Topic 6 - ORGANICS I Flashcards
(85 cards)
1
Q
Features of a homologous series
A
- Same general formula
- Show a trend in physical properties
- Have similar chemical properties
2
Q
What type of bonds are all single bonds?
A
Sigma bonds
3
Q
What are the properties of sigma bonds?
A
- End on overlap
- Large overlap
- Directly between nuclei
- Strong attraction
4
Q
What are the properties of pi bonds?
A
- Side on overlap
- Smaller overlap
- Not directly between nuclei
- Significantly weaker
5
Q
What type of bonds are double bonds?
A
A sigma bond surrounded by 2 pi bonds
6
Q
What are structural isomers?
A
Molecules with:
- Same molecular formula
- Different structural formula
7
Q
What are geometric isomers?
A
- Same molecular formula
- Different structural formula
- Restricted rotation about a C=C double bond
- Different groups on the C atoms
8
Q
What is a hydrocarbon?
A
Molecules made of hydrogen and carbon atoms only
9
Q
Definition of an alkane
A
Hydrocarbons with the general formula CnH2n+2
10
Q
What is the trend of boiling points as alkane size increases?
A
Bp/mp increases
11
Q
Why does boiling point increase as alkane size increases?
A
- London forces increase
- More electrons per molecule
- More energy required to overcome IMFs
12
Q
What state is C4H10?
A
Gas
13
Q
What state is C5H12?
A
Liquid
14
Q
What is miscibility?
A
The ability of two solutions to combine and form a homogeneous solution
15
Q
Are alkanes miscible in H2O?
A
No
- CnH2n+2 and H2O cannot form hydrogen bonds
16
Q
Are alkanes miscible in cyclohexane?
A
Yes
- Both CnH2n+2 and C6H12 only form London forces
17
Q
Can alkanes bond with other reactants?
A
Not likely
- Alkanes have sigma bonds which are very strong
- Hence low reactivity
18
Q
What type of reactions can alkanes undertake?
A
- Combustion reaction
- Substitution with halogens
19
Q
Describe the process of obtaining fuel from perch
A
- Dead matter from the seabed is compressed and heated, producing hydrocarbons
- Drilling removes the crude oil from the sea
- Fractional distillation separates the crude oil into fractions
- Cracking converts long hydrocarbon chains to shorter, more useful chains
- Reformation converts these chains to shorter, thick branched isomers
20
Q
What are the main fractions produced in fractional distillation?
Lightest->heaviest
A
- Refinery gases
- Gasoline
- Kerosene
- Diesel
- Fuel oil
- Bitumen
21
Q
What are the conditions necessary for cracking?
A
~ 650oC
- Catalysts such as aluminium oxide/silica dioxide
22
Q
Why is reformation useful?
A
- Isomers are short, thick and branched
Isomers pack less closely together, therefore:
- Weaker London forces
- More efficient combustion
23
Q
What are the products of complete alkane combustion?
A
- Highest oxides
- CO2
- Exothermic, releases energy
Only when there is sufficient O2
24
Q
What are the products of incomplete alkane combustion?
A
- Lower oxides
- CO2, CO and C
When there is insufficient O2
25
What are the consequences of pollution by carbon oxides?
CO2 and CO
CO2: Greenhouse effect, climate change (long term environmental problem)
CO: Toxic (short term health problem)
26
What are the consequences of pollution by nitrous oxides?
- Acid rain (Long term environmental problem)
- Toxic (short term health problem)
27
How are sulphur oxides produced?
When impurities in the oil react in the engine
28
What are the consequences of pollution by sulphur oxides?
SO2 and SO3
- Acid rain (long term environmental problem)
- Toxic (short term health problem)
29
How do catalytic converters reduce the harm caused by pollutants?
- Made of platinum/rhodium
- Oxidises harmful oxides
Eg.
NO + CO --> 0.5N2 + CO2
30
What type of reaction is methane + bromine?
Alkane (radical) substitution
31
What is the net reaction of CH4 + Br2 --> ?
CH4 + Br2 --> CH3Br + HBr
32
What are the 3 steps of the alkane substitution mechanism?
- Initiation
- Propagation
- Termination
33
Explain what initiation is in the alkane substitution mechanism?
Halogen breaks apart homolytically due to energy from UV light
34
Explain what is propagation in the alkane substitution mechanism?
- 2 step process in which reactants -> products
- Catalysed by halogen radical
35
Explain what is termination in the alkane substitution mechanism?
When any two free radicals combine
36
What is the role of UV light in the substitution mechanism?
- Breaks the X-X bond, where X is a halogen
- It is the only bond that is weak enough for the UV to break
37
What is a radical?
