Q.33. - Organic Chemistry

Question

Question: Label each compound as aromatic, antiaromatic, or not aromatic. Assume all completely conjugated rings are planar.

Step-by-Step Solution

Answer

Answer

1. Not an aromatic compound.
2. Aromatic compound.
3. Not an aromatic compound.
4. Anti-aromatic compound.

Step 1: Aromatic compounds

The compounds which are cyclic and planar in structure, and are completely conjugated with a total of $\left(4n+2\right)\mathrm{\pi }$ electrons are known as aromatic compounds. The aromatic compounds are more stable than the similar acyclic compounds.

The cyclic compounds which are planar and are also completely conjugated with $4n\mathrm{\pi }$ electrons are known as antiaromatic compounds. The antiaromatic compound is less stable than the similar acyclic compound with the same number of $\mathbf{\pi }$ electrons.

The compound which does not have either the $4n\mathrm{\pi }$ electrons or the $\left(4n+2\right)\mathrm{\pi }$  electrons are known as the non-aromatic compounds. The non-aromatic compound is similarly stable to the acyclic compound with the same number of  electrons.

Step 2: Classification of the given compounds as aromatic, antiaromatic, and not aromatic compounds.

1. This compound has two carbon atoms which are not $s{p}^2$hybridized. These $s{p}^2$ hybridized carbon atoms are marked with a * in the following structure. Therefore, this compound is not aromatic in nature.
2. This compound has a total of $10\mathrm{\pi }$ electrons which are present in a $10$ membered ring. Therefore, this compound is aromatic in nature.
3. This compound has one carbon atom marked with a * which is not $s{p}^2$ hybridized. This marked carbon atom is $s{p}^3$ hybridized which makes the compound non-aromatic in nature.
4. The given compound has a total of four $\mathrm{\pi }$ electrons. As a result, this compound is antiaromatic in nature.