A2 CHEMISTRY NOTES - BENZENE
Aromatic chemistry
This is the study of compounds containing __________ rings.
Structure of Benzene
Faraday discovered benzene in 1825. He found that it had
an empirical formula of ____ and relative mass of 78. This
gives a molecular formula of ______, which indicates that
benzene has a lot of ________ bonds or is highly
_____________. From this it was expected that benzene
would be __________ and undergo the _________
reactions that alkenes do.
Kekule
German chemist named Kekule working on this
problem dreamed of snakes swallowing their
tales and from this got the idea that benzene
could have ________ structure.
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A2 CHEMISTRY NOTES - BENZENE
Problems with Kekule structure
If we investigate the reactivity of benzene, we see it is unlikely to have three double
bonds in the molecule, the structure proposed by Kekule.
Activity
Compound
Reaction with Bromine in organic solvent
Reactivity
Cyclohexane
Cyclohexene
Benzene
Hydrogenation Enthalpy Values
Comparing Hydrogenation Values
Benzene is ______kJ mol-1 more stable than cyclohexatriene would be.
Evidence for Kekule’s structure not being fully correct is supplied by:
 Reactivity: Benzene does not undergo the _______ reactions expected
 Thermodynamic data: The benzene structure is more _______ than Kekule’s
Also
 There are fewer __________ of di-substituted product.
 X-ray diffraction patterns: Shows all C-C bond lengths to be the ______.
 Spectroscopy: IR shows a much _________ spectrum than expected.
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A2 CHEMISTRY NOTES - BENZENE
The Actual Structure of Benzene
This can be seen as somewhere between the two Kekule structures.
Each C has __ C-C bonds
Each H has 1 C-H bond
Each C also has a p orbital with __ electron
So there are 6p orbitals each containing _ electron
The p electrons are ____________
around the ring and give it stablility
Modern techniques show that benzene possesses:
 _________ structure
 A regular _________ shape
 __ C to C bond lengths of 0.139nm
 bond angles of ____º
 __ C-H bonds
 6 _________ electrons orbital
[C-C = 0.154nm, C=C = 0.134nm]
Drawing benzene
Benzene is represented as:
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A2 CHEMISTRY NOTES - BENZENE
Electrophilic Substitution Reactions of Benzene
General Electrophilic Substitution of benzene Mechanism
Nitration of benzene
Reaction Reagents
Benzene reacts with a mixture of


Reaction Conditions
 At ___C.
Reaction Equation
Name of Reaction Mechanism
This is an ___________ ____________ reaction
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A2 CHEMISTRY NOTES - BENZENE
Reaction Mechanism
The electrophile is _____ and is generated by the sulphuric acid acting as a
homogenous ____________ and an acid and the nitric acid acting as a base.
Step 1 – generating ________________
Step 2 - substitution of a Hydrogen ion for the ____________ ion via electrophlic attack
followed by loss of _______ ion and recovery of _________ ________ pi system.
Uses of Nitrobenzene
Approximately 95% of nitrobenzene is consumed in the production of _______, which
is a precursor to ______ chemicals, ________, _____, _______, and ___________.
Trinitrotoluene (TNT)
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A2 CHEMISTRY NOTES - BENZENE
Azo Dyes
Acylation of benzene with a Friedel-Crafts catalyst
Reagents:
________ chloride, Aluminium chloride ____________
Reaction Conditions:
Heat under reflux and ____________ conditions
Reaction Equation
Reaction Mechanism
This is an ELCTROPHILIC SUBSTIUTION REACTION
Name of Reaction Mechanism
This is an ____________ _____________ reaction
Reaction Mechanism
Step 1 – generating _______________
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A2 CHEMISTRY NOTES - BENZENE
Step 2 - substitution of a Hydrogen ion for the ______________ ion via electrophlic
attack followed by loss of ___ ion and recovery of _________ __________ pi system.
Why the reaction is important
Friedel-Crafts acylation is a very effective way of attaching a hydrocarbon-based
group to a ________ ring. Although the product is a ketone it is easily converted into
other things. For example the carbon-oxygen double bond can be reduced to give a
secondary __________, which in turn can undergo lots of other reactions.
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