A2- Benzene Flashcards

1
Q

Draw benzene and give its formula

A

regular hexagon, with ring/circle in the middle
C6H6

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2
Q

Why is benzene stable?

A

because it has delocalised pi orbital system of electrons

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3
Q

Based on shape only, why can we say cyclohexatriene is only a hypothetical structure?

A

as the bonds lengths would not be possible if it was in this shape, therefore benzene has an intermediate bond length making it a regular hexagon

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4
Q

How does hydrogenation show the hypothetical cyclohexatriene/kekule is not the real structure of benzene?

A

as the expected enthalpy change would be 152kJ mol-1 more negative than the value obtained.This means benzene is 152kJ mol-1 more stable, which is due to the delocalised rings

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5
Q

Why might the reactions of benzene suggest it is not the kelule structure?

A

does not undergo addition reactions, as would be expected

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6
Q

How does adding other atoms impact the stability of benzene?

A

it makes is less stable, as it uses some of the delocalised electrons

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7
Q

Give the equation and reaction conditions for the nitration of benzene

A

Benzene + HNO3 –> Nitrobenzene + H2O
- 50C
- conc. H2SO4 as a catalyst

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8
Q

What 2 equations show the formation of NO2+ ions?

A

HNO3 + H2SO4 –> HSO4- + [N2NO3]+
[H2NO3]+ –> H2O + NO2+

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9
Q

What mechanism is the nitration of benzene?

A

electrophilic substitution

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10
Q

Describe the bonding in Benzene

A
  • 6 C-C sigma bonds
  • 6 C-H sigma bonds
  • P orbitals of C atoms overlap
  • forms delocalised Pi system
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11
Q

What is needed for benzene to react with chlorine?

A

halogen carrier, AlCl3

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12
Q

What are the reaction conditions for the chlorination of benzene?

A

25C, AlCl3 and Cl2

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13
Q

How is a Cl+ generated for the chlorination of benzene?

A

in situ, by mixing AlCl3 with Cl2 and Benzene
AlCl3 + Cl2 –> AlCl4- + Cl+

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14
Q

How is AlCl3 regenerated?

A

AlCl4- + H+ –> AlCl3 + HCl

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15
Q

What are Friedel crafts reactions?

A

substitution reactions where an alkyl or acyl chain replaces a hydrogen on an aromatic compound

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16
Q

What are the reaction conditions for alkylation?

A

room temp, AlCl3 and chloroalkane

17
Q

What are the reaction conditions for acylation?

A

AlCl3, 60C, halogen carrier and acyl chloride, anhydrous conditions

18
Q

What would happen if water was present in an acylation reaction?

A

acyl chloride would react to form COOH and HCl(g)

19
Q

How could a reaction mixture after alkylation be separated?

A

fractional distillation

20
Q

What will an excess of benzene lead to in electrophilic substitutions?

A

single substitution

21
Q

Describe the structure/shape of benzene

A
  • planar
  • regular hexagon
  • same bond angles and lengths