Topic 18 - Organic Chemistry III Flashcards
1
Q
What is the formula of benzene?
A
C₆H₆
2
Q
How can the structure of benzene be described?
A
It is cyclic.
3
Q
What are the two ways of representing the structure of benzene?
A
- Kekulé model
* Delocalised model
4
Q
Which of the models of benzene structure came first?
A
Kekulé model
5
Q
Describe the Kekulé model of benzene structure.
A
- Planar ring of 6 carbon atoms
- Alternating single and double bonds between carbons
- Each carbon is bonded to one hydrogen atom
- Single and double bonds are constantly switching over
6
Q
Describe how the Kekulé model can be drawn using skeletal formulae.
A
Hexagon with alternating single and double lines.
See diagram pg 205 of revision guide
7
Q
What are the two different structures of benzene in the Kekulé model referred to as?
A
Isomers
8
Q
Remember to practice drawing out the structure of benzene in the Kekulé model.
A
Pg 205 of revision guide
9
Q
Why was the Kekulé model for the structure of benzene shown to be incorrect?
A
- The model predicts that 3 of the bonds would be shorter (C=C) and 3 would be longer (C-C)
- X-ray diffraction showed that all the carbon-carbon bonds were of the same length, suggesting delocalisation
10
Q
Describe and explain the delocalised model of benzene structure.
A
- Planar ring of 6 carbon atoms
- Each carbon atom forms three σ-bonds -> 1 to a hydrogen atom, 1 to each of its neighbouring carbon atoms (these are due to head-on overlap of orbitals)
- Each carbon has one p-orbital that sticks out above and below the plane -> These overlap sideways to form a ring of π-bonds that are delocalised around the carbon ring
- The delocalised π-bonds are made of two ring-shaped clouds of electrons (above and below the plane)
- All the bonds in the ring are the same length
11
Q
In the delocalised model of benzene structure, how does the delocalised ring of electrons form?
A
- Each carbon has one remaining p-orbital that sticks out above and below the ring
- These p-orbitals overlap sideways to form two rings of π-bonds
- This is the delocalised ring of electrons
12
Q
Why are the electrons in the benzene ring said to be delocalised?
A
They don’t belong to a specific carbon atom.
13
Q
How is the delocalised ring of electrons represented in benzene?
A
A circle within the hexagon (although sometimes the structure is drawn as the Kekulé model)
14
Q
Describe how the delocalised model of benzene structure can be drawn using skeletal formulae.
A
Hexagon with a circle inside it.
15
Q
Remember to practise drawing out the structure of benzene in the delocalised model.
A
Pg 205 of revision guide
16
Q
Remember to revise the formation of a delocalised ring of electrons in benzene.
A
Diagram at bottom of pg 205 of revision guide.
17
Q
What is hydrogenation in alkenes?
A
When an alkenes reacts with hydrogen, so two hydrogen atoms add across the double bond.
18
Q
What is the enthalpy change of hydrogenation?
A
The enthalpy change when hydrogen reacts with an alkene.
19
Q
How many C=C bonds does cyclohexane have?
A
1
20
Q
What is the enthalpy of hydrogenation of cyclohexane?
A
-120kJ/mol
21
Q
Given that the enthalpy of hydrogenation of cyclohexane is -120kJ/mol, what would you expect the enthalpy be for the Kekulé structure of benzene?
A
3 x -120 = -360kJ/mol
22
Q
How does the expected enthalpy of hydrogenation of the Kekulé structure of benzene compare to the actual enthalpy of hydrogenation of benzene?
A
- The expected enthalpy for Kekulé structure is -360kJ/mol
- The actual enthalpy is -208kJ/mol
- This means that the structure must be more stable than predicted by Kekulé’s model
23
Q
Why is the expected enthalpy of hydrogenation of the Kekulé model of benzene more exothermic than the actual value?
A
The delocalised model of benzene is more stable, so more energy is required to overcome this, making the overall enthalpy less exothermic.
24
Q
What are the conditions in hydrogenation of benzene?
A
- Nickel catalyst
* 200°C
25
Does benzene easily undergo addition reactions? Why?
No, because:
• The delocalised ring of electrons is very stable
• The charge is so spread out in the delocalised ring
26
Why is benzene so stable?
The delocalised ring of electrons.
27
When will benzene undergo addition reactions?
When there is:
• Hot benzene
• UV light
28
Will bromine water be decolourised by cyclohexane and benzene?
* Cyclohexane - Yes
| * Benzene - No
29
What is the preferred reaction type of benzene?
Electrophilic substitution
30
What are some pieces of evidence for the delocalised model of benzene over the Kekulé model?
* Bond lengths (X-ray diffraction studies)
* Enthalpy changes of hydrogenation
* Reluctance to undergo addition reactions
31
Give the equation of benzene burning in air.
2C₆H₆ + 15O₂ -> 12CO₂ + 6H₂O
32
What is the type of flame when benzene is burnt in air?
Smoky, because there is insufficient oxygen to burn the benzene completely.
33
Why does combustion of benzene give a smokey flame?
Due to the high ratio of C to H in benzene.
34
What are aromatic compounds?
Compounds derived from benzene (i.e. that contain a benzene ring).
35
What are arenes?
Another name for aromatic compounds (those derived from a benzene ring).
36
What are the two ways of naming aromatic compounds?
1) Substituted benzene ring (e.g. NITRObenzene)
2) Compounds with a phenyl group attached (e.g. PHENol)
There is no easy way to tell which to use.
(See pg 207 of revision guide)
37
What is a phenyl group?
* C₆H₅
| * It is the name sometimes used when a benzene ring is attached onto a compound.
38
What are the rules for naming aromatic compounds with more than one functional group?
Number the carbons using these rules:
• If all the functional groups are the same, pick the group to start on that gives the smallest numbers when you count round
• If the functional groups are different, start from the functional group that gives the molecule its suffix and count the way round that gives the smallest numbers
39
When naming aromatic compounds, what are the rules used when all of the functional groups attached to the benzene are the same?
