Benzene

• Benzene is a planar system of p-orbitals.

  Overlapping p-orbitals create a new pi-system above and below the molecule.

  These electrons are delocalised & spread out through the entire ring.
• Benzene is aromatic
• Benzene is not an alkene because,

  It doesn't undergo electrophilic addition or decolorise bromine water.

  The length of the C-C bonds are the same.

  Enthalpy change of hydrogenation is less exothermic than expected (bezene is stable)
• When benzene has >7C alkyl group or functional groups, OH or carbonyls its Suffix = Phenyl

  This is phenylethanone

  
• When benzene has <7C alkyl group or functional groups, nitro (NO2), halogens its Prefix = benzene

  eg. chlorobenzene, nitrobenzene, ethylbenzene
• what does nitrobenzene look like


  NO2 = nitro

  
• what does phenylmethanal look like

  methyl group and aldehyde/ carbonyl

  
• what does benzoic acid look like

  carboxylic acid group

  
• Nitration of benzene requires; conc HNO3 & conc H2SO4 (catalyst)
• Methylation of benzene requires; AlCl3 (halogen carrier) & CH3Cl
• Halogenation of benzene (eg Br) requires; AlBr3 (halogen carrier) & Br2
• Acylation of benzene (adding carbonyl group) requires; AlCl3 & CH3COCl
• benzene undergoes electrophilic substitution reactions
• electrophile = an electron pair acceptor
• Benzene is much less reactive than alkenes because the pi-bond in alkenes have localised electrons making its electron density high.

  Whereas in benzene its pi-system has delocalised electrons making its electron density low.

  Meaning benzene more readily attracts electrophiles.