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Flashcards

25.1 Introducing benzene

Urvi B Chemistry A level English 45 cards

Draw the two ways benzene is shown

Cards in this deck (45)

  1. 1What is the molecular formula for benzene?C6H6
  2. 2What are the properties of benzene? (3)- Colourless, sweet smelling, highly flammable liquid
    - Found naturally in crude oil, is a component of petrol and also found in cigarette smoke
    - Classified as a carcinogen, can cause cancer
  3. 3What is the structure of benzene?Hexagonal ring of 6 carbon atoms each carbon joined to 2 other arbon atoms and one to hydrogen atom
  4. 4What classification is benzene?Aromatic hydrocarbon
    Arene
  5. 5Draw the two ways benzene is shownDraw the two ways benzene is shown
  6. 6Does benzene react in the same way as alkenes?Nope
  7. 7Historically, what was aromatic the term used to classify what types of compounds?Derivaties of benzene
    Pleasant smelling compounds contained a benzene ring
    However, many odourless compounds have been found to contain an benzene ring but aromatic is still used
  8. 8What did the molecular formula of C6H6 suggest about benzene's structure?Structure containing many double bonds or a structure containing double or triple bonds
    Compounds containing multiple bonds were known to be very reactive, however benzene appeared unreactive
  9. 9What did the Kekule model suggest about benzene's structure?6 carbon membered ring of carbon atoms joined by alternate single and double bonds
  10. 10What are the 3 main reasons why chemists did not accept Kekule's model?Lack of reactivity of benzene
    The lengths of the carbon-carbon bonds in benzene
    Hydrogenation enthalpies
  11. 11Kekule Model The lack of reactivity of benzene If benzene contained the C=C bonds it should do what to bromine in what reaction?Decolourise bromine in an electrophilic addition reaction
  12. 12Kekule Model The lack of reactivity of benzene However what can't benzene do?Benzene does not undergo electrophilic addition reactions
    Benzene does not decolourise bromine under normal conditions
  13. 13Kekule Model The lack of reactivity of benzene What has this led scientists to suggest?Benzene cannot have any C=C bonds in its structure
  14. 14Kekule Model The lengths of the carbon-carbon bonds in benzene What is the technique used to measure bond lengths in a molecule?X-ray diffraction
  15. 15Kekule Model The lengths of the carbon-carbon bonds in benzene What did Kathleen Londsale found that bonds in benzene to be?All the bonds in benzene were 0.139nm in length
  16. 16Kekule Model The lengths of the carbon-carbon bonds in benzene What are the lengths of a single bond and a double bondSingle bond - 0.153nm
    Double bond - 0.134nm
  17. 17Kekule model Hydrogenation enthalpies What is the other name the Kekule structure of benzene can be called?cyclohexa-1,3,5-triene (to indicate the position of the double bonds)
  18. 18Kekule model Hydrogenation enthalpies If benzene did have the Kekule structure would would its enthalpy change of hydrogenation be?Three times that of cyclohexene
  19. 19Kekule model Hydrogenation enthalpies When cyclohexene is hydrogenated what happens and what is its enthalpy change of hydrogenation?One double bond reacts with hydrogen
    The enthalpy change of hydrogenation is -120kJmol-1
  20. 20What is hydrogenation?Addition of hydrogen to an unsaturated compound
  21. 21Kekule model Hydrogenation enthalpies What is the expected enthalpy change for reacting three double bonds with hydrogen?-360kJmol-1
  22. 22Kekule model Hydrogenation enthalpies What is the actual enthalpy change of hydrogenation of benzene?-208kJmol-1
    Means that 152kJmol-1 less energy is produced than expected
  23. 23Kekule model Hydrogenation enthalpies What does this suggest?Actual structure of benzene is therefore more stable than the theoretical Kekule model of benzene
    Information led scientists to propose the delocalised model of benzene
  24. 24Main features of delocalised model of benzene What is benzenes structure?Benzene is a planar, cyclic, hexagonal hydrocarbon containing 6 carbon atoms and 6 hydrogen atoms
  25. 25Main features of delocalised model of benzene What are the bonds the carbons form?Each carbon atom uses 3 of its available four electrons in bonding to two other carbon atoms and to one hydrogen atom
  26. 26Main features of delocalised model of benzene Each carbon atom has one electron where at what angles?Each carbon atom has one electron in a p-orbital at right angles to the plane of the bonded carbon and hydrogen atoms
  27. 27Main features of delocalised model of benzene What are the positions of the p-orbital electrons?Overlap sideways, in both directions, above and below the plane of the carbon atoms to form a ring of electron density
  28. 28Main features of delocalised model of benzene What does this overlapping of the p-orbitals create a system of?This overlapping of the p-orbitals creates a system of π-bonds which spread over all six of the ccarbon atoms in the ring structure
  29. 29Main features of delocalised model of benzene What are the 6 electrons said to be?The six electrons occupying this system of π-bonds are said to be delocalised
  30. 30Draw the structure of the delocalised model of benzeneDraw the structure of the delocalised model of benzene
  31. 31What groups are shown as prefixes to benzene?Short alkyl chains
    Halogens
    Nitro groups
  32. 32Aromatic compounds with one substituent group are what?Minsubstituted
  33. 33In aromatic compounds the benzene ring is considered to be the what chain?Parent chain
  34. 34Give examples of alkyl groups, halogens and niro group.Alkyl groups - CH3, C2H5
    Halogens - F, Cl, Br, I
    Nitro - NO2
  35. 35What is this compound?ethylbenzeneWhat is this compound?
  36. 36What is this?chlorobenzeneWhat is this?
  37. 37What is this?NitrobenzeneWhat is this?
  38. 38When is benzene considered to be a substituent?When a benzene ring is attached to an alkyl chain with a functional group or to an alkyl chain with 7 or more carbon atoms
  39. 39When benzene is a substituent instead of benzene what is the prefix used in the name?Phenyl
  40. 40What is this compound?PhenylethanoneWhat is this compound?
  41. 41What is this compound?2-phenyloctaneWhat is this compound?
  42. 42What are 3 common aromatic compounds that do not go with these rules?Benzoic acid (benzenecarboxylic acid)
    Phenylamine
    Benzaldehyde (benzenecarbaldehyde)
  43. 43Draw structure of benzoic acid.Draw structure of benzoic acid.
  44. 44Draw the structure of phenylamine.Draw the structure of phenylamine.
  45. 45Draw the structure of benzaldehydeDraw the structure of benzaldehyde

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A level Chemistry (Module 6: Organic chemistry and analysis) Flashcards on 25.1 Introducing benzene, created by Urvi B on 06/10/2018.
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