NEET 2023 — Chemistry solution

NEET2023Chemistry

Consider the following compounds/species:

The number of compounds/species which obey Huckel's rule is ______.

A
$6$
B
$2$
C
$5$
D
$4$

Solution

Hückel's rule for aromaticity requires a planar, fully conjugated cyclic system with $(4 n + 2) π$ electrons.

Counting $π$ electrons: (i) naphthalene $10 π$ ✓; (ii) cyclopentadienyl anion $6 π$ ✓; (iii) cyclobutadiene $4 π$ ✗ (antiaromatic); (iv) cyclopropenyl anion $4 π$ ✗; (v) cyclopropenyl cation $2 π$ ✓; (vi) cyclooctatetraene $8 π$ ✗ (and non-planar tub shape); (vii) anthracene $14 π$ ✓.

Four species — (i), (ii), (v), (vii) — obey Hückel's rule.

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