When numbering the carbons, start on the carbon that gives the smallest numbers when you count round.
40
When naming aromatic compounds, what are the rules used when the functional groups attached to the benzene are different?
When numbering the carbons, start from the functional group that gives the molecule its suffix and count the way round that gives the smallest numbers.
41
What is the name for chlorine attached to a benzene ring?
Chlorobenzene
42
What is the name for a nitro (NO₂) group attached to a benzene ring?
NITRObenzene
43
What is the name for a 2 methyl groups attached to a benzene ring (two carbons apart)?
1,3-dimethylbenzene
44
What is the name for a hydroxide group attached to a benzene ring?
Phenol
45
What is the name for an NH₂ group attached to a benzene ring?
Phenylamine
46
What is a the name for a benzene with these functional groups:
• CH₃
• 2 x NO₂ (1 and 3 carbons away from the CH₃)
2,4-dinitromethylbenzene
47
What is a the name for a benzene with these functional groups:
• CH₃
• OH (on adjacent carbons)
2-methylphenol
48
Remember to practise naming aromatic compounds.
Pg 207 of revision guide
49
When benzene undergoes electrophilic substitution, what is replaced by what?
A hydrogen is replaced by the electrophile.
50
What are the two steps of the mechanism for electrophilic substitution in benzene?
1) Addition of electrophile to form positively charged intermediate
2) Loss of H⁺ from the carbon atom attached to the electrophile
51
How is an electrophile symbolised in mechanisms?
E
52
Describe how to draw the mechanism for electrophilic substitution in benzene.
(NOTE: Electrophile must be generated first)
First step:
• Arrow goes from circle in benzene to E⁺
• Now there is an E and a H bonded to a single carbon. The circle has been replaced by a horseshoe that does not go beyond the adjacent carbons. There is a + charge in the middle.
Second step:
• Arrow goes from C-H bond to the positive charge in the ring
• The product is a benzene ring with E bonded to it, plus a H⁺ ion
53
Remember to practise drawing out the mechanism for electrophilic substitution in benzene.
See diagram pg 208 of revision guide
54
With arenes undergoing electrophilic substitution, what must you remember about the intermediate?
The horseshoe in the benzene ring cannot go beyond the two adjacent carbons to where to electrophile has attached.
55
What sort of electrophile is required to react with benzene and why?
A strong electrophile, because the negative charge density in benzene is spread out across the whole ring.
56
What can be used to make a stronger electrophile (for a reaction with a benzene ring)?
Halogen carriers
57
What are halogen carriers?
* Molecules that increase the polarisation in an electrophile, so much that sometimes a carbonation forms.
* This allows for the electrophile to be strong enough to react with a benzene ring
58
How does a halogen carrier work?
* Halogen carrier accepts a lone pair of electrons from the electrophile, polarising it more
* Sometimes a carbocation forms
* This makes the electrophile stronger
59
Give an example of a halogen carrier.
AlCl₃
60
An what molecules do halogen carriers work?
* Halogens
* Acyl chlorides
* Halogenoalkanes
61
Practice drawing out the mechanism by which a halogen carrier works.
Pg 208 of revision guide
62
What are some of the different halogen carriers?
* Aluminium halides
* Iron halides
* Iron
63
What reactions of benzene do you need to know about?
* Combustion
* Bromination
* Nitration (H₂SO₄ + HNO₃)
* Sulphonation (Fuming H₂SO₄)
* Alkylation (Friedel Crafts)
* Acylation (Friedel Crafts)
64
What is bromination of benzene?
The electrophilic substitution of a halogen for a hydrogen in a benzene ring
65
What is the catalyst for the bromination of benzene?
Iron(III) Bromide (FeBr₃)
66
What are the reactants and products of the bromination of benzene?
```
REACTANTS:
• Benzene
• Bromine
CATALYST:
• Iron(III) bromide (Halogen carrier catalyst)
PRODUCTS:
• Bromobenzene
• HBr
```
67
Describe the preparation of the electrophile in the bromination of benzene.
* Fe + 3/2Br₂ -> FeBr₃
* FeBr₃ + Br₂ -> [FeBr₄]⁻ + Br⁺
(The Br⁺ is the electrophile)
68
What are the conditions for the bromination of benzene?
* FeBr₃ catalyst (Hydrogen carrier)
| * RTP
69
Remember to practise drawing out the mechanism for bromination of benzene.
See diagram pg 208 of revision guide
70
What is the general name for the substitution of a halogen atom for a hydrogen atom in benzene?
Halogenation
71
What is alkylation of benzene?
The substitution of an alkyl group (e.g. CH₃CH₂) onto a benzene ring.
72
What are the two types of Friedel-Crafts reaction?
* Alkylation
| * Acylation
73
What is the catalyst in the alkylation of benzene?
Aluminium chloride (AlCl₃)
74
What are the reactants and products of the alkylation of benzene (with a normal alkyl electrophile)?
```
REACTANTS:
• Benzene
• Halogenoalkane
CATALYST:
• AlCl₃ catalyst (Hydrogen carrier catalyst)
PRODUCTS:
• Alkylbenzene
• HCl
```
75
Give the equation for the preparation of the electrophile in the alkylation of benzene.
R-Cl + AlCl₃ -> R⁺ + [AlCl₄]⁻
| Where R⁺ is the electrophile
76
Describe the mechanism for the generation of the electrophile in the alkylation of benzene.
```
1-step reaction:
• At the start, there is R-Cl and AlCl₃
• Arrow goes from R-Cl bond to the Cl
• Arrow goes from the lone pair on the Cl to the Al in the AlCl₃
• R⁺ and [AlCl₄]⁺ are produced
```
77
In the alkylation of benzene, what is the electrophile?
The carbocation generated when the halogen is lost from a halogenoalkane.
78
What are the conditions for the alkylation of benzene?
* AlCl₃ catalyst (Halogen carrier catalyst)
| * Heating under reflux
79
What is the general equation for alkylation of benzene?
C₆H₆ + R-X -> C₆H₅R + HX
| AlCl₃ catalyst + Heating under reflux
80
Remember to practise drawing out the mechanism for the alkylation of benzene with an electrophile containing an OAlCl₃⁻ group.
