Chapter 14, Problem 14.17P

Interpretation Introduction

Interpretation:

It is to be explained whether the given compound is aromatic, antiaromatic, or nonaromatic.

Concept introduction:

The rule for aromaticity or antiaromaticity applies only if the system is planar, cyclic and has an overlapping p-orbital which could contribute to conjugation. Huckel’s rule for aromaticity states that if a species possesses a pi system of molecular orbitals constructed from p-orbitals that are fully conjugated around a ring, then such a system is:

1) Aromatic if the number of electrons in that $\text{π}$ - system is $\text{2, 6, 10, 14, 18}$ and so on. (These numbers are called Huckel numbers).

2) Antiaromatic if the number of electrons in that $\text{π}$- system is $\text{4, 8, 12, 16, 20}$ and so on. (These numbers are called anti-Huckel numbers).

3) All other species are considered nonaromatic.

In other words, if a species contains an odd number of pi electrons then it is said to be aromatic. If it contains an even number of pi electrons then it is anti-aromatic.