Question

The cyclic \(π\)-molecular orbital formed by overlap of p-orbitals must contain,

• A. \((4n+2)\) p electrons.
• B. \((2n+2)\) p electrons.
• C. \((4n-2)\) p electrons.
• D. \((2n-2)\) p electrons.

Hint:

Huckel rule for aromatic stability needs 4n+2 pi electrons.

Answer 1

The Correct Option is A

Step 1: Understanding the Concept:
A cyclic, planar, fully conjugated system is aromatic and specially stable when its pi electron count obeys the Huckel rule.

Step 2: Key Formula or Approach:
\[ \text{number of } \pi \text{ electrons} = 4n + 2, \quad n = 0, 1, 2, \ldots \]

Step 3: Detailed Explanation:
For \(n = 0, 1, 2\) the count is 2, 6, 10. Benzene has 6 pi electrons (\(n = 1\)) and is aromatic. A count of \(4n\) electrons (such as 4 or 8) gives an anti-aromatic, unstable ring.

Step 4: Check the options.
(B) \(2n+2\) gives 2, 4, 6, 8, which includes anti-aromatic counts. (C) \(4n-2\) and (D) \(2n-2\) are not the Huckel expression. Only (A) matches.

Final Answer:
The cyclic pi system needs \((4n+2)\) p electrons, option (A). \[ \boxed{(4n+2)} \]