Aromatics

Question 1

Benzene Mr

Answer 1

C6H6

Question 2

what is it called when benzene is the substitute group

Answer 2

-phenyl
-eg. phenylethene

Question 3

describe the Kekule model

Answer 3

-theoretical model
-ring of 6 carbons
-alternating single and double bonds

Question 4

Benzene vs Kekule model- reacting with Bromine

Answer 4

Kekule model
-bromine would decolourise
-bonding is completely changed

Benzene model
-no colour change
-bonding stays the same
-electrophilic substitution accours
-only reacts at high temp+catalyst

Question 5

Benzene vs Kekule model- enthalpy of hydrogenation

Answer 5

-kekule is 360KJmol-1
-benzene is -208KJmol-1
-benzene is less exothermic because it is more stable due to the ring of delocalised electrons

Question 6

Benzene vs Kekule model- bond length

Answer 6

-kekule single bonds longer then double
-benzene bond lengths are equal
-benzene has intermediate bonds between single and double bonds

Question 7

Benzene delocalised ring

Answer 7

• benzene has a ring of 6 carbons
  -3/4 e- in each carbon used for H in sigma single bonds
  -1/4 e- is in p orbital
  -all together 6 p orbitals
• 2 p orbitals overlap to form pi bond = 3 pi bonds
  -pi bond is shaped like a donut
  -electrons are delocalised

Question 8

benzene physical propeties

Answer 8

• colourless at room temp
• similar BP
• higher MP [planar, stacked well in solid state,VDW harder to break]

Question 9

reactivity of benzene

Answer 9

-ring is an area with high electron density due to delocalisation
-react with electrophiles
-almost all reactions, ring stays intact

Question 10

shape of benzene

Answer 10

• planar shape
• hexagonal 120 bond angle
• C-C bond equal length

Question 11

electrophilic substitution reagents

Answer 11

conc. H2SO4 + conc. HNO3

Question 12

electrophile needed for electrophilic substitution

Answer 12

NO2+

Question 13

how to make the electrophile for electrophilic substitution

Answer 13

H2SO4 + HNO3 –> HSO4- +H2NO3
H2NO3 –> +NO2 + H2O

Question 14

regeneration of catalyst within electrophilic substitution

Answer 14

HSO4- + [H]+ –> H2SO4

Question 15

Name and outline mechanism for benzene + nitronium ion

Name the reagent
Outline the equation to generate the nitronium ion
Outline the equation to regenerate the catalyst

Answer 15

-Electrophilic substitution

-curly arrow from line of ring to N
-open ring in direction of desired carbon with ‘+’ in middle
-H shown on same carbon
-curly arrow from bond of H to middle of ring
-nitronium ion bonded and H+ produced

H2SO4 + HNO3 –> HSO4- +H2NO3
H2NO3 –> +NO2 + H2O

HSO4- + H+ –> H2SO4

Question 16

reagent needed for Friedel-Crafts Acylation

Answer 16

• acyl chloride
• eg. ethanoyl chloride
• CH3COCl

Question 17

electrophile needed for friedel-crafts

Answer 17

+CH3CO

Question 18

name and make the electrophile for friedel-crafts acylation

Answer 18

• acylium ion
  CH3COCl + AlCl3 –> +CH3CO +AlCl4-

Question 19

regeneration of the aluminium chloride catalyst

Answer 19

+H + AlCl4 –> AlCl3 + HCl

Question 20

Name and outline mechanism for benzene + acylium ion

Name the reagent and catalyst
Outline the equation to generate the acylium ion
Outline the equation to regenerate the catalyst

Answer 20

-Friedel-Crafts acylation
-Electrophilic substitution

-curly arrow from line of benzene ring to positive carbon
-open ring in direction of desired carbon with ‘+’ in middle
-curly arrow from H+ bond to middle of ring
-acylium ion bonded and H+ produced

CH3COCl + AlCl3 –> +CH3CO +AlCl4-

+H + AgCl4 –> AlCl3 + HCl