According to Hückel's rule, a planar cyclic conjugated compound exhibits aromatic stabilit… — JAMB UTME

According to Hückel's rule, a planar cyclic conjugated compound exhibits aromatic stability if the number of delocalized $\pi$ -electrons in its conjugated ring system is equal to which expression, where $n$ is a non-negative integer?

$4n + 2$ Answer
B
$4n$
C
$2n + 2$
D
$4n - 2$

Answer

The expression for the number of delocalized

\pi

-electrons in an aromatic compound is

4n + 2

Hückel's rule states that a cyclic, planar, fully conjugated molecule possesses aromatic stability when it contains

(4n + 2)

delocalized

\pi

-electrons, where

n

is an integer (

0, 1, 2, 3, \dots

). For example, benzene has

6

\pi

-electrons, satisfying the rule for

n = 1

Step-by-Step Solution

Recall the structural criteria for aromaticity.

An aromatic molecule must be cyclic, planar, fully conjugated, and possess a specific number of delocalized

\pi

-electrons.

These structural conditions allow complete ring delocalization of

\pi

-electrons.

Apply Hückel's rule to determine the required

\pi

-electron count.

The total number of delocalized

\pi

-electrons must equal

(4n + 2)

, where

n = 0, 1, 2, 3, \dots

This formula predicts closed-shell electronic stability for planar conjugated rings.

Key Concept

Hückel's Rule of Aromaticity

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