ORGANIC CHEMISTRY: 2

EDUCATION THROUGH COMMUNICATION

 

Benzene and the Aromatic Compounds

BONDING: THE SIGMA BONDS

Analysis of  the Kekulé structure and the authentic Benzene structure

The following is the evidence that proves that the structure that was proposed by Kekulé doesn't match the actual structure of benzene:

1. Benzene is more stable because:
• it has a perfectly regular hexagon
• all carbon-to-carbon (C-C) single bonds have the same length  
• There are delocalised electrons above and below the plane of the ring, therefore benzene is mainly stable
2. With Kekulé's structure, the benzene will have to undergo addition reations like alkenes (which decolourise bromine water on mixing) since it is unsaturated because it has the carbon-to-carbon (C=C) double bonds. However, the actual benzene does not undergo addition reactions like alkenes do, it will require more intense conditions.
3. With the enthalpy change of hydrogenation:

4. No normal C-C bonds, no reaction between KMnO4(aq) to form a diol.

CHEMICAL REACTIONS OF BENZENE

Benzene undergoes electrophilic substitution and not electrophilic addition because the benzene structure is stabilized by the delocalised pi system of the benzene ring.

Electrophilic Substitution

In the following reactions, a hydrogen atom is substituted by the respective functional groups:

ALKYLATION REACTION

NITRATION REACTION

The following is a presentation by Zimba on Nitrogen compounds:

some information on Electrophoresis: