Topic 6a - Organic Chemistry I Flashcards
1
Q
What are the different types of formulas that can be used to represent a molecule?
A
- General formula
- Empirical formula
- Molecular formula
- Structural formula
- Skeletal formula
- Displayed formula
2
Q
What is a general formula?
A
- An algebraic formula that can describe any member of a family of compounds
- e.g. CnH2n
3
Q
What is an empirical formula?
A
- Simplest whole number ratio of atoms of each element in a compound
- e.g. CH3 for ethane
4
Q
What is a molecular formula?
A
- Actual number of atoms of each element in a molecule (by grouping all the atoms of each element together)
- e.g. C2H5O for ethanol
5
Q
What is a structural formula?
A
- Shows the arrangement of atoms carbon by carbon, with the attached hydrogens and functional groups
- e.g. CH3CH2OH
6
Q
What is a skeletal formula?
A
- Shows the bonds of the carbon skeleton only, with lines as C-C bonds
- Carbons and hydrogens are not shown, unless in a functional group, such as an OH
- e.g. See pg 70 of revision guide
7
Q
What is a displayed formula?
A
- Shows how all the atoms are arranged and all the bonds between them
- e.g. See diagram pg 70 of revision guide
8
Q
What is the difference between a molecular and structural formula?
A
- Molecular -> All the atoms are grouped together (e.g. C4H10O)
- Structural -> The arrangement of atoms is shows carbon by carbon (e.g. CH3CH2CH2CH2OH)
9
Q
What is the general formula for alcohols?
A
CnH2n+1OH
10
Q
What is the empirical formula for ethane?
A
CH3
11
Q
What is the molecular formula for butan-1-ol?
A
C4H10O
12
Q
What is the structural formal for butan-1-ol?
A
CH3CH2CH2CH2OH
13
Q
What is the skeletal formula for butan-1-ol?
A
4 zig-zag lines with an OH on the end
14
Q
What is the displayed formula for butan-1-ol?
A
See pg 70 of revision guide
15
Q
Remember to practise writing our for butan-1-ol: • General formula • Empirical formula • Molecular formula • Structural formula • Skeletal formula • Displayed formula
A
See table pg 70 of revision guide.
16
Q
What is nomenclature?
A
The naming of organic compounds.
17
Q
What is the system used for naming organic compounds called?
A
IUPAC system
18
Q
What are the steps in naming an organic compound?
A
1) Count the longest carbon chain -> This gives you the stem (e.g. prop-).
2) Find the main functional group -> This gives you the prefix or suffix (e.g. -ol).
3) Number the carbon chain so the main functional group has the lowest possible number. If there’s more than one longest chain, pick the one with the most side chains. -> This gives the number before the functional group (e.g. -2-ol)
4) Add side-chains and less important functional groups at the start of the name. Put them in alphabetical order (ignoring di, tri and tetra), after the number of the carbon they’re attached to.
5) If there’s more than one identical side-chain or functional group, use di-, tri- or tetra- before that part of the name.
19
Q
Remember to practice naming organic compounds.
A
Pg 70 of revision guide + find examples.
20
Q
Name: CH3CH(CH3)CH(CH2CH3)C(CH3)2OH
A
3-ethyl-2,4-dimethylpentan-2-ol
1) Longest chain is 5 carbons. So the stem is pent-.
2) Main functional group is -OH. So the name will be based on pentanol.
3) Numbering the longest carbon chain so that -OH has the lowest possible number (and you hae the most side chains) puts -OH on carbon 2. So it’s some sort of pentan-2-ol.
4) Side chains are the ethyl group on carbon 3, and methyl groups on carbons 2 and 4, so the systematic name is 3-ethyl-2,4-dimethylpentan-2-ol.
21
Q
When naming organic compounds, when there are two longest carbon chains of the same length, which do you use as the main chain?
A
The one with the most side-chains.
22
Q
What is a homologous series?
A
- A set of organic compounds with the same functional group and general formula.
- Consecutive members differ by a -CH2-.
23
Q
What things do members of a homologous series have in common?
A
- Functional group
* General formula
24
Q
How do members of a homologous series differ?
A
Consecutive members differ by a -CH₂-.
25
What is a functional group?
* A group of atoms in a molecule responsible for the characteristic reactions of that compound.
* e.g. -OH hydroxyl group
26
Is alkane a functional group?
* Usually, it is considered that alkanes have no functional group
* Some may claim that alkane is a functional group however
27
What is the functional group in alkenes?
The C=C bond.
28
What is the simplest homologous series?
Alkanes
29
What are the homologous series you need to know about?
* Alkanes
* Branched alkanes
* Alkenes
* Halogenoalkanes
* Alcohols
* Aldehydes
* Ketones
* Cycloalkanes
* Carboxylic acids
30
What is the prefix or suffix for alkanes?
-ane
31
What is the prefix or suffix for branched alkanes?
alkyl- (-yl)
| e.g. methyl
32
What is the prefix or suffix for alkenes?
-ene
33
What is the prefix or suffix for halogenoalkanes?
chloro-/bromo-/iodo-
34
What is the prefix or suffix for alcohols?
-ol
35
What is the prefix or suffix for aldehydes?
-al
36
What is the prefix or suffix for ketones?
-one
37
What is the prefix or suffix for cycloalkanes?
cyclo-...-ane
38
What is the prefix or suffix for carboxylic acids?
-oic acid
39
What is the homologous series of propane?
Alkane
40
What is the homologous series of methylpropane?
