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The structure of benzeneL.O.:
Explain the structure of benzene.
Use evidence from enthalpies ofhydrogenation to illustrate
aromatic stability.
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Starter:
You are a great chemist called Kekul who has heard that Faraday
has discovered a new compound. The molecular formula is C6H6.
Propose a structure for this new compoundClue: he had a dream.
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STRUCTURE OF BENZENE
Benzene = C6H6Its structure was a mystery for many years - until
Kekules dream.
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STRUCTURE OF BENZENE
Problems with Kekules structure:1)C-C bonds are all the same
length (between C-C and C=C length).2)Benzene does not undergo
addition reactions readily (e.g. with bromine water).3)Do not get
isomers like this:4)H hydrogenation about 152 kJ mol-1 less than
expected.
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Each carbon has three covalent bonds one to a hydrogen atom, and
the other two carbon atoms. The fourth electron of each carbon is a
p-orbital. There are six of these. The electrons in the p-orbitals
overlap and are delocalised.
The delocalised system makes benzene unusually stable (aromatic
stability)
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STRUCTURE OF BENZENE
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6 electrons in a delocalised bond
STRUCTURE OF BENZENE
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STRUCTURE OF BENZENE
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STRUCTURE OF BENZENE
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Enthalpy(kJ mol-1)-120-208-152 kJmol-1delocalisation energy
HYDROGENATION OF BENZENE
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You will create an A3 poster which will show the different
representations of benzene. You should include diagrams of at least
three different representations of benzene. You will explain how
each model shows the structure and any drawbacks to the model. You
should also include information about who discovered the structure
of benzene and how this was done.
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Task:
worksheet
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NAMING AROMATIC COMPOUNDS
methylbenzene(toluene)chlorobenzenenitrobenzenebenzenecarboxylic
acid(benzoic acid)
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NAMING AROMATIC COMPOUNDS
1,3-dimethylbenzene(m-xylene)4-methyl-1-chlorobenzene2-hydroxybenzenecarboxylic
acid
3,5-dinitrobenzenecarboxylic acid
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NAMING AROMATIC COMPOUNDS
phenylamine(aniline)2-phenylbutanephenylethene
phenylethanone
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NAMING AROMATIC COMPOUNDS
phenylethanoatemethyl benzenecarboxylate(methyl
benzoate)N-phenylethanamide
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NAMING AROMATIC COMPOUNDS
phenolbenzene-1,2-diol2,4,6-trichlorophenol(TCP)2-nitrophenol
Allans Page 111&112 (some Qs only)Print out from
http://www.chemguide.co.uk/basicorg/bonding/benzene1.htmlA3
paper.
***********Work in groups of 4. Hand out print out from
http://www.chemguide.co.uk/basicorg/bonding/benzene1.html
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