Chapter 14, Problem 14.19P

Interpretation Introduction

Interpretation:

The given compound is aromatic, antiaromatic, or nonaromatic is to be predicted.

Concept introduction:

Heterocyclic compounds are defined as cyclic compounds which contain at least one ring heteroatom. Heterocyclic compounds can be aromatic, nonaromatic, or antiaromatic. In some of the heterocyclic compounds, the heteroatom contributes a p atomic orbital to the aromatic $\text{π}$ system. Thus, a heteroatom can contribute a lone pair of electrons to the $\text{π}$ system to attain aromaticity. In some cases, this may involve a change in the hybridization of the heteroatom from ${\text{sp}}^3$ to ${\text{sp}}^2$ in spite of the angle strain.

According to Huckel’s rules for aromaticity, a species must possess a fully conjugated $\text{π}$ system around the ring. The molecule must be planar, which also means all the ring atoms must be ${\text{sp}}^2$ hybridized. The number of electrons in the $\text{π}$ system must be $\text{(4n + 2), n = 0, 1, 2, }\mathrm{...}$

If the number of electrons in the $\text{π}$ system is $\text{4n, n = 0, 1, 2, }\mathrm{...}$, the compound is antiaromatic.

All other compounds are nonaromatic.