Branched alkane
41
What is the homologous series of propene?
Alkene
42
What is the homologous series of chloroethane?
Halogenoalkane
43
What is the homologous series of ethanol?
Alcohol
44
What is the homologous series of ethanal?
Aldehyde
45
What is the homologous series of propanone?
Ketone
46
What is the homologous series of cyclohexane?
Cycloalkane
47
What is the homologous series of ethanoic acid?
Carboxylic acid
48
Remember to practise recognising the different homologous series.
Pg 71 of revision guide.
49
What are the different types of reaction in organic chemistry?
* Addition
* Polymerisation
* Elimination
* Substitution
* Hydrolysis
* Oxidation
* Reduction
50
What is a species?
An atom, ion, radical or molecule.
51
What is a good catch all term for atoms, ions radicals and molecules?
Species
52
What is an addition reaction?
Joining two or more molecules together to form a larger molecule.
53
What is a polymerisation reaction?
Joining together lots of simple molecules to form a giant molecule.
54
What is an elimination reaction?
When a small group of atoms breaks away froma larger molecule.
55
What is a substitution reaction?
When one species is replaced by another.
56
What is a hydrolysis reaction?
Splitting a molecule into two new molecules by adding H+ and OH- derived from water.
57
What is an oxidation reaction?
Any reaction in which a species loses electrons.
58
What is a reduction reaction?
Any reaction in which a species gains electrons.
59
What is a reaction mechanism?
* A diagram used to break reactions down into individual stages to show how substances react together.
* Curly arrows may be used to to show where a pair of electron goes (not with radicals though, usually).
60
How are curly arrows used in reaction mechanisms?
* Arrow starts at the bond or lone pair where a pair of electrons are at the start of a reaction.
* Arrow points to where the new bond is formed or where the electrons go.
61
What's the differene between a reaction and a mechanism?
* Reaction just shows the reactants and products
| * Mechanism shows the different stages of a reaction, with the movement of electrons included
62
Are all ions included in a reaction mechanism?
No, if an ion isn't directly involve, it may not be included.
63
What are the different types of reaction mechanism?
* Free radical substitution
* Electrophilic addition
* Nucleophilic substitution
64
When does free radical substitution happen?
Substitution of halogens into alkanes to make halogenoalkanes.
65
When does electrophilic addition happen?
* Addition of hydrogen halides to alkenes to make halogenoalkanes.
* Addition of halogens to alkenes to make halogenoalkanes.
66
When does nucleophilic substitution happen?
* Substitution of primary halogenoalkanes with aqueous potassium hydroxide to make alcohols.
* Substitution of primary halogenoalkanes with ammonia to make amines.
67
Remember to revise the difference between a reaction and a mechanism.
See diagram about potassium hydroxide on pg 72 of revision guide.
68
What things must you consider when working out the type of reaction in a given organic reaction?
* First, consider whether it is addition, substitution, etc.
* Then work out whether the reacting species are nucleophiles, electrophiles or free radicals
* Put the two together to give the name
69
What is a nucleophile?
* Electron pair donor
* Negatively-charged ion or species with a lone pair of electrons
* Like to react with positive ions and positive regions
70
Give two types of nucleophile.
* Negatively charged ions (e.g. halide ions)
| * Species with a lone pair of electrons (e.g. oxygen atoms in water)
71
What do nucleophiles react with?
* Positive ions
| * d+ areas on molecules with polar bonds (e.g. the carbon d+ in carbon-halogen bonds)
72
Explain simply how nucleophilic substitution works.
* Nucleophiles are attracted to the carbon d+ atom in a polar carbon-halogen bond.
* Carbon-halogen bond breaks and the halogen takes both electrons.
* Nucleophile takes the halogen's place.
73
What is an electrophile?
* Electron pair acceptor
* Positively charged ion or d+ areas
* Like to react with negative ions, atoms with lone apirs and the electron-rich area in a C=C bond
74
Give two types of electrophile.
* Positively charged ions (e.g. H+)
| * d+ areas (hydrogen d+ in a hydrogen halide bond)
75
What do electrophiles react with?
* Negative ions
* Atoms with lone pairs
* Electron-rich area around a C=C bond
76
Explain simply how electrophilic addition works.
* Molecule with a polar bond (e.g. H-Br) is attracted by its d+ end to a C=C bond in an alkene
* This polarises the H-Br more until it breaks.
* Br receives electrons from the H-Br bond and H receives electrons from the C=C bond.
* This forms a carbocation, which reacts with the negative Br.
77
What is a radical?
* Species with an unpaired electron.
| * They are very reactive.
78
Give an example of a radical.
Cl•
79
What do radicals react with?
Everything, regardless of charge.
80
What is one of the only things that reacts with alkanes and why?
* Radicals
* Because radicals are the only things that attack stable non-polar bonds like C-C and C-H, unlike electrophiles and nucleophiles
81
Are radical substitution reactions useful for obtaining a pure product?
No, becasue there are lots of possible end reactions, so there is a mixture of products.
82
What are isomers?
Molecules with the same molecular formula but with differently arranged atoms.
83
What are the two types of isomers?
* Structural isomers
| * Stereoisomers
84
What are structural isomers?
Molecules with the same molecular formula, but with different structural formulae (a different bonding arrangement among the atoms).
85
What are the three types of structural isomer?
1. Chain isomers
2. Positional isomers
3. Functional group isomers
(See page 74 of revision guide)
86
What are chain isomers?
* When the carbon skeleton is arranged differently (in different isomers).
