Aromatic Chemistry

• What is benzene?

  It is C6 H6, it is colourless, sweet, highly flammable and found in crude oil
• What is the structure of Benzene?

  Hexagonal ring of six carbon atoms with each carbon bonded to two others, it is considered as an aromatic hydrocarbon or arene,
• What was Kekules Benzene model?

  He suggested it was based on six carbon atoms joined by single and double bonds.
• What was the evidence to disprove Kekule's model? (1)

  1. Lack of reactivity in Benzene, if it had the double bond then it would discolour bromine, however it doesn't discolour it or undergo any electrophilic addition
• What was the evidence to disprove Kekule's model? (2)

  The lengths of the carbon carbon bonds, if Kekule's was true then the Double bonds and single bonds will have different lengths, but it was found that they all had the same bond lengths.
• What was the evidence to disprove Kekule's model? (3)

  Hydrogenation enthalpies, if it had the benzene had the DB then the enthalpy change would be 3 times cyclohexene (-360kjmol-1), where as in reality it is much higher being (-208kjmol-1) meaning it must be incorrect
• What is the delocalised model of Benzene?

  Benzene is planar, hexagonal, cyclic with 6Cs and 6Hs

  Each carbon uses three of its electrons in bonding

  Each carbon has one electron in a P orbital at 90 degrees to the plane

  Adjacent P orbital electrons overlap sideways, in both ways above and below and form a ring of electron density

  The overlap causes what is called a pi bond system which spread over all six carbons is the ring structure

  The six electrons above and below are delocalised
• How do you name aromatic compounds with one substituent group?

  You add the name to the prefix i.e. ethylbenzene or chlorobenzene
• How do you name a benzene which has functional group or more than 7 carbons?

  Use the prefix (Phenyl)
• What are some exceptions of using phenyl?

  Benzoic acid (carboxylic acid), benzaldehyde (aldehyde), phenylamine
• How do you name a benzene compound w more than one substituent group?

  1. Start by numbering making sure it will give the lowest number possible for functional groups
  2. Name alphabetically with functional groups
• What mechanisms do benzene undergo?

  Electrophilic substitution
• What are the conditions for the nitration of benzene?

  Nitric acid, (catalyst-sulphuric acid), 50 degrees
• What will happen if there is no temperature control on the mechanism of benzene?

  Further substitutions occurring leading to the production of dinitrobenzene
• What are the uses of nitrobenzene?

  dyes, pharmaceuticals and pesticides
• What is needed in the halogenation of benzene?

  A halogen carrier (e.g. AlCl3, FeCl3, AlBr3, FeBr3,)
• What are alkylation reactions?

  It is the substitution of one hydrogen to an alkyl group
• What are the conditions for alkylation reactions?

  Haloalkane, in the presence of a halogen carrier
• What is an acylation reaction?


  Benzene reacting with an acyl chloride in the presence of AlCl3,
• What is the process of an alkene being discoloured by bromine?

  1. The pi bond contains localised electrons above and below the plane, producing an area of high electron density
  2. Localised electron produces a dipole in the non polar bromine molecule causing it produce a slightly positive and slightly negative molecule
  3. The slightly positive and negative which makes an electrophile