Question

Why is $1,3$ cyclobutadiene not aromatic?

Answer 1

Hint: In organic chemistry, the term aromaticity is used to describe the properties of cyclic planar molecules with resonant bonding rings, which exhibit greater stability than other connected or geometric arrangements of the same group of atoms. Aromatic compounds are aromatic. Aromatic molecules do not react easily with other compounds and remain stable. In the solution, we will look at the aromaticity condition, and then we will continue to define $1,3-cyclobutadiene$ is not aromatic.

Complete answer:
We know that in organic chemistry, Huckel's rule estimates whether a planar ring molecule is aromatic. Huckel's rule states that to be aromatic, a molecule must have a certain number of $\pi$ electrons in a closed ring parallel to adjacent p orbitals (that is, have a pi bond or a lone pair of electrons in the p orbital). More specifically, we can say that if a cyclic planar molecule has $(4n+2)\pi$ electrons, it is an aromatic molecule. Here n is an integer with a value of $0,1,2\dots$ and so on.
The structure of cyclobutadiene is:

The figure above is a schematic diagram of $1,3$ Cyclobutadiene . It can be clearly seen from the figure that the number of $\pi$ electrons it has is four. Therefore, it does not meet the electrons criteria of the Huckel rule. So we can say that $1,3$ Cyclobutadiene does not meet the requirements of the Huckel Rule.
Therefore, $1,3$ cyclobutadiene is not aromatic.

Note:
We remember that aromatic functional groups are called aryl groups. Aromatic compounds have certain characteristics, for example aromatic compounds have extremely high resonance energy. They undergo substitution reactions rather than additional reactions. These compounds have delocalized skin electrons.