* e.g. Straight chain or branched carbon chains
87
Compare the chemical and physical properties of chain isomers.
* Similar chemical properties
| * Different physical properties -> Due to change in shape of the molecule
88
What are positional isomers?
* When the skeleton and functional groups are the same, but the functional group is attached to a differernt carbon atom (in different isomers).
* e.g. Butan-1-ol and butan-2-ol
89
Compare the chemical and physical properties of positional isomers.
* Chemical properties may be different
| * Different physical properties
90
What are functional group isomers?
* When the same atoms are arranged to give different functional groups (in different isomers).
* e.g. Butanoic acid and methylpropanoate
91
Compare the chemical and physical properties of functional group isomers.
* Different chemical properties
| * Different physical properties
92
What type of isomers are butane and methylpropane?
Chain isomers
| See pg 74 of revision guide
93
What type of isomers are butan-1-ol and butan-2-ol?
Positional isomers
| See pg 74 of revision guide
94
What type of isomers are butanoic acid and methylpropanoate?
Functional group isomers
| See pg 74 of revision guide
95
Remember to revise the different types of structural isomers.
Pg 74 of revision guide.
96
When looking at structural isomers, what must you be careful of?
Atoms can rotate around C-C bonds, so atoms around a single carbon can be rotated, making it appear as if the two combinations are isomers, when they're not.
(See diagrams pg 75 of revision guide).
97
What are alkanes?
* A homologous series of saturated hydrocarbons
| * With the general forumla CnH2n+2.
98
What are hydrocarbons?
Compounds containing only hydrogen and carbon atoms.
99
What is the formula for cycloalkanes?
CnH2n
| NOTE: This is different from normal alkanes.
100
What is the breaking of a covalent bond to give two species called?
Bond fission
101
What are the two types of bond fission?
* Homolytic
| * Heterolytic
102
What is heterolytic fission of a single bond?
* When the bond breaks unevenly so that one of the atoms receives both of the bonding pair of electrons, while the other gets none.
* Two different substances formed (e.g. anion and cation)
103
What is homolytic fission of a single bond?
* When the bond breaks evenly so that each of the atoms receives one electron from the bonding pair
* Two radicals are formed
104
Give an equation for heterolytic fission.
X-Y -> X+ + Y-
105
Give an equation for homolytic fission.
X-Y -> X• + Y•
106
How is the mechanism for heterolytic fission shown?
Double-headed arrow points from the bond to one of the two atoms.
107
How is the mechanism for homolytic fission shown?
Single-headed arrow points from the bond to each of the two atoms.
108
What makes radicals reactive?
They have an unpaired electron.
109
How are radicals shown?
With a • next to the species.
110
What is free radical substitution in alkanes?
When a hydrogen atom in an alkane is replaced by a halogen radical in the presence of UV light.
111
What is the name for the reaction of halogens with alkanes?
Photochemical reactions (started by light) -> This has a free radical substitution mechanism.
112
What are photochemical reactions?
Reactions that are started by light.
113
What is formed when halogens react with alkanes?
Halogenalkanes.
114
Under what conditions do halogens react with alkanes and why?
* UV light
| * This is needed to produce the radicals for free radical substitution
115
What type of reaction is the reaction between a halogen and alkane to give a halogenoalkane?
Free radical substitution
116
Give the equation and reaction type for chlorine reacting with methane.
CH4 + Cl2 ---UV---> CH3Cl + HCl
| This is free radical substitution.
117
What are the three stages of free radical substitution?
* Initiation
* Propagation
* Termination
118
What is the initiation stage of free radical substitution?
* Homolytic fission (of halogen) occurs
| * Free radicals are produced
119
What is the propagation stage of free radical substitution?
* Radicals are used up and created in a chain reaction
| * This continues until all of the halogen or alkane are used up
120
What is the termination stage of free radical substitution?
* Radicals are mopped up by reacting with each other to form stable molecules
* Lots of different possible reactions, since any radical can react with any radical
121
Give the full mechanism for chlorine reacting with methane in UV light.
```
INITIATION:
1) Cl2 -> 2Cl•
PROPAGATION:
1) Cl• + CH4 -> •CH3 + HCl
2) •CH3 + Cl2 -> CH3Cl + Cl•
TERMINATION:
1) Cl• + •CH3 -> CH3Cl
2) •CH3 + •CH3 -> C2H6
3) Other reactins are possible!
```
122
In the initiation stage of free radical substitution, what is the breaking of a halogen bond in UV light called?
Photodissociation (this is homolytic fission).
123
In free radical substitution, how many products are there?
There may be several.
124
When drawing the mechanismfor free radical substitution, what is it important to remember?
* It isn't usually drawn with displayed formulae and curly arrows.
* Instead, the equations are just written out (with perhaps the initiation having single-headed arrows).
125
Remember to practise writing out the mechanism for free radical substitution.
Pgs 76-77 of revision guide.
126
Why can free radical substitution produce many different products?
• Many different termination steps are possible.
AND
• An excess of the halogen can cause further propagation steps to happen, making new products (e.g. dichloromethane, trichloromethane, etc.)
AND
• Free radical substitution can happen along any point in a carbon chain -> So many structural isomers possible.
127
Explain what happens when methane reacts with *excess* chlorine in the presence of UV light.
* Normal reaction produces chloromethane.
* Then, propagation can happen again to make dichloromethane.
* Then, the dichloromethane can take part in propagation again to make trichloromethane.
* Finally, the trichloromethane can take part in propagation again to make tetrachloromethane -> This is now full of chlorine, without hydrogen.
