Chapter 17.5, Problem 13PTS

Interpretation Introduction

Interpretation For the given compounds, it should be determined which lone pair will participate in aromaticity.

Concept introduction:

• The criteria’s for aromatic compound are,

1. 1. 1. It should be planar
   2. 2. It must obey the Huckel’s rule

The requirement of an odd number of electron pair is called Huckel’s rule. A     compound can only be aromatic if the number of $\text{π}$ electron in the ring is 2, 6,10,14,18 and so on. This series of number can be expressed mathematically as $\text{4n+2}$, where n should be an integer and the compound is aromatic.

1. 3. Continuous conjugated $\text{π}$ system(all carbon should be in ${\text{sp}}^{\text{2}}$ hybridized state)

• In order for the heterocycle to achieve a continuous system of overlapping p orbitals, the lone pair of the hetero atom must occupy a p orbital with six $\text{π}$ electrons that is four from the $\text{π}$ bonds and two from the lone pair. Then this compound is aromatic.