Benzene

• Benzene is classified as an aromatic hydrocarbon with the molecular formula C6H6.
• It consists of a ring of six carbon atoms, with an alternating arrangement of single and double bonds.
• Each carbon atom in the benzene ring is bonded with one hydrogen atom, forming a sigma bond.
• The remaining three bonds of the carbon atom are with its neighbouring carbon atoms. Two are sigma bonds, and one is a pi bond, contributing to the cyclic structure of benzene.
• The delocalized model of benzene suggests a ring of pi electrons above and below the plane of the carbon atoms, creating a region of high electron density which can easily attract electrophiles.
• This pi electron cloud represents the extra stability of benzene as compared to an ordinary cyclohexatriene. This is known as aromatic stability.
• Benzene undergoes reaction by electrophilic substitution, where an electrophile is attracted to the electron-rich benzene ring and replaces one of the hydrogen atoms. This is because the benzene ring tends to preserve its stability.
• Common reactions with benzene include nitration, halogenation, alkylation, and acylation.
• Nitration of benzene involves the addition of nitric acid and sulfuric acid to replace one of the hydrogen atoms with a nitro group (-NO2).
• Halogenation is the replacement of a hydrogen atom with a halogen (such as chlorine or bromine) in the presence of a catalyst like FeBr3 or AlCl3.
• Friedel-Crafts Alkylation is the formation of an alkyl benzene where a hydrogen atom is replaced with an alkyl group (R), often using aluminium chloride as a catalyst.
• Friedel-Crafts Acylation involves the substitution of an acyl group (RCO-), with the aid of acid chlorides and anhydrides in presence of AlCl3.