128
Give the further propagation reactions to give dichloromethane and trichloromethane in the reation between chlorine and methane in UV light.
```
(First, chloromethane is produced)
DICHLOROMETHANE:
1) Cl• + CH3Cl -> •CH2Cl + HCl
2) •CH2Cl + Cl2 -> CH2Cl2 + Cl•
TRICHLOROMETHANE:
1) Cl• + CH2Cl2 -> CHCl2• + HCl
2) CHCl2• + Cl2 -> CHCl3 + Cl•
```
129
When reacting methane with chlorine to try and obtain chloromethane, what is the best way to reduce the chances of obtaining by-products (i.e. dichloromethane, etc.)?
Have an excess of methane, so there's a larger chance of a chlorine radical colliding with a methane molecule instead of a chloromethane molecule.
130
Name the major product formed when a large excess of bromine reacts with methane in the presence of UV light.
Tetrachloromethane
131
What is another name for crude oil?
Petroleum
132
What is crude oil?
A naturally ocurring petroleum product made of a mixture of hydrocarbons.
133
What is curde oil made of?
Hydrocarbons - mostly alkanes.
134
Is crude oil useful?
No, but it can be separated into its useful fractions.
135
By what process can crude oil be separated into fractions?
Fractional distillation
136
Describe how fractional distillation works.
1) Crude oil is vaporised at 350*C.
2) This goes into a fractionating column and rises up through the trays.
3) The largest hydrocarbons don't vaporise at all because of their high boiling points -> These run to the bottom and form a gooey residue (made of fuel oil, wax and bitumen).
4) As the vapour rises up through the column, it gets cooler. Because the alkane molecules have different chain lengths, they have different boiling points and so condense at different levels, where they're drawn off.
5) The hydrocarbons with the lowest boiling points don't condense -> They're drawn off as gases at the top of the column.
137
What is the piece of equipment used for fractional distillation of crude oil called?
Fractionating column
138
In the residue piped off at the bottom of the fractionating column, what fractions are present?
* Fuel oil
* Wax, Grease
* Bitumen
139
How many fractions of crude oil are there?
9
140
What are the 9 fractions of crude oil (from top to bottom)?
* Gas
* Petrol (gasoline)
* Naphtha
* Kerosene (paraffin)
* Gas oil (diesel)
* Mineral oil (lubricating)
* Fuel oil
* Wax, grease
* Bitumen
141
How does the boiling point and carbon chain length of hydrocarbons change from the bottom to the top of a fractionating column?
* Boiling point -> Gets lower.
| * Chain length -> Gets shorter.
142
What is the temperature at the bottom of a fractionating column?
350*C
143
```
Give the number of carbons in each of these fractions:
• Gas
• Petrol (gasoline)
• Naphtha
• Kerosene (paraffin)
• Gas oil (diesel)
• Mineral oil (lubricating)
• Fuel oil
• Wax, grease
• Bitumen
```
* Gas -> 1-4
* Petrol (gasoline) -> 2-12
* Naphtha -> 7-14
* Kerosene (paraffin) -> 11-15
* Gas oil (diesel) -> 15-19
* Mineral oil (lubricating) -> 20-30
* Fuel oil -> 30-40
* Wax, grease -> 40-50
* Bitumen -> 50+
144
What are the uses of the gases at the top of a fractinating column?
* LPG - Liquefied petroleum gas (LPG)
| * Camping gas
145
What are the uses of the petrol (gasoline) fraction?
Petrol
146
What are the uses of the naphtha fraction?
Processed to make petrochemicals
147
What are the uses of the kerosene fraction?
* Jet fuel
* Petrochemicals
* Central heating fuel
148
What are the uses of the gas oil (diesel) fraction?
* Diesel fuel
| * Central heating fuel
149
What are the uses of the mineral oil (lubricating) fraction?
Lubricating oil
150
What are the uses of the fuel oil fraction?
* Ships
| * Power stations
151
What are the uses of the wax, grease fraction?
* Candles
| * Lubrication
152
What are the uses of the bitumen fraction?
* Roofing
| * Road surfacing
153
Compare how useful hydrocarbons of different chain lengths are.
Short-chain alkanes (and alkenes) are more useful than long-chain alkanes.
154
What is cracking?
* The process of breaking long-chain alkanes into smaller hydrocarbons (including alkenes).
* It involves breaking C-C bonds.
155
Why is cracking needed?
Short-chain hydrocarbons are in higher demand than long-chain ones, so there is an abundance of long-chain hydrocarbons produced in fractional distillation.
156
What bond is broken in cracking?
C-C
157
Can you predict the products of cracking and why?
No, because where the chain breaks is random.
158
Give an example of how decane (C10H22) could be cracked.
C10H22 -> C2H4 + C8H18
159
What are the two types of cracking?
* Thermal cracking
| * Catalytic cracking
160
What is thermal cracking and what does it produce?
* Cracking at high temperatures and high pressures.
| * Produces lots of alkenes
161
What is catalytic cracking and what does it produce?
* Cracking using a zeolite catalyst, at slight pressure and high temperature
* Produces mostly aromatic hydrocarbons and motor fuels
162
What are the conditions for thermal cracking?
* High temperature - up to 1000*C
| * High pressure - up to 70 atm
163
What are the products of thermal cracking used for?
* Products: Alkenes
| * Used to make polymers, such as polyethene
164
What are the conditions for catalytic cracking?
