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Alevel Chemistry OCR A > Module 6: Aromatic Chem > Flashcards

Module 6: Aromatic Chem Flashcards

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1
Q

Structure of benzene
What is benzene’s formula

A

C6H6

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2
Q

Structure of benzene
What is benzene basic structure

A

Six C atoms in a hexagonal ring with onto H atom bonded to each carbon atom
Molecule is planar

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3
Q

Structure of benzene
What is true to length of all bonds in benzene

A

All same length-intermediate between single and double bonds

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4
Q

Structure of benzene
How many sigma bonds does each C atom make with what

A

3 sigma bonds, 2 with C atoms, one with H atom

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5
Q

Structure of benzene
Where is the 4th unused electron on each C atom

A

In a p orbital perpendicular to plane of ring

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6
Q

Structure of benzene
What happens to the p orbital with unused electron

A

Overlaps with neighbouring p orbital forming a pi Bond

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7
Q

Structure of benzene
What is the overall result of pi bonds

A

Ring of negative charge above and below plane of the ring

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8
Q

Structure of benzene
What does the electrons in the pi system being delocalised mean

A

Do not belong to any particular C atom or bond and are free to move throughout whole pi system

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9
Q

Structure of benzene
Why is benzene molecule more stable

A

Electrons are delocalised and more spread out and will repel each other less

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10
Q

Structure of benzene
What is the electron density of the pi system

A

Low

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11
Q

Structure of benzene
What are the labels on a detailed benzene diagram

A

P orbitals
Sigma bonds
Pi bonds, electrons from p orbitals delocalise above and below the carbon ring =lower electron density

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12
Q

Structure of benzene
What are the bonding angles of benzene

A

120

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13
Q

Kekulés structure
What structure did kekule suggest

A

Six carbon ring joined by alternate single and double bonds

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14
Q

Kekulés structure
How many sigma bonds in keklule structure

A

12

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15
Q

Kekulés structure
Labels on kekule diagram

A

P orbitals
Sigma bonds
Pi bonds, sideways overlap of p orbitals= localised electrons between 2 carbon atoms = high electron density

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16
Q

Disproving kekulè model
3 pieces of evidence

A

C-C bond lengths
Addition reactions
Enthalpy of hydrogenation

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17
Q

Disproving kekulè model
Explain c-c bond length

A

All c-c bonds are same length in benzene between length of sing and double carbon bonds
If benzene was triene would expect three longer c-c single and three shorter c=c double

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18
Q

Disproving kekulè model
Explain addition reactions

A

Benzene does not readily undergo addition reactions (eg doesn’t decolourise bromine water)
If benzene was triene would expect it to ready undergo addition

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19
Q

Disproving kekulè model
Explain enthalpy of hydrogenation using numbers

A

Would expect triene to react with 3 H2 to form cyclohexane releasing 360 kj/mol of energy
Benzene only releases 208 kj/mol of energy showing benzene 152 kj/mol more stable
Extra stability due to delocalisation of electrons

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20
Q

Naming aromatics compounds
What groups are shown as prefixes to benzene

A

Alkyl groups, halogens and nitro groups

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21
Q

Naming aromatics compounds
Name with a C2H5 group monosubstutudted

A

Ethylbenzene

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22
Q

Naming aromatics compounds
Name with Cl monosubstituted

A

Chlorobenzene

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23
Q

Naming aromatics compounds
Name with NO2 monosubstituted

A

Nitrobenzene

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24
Q

Naming aromatics compounds
When does the benzene ring become the substituent

A

When ring is attached to alkyl group with functional group or alkyl chain with more than 7 carbon atoms

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25
Q

Naming aromatics compounds
What is the prefix when benzene ring is a substituent

A

Phenyl

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26
Q

Naming aromatics compounds
What are the three common exceptions just learn

A

Benzoic acid or benzenecarboxylic acid
Phenylamine (NH2 group )
Benzaldehyde (benzenecarbaldehyde)

