Question:

a. How many $\mathbf{\pi }$electrons does C contain?

b. How many $\mathbf{\pi }$electrons are delocalized in the ring?

c. Explain why C is aromatic.

The overlapping of two unhybridized orbitals leads to the generation of a pi bond. These bonds are weaker when compared to sigma bonds and possess no symmetry.

Aromatic compounds can be categorized into several types, and they include benzenoid compounds and non-benzenoid compounds. Hydrocarbons executing Huckel’s rule are categorized as aromatic compounds.

a. Compound C consists of $16\mathrm{\pi }$electrons that are formed from $8\mathrm{\pi }$bonds.

b. Two of the electrons present in the triple bond are localized between the two carbons, perpendicular to the pi electrons delocalized in the ring. The remaining $12$ electrons take part in electron delocalization. Hence, $14\mathrm{\pi }$electrons are delocalized in the ring.

c. Compound C is cyclic, planar, completely conjugated, and follows Huckel’s rule. The count of pi electrons can be given as:

$$\begin{gathered} \left(4n+2\right)\mathrm{\pi }=\left(4\times 3+2\right)\mathrm{\pi } \\ =14\mathrm{\pi } \end{gathered}$$

Hence the compound contains $14\mathrm{\pi }$electrons and is aromatic.