F324 Unit 4: Arenes

Arene: aromatic hydrocarbon. Aromatic: ring structure

Benzene

Molecular formula: C6H6

Kekule structure: alternate single and double C bonds

Delocalised: Ring of delocalised electrons formed above C planes due to the overlap of p orbitals. Overlap produces a series of pi bonds spread across all 6 C.

• Evidence for delocalised structure not kekule:
  • C-C bond lengths in benzene are all the same intermediate length but C-C and C=C have a different length so can't be kekule (seen in x ray crystallography)
  • Benzene does not decolourise Br water, should happen if C=C present
  • Hydrogenation for benzene should be 3x Cyclohexene if kekule structure but in reality is is much lower than expected

Benzene's reactions - Electrophilic substitution

Nitration - conc H2SO4 catalyst at 50 degrees/ Halpgenation - halogen carrier (FeCl3/AlCl3/Fe)

Reactivity

 Cyclohexane decolourises Br water…