See diagram pg 209 of revision guide.
81
Remember to practise drawing out the mechanism for alkylation of benzene.
See diagram pg 209 of revision guide
82
Does Friedel-Crafts alkylation only happen with halogenoalkanes?
No, it can also happen with electrophiles containing OAlCl₃⁻ groups.
83
What other group do you need to know about that can be the electrophile in the alkylation of bromine?
The electrophile can be an alkyl chain containing an OAlCl₃⁻ group.
84
What is produced when the electrophile in alkylation of benzene contains an OAlCl₃⁻?
An alcohol containing a benzene ring.
85
What are the reactants and products of the acylation of benzene?
```
REACTANTS:
• Benzene
• Acyl chloride
CATALYST:
• AlCl₃ catalyst (Hydrogen carrier catalyst)
PRODUCTS:
• Phenylketones (or benzaldehyde)
• HCl
```
86
What is the exception to the products of the acylation of benzene?
* Most of the time, the organic product is a phenylketone
| * However, if R = H in RCOCl, then the organic product is an aldehyde called benzaldehyde
87
What is acylation of benzene?
The substitution of an acyl group (e.g. COCl) onto a benzene ring.
88
What is the catalyst in the acylation of benzene?
Aluminium chloride (AlCl₃)
89
Remember to practise drawing out the mechanism for acylation of benzene.
See diagram pg 209 of revision guide
90
In the acylation of benzene, what is the electrophile?
The carbocation generated when the chlorine is lost from the acyl chloride.
91
Describe the preparation of the electrophile in the acylation of benzene.
AlCl₃ + CH₃COCl -> CH₃C⁺O + [AlCl₄]⁻
92
Give the general equation for the preparation of the electrophile in the acylation of benzene.
R-COCl + AlCl₃ -> RCO⁺ + [AlCl₄]⁻
| Where R⁺ is the electrophile
93
Describe the mechanism for the generation of the electrophile in the acylation of benzene.
1-step reaction:
• At the start, there is R-COCl and AlCl₃
• Arrow goes from C-Cl bond to the Cl
• Arrow goes from the lone pair on the Cl to the Al in the AlCl₃
• RCO⁺ and [AlCl₄]⁺ are produced
94
In the acylation of benzene, what is the electrophile?
The carbocation generated when the chlorine is lost from an acyl chloride.
95
What are the conditions for the acylation of benzene?
* AlCl₃ catalyst (Halogen carrier catalyst)
| * Heating under reflux in dry ether
96
What is the general equation for acylation of benzene?
C₆H₆ + RCOCl -> C₆H₅COR + HCl
| AlCl₃ catalyst + Heating under reflux in dry ether
97
What is nitration of benzene?
Substitution of an NO₂ into the benzene ring.
98
What is the catalyst in the nitration of benzene?
Concentrated sulphuric acid
99
What are the reactants and products of the nitration of benzene?
```
REACTANTS:
• Benzene
• Concentrated sulphuric acid
CATALYST:
• Concentrated nitric acid
PRODUCTS:
• Nitrobenzene
• Water
```
100
In the nitration of benzene, what is the electrophile?
Nitronium ion (NO₂⁺)
101
Give the equation for the preparation of the electrophile in the nitration of benzene.
* HNO₃ + H₂SO₄ -> H₂NO₃⁺ + HSO₄⁻
* H₂NO₃⁺ -> NO₂⁺ + H₂O
(NO₂⁺ is the electrophile)
102
Describe the mechanism for the preparation of the electrophile in the nitration of benzene.
First step:
• There is the HO-NO-O (nitric acid) with a positive charge on the N, negative charge on the right O and 2 lone pairs on the left O
• There is the H-OSO₃H (sulphuric acid)
• Arrow goes from a lone pair on the O in the nitric acid to the H on the sulphuric acid
• Arrow goes from the same H-O bond to the S
• This produces H₂O⁺-NO-O and HSO₄⁻
Second step:
• Arrow goes from left O-N bond in the nitric acid to the positive O on the left
• Arrow goes from the right O to the same N-O bond on the right
• This produces O=N=O, H₂O and HSO₄⁻
103
What are the conditions for the nitration of benzene?
* Sulphuric acid catalyst
| * 50°C for benzene (lower temperatures for other benzenes)
104
What is the equation for the nitration of benzene?
C₆H₆ + HNO₃ -> C₆H₅NO₂ + H₂O
105
Remember to practise drawing out the mechanism for the nitration of benzene.
Pg 210 of revision guide
106
What bearing does temperature have on the nitration of benzene?
* At 50°C -> 1 NO₂ group is added
| * Above 50°C -> 2 NO₂ groups are added
107
When nitration of benzene happens above 50°C, at what position is the extra NO₂ group added and why?
* In the 3rd position (2 carbons away from the first NO₂)
| * Due to the electron withdrawal due to the extra NO₂ group
108
How many times can nitration of benzene occur?
Twice - the ring is too stable for more NO₂ groups.
109
What is the name for adding just one nitro group to a benzene?
Mononotration
110
What is sulphonation of benzene?
Substitution of the SO₃H group onto the benzene ring.
111
What are the reactants and products in the sulphonation of benzene?
```
REACTANTS:
• Benzene
• SO₃
• Sulphuric acid
PRODUCTS:
• Benzesulphonic acid (C₆H₅SO₃H)
```
112
What is fuming sulphuric acid?
Mixture of:
• Concentrated H₂SO₄
• SO₃
It is used in the sulphonation of benzene.
113
In the sulphonation of benzene, what is the electrophile?
SO₃
114
Why can SO₃ act as an electrophile in electrophilic substitution in benzene?
Because the S is so positive due to the oxygens.
115
What are the conditions for the sulphonation of benzene?
* Fuming sulphuric acid (H₂SO₄ + SO₃)
| * Heat
116
What is the equation for the sulphonation of benzene?
