Arenes – Benzene

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Arenes (aromatic hydrocarbons)
Long-term exposure may cause certain types of cancer.
Used as feedstock for production of many chemicals.
Complete combustion:
o Sooty flame
o Due to high carbon to hydrogen ratio.
Kekulé Model:
Ring of carbon atoms.
Alternating single and double bonds.
Later adaption states that benzene molecule existed as two isomers that
it flipped between (switching over double and single bonds).
Advantages: Disadvantages:
Explains many of the Doesn't explain data from
properties of benzene. experiments about:
o Bond length
o Thermochemitsry
o Reaction with bromine
Representation of benzene:
Delocalised Model:
Each carbon forms three sigma-bonds (2 carbon and 1 hydrogen).
Leaving one p-orbital on each carbon, which is perpendicular to the
plane of the ring ­ creating pi-bonds.
Each p-orbital contains a single electron that can move through the
whole pi-system (delocalised).
The delocalisation gives benzene extra stability ­ electrons repel each
other, so a system where they're as far apart from one another as
possible will involve minimum repulsion and will therefore be

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The Delocalised Model of Benzene
The molecular formula of benzene is C6H6.
The delocalised model suggests that each carbon forms three sigma-bonds.
Therefore, there's one p-orbital on each carbon that is perpendicular to the
plane of the ring, which created pi-bonds. A pi-system is created from the
overlapping of p-orbitals and so the delocalisation is extended over all six
carbon atoms.
There're many pieces of evidence that support this model.…read more


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