ORGANIC CHEMISTRY- I (NATURE OF BONDING AND STEREOCHEMISTRY)- HOMOAROMATICITY

ORGANIC CHEMISTRY- I (NATURE OF BONDING AND STEREOCHEMISTRY)- HOMOAROMATICITY

**A homoaromatic molecules showed discontinuity in the p orbital overlap due to the presence of a single sp³ hybridized atom, so we can say that those compounds where the stable configuration systems with (4n+2) π e can only be formd by bypassing One saturated sp³ hybridized carbon atom leads to homoaromaticity.

** The homotropylium cation (C8H9) is the best studied example of a homoaromatic compound. 

**Criteria for a compourd to be homoaroatic are :

#The molecule should posses one or more homoconjagative interactions. 

#A closed cyclic system must show electron delocalization.

#The member of π-electrons participating in cyclic electron delocalization should be close to 4n +2.

#No-bond homoaromatic systems should posses exceptional magnetic properties #Homoaromaticity should have resonance anergy greater than 2 leak mol¹ which leads to stabilization. 

**Classify the homoaromatic compounds depending on the type of interactions as no bond homoaromatics, sigma bond homoaromatics and homoarcmatics having transannular homoconjugative interactions. **Examples of homoaromatics including cationic, neutral and anionic homoaromatic compounds.

 

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.

 

ORGANIC CHEMISTRY- I (NATURE OF BONDING AND STEREOCHEMISTRY)- ANNULENES

ORGANIC CHEMISTRY- I (NATURE OF BONDING AND STEREOCHEMISTRY)- ANNULENES

**Annulenes are the completely conjugated monocyclic hydrocarbons containing an even number of carbon atoms. They have the general formula CnHn (when n is an even number) or Cn.Hn+1 (when n is an odd number) 

**The first 3 members of the series, (4]-, [6]-, and [8]-annulene but you must have used their name as 1,3- cyclobutadiene, benzene and 1,3,5,7- cyclooctatetraene. 

**Annulenes could be aromatic, anti aromatic or non-aromatic.

#[4] Annulene: anti-aromatic 

#[6] Annulene: aromatic 

#[81 Annulene: non-aromatic

#[10] Annulene: non-aromatic 

#[12] Annulene anti-aromatic 

#[14] Annulene: anti-aromatic.

#[18] Annulene: aromatic. 

**The following bridgehead [10] annulenes are aromatic: 

#9,10 methane [10] annulene 

#9,10 oxa [10] annulerne 

#9,10 aza [10] annulene 

**Preparation of [14] annulene, [18] annulene and 9,10-methane [10] annulene from simple and easily available molecules.