Question

Among the following which is correct?
(A) Both cyclopentadienyl anion and benzene are aromatic and have the same stability
(B) Benzene is aromatic and more stable than cyclopentadienyl anion and it is nonaromatic
(C) Both cyclopentadienyl anion and benzene are aromatic but benzene is more stable than cyclopentadienyl anion
(D) Cyclopentadienyl anion is more stable than benzene although both are aromatic

Answer 1

Hint: According to the rules of organic chemistry a compound is said to be aromatic if it has $ (4n + 2)\pi $ electrons which are delocalised in the structure and the structure is planar. Also, a thing to remember is that neutral molecules are always more stable than the charged particles.

Complete answer:
So here we have two products cyclopentadienyl and benzene and we need to comment on their aromaticity and their stability.
Here we first need to understand that a compound is said to be aromatic only if it has $ (4n + 2)\pi $ electrons which are delocalised and the final structure of the compound needs to be planar. Also, the compound needs to be cyclic.
First let’s talk about cyclopentadienyl having $ 6\pi $ electrons in its delocalised orbital and also it follows the principle of $ (4n + 2)\pi $ electrons. Now the electrons are delocalised and the structure is also cyclic. It follows all the necessary conditions for the compound to be cyclic. But there is a drawback that it has a negative charge on it and that makes it a less stable structure than any neutral structure.
Now let’s talk about benzene. It also has $ 6\pi $ electrons in its delocalised orbital which follows the principle of $ (4n + 2)\pi $ electrons and also the structure of benzene is planar, which satisfies all the necessary conditions for the structure to be aromatic. Now it is a neural structure and also it has less angular strain than cyclopentadienyl.
Option (C) Both cyclopentadienyl anion and benzene are aromatic but benzene is more stable than cyclopentadienyl anion.

Note:
One of the general mistakes made when deciding if a compound is aromatic or to, we need to see if it satisfies all the properties for being aromatic. Now if it doesn’t satisfy even one of the conditions then it cannot be declared as aromatic.