Question

Which of the following are aromatic?

• A. B and D only
• B. A and C only
• C. A and B only
• D. C and D only

Answer 1

The Correct Option is A

To determine which of the compounds are aromatic, we need to apply the rules of aromaticity. A compound is aromatic if it satisfies the following conditions:

1. It must be cyclic.
2. It must be planar.
3. It must have a continuous ring of p-orbitals (fully conjugated system).
4. It must follow Huckel's rule, which states that the number of π-electrons in the ring must be \(4n + 2\), where \(n\) is a non-negative integer.

Let's analyze each compound provided in the image:

1. Compound A: This is naphthalene. It is cyclic, planar, and fully conjugated with 10 π-electrons. It satisfies Huckel's rule (\(4n + 2 = 10\) where \(n = 2\)). Therefore, it is aromatic.
2. Compound B: This is benzene. It is cyclic, planar, and fully conjugated with 6 π-electrons. It satisfies Huckel's rule (\(4n + 2 = 6\) where \(n = 1\)). Therefore, it is aromatic.
3. Compound C: This is not completely planar due to steric hindrance between hydrogens in the formation of a tubular structure that disrupts the planarity. Hence, it is not aromatic.
4. Compound D: This is anthracene. It is cyclic, planar, and fully conjugated with 14 π-electrons. It satisfies Huckel's rule (\(4n + 2 = 14\) where \(n = 3\)). Therefore, it is aromatic.

Based on the analysis, compounds B and D are aromatic because they meet all the criteria for aromaticity.

The correct answer is: B and D only

Answer 2

For a compound to be aromatic, it must satisfy Hückel's rule ($4n + 2 \, \pi$ electrons, where $n$ is an integer), and it must be cyclic and planar with a conjugated system.
Compound A is non-aromatic.
Compound B is aromatic as it has a conjugated planar ring with a total of 6 $\pi$ electrons.
Compound C is non-aromatic due to lack of conjugation.
Compound D is aromatic with a conjugated planar ring and 6 $\pi$ electrons.