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Organic 2 > Arenes > Flashcards

Arenes Flashcards

1
Q

Benzenes physical properties
Description of state
Boiling temp
Solubility
Where is it found

A
  • colourless liquid
  • boiling temp = 80°C
  • insoluble in water

Found in crude oil

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2
Q

Benzene molecular formula

A

C6H6

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3
Q

Is benzene saturated or unsaturated

A

Unsaturated

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4
Q

How was the empirical formula of CH of benzene found

A

Through combustion analysis

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5
Q

Uses of benzene

A
  • organic synthesis
  • manufacture of detergents, explosives
  • was used for decaffeinated coffee - dissolves caffeine
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6
Q

Describe and draw Kekules structure

A

Six member ring, alternate single and double bonds
Check oneNote for drawing

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7
Q

List the problems with Kekules structure

A
  1. Bromine test and reactivity
  2. Isomers
  3. Bond length
  4. Enthalpy changes
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8
Q

Describe the issues with reactivity and the bromine test with kekules structure

A

If benzene had 3x C=C it should decolourise bromine, it does not suggesting no double bonds
Benzene is much less reactive than equivalent alkenes - doesn’t take part in electrophilic addition.

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9
Q

Describe the issues with isomers with kekules structure

A

If Kekules model is correct there should be 4 isomers however there are only 3 found to exist.
Suggests bonds in benzene are the same and not different

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10
Q

Describe the issues with bond length with kekules structure
What was used to discover this

A

C-C bond length = 0.153nm
C=C bond length = 0.134nm
In Benzene all bond lengths = 0.139nm

They are all the same (intermediate bonding) and this was determined using x-ray crystallography.

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11
Q

Describe the issues with enthalpy changes with kekules structure
Use numbers

A

The model predicts an enthalpy change of hydrogenation to the equivalent for 2x C=C: -360 KJ mol-1

Actual enthalpy change = -208 kj mol-1

Meaning the change is lower by 152kj mol-1

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12
Q

Describe the new benzene model
Draw it

A

After all sigma bonds have formed there is one electron in each p orbital.
One large pi bond forms from all 6 electrons, three above and three below the atom.
6 electrons form a delocalised pi bond.

Check drawing on oneNote

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13
Q

How does the new model agree with the bromine test and reactivity

A

There are no individual C=C bonds so less reactivity or addition reaction with bromine

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14
Q

How does the new model agree with isomers

A

3 not 4 isomers as there is now no difference in the arrangement of electrons between these atoms

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15
Q

How does the new model agree with bond length

A

The carbon-carbon bonds are now all the same length as they are not individual c-c or c=c

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16
Q

How does the new model agree with enthalpy

A

As charge is spread around the species there is an increased stability explaining why benzene has a greater stability.
2 electron clouds, delocalised electrons cause charge to spread around the species.

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17
Q

Why does a reaction with Br2 only let one Br bond to benzene

A

As it preserves the stability of the delocalised electrons in the pi bonds.

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18
Q

What does aromatic mean
And does it apply
Draw the new structure

A

A cyclical structure in chemistry
Yes
Check on OneNote

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19
Q

List the general reactions of benzene

A

Hydrogenation
Combustion

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20
Q

Equation for the hydrogenation of benzene
What is the product called
Draw the new structure

A

C6H6 + 3H2 —> C6H12
Cyclohexane
Check drawing on oneNote

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21
Q

Conditions for the hydrogenation of benzene

A

Benzene and hydrogen react under reflux with a nickel catalyst

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22
Q

Equation for the combustion of benzene

A

C6H6 + 7 1/2 O2 —> 6CO2 + 3H2O

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23
Q

Conditions and observations - why

A

Burning in oxygen
Burns with a smoky flame due to high C to H ratio

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24
Q

List the substitution reactions of benzene

A

Bromination
Nitration
Sulfonation

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25
Q

Equation to form the electrophile for the bromination of benzene

A

AlCl3 + Br2 —> Br+ + AlCl3Br-

26
Q

Equation for the reaction between bromine and benzene

A

C6H6 + Br2 —> C6H5Br + HBr

27
Q

Equation to form the inorganic product within the bromination of benzene
Which product can be reused

A

AlCl3Br- + H+ —> AlCl3 + HBr
AlCl3

28
Q

Conditions for the bromination of benzene

A

In the presence of UV light, heated under reflux in the presence of a halogen carrier catalyst (AlCl3)