* Zeolite catalyst (hydrated aluminosilicate)
* Slight pressure
* High temperature - about 500*C
165
What catalyst is used in catalytic cracking?
Zeolite catalyst (hydrated aluminosilicate)
166
Compare thermal and catalytic cracking in terms of conditions and products.
THERMAL
• Conditions: Up to 1000*C and 70 atm
• Products: Alkenes
CATALYTIC
• Conditions: Up to 500*C, slight pressure and zeolite catalyst (hydrated aluminosilicate)
• Products: Aromatic hydrocarbons and motor fuels
167
Why is a zeolite catalyst used in catalystic cracking?
Cuts cost because:
• Reaction can be done at lower pressure and low temperature
• Reaction is faster
168
What are aromatic hydrocarbons?
Aromatic compounds conain benzene rings -> Benzene rings contain a ring of 6 carbon atoms with a delocalised ring of electrons. (This comes up at A-Level)
169
What are zeolites?
Complex aluminosilicates -> Large lattices of aluminium, silicon and oxygen atoms carrying a negative charge.
170
Explain how changing the cracking conditions changes the yield.
* High temperature in presence of steam -> Higher yield of alkenes
* With catalyst -> Higher yield of branched and cyclic alkanes
171
How do zeolites work?
The zeolite has a 3D structure with tunnels and cavities into which small molecules can fit.
172
Remember to ask teacher about fraction order in fractional distillation.
Do it!
173
What is knocking?
When alkanes explode of their own accord in car engines as a result of the fuel/air mixture being compressed.
174
What hydrocarbons are most likely to cause knocking?
Straight chain alkanes.
175
How can knocking in car engines be prevented?
Adding branched chain and cyclic hydrocarbons to the petrol mixture -> These are less likely to cause knocking, so combustion is more efficient.
176
What is reforming?
The process of converting straight-chain alkanes into branched chain alkanes and cyclic hydrocarbons.
177
Why is reforming necessary?
The products of reforming are less likely to cause knocking in car engines than the straight-chain alkanes.
178
What are the conditions for reforming?
* 500*C
| * Platinum catalyst (stuck on aluminium oxide)
179
Describe the reforming of hexane.
* Hexane is reformed into cyclohexane and hydrogen gas.
* Cyclohexane can then be reformed into benzene (C6H6) and hydrogen gas.
(See diagram pg 79 of revision guide)
180
Give the word and symbol equations for the reforming of hexane.
* Hexane -> Cyclohexane + Hydrogen
* Cyclohexane -> Benzene + Hydrogen
* CH3CH2CH2CH2CH2CH3 -> Hexagon + H2
* Hexagon -> Hexagon with circle inside + 3H2
(See daigram pg 79 of revision guide)
181
How is benzene shown in diagrams?
Hexane with a circle inside.
| See diagram pg 79 of revision guide
182
Describe the reforming of octane.
• Octane is reformed into 2,5-dimethylhexane
| See daigram pg 79 of revision guide
183
Give the word and symbol equations for the reforming of octane.
* Octane -> 2,56-dimethylhexane
| * See diagram pg 79 for symbol equation
184
What does complete combustion of alkanes produce?
* Carbon dioxide
| * Water
185
What does incomplete combustion of alkanes produce?
* Carbon monoxide
* Carbon
* Water
* (Some) Carbon dioxide
186
What is the chemical equation for the complete combustion of propane (C3H8)? Include state symbols.
C3H8(g) + 5O2(g) -> 3CO2(g) + 4H2O(g)
187
What is a chemical equation for the incomplete combustion of ethane (C2H6)? Include state symbols.
C2H6(g) + 2O2(g) -> C(s) + CO(g) + 3H2O(g)
188
What state must alkanes be in for combustion and what is the implication of this?
* They must be gases.
* Therefore, liquid alkanes have to be vaporised first -> Smaller alkanes turn into gases more easily, so they'll burn more easily too.
189
Are combustion reactions exothermic or endothermic?
Exothermic
190
Compare how much energy small and large alkanes release per mole in combustion.
Large alkanes release more energy because they have more bonds to react.
191
Give some examples of alkanes being used as fuels.
* Methane -> Used for central heating and cooking in homes
* Petrol (5-12 carbon atoms)
* Kerosone (11-15 carbon atoms) -> Jet fuel
* Diesel (15-19 carbon atoms)
192
What are some pollutants that are released by burning fossil fuels?
* Carbon monoxide
* Sulfur oxides
* Nitrogen oxides
* Unburnt hydrocarbons
* Carbon particulates
193
Why is carbon monoxide harmful?
* Carbon monoxide binds to haemoglobin in your blood better than oxygen can
* So less oxygen can be carried around the body, leading to oxygen deprivation
* At high concentrations, it can be fatal
194
How are sulfur oxides produced by burning fossil fuels?
If the fossil fuel contains sulfur, the sulfur burns to produce sulfur dioxide gas.
195
How are nitrogen oxides produced by burning fossil fuels?
In car engines, the high temperatures and pressures in a car engine cause the nitrogen and oxygen in the air to react.
196
Why are sulfur dioxide and nitrogen oxides harmful?
* Sulfur dioxide -> Enters the atmosphere, dissolves in moisture, and makes sulfuric acid
* Nitorgen oxides -> Enter the atmosphere, dissolve in moisture, and make nitric acid.
* Together, this can fall as acid rain -> Destroys trees and vegetation, corrodes buildings, and kills fish in lakes
197
In what ways is acid rain damaging?
