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 follow these steps:

### Step 1: Understand Huckel's Rule
Huckel's rule states that a cyclic planar conjugated system is aromatic if it contains a specific number of π (pi) electrons. The formula to determine this number is given by:

\[ \text{Number of π electrons} = 4n + 2 \]

where \( n \) is a non-negative integer (0, 1, 2, ...).

### Step 2: Identify the Structure
To apply Huckel's rule, we must first identify if the compound in question is cyclic, planar, and conjugated. A cyclic structure means it forms a closed loop, planar indicates that all atoms are in the same plane, and conjugated refers to alternating single and double bonds.

### Step 3: Count the π Electrons
Next, we need to count the number of π electrons in the system. Each double bond contributes 2 π electrons, and lone pairs on atoms in the ring can also contribute if they are part of the conjugated system.

### Step 4: Apply Huckel's Rule
Using the formula \( 4n + 2 \), we check if the total number of π electrons fits this pattern. If the total number of π electrons can be expressed as \( 4n + 2 \), then the compound is aromatic.

### Step 5: Conclusion
If the compound meets all the criteria (cyclic, planar, conjugated) and has \( 4n + 2 \) π electrons, it is classified as aromatic.

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

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