Resonance effect is not observed in

Options

A. `CH_2 = CH - CH = CH_2`
B. `CH_2 = CH - C -= N`
C. `CH_2 = CH - CI`
D. `CH_2 = CH - CH_2 - NH_2`

Answer

To determine where the resonance effect is not observed, we need to analyze the compounds provided in the question. The resonance effect occurs when there is a possibility of delocalization of electrons through conjugation. This typically happens when there are alternating double bonds, lone pairs, or charges that can participate in resonance.

### Step-by-Step Solution:

1. **Understanding Resonance**:
- Resonance occurs when there are multiple valid Lewis structures for a molecule, allowing for the delocalization of electrons. This typically requires alternating single and double bonds or lone pairs adjacent to double bonds.

2. **Analyzing the First Compound (CH2=CH-CH=CH2)**:
- This compound has alternating double bonds. The double bonds can shift, allowing for resonance. Thus, resonance is observed here.

3. **Analyzing the Second Compound (CH2=CH-C≡N)**:
- In this compound, there is a double bond adjacent to a triple bond. The double bond can participate in resonance with the triple bond. Therefore, resonance is also observed here.

4. **Analyzing the Third Compound (CH2=CH-Cl)**:
- Here, there is a double bond and a chlorine atom with a lone pair. The lone pair on chlorine can participate in resonance with the double bond, allowing for electron delocalization. Thus, resonance is observed here as well.

5. **Analyzing the Fourth Compound (CH2=CH-CH2-NH2)**:
- In this case, the lone pair on the nitrogen is not adjacent to a double bond. The structure has a single bond between the nitrogen and the carbon chain, which prevents the lone pair from participating in resonance with the double bond. Therefore, resonance is **not** observed in this compound.

### Conclusion:
The correct answer is that resonance effect is not observed in the fourth compound (CH2=CH-CH2-NH2).