C₆H₆ + H₂SO₄ -> C₆H₅SO₃H + H₂O
OR
C₆H₆ + SO₃ -> C₆H₅SO₃H
117
What is the name of the product of the sulphonation of benzene?
Benzesulphonic acid
118
In sulphonation of benzene, where does the extra H on the OH of the benzesulphonic acid product come from?
* It is the hydrogen that is being substituted
| * This is because the hydrogen does not have to be used to regenerate the catalyst like in other reactions
119
Remember to practise drawing out the reaction mechanism for the sulphonation of benzene.
See diagram online or pg 11 of booklet 5.4
120
What is a phenol?
A benzene ring with an OH group attached
121
What is the formula of phenol?
C₆H₅OH
122
What is the name for a benzene ring with these functional groups:
• OH
• Cl (opposite the OH group)
4-chlorophenol
123
What is the name for a benzene ring with these functional groups:
• OH
• NO₂ (opposite the OH)
4-nitrophenol
124
What is the result of phenol being more reactive than benzene?
It is more likely to undergo electrophilic substitution.
125
What is the name for a benzene ring with these functional groups:
• OH
• 2 x CH₃ (1 and 3 carbons away from the OH)
2,4-dimethylphenol
126
What happens when the product of the sulphonation of benzene is reacted with sodium hydroxide?
It forms a salt and water.
-SO₃H -> -SO₃Na + H₂O
127
What is more reactive, benzene or phenol? Why?
Phenol, because:
• One of the lone pairs of the O in the OH overlaps with the delocalised π-bonds in the benzene
• So the lone pair of electrons from the oxygen is partially delocalised into the π-system
• This increases the electron density of the ring, making it more likely to be attacked by electrophiles
128
When naming a phenol, where does numbering of the carbons start?
The -OH carbon is number 1.
129
Describe the two reactants in the production of aspirin.
* Salicylic acid
| * Ethanoic anhydride
130
Describe the structure of salicylic acid.
* Phenol ring
* -COOH group is attached to the carbon next to the -OH on the phenol
This is a phenol derivative.
(See diagram pg 211 of revision guide)
131
Describe the structure of ethanoic anhydride.
CH₃CO-O-COCH₃
This is a symmetrical molecule.
(See diagram pg 211 of revision guide)
132
Write the word equation for the synthesis of aspirin.
Salicylic acid + Ethanoic anhydride -> Aspirin + Ethanoic acid
133
What type of reaction is the production of aspirin?
Esterification -> The reaction is essentially between an alcohol (the salicylic acid) and a carboxylic acid (ethanoic anhydride is similar).
134
Describe how aspirin can be synthesised.
1) Add some ethanoic anhydride and a few drops of phosphoric acid to salicylic acid in a test tube.
2) Warm the reaction mixture to 50°C and leave for 15 minutes.
3) Filter the crystals under reduced pressure.
4) Recrystallise the aspirin in a mixture of water and ethanol.
135
What are the conditions for the synthesis of aspirin?
* 50°C
| * Acid (e.g. phosphoric acid)
136
Remember to practise drawing out the displayed reaction for the formation of aspirin.
Pg 211 of revision guide
137
What is an amine?
A ammonia molecule (NH₃) where one or more of the hydrogen’s is replaced with an organic group.
138
What is the functional group for an anime?
-NR₂
Where R is an alkyl group or H.
139
What is a primary amine?
A molecule of NH₃ where only 1 of the H’s is replaced by an organic group.
140
What is a secondary amine?
A molecule of NH₃ where 2 of the H’s are replaced by organic groups.
141
What is a tertiary amine?
A molecule of NH₃ where all 3 of the H’s are replaced by organic groups.
142
What is the name for a nitrogen atom bonded to four alkyl groups?
Quaternary ammonium ion
| Positively charged
143
What are the two types of amine in terms of the attached groups?
* Aliphatic amines
| * Aromatic amines
144
What is the name and type of this molecule:
• Central N atom
• 2 x H attached to the N
• CH₃ attached to the N
Methylamine
| Primary amine
145
What is the name and type of this molecule:
• Central N atom
• H attached to the N
• 2 x CH₃ attached to the N
Dimethylamine
| Secondary amine
146
What is the name and type of this molecule:
• Central N atom
• 3 x CH₃ attached to the N
Trimethylamine
| Tertiary amine
147
What is the name and type of this molecule:
• Central N atom
• 4 x CH₃ attached to the N
Tetramethylamine ion
| Quaternary ammonium ion
148
What is the name and type of this molecule:
• Central N atom
• 2 x H attached to the N
• Benzene ring attached to the N
Phenylamine
(Primary amine)
(Note: This is called an aromatic amine)
149
When synthesising aspirin from salicylic acid and ethanoic anhydride, what is the by-product?
Ethanoic anhydride
150
What are the different ways in which an aliphatic amine can be produced?
1) Halogenoalkane + Ethanolic ammonia
2) Reducing a nitrile
(Note: These give a primary amine at first, but more halogenoalkane can be used to create other amines.)
151
Describe how an aliphatic amine can be produced from a halogenoalkane.
The halogenoalkane is made to react with an excess of ethanolic ammonia.
152
What is the problem with producing aliphatic amines from halogenoalkanes? How can this be overcome?
* It produces a mixture of primary, secondary and tertiary amines and quaternary ammonium salts
* This is because the N has a lone pair so it can take part in multiple nucleophilic substitution reactions, so more than one hydrogen is replaced
* This can be overcome by using an excess of ethanolic ammonia, which produces mostly primary amines. If a different type is needed, more halogenoalkanes can be added.
153
Describe how an aliphatic amine can be produced from a nitrile.
The nitrile can be reduced in 2 ways:
1) Using LiAlH₄ in dry ether, then dilute acid
2) Using H₂ gas with a Pt/Ni catalyst at high temperature and pressure
154
Describe how a nitrile can be reduced using lithium aluminium hydride.
It is reduced:
• In dry ether
• Followed by some dilute acid
This produces a primary aliphatic amine.
155
Give the general equation for reducing a nitrile using aluminium hydride.
