The document presents a slideshow on the topic of benzene, covering its structure, bonding properties, resonance, nomenclature, reactions, and industrial uses. It discusses benzene's molecular structure and hybridization, how resonance leads to delocalized pi bonding and aromaticity. Examples of benzene's industrial applications include use as a solvent and precursor to other aromatic compounds used in dyes, plastics, drugs, and explosives.

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Presented by-
Chiranjib Acharjee
Roll-1299
B.Sc. 2nd Semester
Chemistry(M)
Bholanath College, Dhubri

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 Statistics
 Structure
Resonance in benzene
 Bonding
 Nomenclature
 Reactions
 Industry uses and preparation.
CONTENTS:

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 Discovered by Michael Faraday in 1825
 Molecular formula:C6H6
 Molar mass: 78.11 g/mol
 Most Basic Aromatic Molecule
 Bond length: C-C 139 pm and C-H 109pm
 Colorless Liquid
 Boiling Point: 8o.08oC
 Melting Point: 5.48oC
 Density: 0.8765g/cm
 Insoluble in Water
 Soluble in Oils & Fats & organic compounds
 Explosive Vapours
 Flammable Liquid
STATISTICS ON BENZENE:

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 These structures given below are known as Kekulé structures.
 Although benzene is still drawn as a six-membered ring with alternating ᴨ bonds,
in reality there is no equilibrium between the two different kinds of benzene
molecules.
 Current descriptions of benzene are based on resonance and electron
delocalization due to orbital overlap.
 In the nineteenth century, many other compounds having properties similar to
those of benzene were isolated from natural sources. Since these compounds
possessed strong and characteristic odors, they were called aromatic compounds.
It should be noted, however, that it is their chemical properties, and not their odor,
that make them special.
Benzene has a cyclic,planar,hexagonal structure.
STRUCTURE:

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The resonance description of benzene consists of two equivalent Lewis
structures, each with three double bonds that alternate with three single
bonds.
The true structure of benzene is a resonance hybrid of the two Lewis
structures, with the dashed lines of the hybrid indicating the position of the 
bonds.
We will use one of the two Lewis structures and not the hybrid in drawing
benzene. This will make it easier to keep track of the electron pairs in the 
bonds (the  electrons).
RESONANCE IN BENZENE:

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BONDING IN BENZENE:
As per the Molecular Orbital Theory(MOT), all the six
carbon atoms in benzene ring are sp2 hybridized. The sp2
hybrid orbitals overlap with each other and with s orbitals
of the 6 hydrogen atoms to form c-c and c-h sigma bonds
All the sigma bonds in benzene lie in one plane and all
the bond angles are 120◦.
Each carbon atom in benzene possesses an unhybridized
p-orbital containing one electron .The p-orbitals are
perpendicular the plane of sigma bond.
The lateral overlap of these p-orbitals produces a ᴨ
molecular orbital containing 6 electrons. One half is above
and other half lies below the plane of sigma-bonds.

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BONDING IN BENZENE CONTINUED:
The six electrons of the p orbitals cover all the six
carbon atoms, and are said to be delocalized. As a result
of which a strong ᴨ bond is formed and the benzene
molecule is stabilized.

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Four structural criteria must be satisfied for a compound to be
aromatic.
THE CRITERIA FOR AROMATICITY—Hückel’s Rule:
[1] A molecule must be cyclic.
To be aromatic, each p orbital must overlap with p orbitals on
adjacent atoms.

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[2] A molecule must be planar.
All adjacent p orbitals must be aligned so that the  electron density
can be delocalized.
.
[3] A molecule must be completely conjugated
Aromatic compounds must have a p orbital on every atom

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[4] A molecule must satisfy Hückel’s rule, and contain
a particular number of  electrons.
Benzene is aromatic and especially stable because it contains 6 
electrons. Cyclobutadiene is antiaromatic and especially unstable
because it contains 4  electrons.
Hückel's rule:

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NOMENCLATURE:
• Monosubstituted Benzene:These are named by prefixing the
name of the substitutent to the word benzene. For eg, benzene in
which one of the hydrogen is replaced with chlorine is called
chlorobenzene.
• Disubstituted benzene:When there are two substituents on the
ring, three positional isomers are possible. The relative positions
are indicated by prefixes ortho (o-) meta(m-) and para(p-) At
position 2 3 4 respectively.

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NOMENCLATURE CONTINUED:
• Polysubstituted benzene:When three or more substitutents are
present on the benzene ring, numbers must be used to designate
their positions. One of the substitutent is put on the top of the
hexagon and numbered 1. The numbering of the remaining
positions is done clockwise or anticlockwise, which gives the
lowest possible group of numbers to the other substitutents.

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 Nitration: Hydrogen in the benzene ring is replaced by
nitrogen (NO2-) to give nitro-benzene
 Halogenation::Hydrogen Replaced by Halogen(X-) to give
halobenzenes.
 Sulphonation::Hydrogen Replaced by (SO3H-)
 Friedel-craft alkylation: Alkyl group (R-) Attaches to ring
to make a alkyl-benzenes
 Friedel-craft acylation:: Acyl group (RCO-) Attaches to
Ring to Make a Ketone which on Clemention reduction
gives n-alkyl benzene.
REACTIONS OF BENZENE:

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Made from Coal Tar (a liquid left over when coal is
heated) and Petroleum
Used as a Source for Almost all Aromatic Compounds
 Make Complicated Aromatic Compounds by Taking
Benzene and Add on Other Rings Piece by Piece
Solvent for:
Sulfur, Phosphorus and Iodine,Gums,Fats, Waxes
and Resins,Simple Organic Compounds
One of the Most Commonly Used Solvents in Organic Chemistry
INDUSTRY USES AND PREPARATION:

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Aniline:
 Dye (Aniline Oil)
 Plastics
 Drugs (Sulfanilamide)
 Explosives
 Phenol:
 Disinfectant
 Antiseptic (Diluted)
 Insecticide
 Explosives
 Detergent
 Raw Material for Aspirin
INDUSTRY USES AND PREPARATION:

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“The greatest enemy of knowledge is not
ignorance, it is the illusion of knowledge.”
--STEPHEN HAWKING