* Destroys trees and vegetation
* Corrodes buildings and statues
* Kills fish in lakes
198
How can some pollutants in car emissions be removed?
Catalytic converters in a car exhaust -> Use a platinum catalyst to change them to harmless or less harmful gases.
199
How do catalytic converters work?
Use a platinum catalyst to change pollutants into less harmful products.
200
How can a catalytic converter get rid of nitrogen monoxide and caarbon monoxide?
React them to give nitrogen and carbon dioxide:
| 2NO(g) + CO(g) -> N2(g) + CO2(g)
201
Are fossil fuels renewable?
No
202
Is the use of fossil fuels sustainble?
No
203
What will be the first fossil fuel to run out?
Oil
204
Give some examples of fossil fuels.
* Coal
* Oil
* Natural gas
205
What are renewable alternatives to fossil fuels called?
Biofuels
206
What are biofuels?
Fuels that are made of living matter over a short period of time.
207
Give some examples of biofuels.
* Bioethanol
* Biodiesel
* Biogas
208
How is bioethanol made?
Fermentation of sugar from crops (such as maize) to give ethanol.
209
How is biodiesel made?
Refining renewable fats and oils (such as vegetable oil).
210
How is biogas made?
Breakdown of organic waste matter.
211
Do biofuels produce CO2 when burnt?
* Yes, but this is CO2 that the plant absorbed when growing
| * So biofuels are classed as carbon neutral
212
Are biofuels carbon neutral?
Yes, but there is likely to be CO2 given out while:
• Refining and transporting the fuel
• Making the fertilisers
• Powering agricultural machinery used to grow and harvest the crops.
213
In what other way can biodiesel and biogas be made?
From waste that would otherwise go to landfill.
214
What are some problems with switching from fossil fuels to biofuels?
* Cars would have to be modified to use fuels with high ethanol concentrations.
* Land used to grow fuel crops can't be used to grow food
215
What are alkenes?
* A homologous series of unsaturated hydrocarbons
| * With the general formula CnH2n
216
What is the general formula for alkenes?
CnH2n
217
What is the general formula for cycloalkenes?
CnH2n-2
218
What type of bond do alkenes contain?
C=C double covalent bond
219
How do covalent bonds form?
* Atomic orbitals from different atoms, each containing a single electron, overlap
* Electrons become shared
* Nuclei of atoms are attracted by electrostatic attraction to the bonding electrons
220
What are the two types of covalent bond?
* Sigma bond (σ)
| * Pi bond (π)
221
What type of bond is a single covalent bond?
Sigma bond
222
How is a sigma bond formed?
• Two orbitals overlap in a straight line
• This gives a single area of electron density between the nuclei -> High electron density
(See diagram pg 82 of revision guide)
223
How is a pi bond formed?
• Two lobes of two *p* orbitals overlap *sideways*
• This gives two areas of eletron density -> One above and one below the axis -> Lower electron density
(See diagram pg 82 of revision guide)
224
What orbitals can form a sigma bond?
Any types, as long as they point towards the other atom.
225
What orbitals can form a pi bond?
p orbitals that overlap sideways (i.e. they're parallel).
226
Remember to revise the shape of a sigma and pi bond.
Pg 82 of revision guide
227
Compare and explain the bond enthalpy of a sigma and pi bond.
* Sigma bond -> One area of overlap -> High electron density -> Stronger electrostatic attraction with nuclei -> Higher enthalpy
* Pi bond -> Two areas of overlap -> Electron density spread out -> Weaker electrostatic attraction with nuclei -> Lower enthalpy
228
What is stronger, a pi bond or a sigma bond?
Sigma bond
229
Do pi bonds exist in single covalent bonds?
No, only in double or triple covalent bonds.
230
Describe the structure of a double covalent bond.
* Sigma bond along molecular axis
* Each arm of pi bond above and below the sigma bond
(See diagram pg 82 of revision guide)
231
Is a double covalent bond twice as strong as a single covalent bond?
* No, because a pi bond is less strong than a sigma bond.
| * So a sigma bond + a pi bond is less than twice as strong as a simga bond.
232
What are the different orbital combinations that can make up a sigma bond?
* Two s-orbitals
* Two p-orbitals
* One s-orbital + One p-orbital
* Others
233
What type of covalent bond does a C-C contain?
Sigma bond
234
What type of covalent bond does a C-H contain?
Sigma bond
235
What type of covalent bond does a C=C contain?
Sigma and pi bond
236
What is the symbol for a pi bond?
π
237
What is the symbol for a sigma bond?
σ
238
Remember to practise drawing out the structure of a double covalent bond.
Pg 82 of revision guide
239
What are the characteristics of C=C double bonds?
* Carbon atoms and the atoms bonded to these are planar -> Lie in the same plane
* Atoms can't rotate around them
240
Describe the shape of the atoms around a C=C bond.
• Atoms around each C are said to be trigonal planar
• All are in the same plane and form an equilateral triangle
(See diagram pg 83 of revision guide)
241
What are the bond angles around a carbon on a C=C bond?
All are 120*.
242
Are all alkenes planar?
* No, only ethene.
| * In larger alkenes, only the >C=C< unit is planar.
243
Can atoms around a double covalent bond rotate and why?
No, because of the pi bond.
244
Can atoms around a single covalent bond rotate?
Yes.
245
What causes stereoisomerism?
The lack of rotation around a C=C bond.
246
Remember to revise why the alkenes on pg 83 are isomers.
Do it.
247
What are stereoisomers?
Molecules with the same molecular and structural formula, but with a different spatial orientation of groups in the molecule.
