Question

Indicate whether or not each of the following structures is considered to be aromatic, A is aromatic, B is not B is aromatic, A is not. Both A and 6 are aromatic. A and 6 are not aromatic.

Answer 1

Concepts and reason

• The compound with cyclic structure (ring), flat with conjugated double bonds present in the ring is said to be aromatic.

• All cyclic compounds cannot be aromatic; there are non-aromatic cyclic compounds also present.

• The structure should be aromatic or non-aromatic. It can be predicted with the help of the ${\rm{4n + 2}}$ rule.

Fundamentals

$\begin{array}{l}\\{\rm{4n + 2}}\,{\rm{rule:}}\\\\{\rm{4n + 2}}\,{\rm{ = }}\,\,{\rm{number}}\,\,{\rm{of}}\,{\rm{\pi }}\,{\rm{electrons}}\\\\\,\,\,\,\,\,\,{\rm{n}}\,\,{\rm{ = }}\,\,{\rm{integer}}\,\,{\rm{(n}}\,{\rm{ = 1,}}\,{\rm{2,}}\,{\rm{3}}\,{\rm{,}}....{\rm{)}}\\\end{array}$

Example:

The above structure has 6 π electrons, and the structure is flat with conjugated double bonds. By substituting $\left( {{\rm{n}}\,{\rm{ = 1}}} \right)$ in the 4n+2 formula:

${\rm{4}}\left( {\rm{1}} \right){\rm{ + }}\,{\rm{2}}\,\,{\rm{ = 6}}$

The above structure obeys the ${\rm{4n + 2}}$ rule ( ${\rm{4}}\left( {\rm{1}} \right){\rm{ + }}\,{\rm{2}}\,\,{\rm{ = 6}}$ ). Therefore, it is aromatic.

B is aromatic and A is not.

B is not aromatic, as it does not obey the ${\rm{4n + 2}}$ rule, and A is aromatic because it obeys the ${\rm{4n + 2}}$ rule.

Both A and B are aromatic.

B is not aromatic, as it does not obey the ${\rm{4n + 2}}$ rule.

A and B are not aromatic.

A is aromatic because it obeys the ${\rm{4n + 2}}$ rule.

A is aromatic and B is not.

A is aromatic because it obeys the ${\rm{4n + 2}}$ rule.

Ans: