1. Free Radical Substitution
Homolytic Fission

2. Substitution Rxn (free radical substitution)
Is a chemical reaction in which an atom or group of atoms in a molecule is replaced by another atom or group of atoms

3. Mechanism of reaction
Is the detailed step by step description of how the overall reaction occurs

4. Methane
Chloromethane H Cl = + + Cl H Cl Cl
Hydrogen Chloride
Chlorine

5. Simple mechanism Substitution Cl Cl
Chloromethane
Methane
Hydrogen and Chlorine have swapped places
Substitution Cl
Hydrogen Chloride Cl
Chlorine

6. Stage 1
Initiation
Getting Started

7. Ultra violet light breaks the bond
Chlorine molecule
Cl2
2 Chlorine radicals each
with an unpaired electron
Both species are the same
Called Homolytic Fission

8. Stage 2
Propagation
Keeping it going

9. The methyl radical is now free to react with a chlorine molecule
Methane
Chlorine radical Cl H
The chlorine radical pulls the hydrogen and one electron across to it.
Lets put in the 2 electrons in this bond
Methyl radical
Hydrogen chloride
The methyl radical is now free to react with a chlorine molecule

10. Chlorine radical Cl Cl Chloromethane
Methyl
radical
Chlorine
Chloromethane
Chlorine radical can now go and react with a methane molecule

11. Stage 3
Termination
Grinding to a halt

12. Three different ways this can happen

13. No free radicals to keep it goingCl Cl
Chlorine molecule
Reaction stops
No free radicals to keep it going
Chlorine
radical
Chlorine
radical

14. Because there are no free radicals to keep it going
Methyl
radical Cl
Chlorine
radical
Chloromethane forms
Reaction stops
Because there are no free radicals to keep it going

15. Methyl
radical
Methyl
radical
Ethane
Reaction stops because no free radicals produced to keep it going
The formation of ethane proves that this is the mechanism
Reaction speeded up by sources of free radicals such as tetramethyl lead.

16. Proof of mechanism
Small amount of ethane detected
Not initiated (start) in dark needs UV light
Tetra methyl lead decomposes to form methyl free radicals, if Tetra methyl lead added it increases rate of reaction
Pb (CH3)4 = Pb + 4 CH3º
THERFORE Methyl radicals are used in reaction
Halogenated alkanes are used as flame retardants

17. Step1: Initiation
UV light stimulates rxn. Cl-Cl molecule splits equally (homolytic fission)
Step 2. Propagation
Free Cl° atoms (RADICAL) attacks methane and forms HCL
Step 3. Propagation
Methyl free radical attacks a Cl-Cl molecule and forms chloromethane. Chain rxn continues.
Step 4: Termination
Cl°+ Cl° =Cl-Cl
Cl°+ °CH3= CH3Cl
CH3+ CH3= C2H6

18. Tetramethyl lead is added to speed up the rxn
It supplies the solution with methl free radicals.
Evidence for free radicals comes from small amounts of ethane being found in the solution
Halogenation of alknaes makes them more flame resistant

19. Addition Reaction (pg. 367)
When two substances react together to form a single substance

20. Addition Reaction Mechanism
and evidence for
Heterolytic Fission

21. Polarising of the bond in bromine
Step 1
Polarising of the bond in bromine

22. Ethene
Concentration of negative charge
Because 4 electrons in this area
Bromine Br2 δ+ δ-
At this point the negative charge of the double bond in ethene forces the electrons to the right Br and it becomes δ− and other one becomes δ+
Moves in this direction

23. Heterolytic Fission Occurs
Step 2
Heterolytic Fission Occurs

24. The two electrons of the bond have been forced across to the right Br making it Br- while the other is Br+
Br+
Br - δ+ δ-
At this point the negative charge of the double bond in ethene forces the electrons to the right Br and it becomes δ− and other one becomes δ+
The Br2 has been split into 2 different species i.e. Br+ and Br- this is called Heterolytic Fission

25. Formation of the Carbonium Ion
Step 3
Formation of the Carbonium Ion

26. At this point a lot of things happen at the same time
The two electrons are pulled to the Br+
A bond is formed
one of the bonds between the two carbons disappears
The lower carbon becomes ve because it has lost an electron
The two hydrogens on the upper carbon move to make way for the Br
The two electrons of the bond have been forced across to the right Br making it Br- while the other is Br+ Br
Br -
Br+
Br -
Let us put in the two electrons of this bond +
The Br2 has been split into 2 different species i.e. Br+ and Br- this is called Heterolytic Fission
Carbonium ion
Cyclic bromium ion