R-CH₂-CN + 4[H] -> R-CH₂-CH₂-N-H₂
156
Describe how a nitrile can be reduced using hydrogen gas.
It is reduced:
• With a nickel/platinum catalyst
• At a high temperature and pressure
This produces a primary aliphatic amine.
157
Give the general equation for reducing a nitrile using hydrogen gas.
R-CH₂-CN + 2H₂ -> R-CH₂-CH₂-N-H₂
158
What is the name for reducing a nitrile using hydrogen and a catalyst at high temperature and pressure?
Catalytic hydrogenation
159
Which method of reducing a nitrile to a primary amine is better industrially?
* Catalytic hydrogenation
| * Because LiAlH₄ is too expensive to use in industry
160
Describe how an aromatic amine can be made.
* Heat a nitro compound, tin metal and concentrated HCl under reflux -> This produces a salt
* Add NaOH -> This produces the aromatic amine
161
What type of reaction is the production of amines?
Reduction
162
What is the most basic aromatic amine?
Phenylamine
163
Describe the structure of phenylamine.
Benzene ring with NH₂ group attached to it
164
When producing phenylamine from nitrobenzene, what is the by-product?
Water
165
Remember to practise drawing out the formation of phenylamine from nitrobenzene.
Pg 212 of revision guide
166
Describe briefly how you can produce phenylamine from benzene.
```
Benzene to nitrobenzene:
• Conc. HNO₃
+ Conc. H₂SO₄
• Under 55°
Nitrobenzene to phenylamine:
a) Sn + Conc. HCl + Heat
b) NaOH solution
```
167
When producing an aromatic amine, why is NaIH added?
This converts the product from a salt to an amine.
168
Are amines acids or bases? Why?
Weak bases because they accept protons.
169
How can amines accept protons?
* The N in the middle has a lone pair of electrons
| * This allows it to make a dative covalent bond with an H⁺ ion
170
What determines how strong of a base an amine is?
* It depends on the availability of the electrons to form dative covalent bonds with a H⁺ ion
* This depends on the electron density around the N, which depends on the attached groups
171
Describe and explain the order of amines in terms of their strength as bases.
Weakest bases: Primary aliphatic bases
• The benzene ring draws electrons towards itself
• The nitrogen lone pair gets partially delocalised onto the ring, so the electron density on the nitrogen decreases
• So the lone pair is less available to form a dative covalent bond with a H⁺
Middle base: Ammonia
Strongest bases: Primary aliphatic amines
• The alkyl group pushes electrons towards the nitrogen
• The electron density on the nitrogen increases
• So the lone pair is more available to form a dative covalent bond with a H⁺
172
What type of molecule are amines in terms of reactions?
Nucleophiles (due to the lone pair on the N)
173
Can amines react with acids or bases?
Acids
174
What happens when an acid reacts with an amine?
An ammonium salt is produced.
175
CH₃CH₂CH₂CH₂NH₂ + HCl ->
CH₃CH₂CH₂CH₂NH₂ + HCl -> CH₃CH₂CH₂CH₂NH₃⁺Cl⁻
176
Describe and explain the solubility of amines.
Small amines:
• Soluble
• Because the amine group can form hydrogen bonds with the water molecules
Larger amines:
• Less soluble
• The London forces between the amine molecules are greater and require more energy to overcome, so dissolving is not energetically viable
177
How does the solubility of amines change as they increase in size?
The larger the amine, the less soluble.
178
Describe what happens when an amine dissolves.
An alkaline solution is formed, containing:
• Alkyl ammonium ions
• Hydroxide ions
179
CH₃CH₂CH₂CH₂NH₂(aq) + H₂O(l) ->
CH₃CH₂CH₂CH₂NH₂(aq) + H₂O(l) -> CH₃CH₂CH₂CH₂NH₃⁺(aq) + OH⁻ (aq)
180
What complex ions are formed in copper(II) sulfate solution?
[Cu(H₂O)₆]²⁺
181
What is the colour of copper(II) sulfate solution?
Blue
182
Describe and explain what happens when butylamine is added to copper(II) sulfate solution.
Small amount of butylamine:
• The amine acts as a base and takes two H⁺ ions from the [Cu(H₂O)₆]²⁺ complexes
• This gives a pale blue precipitate of copper hydroxide [Cu(OH)₂(H₂O)₄]
With excess butylamine:
• The precipitate dissolves to form a deep blue solution
• Some of the ligands are replaced by the butylamine to give [Cu(CH₃(CH₂)₃NH₂)₄(H₂O)₂]²⁺
183
Describe the colour changes when an amine is added to an aqueous solution of copper ions (such as copper(II) sulphate).
* Starts are blue solution of [Cu(H₂O)
* When some amine is added, pale blue precipitate of [Cu(OH)₂(H₂O)₄] forms
* When excess amine is added, this dissolves and a deep blue solution forms when some of the ligands are replaced by the amine (e.g. [Cu(CH₃(CH₂)₃NH₂)₄(H₂O)₂]²⁺)
184
Remember to practise drawing out the displayed equations for the addition of butylamine to copper(II) sulfate solution.
Pg 213 of revision guide
185
Do all amines form the same complex with copper(II) ions?
The colours will be the same, but the final product may change because as many of the larger amine molecules may not fit around the copper ion.
186
How can other amines be formed from primary amines?
Reacting with a halogenoalkane.
187
Describe and explain the reaction type when:
• Forming a primary amine from a halogenoalkane
• Forming another amine from a primary amine
* Both are nucleophilic substitution
* Because the N in the ammonia or the primary amine has a lone pair
* This means it can act as a nucleophile and it attracted to the δ+ carbon in the halogenoalkane
188
How can an N-substituted amide by formed from a primary amine?
Reacting with an acyl chloride.
189
What type of reaction is a primary amine reacting with an acyl chloride?
Acylation
190
What is an acyl group?
RCO
191
Describe what happens when an acyl chloride reacts with a primary amine.