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27
Q

Naming aromatics compounds
What happens when more than one substituent groups

A

Ring numbered like normal and use di, tri etc

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28
Q

Benzene reactions
What kind of reaction does benzene undergo

A

Electrophilic substitution

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29
Q

Benzene reactions
Why does benzene undergo electrophilic substitution

A

Electrons are in ring with lower electron density

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30
Q

Benzene reactions
Why can’t benzene undergo addition

A

Can’t induce a dipole

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31
Q

Benzene reactions
What are the three types of reactions benzene can undergo

A

Nitration
Halogenation
Friedal-crafts reactions

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32
Q

Nitration of benzene
What is the overall reaction

A

Benzene + HNO3 —> Nitrobenzene + H2O

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33
Q

Nitration of benzene
What are the conditions

A

Conc HNO3
Conc H2SO4
50’C

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34
Q

Nitration of benzene
Why are the conditions needed

A

As benzene cannot generate electrophiles so has to be given

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35
Q

Nitration of benzene
What is step 1 called

A

Generating electrophile

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36
Q

Nitration of benzene
What is the equation for generating the electrophile

A

HNO3 + H2SO4 —> NO2^+ + HSO4^- + H2O

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37
Q

Nitration of benzene
What is the electrophile and what is it called

A

NO2^+
Nitronium ion

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38
Q

Nitration of benzene
What acts as a catalyst

A

H2SO4

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39
Q

Nitration of benzene
What is step 2 called

A

Electrophilic substitution

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40
Q

Nitration of benzene
What is step 2

A

The reaction mechanism LEARN

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41
Q

Nitration of benzene
What is created at the end of step 2

A

Nitrobenzene and a H+ ion

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42
Q

Nitration of benzene
What is step 3 called

A

Regeneration of catalyst

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43
Q

Nitration of benzene
Equation for regeneration of catalyst

A

H^+ + HSO4^- —> H2SO4

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44
Q

Halogenation of benzene
What is the overall equation

A

Benzene + halogen —> halobenzene + hydrogen halide

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45
Q

Halogenation of benzene
Conditions for chlorine

A

AlCl3
Cl2
50’C

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46
Q

Halogenation of benzene
Equation to generate electrophile using chlorine

A

AlCl3 + Cl2 —> Cl^+ + AlCl4^-

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47
Q

Halogenation of benzene
What is AlCl3

A

Halogen carrier

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48
Q

Halogenation of benzene
What is the electrophile

A

Cl^+

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49
Q

Halogenation of benzene
What is the catalyst

A

AlCl3

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50
Q

Halogenation of benzene
What is the mechanism

A

LEARN

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51
Q

Halogenation of benzene
What are the the product of mechanism for chlorine

A

Chlorobenzene + H^+ ion

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52
Q

Halogenation of benzene
Regeneration of catalyst with Cl

A

AlCl4^- + H^+ —> HCl + AlCl3

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53
Q

Halogenation of benzene
Generation of electrophile using Br

A

FeBr3 + Br2 —> Br^+ + FeBr4^-

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54
Q

Halogenation of benzene
What is the electrp[hile when br

A

Br^+

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55
Q

Halogenation of benzene
What is FeBr3

A

Halogen carrier and catalyst

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56
Q

Halogenation of benzene
Products of mechanisms using br

A

Bromobenzene + H^+

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57
Q

Halogenation of benzene
Regeneration of catalyst using br equation

A

FeBr4^- + H^+ —>HBr + FeBr3

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58
Q

Friedal-crafts reactions
What are they useful for

A

Synthesis as is a way of adding C atoms onto an aromatic ring

59
Q

Friedal-crafts reactions
What are the two types

A

Alkylation
Acylation

60
Q

Friedal-crafts reactions alkylation
Overall reaction using Cl

A

Benzene + ClCH3 —AlCl3–> methyl benzene + HCl

61
Q

Friedal-crafts reactions alkylation
Conditions

A

Halogen carrier
Haloalkyl
Ether (dry solvent)
Room temp

62
Q

Friedal-crafts reactions alkylation
What is the catalyst

A

Halogen carrier

63
Q

Friedal-crafts reactions alkylation
Equation to generate electrophile

A

CH3Cl + AlCl3 —> AlCl4^- + CH3^+

64
Q

Friedal-crafts reactions alkylation
What is the electrophile

A

CH3^+

65
Q

Friedal-crafts reactions alkylation
What is the mechanism

A

LEARN

66
Q

Friedal-crafts reactions alkylation
What two products are produced in the mechanism

A

Methylbenzene + H^+

67
Q

Friedal-crafts reactions alkylation
Equation for regeneration of catalyst

A

H^+ + AlCl4^- —> HCl + AlCl3

68
Q

Friedal-crafts reactions acylation
What is an acyl group

A

Contains C=O double bond

69
Q

Friedal-crafts reactions acylation
What is produced when with an acyl chloride

A

Phenylketone or benzaldehyde

70
Q

Friedal-crafts reactions acylation
Overall equation

A

Benzene + acyl chloride —AlCl3-> phenylketone/benzaldehyde + HCl

71
Q

Friedal-crafts reactions acylation
Conditions

A

Halogen carrier
Reflux at 50’C
Acyl chloride
Ether(dry solvent)