- Species with an unpaired electron
- Formed by homolytic fission of a covalent bond
38
What is the general formula of alkenes?
CnH2n
39
Why are alkenes unsaturated?
They contain at least one double bond
40
What occurs in organic reduction?
- Gain of hydrogen
- Loss of oxygen
41
What occurs in organic oxidation?
- Loss of hydrogen
- Gain of oxygen
42
What conditions are needed for alkene reduction? (exclude addition of H2)
- 150 degrees celsius
- Nickel catalyst
43
What is added to an alkene to oxidise it?
- Potassium manganate (VII)/KMnO4
- Dilute sulphuric acid/H2SO4
44
What symbol represents the oxidising agent potassium manganate (VII)?
[O]
45
What is an electrophile?
Electron pair acceptors
46
What mechanism/reaction do alkenes undergo?
Electrophilic addition
47
Why is a greater amount of the major product produced during an electrophilic addition?
The most stable carbocation is produced
48
Which carbocation is the most stable?
Tertiary>secondary>primary
49
How is the covalent bond broken in an electrophilic addition reaction?
Heterolytic fission
50
What happens when an alkene is passed with steam under pressure with a heated phosphoric acid catalyst?
- Addition reaction
- OH added
51
Why are heat and pressure required for polymerisation?
Heat: breaks pi bond
Pressure: forces molecules closer
52
Advantages of polymers
- Feedstock for cracking
53
Disadvantages of polymers
- If burnt can produce toxic fumes
- Last many years
- Can harm wildlife
54
What would the polymer of E- but-2-ene be called?
Polybut-2-ene
55
General formula of halogenoalkanes?
CnH2n+1X where X is Cl, Br or I
56
What are primary halogenoalkanes?
Only one C atom attached to C-X group
57
What are secondary halogenoalkanes?
2 C atoms attached to C-X group
58
What are tertiary halogenoalkanes?
3 C atoms attached to C-X group
59
What state are most halogenoalkanes?
Liquid
60
Are halogenoalkanes miscible in water?
No - no hydrogen bonding
- Layers are observed
61
What is a nucleophile?
Electron pair donors
62
What mechanism/reactions do halogenoalkanes undergo?
Nucleophilic substitution
63
What is added to an alcohol to form a chloroalkane and what is observed?
PCl5
Steamy white fumes
64
How is a bromoalkane formed?
- NaBr + 50% H2SO4 -> HBr + NaHSO4
- HBr is added to the alcohol
65
How is an iodoalkane formed?
- (Red) P + 1.5I2 -> PI3
- PI3 is added to the alcohol
66
What is formed when KOH(aq) is added to a halogenoalkane?
OH- ion forms an alcohol
X- ion removed
67
What is formed when KCN(ethanol) is added to a halogenoalkane?
CN- ion forms a nitrile
X- ion removed
68
What is formed when NH3(ethanol) is added to a halogenoalkane?
NH3 forms an amine
HX removed
69
When is the SN1 mechanism used?
Secondary or tertiary halogenoalkanes
70
When is the SN2 mechanism used?
Primary halogenoalkane
71
Why can't the SN2 mechanism be used for tertiary halogenoalkanes?
- Methyl groups are too bulky for nucleophile to fit
- Known as steric hindrance
72
Conditions needed for a halogenoalkane elimination?
Ethanolic KOH
73
Which halogenoalkane is the most reactive and why?
Iodoalkanes
- C-I bonds are longer therefore weaker
- Less energy needed to break them
- They break faster
74
Is SN1 or SN2 faster?
SN1
- Tertiary is faster
- Unimolecular, not waiting for a collision
75
What is formed when AgNO3(aq) is added to a halogenoalkane?
RX + H2O -> ROH + H+ ion + X-ion
Ag+ + X- -> AgX
- Precipitate of silver halide is observed
76
General formula of alcohols?
CnH2n+1OH
77
Products of alcohol combustion and what is observed?
- CO2
- H2O
- Blue flame
78
What is added and what happens in an alcohol elimination reaction?
- Warm, concentrated H3PO4 added
- Alkene formed
- H2O formed
79
What is added for the oxidation of an alcohol?
- Potassium dichromate (VI)/K2Cr2O7
- Dilute sulphuric acid/H2SO4
80
Products of the partial oxidation of a primary alcohol?
Aldehyde
81
Products of the complete oxidation of a primary alcohol?
Carboxylic acid
82
Products of the oxidation of a secondary alcohol?
Ketone
83
Why can't tertiary alcohols be oxidised?
- There is no spare H atom
- H2O cannot be formed
84
Colour change of the oxidation of primary and secondary alcohols?
Orange->green
85
Colour change of the oxidation of tertiary alcohols?
- No change as no oxidation
- Stays orange