29
Q

Examples of halogen carrier catalysts

A

AlCl3, AlBr3, FeCl3, FeBr3

30
Q

Draw the mechanism for the bromination of benzene

A

Check on OneNote

31
Q

Nitration equation for the formation of the nucleophile

A

HNO3 + 2H2SO4 —> NO2+ + 2HSO4- + H3O+

32
Q

Nitration equation for the formation of the organic product

A

C6H6 + NO2+ —> C6H5NO2 + H2O

33
Q

Nitration equation for the formation of the inorganic product
What is done with the product of this equation

A

HSO4- + H+ —> H2SO4
It is reused

34
Q

Conditions for the nitration of benzene

A

Warming benzene with a mixture of concentrated nitric and sulfuric acids.
Sulfuric acid acts as a catalyst.

35
Q

Draw the mechanism for the nitration reaction with benzene

A

Check oneNote

36
Q

Write the equation for the sulfonation of benzene

A

C6H6 + SO3 —> C6H5SO3H

37
Q

Conditions for the sulfonation of benzene
Why

A

Fuming sulfur acid.
It is a solution of sulfur trioxide (SO3) dissolved in sulfuric acid

38
Q

Draw the mechanism for the sulfonation of benzene

A

Check on OneNote

39
Q

What type of reactions are alkylation and acylation of benzene

A

Friedel-crafts reactions

40
Q

What are the features of friedel-crafts reactions

A
  • One hydrogen atom in benzene is substituted by a reagent and the other is a HX product
  • A catalyst is needed - often aluminium chloride, iron chloride or iron bromide.
  • Anhydrous conditions are needed because water would react with the catalyst and sometimes with the organic product
41
Q

What are the two friedel-crafts reactions with benzene

A

Alkylation
Acylation

42
Q

What is the equation for the formation of the electrophile in alkylation

A

AlCl3 + CH3Cl —> CH3 + + AlCl4 -

43
Q

What is the equation for the alkylation of benzene

A

C6H6 + CH3+ —> C6H5CH3 + H+

44
Q

What is the reaction for the formation of the inorganic products in the alkylation of benzene

A

AlCl4- + H+ —> AlCl3 + HCl

45
Q

What are the conditions for alkylation of benzene

A

A halogenoalkane
Anhydrous conditions
Catalyst of aluminium chloride

46
Q

Equation for the formation of the electrophile for the acylation of benzene

A

AlCl3 + CH3COCl —> CH3CO + + AlCl4 -

47
Q

Equation for the acylation of benzene

A

C6H6 + RCO+ —> C6H5RCO + HCl + AlCl3

48
Q

Equation for the formation of the inorganic products in the acylation of benzene

A

AlCl4 - + H+ —> AlCl3 + HCl

49
Q

Conditions for the acylation of benzene

A

anhydrous
Acyl chloride
AlCl3 catalyst

50
Q

Mechanism for the alkylation of benzene

A

Check oneNote

51
Q

Mechanism for the acylation of benzene

A

Check oneNote

52
Q

What is reused at the end of acylation and alkylation of benzene

A

AlCl3

53
Q

Formula for phenol

A

C6H5OH

54
Q

Draw phenol

A

Check OneNote

55
Q

Equation for the bromination of phenol

A

C6H5OH + 3Br2 —> C6H2OHBr3 + 3HBr

56
Q

Conditions for the bromination of phenol

A

Room temperature
Without a catalyst

57
Q

Giver the name of the organic product form the bromination of phenol

A

2,4,6 - tribromophenol

58
Q

Why does the bromination of phenol occur more readily than the bromination of benzene

A
  • The oxygen in the OH has lone pairs of electrons which can merge with the electrons in the delocalised pi bonds.
  • The electron density above and below the ring of atoms is increased - ‘activation’ occurs because the molecule is now much more reactive towards the electrophile.
  • Bromine molecules are polarised as they approach the benzene ring. The Br-Br bond breaks and the Br+ electrophile attacks the benzene rings.
59
Q

Draw a mechanism for the bromination of phenol

A

Check OneNote

60
Q

What are 2 ways in which phenol is used

A

Manufacture of polymers and pharmaceuticals

Organic 2 (10 decks)

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