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Thursday, October 15, 2015

Organic Chemistry, "Form", Part 26 - Aromatic Compounds; An Introduction

Greetings,

It has been a while since I've posted, but I'm back!  This next series of posts will focus on aromatic compounds.  A good place to begin when discussing aromatic compounds is with benzene.

Benzene is the most fundamental aromatic compound.  All other aromatic compounds are derivatives of benzene.  Benzene has the formula, C6H6.  This simple formula seems to indicate a certain simplicity of the compound itself.  But we find that benzene has several very unusual properties which could not be predicted from its simple formula.  Some examples are; 1) Unusual stability, 2) Inability to easily add groups to the structure, 3) Ability to fuse with other benzene rings, and 4) Ability to form alcohols which are acidic (e.g. phenol).  The examples just mentioned will be explored in future posts.

Benzene is made up of hexagonal molecules with conjugated bonds stretching all the way around the carbon ring.  It consists of two electron resonance arrangements, with its actual structure a hybrid of the two.  The original structural discovery of benzene is called the Kekule` structure, in honor of the scientist who first determined the molecular structure.  The following chart summarizes the structure of benzene.


Because the actual electron arrangement is a hybrid of two resonance structures, a common way to indicate this is to draw a hexagon with a ring in the middle.  This "ring in the middle" method of drawing the benzene molecule is also quite fitting because modern molecular orbital theory explains benzene as having a continuous region of electron density around the entire structure.

That is all for now.  As always, thank you for reading!

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