According to Huckel's rule , a cyclic planar conjugated polyene is aromatic , if it contains `:`

Options

A. `( 4n+1) pi - `electrons
B. `4n pi - `electrons
C. `( 2n +2) pi - `electrons
D. `( 4n + 2) pi - `electrons

Answer

To determine whether a cyclic planar conjugated polyene is aromatic according to Huckel's rule, we need to follow these steps:

### Step 1: Understand Huckel's Rule
Huckel's rule states that a cyclic, planar, and fully conjugated molecule is aromatic if it contains a specific number of π (pi) electrons. The formula for this is \(4n + 2\), where \(n\) is a non-negative integer (0, 1, 2, ...).

### Step 2: Identify the Characteristics of Aromatic Compounds
For a compound to be considered aromatic, it must meet the following criteria:
1. **Cyclic Structure**: The compound must be in a ring form.
2. **Planarity**: The molecule must be flat or planar.
3. **Conjugation**: There must be a continuous overlap of p-orbitals (alternating single and double bonds).
4. **Huckel's Rule**: The number of π electrons must fit the formula \(4n + 2\).

### Step 3: Calculate the Number of π Electrons
To apply Huckel's rule, count the number of π electrons in the molecule. Each double bond contributes 2 π electrons.

### Step 4: Apply Huckel's Rule
Using the formula \(4n + 2\):
- If you can express the total number of π electrons as \(4n + 2\) for some integer \(n\), then the compound is aromatic.
- If the number of π electrons is \(4n\) (where \(n\) is a non-negative integer), the compound is anti-aromatic and not aromatic.

### Step 5: Examples
- **Benzene**: Contains 6 π electrons. Using \(n = 1\), \(4(1) + 2 = 6\). Benzene is aromatic.
- **Naphthalene**: Contains 10 π electrons. Using \(n = 2\), \(4(2) + 2 = 10\). Naphthalene is aromatic.

### Conclusion
According to Huckel's rule, a cyclic planar conjugated polyene is aromatic if it contains \(4n + 2\) π electrons.

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