Which of the following is not planar in structure?

Options

A. `CH_2=CH-CH=CH_2`
B. `CH_2=CH-CN`
C. `CH_2=C=CH_2`
D. `CH_2=C=C=CH_2`

Answer

To determine which of the given compounds is not planar in structure, we need to analyze the hybridization of the carbon atoms in each option and how their geometries affect the overall molecular structure.

### Step-by-Step Solution:

1. **Identify the Compounds**: We will analyze each of the four options provided in the question.

2. **Determine Hybridization**:
- For each compound, we need to determine the hybridization of the carbon atoms.
- Hybridization types:
- **sp**: Linear (180° bond angle)
- **sp²**: Trigonal planar (120° bond angle)
- **sp³**: Tetrahedral (109.5° bond angle)

3. **Analyze Each Option**:
- **Option 1**: All carbon atoms are sp² hybridized.
- Since all carbon atoms are sp², the structure is planar.
- **Option 2**: Similar to option 1, all carbon atoms are sp² hybridized.
- Thus, this structure is also planar.
- **Option 3**: This is a special case known as an "alene".
- Here, we have sp² hybridization for the carbon atoms, but due to the arrangement of the p orbitals, the planes of the bonds are perpendicular to each other.
- This results in a non-planar structure.
- **Option 4**: This compound also has sp² hybridization.
- The arrangement of the orbitals allows for all atoms to lie in the same plane, making it planar.

4. **Conclusion**:
- After analyzing all options, we find that **Option 3** is the compound that is not planar due to the perpendicular arrangement of the p orbitals.

### Final Answer:
**Option 3 is not planar in structure.**