Question

Consider the following compounds/species:
i)
ii)
iii)
iv)
v)
vi)
vii)
The number of compounds/species which obey Huckel's rule is _____

• A. 5
• B. 4
• C. 6
• D. 2

Answer 1

The Correct Option is B

To determine which compounds obey Huckel's rule, we need to check if they follow the (4n + 2) π-electron rule for aromaticity. Huckel's rule states that for a compound to be aromatic, it must be cyclic, planar, and have a (4n + 2) π-electron configuration, where n is a non-negative integer.

This is naphthalene with 10 π-electrons. It fits Huckel’s rule with n = 2 (4n + 2 = 10). 

This is the cyclopentadienyl anion with 6 π-electrons. It fits Huckel’s rule with n = 1 (4n + 2 = 6).

This is a cyclobutadiene with 4 π-electrons. It does not obey Huckel's rule, as 4 isn’t in the form of 4n + 2.

This is the cyclopropenyl cation with 2 π-electrons. It fits Huckel’s rule with n = 0 (4n + 2 = 2).

This is the cyclopropenyl anion with 4 π-electrons. It does not obey Huckel's rule, as 4 isn’t in the form of 4n + 2.

This is cyclooctatetraene with 8 π-electrons. It typically adopts a non-planar conformation, thus not obeying Huckel's rule.

This is anthracene with 14 π-electrons. It fits Huckel’s rule with n = 3 (4n + 2 = 14).

The compounds that obey Huckel's rule are i), ii), iv), and vii), resulting in a total of 4 compounds.