72
Q

Purification of an organic solid
How can they be purified

A

Recrystallisation

73
Q

Purification of an organic solid
Basic concept of recrystallisation

A

Dissolve solid in a solvent to make e a saturated solution and let cool
As cools solubility of product falls and forms crystallises

74
Q

Purification of an organic solid
Steps in purification

A
  1. Very hot solvent added to impure solid until it just dissolves, don’t add too much
  2. Should give a saturated solution of impure product
  3. Solution left to cool slowly over ice , crystals of product form as it cools, impurities stay in solution, present in smaller amounts then product so takes much longer to crystallised
  4. Crystals removed by filtration under reduced pressure and washed with ice cold solvent
  5. Dried on watch glass leaving purer organic solid
75
Q

Purification of an organic solid
What does the solvent have to do to be appropriate

A

Only work if solid very soluble in hot solvent but Nearly insoluble when solvent cold

76
Q

Purification of an organic solid
What would happen if product not soluble enough in hot solvent

A

Won’t be able to dissolve it all all

77
Q

Purification of an organic solid
What will happen if product too soluble in cold solvent

A

Most of it will stay in solution even after cooling and when filter will lose product giving low yield

78
Q

Purification of an organic solid
What os used when filtering under reduced pressure

A

Büchner funnel with damp filter paper

79
Q

Purification of an organic solid
How is Buchner funnel set up

A

With damp filter paper and sealed side arm (hersh) flask connected to a vacuum line causing it to be under reduced pressure

80
Q

Purification of an organic solid
Labels needed on diagram of Büchner funnel

A

Pump
Hirch flask
Filter paper
Büchner funnel
Vacuum pump

81
Q

Purification of an organic solid
What does the reduced pressure do

A

Causes suction through the funnel which causes liquid to pass quickly into the flask leaving dry crystals of product

82
Q

Purification of an organic solid
What is done to check purity

A

Melting and boiling point checked as pure substances have very specific ones

83
Q

Purification of an organic solid
What happens to melting and boiling points ig impure

A

Melting point lowered and boiling point raised

84
Q

Purification of an organic solid
How is melting point accurately measured

A

Small amount put in capillary tube and tube gently tapped to get solid to fall to bottom
Tube placed in beaker of oil with sensitive thermometer
Slowly heated with constant stirring until solid just melted and read thermometer

85
Q

Purification of an organic solid
What do you do with measured melting point to check purity

A

Compare to known melting point of substances

86
Q

Phenol
What are phenols

A

Benzene rings with -OH group attached

87
Q

Phenol
What is the formula

A

C6H5OH

88
Q

Phenol
How do you name phenols with other groups substituted

A

Number carbons starting from the one with the -OH group

89
Q

Phenol
What mechanism does phenol undergo

A

Electrophilic substitution

90
Q

Phenol
Is phenol more or less likely to undergo electrophilic substitution then benzene

A

More likely

91
Q

Phenol
Why does phenols more readily undergo electrophilic substitution

A

One of lone pairs of electrons in p orbital of oxygen atoms overlaps with the delocalised ring of electrons in the benzene ring so partially delocalised into the pi system
This increases electron density of ring so is more likely to be attacked by electrophiles