248
Compare structural isomers and stereoisomers.
STEREOISOMERS:
Molecules with the same molecular and structural formula, but with a different spatial orientation of groups in the molecule.
STRUCTURAL ISOMERS:
Molecules with the same molecular formula, but with different structural formulae (a different bonding arrangement among the atoms).
249
Explain practically what structural isomers and stereoisomers are.
* Structural isomers have a different structural arrangment of atoms, so the atoms are arranged differently
* Stereoisomers have the same structure, but the atoms around a double bond are flipped over
250
Explain how stereoisomerism happens.
* When two carbons at the ends of a C=C bond have different atoms or groups attached to them.
* If the atoms or groups on one carbon are flipped around, this results in stereoisomers -> This is due to a lack of rotation around a C=C bond.
251
What are methods of classifying stereoisomers?
* E/Z isomerism
| * Cis-Trans isomerism
252
What are E isomers?
When the higher priority groups are on OPPOSITE sides of the C=C bond.
(e.g. one above and one below)
253
What are Z isomers?
When the higher priority groups are on the SAME side of the C=C bond.
(e.g. both above)
254
What does the Z in E/Z isomerism stand for?
Zusammen - meaning 'together' in German.
255
What does the E in E/Z isomerism stand for?
Entgegen - meaning 'opposite' in German.
256
What is an easy way to remember what E and Z stand for in E/Z isomerism?
Z -> ze zame zide
| E -> enemies
257
Describe the E/Z isomerism system.
1) Look at the individual atoms directly bonded to each of the C=C carbon atoms -> The atom with the higher atomic number on each side has priority.
2) If the atoms are the same then write out the atoms that are bonded to that atom in order of atomic number -> Now compare the two atoms until there is a difference -> The larger one takes priority.
3) If the priority groups are on the same side of the C=C bond, then it is a Z isomer.
4) If the priority groups are on opposite sides of the C=C bond, then it is an E isomer.
258
Remember to revise the E/Z isomers of but-2-ene.
Pg 83 of revision guide.
259
How is E/Z isomerism indicated in molecule names?
E-name or Z-name
e.g. E-but-2-ene or Z-but-2-ene
260
What is the system for determining priority in E/Z isomerism called?
CIP rules
261
When determining priority of groups in E/Z isomerism, what happens when there is a double bond (not the C=C bond)?
When writing out the atoms attached to an atom, the one with a double bond is listed twice.
https://www.chemguide.co.uk/basicorg/isomerism/ez.html
262
What is a good way of showing stereoisomerism?
Skeletal formulae -> The way the lines point show he direction of the bonds.
263
Remember to practise naming E/Z isomers.
See examples on pg 84 + find practice questions.
264
Remember to ask teacher about what happens in E/Z isomerism when two of the groups are the same, but have different priorities.
Do it!
265
When is cis-trans isomerism used?
When the carbons on each side of the C=C bond have at least one group in common.
266
What is cis isomerism?
When the same groups are on the SAME side of the C=C bond.
| e.g. both above
267
What is trans isomerism?
When the same groups are on OPPOSITE sides of the C=C bond.
| e.g. one above and one below
268
What does cis mean?
Same
269
What does trans mean?
Across
270
Describe the cis-trans isomerism system.
1) Check to see if the carbons on each side of the C=C bond have *at least* one group in common attached to them -> This only works if they do!
2) If the same groups are both one the same side of the C=C bond (e.g. both above), then it is a cis isomer.
3) If the same groups are on opposite sides of the C=C bond (e.g. one above and one below), then it is a trans isomer.
271
How is cis-trans isomerism indicated in molecule names?
Cis-name or trans-name
e.g. trans-1-bromopropene or cis-1-bromopropene
272
How caan you translate between E/Z isomerism and cis-trans isomerism?
There is no rule. You just have to work out each one.
273
Remember to practise naming cis-trans isomers.
Examples on pg 85 of revision guide + find some practise questions.
274
When does the E/Z and cis-trans isomerism system work?
E/Z -> Always
| Cis-trans -> Only if there is at least one group in common
275
What reactions do alkenes undergo?
* Combustion
| * Electrophilic substitution
276
Why does electrophilic addition happen in alkenes?
Electrophiles are attracted to the area of high electron density in the C=C bond.
277
What things can react with alkenes?
* Hydrogen
* Halogens
* Water
* Acidified potassium manganate (VII)
* Hydrogen halides
278
What is hydrogenation and why is it done?
* Adding hydrogen to unsaturated oils to make them saturated.
* This raises the boiling point so they're solid at RTP.
279
How can an alkane be made from an alkene?
* Reacting with hydrogen gas
* Nickel catalyst
* At 150*C
280
What are the conditions for making ethane from ethene and hydrogen?
* Nickel catalyst
| * 150*C
281
How can a dihalogenoalkane be produced from an alkene?
Reacting with a halogen.
282
What is a carbocation?
An organic ion containing a positively charged carbon atom.
283
Describe the reaction mechanism for an alkene reacting with a halogen.
Mechanism: Electrophilic addition
1) Halogen (e.g. Br2) attracted to the C=C bond -> Double bond repels the electrons in Br2, polarising it -> d+ on closer Br, d- on further Br
2) Heterolytic fission of Br2 -> Arrow from C=C bond to Br d+ and arrow from Br-Br bond to the Br d-
3) Br d+ is now joined to one of the carbon, forming a carbocation -> Br- joins onto the C+ -> Arrow from lone pair on Br- to the C+
4) This gives the complete dihalogenoalkane.