Stage 1:
• The acyl chloride and primary amine react to give the N-substituted amide and HCl
(This is what you memorise in the synthesis pathway)
Stage 2:
• The primary amine also reacts with the HCl to give a salt
(See of 214 of revision guide)
192
Remember to practise drawing out the displayed reaction of ethanoyl chloride and butylamine.
Pg 214 of revision guide
193
What amide and salt are ultimately produced when ethanoyl chloride reacts with butylamine?
* N-butyl ethanamide
| * Butylammonium chloride
194
Primary amine + Acyl chloride ->
Primary amine + Acyl chloride -> Amide + Salt
195
Remember to practise naming ammonium salts.
Pg 214 of revision guide
196
How is the reaction between an amine and acyl chloride carried out in a lab?
The acyl chloride is added to a concentrated aqueous solution of the amine.
197
What change is seen when ethanoyl chloride reacts with butylamine?
Solid, white mixture of products.
198
Write the chemical equation for the reaction between ethanoyl chloride and butylamine.
CH₃COCl + 2C₄H₉NH₂ -> CH₃CONHC₄H₉ + [C₄H₉NH₃]⁺Cl⁻
199
What are amides derivatives of?
Carboxylic acids
200
What is the functional group of amides?
-CONH₂
201
Why do amides behave differently to amines?
The carbonyl group in amides pulls the electrons away from the rest of the -CONH₂ group.
202
What are the two types of amide?
* Primary amide
| * N-substituted amide
203
What is the difference between a primary amide and N-substituted amide?
```
Primary amides have around the N:
• COR group
• 2 x H atom
N-substituted amides have around the N:
• COR group
• At least one alkyl group instead of an H
```
(i.e. In an N-substituted amide, at least one of the H’s is substituted by an R group)
204
What suffix do amide have?
-amide
205
How can you name a primary amide?
* Stem of the carbon chain
| * Followed by -amide
206
How can you name an N-substituted amide?
* Prefix to describe the R group on the N -> N-alkyl-
* Followed by the stem of the carbon chain
* Followed by -amide
207
Remember to practise naming amides.
Pg 215 of revision guide.
208
How can a primary amide be formed?
Reacting an acyl chloride with ammonia at RTP.
209
How can an N-substituted amide be formed?
Reacting an acyl chloride with a primary amine at RTP.
210
What is produced when ethanoyl chloride reacts with ammonia?
Ethanamide + HCl
211
What is produced when ethanoyl chloride reacts with methylamine?
N-methylethanamide + HCl
212
Break down the name: N-ethylpropanamide
* N-ethyl -> There is an ethyl group attached to the N
* propanamide -> There is a propane carbon chain attached to the N with the C=O group on the adjacent carbon
Therefore, there must also be a H attached to the N.
213
What types of molecules does condensation polymerisation usually involve?
* Two different types of monomer
| * Each monomer has at least two functional groups
214
How does condensation polymerisation work?
* There are two adjacent molecules, usually each with a functional group at each end
* The functional groups react with each other creating polymer chains
* This releases water
215
What are the different types of condensation polymer you need to know about?
* Polyamides
* Polypeptides
* Polyesters
216
What molecules join to give a polyamide?
* Dicarboxylic acid
| * Diamine
217
What is the name for the bonds formed in a polyamide?
Amide links
218
Describe the structure of an amide link in a polyamide.
-CO-NH-
219
Give the general structure of a polyamide.
-R-CO-NH-R₁-NH-CO-
220
Describe how a polyamide is formed.
* A dicarboxylic acid and diamine are next to each other
* An OH is lost from the -COOH and a H is lost from the NH₂, so overall H₂O is lost
* This produces an amide link
* This can happen at each end of the molecule to give a long chain
221
Remember to practise drawing out how a polyamide is formed.
Pg 216 of revision guide
222
What is the name for the bonds formed in a polypeptide?
Peptide links
223
Describe the structure of a peptide link.
-CO-NH-
224
Describe the general structure of a polypeptide.
-CH(R)-CO-NH-CH(R₁)-CO-NH-
225
Describe how a polypeptide is formed.
* Two amino acids are next to each other
* An OH is lost from the -COOH and a H is lost from the NH₂, so overall H₂O is lost
* This produces a peptide link
* This can happen at each end of the molecule to give a long chain
226
How can you break down a protein into amino acids?
* Add hot aqueous 6mol/dm³ HCl
* Reflux for 24hrs -> This produces ammonium salts
* Neutralise using a base
227
How can you determine the amino acids a protein is made out of?
* Hydrolyse it (6mol/dm³ HCl, reflux for 24hrs)
| * Use chromatography to identify the amino acids
228
Remember to practise drawing out how a polypeptide is formed.
Pg 216 of revision guide
229
What is the difference between polypeptides and polyamides?
Polypeptides are really polyamides.
230
What molecules join to give a polyester?
* Dicarboxylic acid
| * Diol
231
What is the name for the bonds formed in a polyester?
Ester link
232
Describe the structure of an ester link.
-CO-O-
233
Describe the general structure of a polyester.
-R-CO-O-R₁-O-CO-
234
Describe how a polyester is formed.
* Dicarboxylic acid and diol are next to each other
* An OH is lost from the -COOH and a H is lost from the OH, so overall H₂O is lost
* This produces an ester link
* This can happen at each end of the molecule to give a long chain
235
Remember to practise drawing out how a polyester is formed.
Pg 216 of revision guide
236
How can you find the monomers a polymer is made of?
1) Find the amide or ester link. Break it down the middle.
| 2) Add a H or OH to both ends of both molecules to find the monomers.
237
Remember to practise joining monomers to give a condensation polymer.
Pg 217 of revision guide
238
Describe the structure of an amino acid.
```
Central carbon surrounded by:
• Carboxyl group (COOH)
• Amino group (NH₂)
• R group
• H atom
```
239
What is the term for a molecule having both acidic and basic properties?
Amphoteric
240
What makes amino acids amphoteric?
They have:
• Carboxyl group -> Acidic
• Amino group -> Basic
241
What type of amino acids are found in nature?
* 2-amino acids
| * Where the amino group is on carbon-2 (the carboxyl group is always carbon-1)
242
What can amino acids exist as?
