Chapter 18, Problem 37PP

Interpretation Introduction

Interpretation: For the given firefly luciferin, it should be identified which of the rings are aromatic and which lone pairs are participating in resonance.

 Concept introduction:

• The conditions 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)

If any compound which doesn’t satisfy one of the above condition then the compound is not aromatic

• 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. For being aromatic, each atom in the ring can only have one p orbital overlapping with the p orbitals of the ring.