(See diagram pg 86 of revision guide)
284
What is the test for C=C bonds (i.e. for an alkene)?
* Shake the substance with brown bromine water.
| * If C=C bonds are present, the water decolourises, because bromine is added across the double bond.
285
How can an alcohols be made from an alkene?
* Steam hydration (Reacting with water)
* At 300*C
* At 60-70 atm
* Phosphoric(V) acid catalyst
286
What are the conditions for making alcohols by steam hydration of alkenes?
* 300*C
* 60-70 atm
* Phosphoric(V) acid catalyst
287
How can a diol be made from an alkene?
Oxidation by acidified potassium manganate(VII)
288
What can you observe when an alkene is shaken with acidified potassium manganate(VII)?
* Purple solution is decolourised
| * Because the alkene is oxidised
289
In the reaction of an alkene with acidified potassium manganate(VII), what goes along the reaction arrow?
H+/MnO4-
290
How can you add 1 or 2 OH groups to an alkene?
* To add 1 OH (and make an alcohol) -> Add water (steam hydration)
* To add 2 OH (and make a diol) -> Add acidified potassium manganate(VII)
291
How can a halogenoalkane be made from an alkene?
Reacting with a hydrogen halide.
292
How many products can addition of a hydrogen halide to an alkene produce?
* If the alkene is unsymmetrical -> Two, but there will be one major product.
* Otherwise, only one.
293
Why does the addition of a hydrogen halide to an alkene produce more than one product (if the alkene is unsymmetrical)?
The halogen atom can be added to either one of the carbons in the C=C bond.
294
In the addition of a hydrogen halide to an alkene, which is the major product and why?
* The amount of each product depends on how stable the intermediate carbocation is.
* Carbocations with more alkyl groups around the C+ carbon are more stable -> So tertiary carbocations are more likely to form.
* Therefore, major product is formed when the halogen joins onto the carbon with more alkyl groups around it.
295
Which is the most stable carbocation (primary, secondary or tertiary) and why?
Tertiary, because there are more alkyl groups around the C+, to feed electrons towards the positive charge.
296
Remember to revise the stability of carbocations.
Pg 87 of revision guide.
297
What is Markownikoff's rule?
The major product from addition of a hydrogen halide (HX) to an unsymmetrical alkene is the one where hydrogen adds to the carbon with th most hydrogens already attached.
298
Describe the reaction mechanism for an (unsymmetrical) alkene reacting with a hydrogen halide.
Mechanism: Electrophilic addition
1) Hydrogen from the HX is attracted to the C=C bond since it has d+ on H and d- on the halide
2) Heterolytic fission of HX -> Arrow from C=C bond to H d+ and arrow from H-Br bond to the Br d-
MAJOR PRODUCT:
3) H is now joined to the carbon with *more* hydrogens already attached, forming the *more* stable carbocation -> Br- joins onto the C+ -> Arrow from lone pair on Br- to the C+
4) This gives the complete major halogenoalkane
MINOR PRODUCT:
3) H is now joined to the carbon with *fewer* hydrogens already attached, forming the *less* stable carbocation -> Br- joins onto the C+ -> Arrow from lone pair on Br- to the C+
4) This gives the complete minor halogenoalkane
(See diagram pg 87 of revision guide)
299
Remember to revise all of the alkene reactions and reaction mechanisms.
Pgs 86-87 of revision guide
300
Alkene + Hydrogen ->
| Conditions?
Alkene + Hydrogen -> Alkane
| Conditions: 150*C, Nickel catalyst
301
Alkene + Halogen ->
Alkene + Halogen -> Dihalogenoalkane
302
Alkene + Water ->
| Conditions?
Alkene + Water -> Alcohol
| Conditions: 300*C, 60-70 atm, Phosphoric(V) acid catalyst
303
What is steam hydration?
Adding water at high temperatures and pressures to an alkene to make an alcohol.
304
Alkene + Acidified Potassium Manganate(VII) ->
Alkene + Acidified Potassium Manganate(VII) -> Diol
305
What type of reaction is an alkene reacting with acidified potassium manganate(VII)?
Oxidation
306
Alkene + Hydrogen Halide ->
Alkene + Hydrogen Halide -> Halogenoalkane
307
H2C=CH2 + H2 ->
H2C=CH2 + H2 -> CH3CH3
| At 150*C with nickel catalyst
308
H2C=CH2 + Br2 ->
H2C=CH2 + Br2 -> CH2BrCH2Br
309
H2C=CH2 (g) + H2O (g) ->
H2C=CH2 (g) + H2O (g) -> CH3CH2OH
| At 300*C and 60-70 atm with phosphoric(V) acid catalyst
310
H2C=CH2 ->
| With acidified potassium manganate(VII)
H2C=CH2 -> CH2OHCH2OH
| See diagram pg 87 of revision guide
311
H2C=CH2 + HBr ->
H2C=CH2 + HBr -> CH2BrCH3
| Only one product because it's symmetrical
312
H2C=CHCH3 + HBr ->
MAJOR: H2C=CHCH3 + HBr -> CH3CHBrCH3
MINOR: H2C=CHCH3 + HBr -> CH2BrCH2CH3
313
```
IMPORTANT
By what mechanism do these usually react:
• Alkenes
• Alkanes
• Halogenoalkanes
```
* Alkenes -> Electrophilic addition
* Alkanes -> Free radical substitution
* Halogenoalkanes -> Nucleophilic substitution