92
Q

Phenol
What does this mean for reactions

A

Don’t require catalyst

93
Q

Phenol
What is phenol standard state

A

Almost colourless crystalline solid

94
Q

Phenol
What is phenol standard state

A

Almost colourless crystalline solid

95
Q

Phenol
Is phenol soluble

A

Yes

96
Q

Phenol
Why is it soluble

A

Can form hydrogen bonds

97
Q

Reactions of phenol
What does it produce in complete combustion

A

CO2 + H2O

98
Q

Reactions of phenol
Equation for complete combustion

A

C6H5OH + 7O2 —>6CO2 + 3H2O

99
Q

Reactions of phenol
What is observed for combustion

A

Sooty flame

100
Q

Reactions of phenol
Why is a sporty flame the observation for combustion

A

Incomplete combustion more likely due to high % of carbon

101
Q

Reactions of phenol
How can you test from phenol from benzene

A

Reaction with bromine water

102
Q

Reactions of phenol
What is observed from phenol and bromine water

A

Decolourises br2
White ppt

103
Q

Reactions of phenol
How is bromine used to test phenol from benzene

A

Phenol is more reactive so decolourises bromine but benzene does not

104
Q

Reactions of phenol
What is produced when reacted with bromine

A

2,4,6-tribromophenol

105
Q

Reactions of phenol
What can u smell when reacted with bromine

A

Antiseptic

106
Q

Reactions of phenol
What is the equation for phenol and bromine

A

Phenol + 3Br2 —> 2,4,6-tribromophenol + 3HBr

107
Q

Reactions of phenol
Equation for chlorine and phenol

A

Phenol + 3Cl2 —> 2,4,6-trichlorophenol + 3HCl

108
Q

Reactions of phenol
What is produced in nitration of phenol

A

Two isomers of nitrophenol and water

109
Q

Reactions of phenol
What two isomers are produced in nitration of phenol

A

2-nitrophenol
4-nitrophenol

110
Q

Reactions of phenol
What colour does phenol go in universal indicator

A

Orange

111
Q

Reactions of phenol
What ph does phenol have and what does this mean

A

3/4
Is a weak acids

112
Q

Reactions of phenol
What does phenol dissociate to form

A

Phenoxide ion and hydrogen ion

113
Q

Reactions of phenol
Equation four dissociation of phenol

A

Phenol <==> phenoxide ion + H+

114
Q

Reactions of phenol
What type fo reaction is phenol and sodium hydroxide

A

Neutralisation

115
Q

Reactions of phenol
Equation for phenol and sodium hydroxide

A

Phenol + NaOH —> C6H5O- Na+ + H2O

116
Q

Reactions of phenol
Does phenol react with sodium carbonate

A

No

117
Q

Reactions of phenol
Why doesn’t phenol react with Na2CO3

A

Not strong enough acid top displace O2

118
Q

Reactions of phenol
Why is phenol and acid

A

Partially delocalised electron and dipole in O-H bond so bond is weaker and easier to donate proton, H+

119
Q

Reactions of phenol
Equation for phenol with sodium

A

2Phenol + 2Na —> C6H5O- Na+ + H2(g)

120
Q

Reactions of phenol
What type of reaction is sodium and phenol

A

Redox

121
Q

Reactions of phenol
What is the salt produced on sodium and phenol called

A

Sodium phenoxide

122
Q

Reactions of phenol distinguishing acid
How does C6H5OH react with Na and CO3 2-

A

Effervescence from H2(g) with Na
No reaction with CO3 2-

123
Q

Reactions of phenol distinguishing acid
How does C4H9OH react with Na and CO3 2-

A

No reaction with either

124
Q

Reactions of phenol distinguishing acid
How does C4H9COOH react with Na and CO3 2-

A

Effervescence with both

125
Q

Reactions of phenol distinguishing acid
Strength is order for C6H5OH, C4H9OH, C4H9COOH

A

C4H9COOH strongest then C6H5OH then C4H9OH

126
Q

Reactions of phenol distinguishing acid
Dissociation of C4H9COOH

A

—> C4H9COO- + H+

127
Q

Reactions of phenol distinguishing acid
Why is C4H9COOHthe strongest

A

Pulls electrons away

128
Q

Reactions of phenol distinguishing acid
Dissociation of C6H5OH

A

<==> C6H5O- + H+

129
Q

Reactions of phenol distinguishing acid
Dissociation of C4H9OH

A

Doesn’t

130
Q

directing groups
when does directing effects happen

A

substitution of second groups on a benzene ring

131
Q

directing groups
what are directing groups

A

1st group directs positions of second substituted groups

132
Q

directing groups
why does the directing effect happen on substituted benzene rings

A

functional group can change electron density at certain carbon atoms making them more or less likely to react

133
Q

directing groups
what are the two types of directing groups

A

2- and 4-directing groups
3- directing groups

134
Q

directing groups
what types of groups are 2- 4- directing groups

A

activating groups
electron donating groups

135
Q

directing groups
why are electron donating groups 2- 4- directing

A

have electrons in orbitals that overlap with delocalised ring and increase its electron density in particular at carbons 2 4 and 6 so most likely to react at those postions

136
Q

directing groups
what are two most common 2- 4- directing groups

A

-OH
-NH2

137
Q

directing groups
possible positons names for electron donating groups

A

2-
2,4-di
4-
2,6-di

138
Q

directing groups what types of groups are 3- directing groups

A

deactivating groups
electron withdrawing groups

139
Q

directing groups
why are electron with drawing groups 3- directing

A

don’t have electrons in orbitals that are overlapping with the delocalised ring and is electronegative so withdraws electron density particularly withdrawing at carbons 2- 4- 6- unlikely to react here and has effect of direction electrophilic subsitittion at 3- 5- psotuons

140
Q

directing groups
what is common 3- directing group

A

-NO2

141
Q

directing groups
possible position names for electron withdrawing groups

A

3-
3,5-di

142
Q
A
143
Q
A

Alevel Chemistry OCR A (13 decks)

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