Benzene

Question 1

What is the name when the benzene ring is regarded as a substitute group?

Answer 1

Phenyl groups- amines, alleles and alcohols are all priority groups

Question 2

Kekule vs Benzene

Answer 2

Bond lengths are an intermediate between short c=c and long c-c
Hydrogenation is less exothermic than expected because benzene is more stable
benzene is less reactive than an allele, it doesn’t undergo an addition reaction to decolourise bromine, instead it undergoes substitution to maintain the ring of delocalised electrons (break delocalised ring)
-each carbon has 3 covalent bonds
-Spare electrons in p orbitals overlap to form pie cloud
-delocalisation
-planar
-hexagon/6rings
-c-c equal in length
-expected hydrogenation of cyclohexane- -360 kjmol-1
-hydrogen benzene is less exothermic by 152kjmol-1
-benzene lower in energy/more stable

Question 3

Delocalisation and stability

Answer 3

Alternating double bonds- some delocalisation- less inclined to react. less exothermic. Extra stability- less exothermic

Question 4

Reactivity of aromatic compounds

Answer 4

Aromatic ring is the area of high electron density due to delocalisation meaning arenas will react with electrophiles
The aromatic ring is very stable. Energy has to be put into break the ring system. this means in almost all reactions the ring remains in tact at the end of the reaction.

Question 5

What happens when arenas burn?

Answer 5

Incomplete combustion- burn with a smoky flame.

Question 6

Nitration

Answer 6

Reagents: Conc H2SO4 and conc HNO3
Equation: H2SO4 + HNO3–> HSO4- +H2O +NO2+
Broken into 2 steps: H2SO4 + HNO3–> HSO4- + H2NO3+
H2NO3+—> NO2+ + H2O
NO2+ is the Electrophile
Regeneration: HSO4- + H+—>H2SO4

Question 7

Friedel- Crafts Acylation

Answer 7

Regents: Acyl chloride and AlCl3
Reaction- RCOCL +AlCl3–> RCO+ +AlCL4-
Formation of catalysts
H+ +AlCL4–> AlCl3 +HCl