August 24, 2019

ORGANIC CHEMISTRY- I (NATURE OF BONDING AND STEREOCHEMISTRY)- AROMATICITY OF FUSED RINGS


ORGANIC CHEMISTRY- I (NATURE OF BONDING AND STEREOCHEMISTRY)- AROMATICITY OF FUSED RINGS

**A fused aromatic ring is one which shares one side of the ring. These are monocyclic rings that shares their connecting bond.

** Fused ring systems arc classified into two categories depending on the number of atoms and bonds shared by the rings. 

Orho-fused rings-If the two rings of the fused system that have only two atoms and one bond is common between the rings. Ortho and peri fused rings-If three atoms are common between the first ring and the other two rings then it is said to be Ortho and pert fused rings. 

**The criteria for the aromaticity in the fused rings also follows the same rule as applied to the monocyclic systems. 

1. It is cyclic, planar and has continuous delocalization of π electrons (electrons in p orbitals) with or without the participation of lone pair(s)/- charge/ + charge (Le., having electrons or vacant p orbital). 

2. The delocalized π-electron cloud must contain a total of (4n+2) π electrons, where n is a whole number (i.e., n =0.1,2,3 and so on) 

**Aromaticity of some benzenoid fused rings like naphthalene, anthracene and phenanthrene. 

**The resonance energy of fused system is generally less than of the number of benzene ring present in that system. 

**Aromaticity of some non-benzenoid fused rings like azulene and oxaazulanones. **Aromaticity of some way ergy of fused system is generally less than of the number of benzene special molecules like phenalene, ferrocene and benzo cyclobutadiene.