Aromatic compounds are characterized by planar, conjugated ring structures with delocalized pi-electrons. Benzene, with its cyclic structure of six carbon atoms each bonded to one hydrogen atom, is the simplest aromatic compound. It exhibits atypical stability and undergoes substitution rather than addition reactions. While some aromatic compounds have pleasant smells, aroma is not a requirement - anthracene is aromatic but odorless. The Hückel rule defines a compound as aromatic if it has (4n+2) pi electrons in its conjugated ring system, where n is an integer.

1. Aromatic compound
• pleasant fragrance smell(Greek-aroma).
• Benzene and there compound is one such
important aromatic compound.
• Not all aromatic compound have pleasant
smell. Eg. Anthracene.
• Not all pleasant compound is benzene. Eg.
Methyl acetate, chloroform, ethyl acetate.
• We cant detect Aromatic compound with
there smell.

2. Resins- high viscous substance.

3. Balsams- flowering plant

5. Benzene doesn’t have pleasant smell?
Aromatic compound

6. Benzene (C6H6)
First synthesis by
berthelot(1870)
Also called arenes.
Aryls – Ar.
Also called phene. Eg.
C6H5 phenyl group.
Colourless, liquid,
odour, B.P. 353K.
PREPARE from
acetylene.

7. Characteristics of aromatic compounds
result burn with
sooty (smoke
release C) flame
Higher percentage of C-atom:-

8. Characteristics of aromatic compounds
Thermal stability:-
highly stable burn
with less amount
heat.

9. Characteristics of aromatic compounds
Chemical behaviour:-
Substitution rxn- eg.
Halogenation.
Addition rxn – cant
decolourized KMnO4.

10. Structure formula and electronic
structure
• Micheal faraday 1825 – benzene (C6H6).
• unsaturated. Not like alkene and alkyne.
• Cyclic structure 6C-atom alternate double
bond and 1 H-atom attached to each H-atom.
• Kekule suggested the concept of oscillating
nature of double in benzene.
• All C-atom sp2 hybridized.

30. Sooty flame.
Release C black.

32. Huckel rule
• Huckel rule help to predict whether a
compound is aromatic or not.
• Cyclic, planar.(Sp2 hybridization)
• Conjugated – alternate double bond.
• Delocalization (4n + 2)∏ electron.
n=0,1,2,…
• Eg. Benzene 3∏ bond. i.e 6∏ electron.

33. Huckel rule

35. alternate
double bond.

41. • Electronic dot structure.
• Kekules structure of benzene fails to explain
its unusual stability and substitution rxn.
Which later explain by resonance.
Structure formula and electronic
structure

110. Preparation

173. Many compound obtain from natural
resources like

175. Carcinogenicity and Toxicity
• Carcinogenicity- cancer causing and toxic.
• Polycyclic – hydrocarbon contain 2 benzene
ring fuse together.
• Several polycyclic produce incomplete
combustion of Tabacoo, coal and petroleum.
• In liver, benzene Is oxidized to an
epoxide(cyclic ether).
• benzopyrene converted into epoxydiol. These
substance are carcinogenic and can react
with DNA which stop certain growth of cell.

176. Chemical properties

177. Chemical properties
A. Addition reaction
1. Addition of chlorine(3Cl2, bright sunlight)
2. Addition of hydrogen(3H2, Ni at 458K-473K)
B. Substitution reaction
1. Halogenation (Cl2,anhyd AlCl3 & Br2, FeBr3)
2. Nitration (conc.HO-NO2, conc. H2SO4 heat)
3. Sulphonation(HO-SO3H, fuming H2SO4 heat)