Why cyclooctatetraene is nonplanar.

Answer

### Step-by-Step Text Solution:

1. **Understanding the Structure of Cyclooctatetraene**:
Cyclooctatetraene (COT) is a cyclic compound that consists of eight carbon atoms. The term "octa" indicates the presence of eight carbons, and "cyclo" indicates that these carbons are arranged in a ring.

2. **Drawing the Structure**:
The structure of cyclooctatetraene can be represented as:
```
C=C=C=C
| |
C=C=C=C
```
Here, we have alternating double bonds, indicating that it has a conjugated system.

3. **Counting Pi Electrons**:
Each double bond contributes two pi electrons. Since there are four double bonds in cyclooctatetraene, the total number of pi electrons is:
\[ 4 \text{ double bonds} \times 2 \text{ pi electrons per double bond} = 8 \text{ pi electrons} \]

4. **Determining Aromaticity**:
According to Hückel's rule, a compound is aromatic if it follows the \(4n + 2\) rule for pi electrons, where \(n\) is a non-negative integer. Cyclooctatetraene has 8 pi electrons, which fits the \(4n\) rule (where \(n = 2\)), indicating that it is anti-aromatic.

5. **Planarity and Stability**:
Anti-aromatic compounds are generally unstable due to their electronic configuration. To minimize this instability, cyclooctatetraene adopts a non-planar conformation.

6. **Adopting a Non-Planar Structure**:
Cyclooctatetraene distorts from a planar structure to a tub-like or non-planar structure. This change allows the compound to avoid the anti-aromatic character and become more stable.

7. **Conclusion**:
The non-planar structure of cyclooctatetraene is a result of its attempt to increase stability by avoiding the anti-aromatic nature associated with planarity. Thus, cyclooctatetraene is non-planar and non-aromatic.