OCR F324 (Chains, rings and spectroscopy) 28/06/10
Chemistry exam discussion - share revision tips in preparation for GCSE, A Level and other chemistry exams and discuss how they went afterwards.
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Re: The Official OCR Chemistry- Rings, Polymers and Analysis. F324.Hey
This is probably the exam I'm most worried about at the moment
I attempted to start revising this morning but I only got as far as aldehydes and ketones before ending up on here lol. -
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Re: The Official OCR Chemistry- Rings, Polymers and Analysis. F324.Not yet... well. I have cards, just not on the computer.. we could try to put overviews on here or something =D
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Re: The Official OCR Chemistry- Rings, Polymers and Analysis. F324.(Original post by skatealexia)
cgp is awesome.
Ok, I've now gone through the text book and revision guide for the first module (up to amines) so one down two to go
xxx -
Re: The Official OCR Chemistry- Rings, Polymers and Analysis. F324.
I've started my revision. Just thought I'd share what I've learnt so far on Benzene:
Problems with the Kekule structure of benzene:
1) Low reactivity - C=C present so should react in similar way to alkenes
- C=C should decolourise Bromine water.
But this does not happen, does not undergo electrophilic addition, undergoes electrophilic substitution.
2) Bond length - C-C and C=C have different bond lengths.
But this is not the case, according to xray studies all C-C bonds are the same, equal length.
3) Hydrogenation - expected enthalpy change of hydrogenation of benzene is -360kj mol-1, but the actual enthalpy change of hydrogenation of benzene is -208kj mol-1
>>> Therefore the actual structure of benzene is more stable than kekule's.
Delocalised model of benzene
- Trigonal Planar 120 degrees
- p-orbitals overlap around the whole of the ring forming a system of pie bonds.
- electron spread all the whole of the ring >>> delocalised >>> more stable.
- All C-C bonds are identical.
Nucleophilic substitution
Nitration of benzene:
Uses: Dyes and pharmaceuticals.
Conditions: Conc. H2SO4, conc. HNO3, 50 degrees C
C6H6 + HNO3 >>> C6H5NO2 + H20
Halogenation of benzene
- Only reacts in the presence of a halogen carrier - AlCl3, FeCl3
Benzene + Halogen >>> Halogenobenzene + Hydrogen Halide
The mechanisms for the nitration and halogenation of benzene are attached.
Enjoy. -
Re: The Official OCR Chemistry- Rings, Polymers and Analysis. F324.
Some flashcards summarising the spec you guys might find helpful
http://www.flashcardexchange.com/flashcards/view/944334

Would help me alot.