon atoms (C=C) and a chlorine atom attached to one of the carbons.
- The chlorine atom has a lone pair of electrons, which can participate in resonance with the double bond.
- Therefore, this molecule has a conjugate system.

**Hint:** Look for lone pairs and double bonds that can interact.

### Step 2: Analyze Option B - CH2=CH-CH=O
- This molecule has two double bonds: one between the first two carbon atoms (C=C) and another between the second carbon and oxygen (C=O).
- The C=O bond can also participate in resonance with the adjacent C=C bond.
- Thus, this molecule also has a conjugate system.

**Hint:** Check for multiple double bonds and their ability to interact.

### Step 3: Analyze Option C - CH3-CH=CH2
- In this molecule, there is a double bond between the second and third carbon atoms (C=C).
- However, there are no lone pairs present on any of the atoms that can participate in resonance with the double bond.
- Therefore, this molecule does not have a conjugate system.

**Hint:** Identify if there are any lone pairs that can participate in resonance.

### Step 4: Analyze Option D - CH2=CH-CH=CH2
- This molecule contains two double bonds: one between the first two carbon atoms and another between the third and fourth carbon atoms.
- The alternating double bonds allow for resonance, creating a conjugate system.

**Hint:** Look for alternating double bonds that can interact.

### Conclusion:
After analyzing all options, we find that **Option C (CH3-CH=CH2)** does not have a conjugate system.

**Final Answer:** C part.