Zwitterions
243
What is a zwitterion?
An overall neutral molecule that has both a positive and negative charge in different parts of the molecule.
244
When can an amino acid exist as a zwitterion?
* Near its isoelectric point
| * This is the pH where the overall charge on the amino acid is 0
245
What is the isoelectric point of an amino acid?
The pH where the overall charge on the amino acid is 0.
246
Is the isoelectric point the same for all amino acids?
No, it depends on their R group.
247
What happens to amino acids in conditions more acidic than the isoelectric point?
* The -NH₂ group is protonated, making it -NH₃⁺.
* The -COOH group is unchanged.
(See diagram of 218 of revision guide)
248
What happens to amino acids at the isoelectric point?
* The -NH₂ group is protonated, making it -NH₃⁺.
* The -COOH group loses its proton, making it -COO⁻.
* This is now a zwitterion.
(See diagram of 218 of revision guide)
249
What happens to amino acids in conditions more alkaline than the isoelectric point?
* The -NH₂ group is unchanged.
* The -COOH group loses its proton, making it -COO⁻.
(See diagram of 218 of revision guide)
250
Which amino acids will exist as zwitterions when dissolved in solution and will have a pH around 7?
Those with the same number of carboxyl groups as amino groups.
251
What can be said about the optical activity of amino acids?
They are often chiral and therefore have two optical isomers.
252
What is the 3D structure of an amino acid?
Tetrahedral around the carbon.
253
What is the exception to the optical activity of amino acids?
* Glycine
* The R group is just a hydrogen atom.
* So the molecule is not chiral, since there are two H’s around the central carbon.
* This means it won’t rotate plane-polarised light.
254
What molecules join to give a polypeptide?
Amino aicds
255
What two types of chromatography can be used to identify amino acids?
* Paper chromatography
| * Thin-layer chromatography
256
Remember to revise how to do paper chromatography for amino acids.
Pg 219 of revision guide
257
What is the formula for the Rf value in chromatography?
Rf = A / B = Distance travelled by spot / Distance travelled by solvent
258
How are spots of amino acid in paper chromatography made visible?
* Spraying ninhydrin to turn them purple
| * Dipping the paper into a jar containing a few crystals of iodine, which sublimes
259
What is thin-layer chromatography?
The same as paper chromatography, except you use a plate covered in a thin layer of silica (SiO₂) or alumina (Al₂O₃) as the stationary phase.
260
What is the general formula for Grignard reagents?
RMgX
Where:
• R = Alkyl group
• X = Halogen
261
How is a Grignard reagent prepared?
Refluxing a halogenoalkane with magnesium in dry ether.
262
Give the general equation for the formation of a Grignard reagent.
R-X + Mg -> RMgX
| Note: This is done in dry ether!
263
Give the equation for the formation of a Grignard reagent from bromoethane and magnesium.
CH₃CH₂Br + Mg -> CH₃CH₂MgBr
| Note: This is done in dry ether!
264
What are the two things you can make from a Grignard reagent?
* Carboxylic acid
| * Alcohol
265
Describe how a carboxylic acid can be made from a halogenoalkane.
1) Grignard reagent is prepared by reacting the appropriate halogenoalkane with Mg in dry ether
2) CO₂ is bubbled through this
3) A dilute acid is added
266
When using Grignard reagents to product organic compounds, what is the byproduct?
MgX¹X²
Where:
• X¹ = Halogen from the halogenoalkane
• X² = Anion from the acid
267
Give the equation for a Grignard reagent (made from a bromoalkane) reacting to give a carboxylic acid.
R-MgBr + CO₂ -> R-COOH + MgBrCl
268
Describe how the reaction of a Grignard reagent with CO₂ to give a carboxylic acid works.
* A new C-C bond forms between the carbon atom in CO₂ and the C-Mg carbon in the Grignard reagent
* One of the C=O bonds in CO₂ breaks to form a -COO⁻ group
* This is then protonated by the dilute acid to form -COOH
269
Butanoic acid can be synthesised from bromopropane in three steps. Give the reagents and conditions needed for each step, and the product formed at each stage of the synthesis.
CH₃CH₂CH₂Br ——Mg, Dry ether)——> CH₃CH₂CH₂MgBr ——(1)CO₂, dry ether (2)Dilute HCl——> CH₃CH₂CH₂COOH + MgBrCl
270
Describe how a alcohol can be made from a halogenoalkane (not using aqueous KOH).
1) Grignard reagent is prepared by reacting the appropriate halogenoalkane with Mg in dry ether
2) Aldehyde or ketone (carbonyl compounds) are added
3) A dilute acid is added
271
Give the equation for a Grignard reagent (made from a bromoalkane) reacting to give an alcohol.
R-MgBr + R¹COR² -> CRR¹R²OH + MgBrCl
272
Describe how the reaction of a Grignard reagent with an aldehyde/ketone (carbonyl) to give an alcohol works.
* A new C-C bond forms between the carbon atom in C=O of the carbonyl and the C-Mg carbon in the Grignard reagent
* This causes the C=O bond to break
* The oxygen is then protonated by the dilute acid to form an -OH group
273
When a Gringard reagent reacts with an aldehyde, what is produced?
Secondary alcohol (except methanal)
274
When a Gringard reagent reacts with a ketone, what is produced?
Tertiary alcohol
275
Remember to practise drawing out Gringard reagent formation and reactions.
Pg 220 of revision guide
276
Give the full list of homologous series you have studied.
