Benzene - (Evidence and Models)
- Created by: ButterflyFlower
- Created on: 23-10-15 11:58
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- Benzene
- Models of Benzene
- Kekule
- Alternating single and double bonds
- Has 3 C=C and 3 C-C bonds. Represented as a symmetrical molecule.
- Suggested that benzene had 2 forms, differing only by the positions of the double bonds
- Chemical name is Cyclohexa-1,3,5-triene
- Alternating single and double bonds
- Delocalised
- Cyclic hydrocarbon with six carbon atoms and six hydrogen atoms.
- 6 carbon atoms arranged in a planar hexagonal ring. Each carbon atom is bonded to 2 other carbon atoms and 1 hydrogen atom.
- Shape arund each carbon atom is trigonal planar with a bond angle of 120
- Each carbon atom has 4 outer shell electrons. 3 bond to 2 other carbon atoms and 1 hydrogen atoms. Three bonds(sigma) 4th outer shell electron in a 2p orbital above and below the plane of carbon atoms.
- Electron in a p-orbital of a carbon atom overlaps with the electrons in the p-orbitals of the carbon atoms on either side, results in electron density above and below.
- Overlap produces a system of pi bonds which spread over all 6 C atoms. Electrons are now delocalised.
- Kekule
- Evidence of Delocalised model
- X ray studies
- Six carbon carbon bond lengths are the same: 0.139 nm, between the C-C (0.153) and C=C (0.134)
- Halogenation of Benzene
- One C=C bond has ECOH : -120kj mol
- 3 C=C bonds would be expected to have a ECOH of -360 kj mol
- When hydrogenated, actual experimental value is -208 kj mol, 152 kj mol less than expected value.
- 3 C=C bonds would be expected to have a ECOH of -360 kj mol
- Real structure of benzene is more stable than Kekule.
- One C=C bond has ECOH : -120kj mol
- Does not react with bromine water and decolourise it, doesn't take part in electrophilic addition reactions.
- X ray studies
- Models of Benzene
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