* Alkane
* Alkene
* Aromatic compounds
* Alcohol
* Halogenoalkane
* Amine
* Amide
* Nitrile
* Aldehyde/Ketone
* Carboxylic acid
* Ester
* Acyl chloride
277
For an alkane, give the:
• Functional group
• Properties
• Typical reactions
* Functional group -> C-C
* Properties -> Non-polar, Unreactive
* Typical reactions -> Radical substitution
278
For an alkene, give the:
• Functional group
• Properties
• Typical reactions
* Functional group -> C=C
* Properties -> Non-polar, Electron-rich double bond
* Typical reactions -> Electrophilic addition
279
For an aromatic compound, give the:
• Functional group
• Properties
• Typical reactions
* Functional group -> C₆H₅-
* Properties -> Stable, Delocalised ring of electrons
* Typical reactions -> Electrophilic substitution
280
For an alcohol, give the:
• Functional group
• Properties
• Typical reactions
* Functional group -> C-OH
* Properties -> Polar C-OH bond, Lone pair on O can act as nucleophile
* Typical reactions -> Nucleophilic substitution, Dehydration/Elimination, Esterification, Nucleophilic substitution (acting as the nucleophile)
281
For a halogenoalkane, give the:
• Functional group
• Properties
• Typical reactions
* Functional group -> C-X
* Properties -> Polar C-X
* Typical reactions -> Nucleophilic substitution, Elimination
282
For an amine, give the:
• Functional group
• Properties
• Typical reactions
* Functional group -> C-NH₂ / C-NR₂
* Properties -> Lone pair on N is basic and can act as a nucleophile
* Typical reactions -> Neutralisation, Nucleophilic substitution (acting as the nucleophile)
283
For an amide, give the:
• Functional group
• Properties
• Typical reactions
* Functional group -> -CONH₂ / -CONR₂
* Properties -> N/A
* Typical reactions -> N/A
284
For a nitrile, give the:
• Functional group
• Properties
• Typical reactions
* Functional group -> C-CN
* Properties -> Electron deficient carbon centre
* Typical reactions -> Reduction, Hydrolysis
285
For an aldehyde/ketone, give the:
• Functional group
• Properties
• Typical reactions
* Functional group -> C=O
* Properties -> Polar C=O bond
* Typical reactions -> Nucleophilic addition, Reduction, Oxidation (only aldehydes)
286
For a carboxylic acid, give the:
• Functional group
• Properties
• Typical reactions
* Functional group -> -COOH
* Properties -> Electron deficient carbon centre
* Typical reactions -> Neutralisation, Esterification, Reduction
287
For an ester, give the:
• Functional group
• Properties
• Typical reactions
* Functional group -> RCOOR¹
* Properties -> Electron deficient carbon centre
* Typical reactions -> Hydrolysis
288
For an acyl chloride, give the:
• Functional group
• Properties
• Typical reactions
* Functional group -> -COCl
* Properties -> Electron deficient carbon centre
* Typical reactions -> Nucleophilic addition-elimination, Condensation (lose HCl), Friedel-Crafts acylation
289
What is a synthetic route?
A series of reactions used to get from one compound to another.
290
If you’re asked how to make one compound from another in the exam (in multiple steps), what must you remember to include?
1) Any special procedures (e.g. refluxing)
2) Conditions (e.g. high temperature or pressure, or the presence of a catalyst)
3) Safety precautions (e.g. do it in a fume cupboard)
291
When chemists are planning a synthetic route, what is it important to keep in mind?
1) Stereoisomers
| 2) Safety
292
When chemists are planning a synthetic route, why is it important to keep stereoisomers in mind?
Different stereoisomers have different properties, which is important in the pharmaceutical industry.
293
When chemists are planning a synthetic route, why is it important to keep safety in mind?
To reduce the risk to the person doing the synthesis.
294
What are some examples of safety measures that can be taken in planning a synthetic route?
* Fume hoods to remove toxic gases
| * Water baths to heat solutions so there are no naked solutions near flammable reagents
295
Remember to practise drawing out the flowchart for the synthesis of aliphatic compounds.
Pg 222 of revision guide
296
Remember to practise drawing out the flowcharts for the synthesis of aromatic compounds.
Pg 223 of revision guide
297
What is combustion analysis used for?
Looking at information from burning an organic product in order to work out its empirical formula.
298
How can you work out the empirical formula of an organic compound (containing C, H and O) when you are told the mass of water and CO₂ produced when a given mass of it is burned?
1) Work out the moles of water and CO₂
2) Work out the moles of C and H in these
3) Work out the masses of C and H in the organic product, and therefore the remainder must be O
4) Work out the moles of O
5) Find the ratio of the moles of C, H and O
6) This tells you the empirical formula
300
How can you work out the molecular formula of an organic compound (containing C, H and O) when a given mass of it is burned with a known volume of oxygen and produced a known volume of water/CO₂?
* All gases at the same temperature and pressure have the same molar volume
* This means you can use the ratios of the gases as molar ratios
* This is used to work out the molecular formula of the organic compound since all of the C, H and O atoms in the products must be accounted for by this or the oxygen
301
30cm³ if hydrocarbon X combusts completely with 180cm³ oxygen. 120cm³ carbon dioxide is produced. What is the molecular formula of hydrocarbon X?
• The reaction can be written as:
30X + 180O₂ -> 120CO₂ + ?H₂O
• This simplifies to:
X + 6O₂ -> 4CO₂ + nH₂O
• 6 moles of O₂ = 12 O atoms. 8 of these are accounted for by the CO₂, so the remainder must be in the H₂O. Therefore, n = 4.
• So the equation is: X + 6O₂ -> 4CO₂ + 4H₂O.
• All of the carbons and hydrogen must come from the hydrocarbon, so the molecular formula must be C₄H₈.
302
When 7.2g of a carbonyl compound is burnt in excess oxygen, it produces 17.6g of carbon dioxide and 7.2g of water. Calculate the empirical formula for the carbonyl compound.
Stage 1
• No. of moles of CO₂ = 17.6 / 44.0 = 0.40 moles
• This means there are 0.40 moles of C
• No. of moles of H₂O = 7.2 / 18.0 = 0.40 moles
• This means there are 0.80 moles of H
Stage 2
• Mass of C = 0.40 x 12.0 = 4.8g
• Mass of H = 0.80 x 2.0 = 1.6g
• Mass of O = 7.2 - (4.8 + 1.6) = 0.10 moles
Stage 3
Molar ratio = C : H : O = 0.40 : 0.80 : 0.10 = 4 : 8 : 1
Empirical formula = C₄H₈O