27. Attack on carbonium ion by Br-
Step 4
Attack on carbonium ion
by Br-

28. The negative bromide ion is attracted by the positive carbonium ion
The two electrons of the bromide ion are used to form the bond
The two hydrogen atoms move round to allow the Br in
The negative and positive cancel each other out Br
Br - + Br
Carbonium ion
1,2 dibromoethane
Called Ionic Addition because the species are ions when they add on

29. Step 5
Proof of
mechanism

30. Br
Br - + Cl
Br -
Cl -
Proof of the mechanism is that if there are Cl- in the environment then some 1-bromo, 2-chloroethane will be formed.
This can be identified by its different Relative Molecular Mass

31. Step1:
σ+Br-σ-Br-
Carbon double bond is region of high e-density. Br2 becomes polar as comes close
Step 2.
Ionic addition
Br2 splits into ions.heterolytic fission because Br+ and Br- created
Step 3.
Br+ molecule attacks double bond and forms cyclic bromonium ion/ carbonium ion
Step 4: Termination
Br- now attacks the carbonium ion

32. Hydrogenation Adding of hydrogen's into a molecule (addition)
Occurs in manufacture of margarine
Add hydrogen into double bonds causes oils to become solid
Unsaturated fats are better for you that saturated fats

33. Evidence for the carbonium ion
When bromine and chlorine ions present
Ethene forms 1-bromo-2-chloroethane as well as 1, 2 dibromoethane

34. Polymerisation rxns
Molecules that contain double bonds undergo addition to become less unsaturated (addition polymers such as polythene and polypropene)

35. Polymerisation Reactions
Example of an addition reaction
Ethene molecules add together
Polymers are long chain molecules made by joining together many small molecules + =

36. Polymers Commonly reffered to as plastics
Polyethene used for plastic bags, bowls, lunch boxes, bottles etc
Polypropene is used in toys, jugs, chairs etc
Crude oil is raw material for their manufacture

37. Elimination reactions

38. Elimination reactions
When a small molecule is removed from a larger molecule to leave a double bond in the larger molecule

39. AB  A + B Elimination rxns
a compound breaks down into 2 or more simpler substances
Double bond created
only one reactant
AB  A + B

40. Elimination reactions
Ethene is made from ethanol from removing water using AlO as catalyst
Elimination reaction is one in which a small molecule is removed from a larger molecule to leave a double bond in the larger molecules
Dehydration reaction
Only need to know dehydration of alcohol

41. Elimination reaction
Dehydration of an alcohol is an example of an elimination reaction
In this reaction, a larger alcohol molecule reacts to form a smaller alkene molecule and an even smaller water molecule
The change in structure is from tetrahedral to planar

42. Dehydration of ethanol
Ethanol is dehydrated to ethene
This reaction is used in the preparation of ethene

43. Dehydration of ethanol to ethene

44. Reaction conditions
Heat
Aluminium oxide catalyst

45. Preparation of ethene

46. Elimination rxn
Is when a small molecule is removed from a larger molecule to leave a double bond in the larger molecule
Alcohol =water + alkene
Dehydration reaction since water is removed
Ethanol=ethene + water
2 methanol +sulphuric acid =methoxymethane ether +water

47. C. Decomposition
2 H2O(l)  2 H2(g) + O2(g)

48. Redox reactions

49. Redox reactions
These reactions involves oxidation and reduction reactions
The removal or addition of lectrons from the molecule

50. -3 -2 -1 1 2 3 Receives electrons Looses electrons1 2 3
Reduction
Oxidation
Receives electrons
Looses
electrons
Reducing agents give electrons
Oxidation agents take electrons

51. Redox reactions of primary alcohols
Primary alcohols react with oxidising agents such as potassium manganate(VII) or sodium dichromate(VI), forming the corresponding aldehyde
For example, ethanol reacts forming ethanal
Ethanal is also formed in the metabolism of ethanol in the human body

52. Redox reaction Primary alcohol oxidised to an aldehyde
Oxidising agent: sodium dichromate or potassium permanganate
The oxidising agent must be limited to prevent the aldehyde from being further oxidised to an carboxylic acid

53. Reaction of ethanol with sodium dichromate(VI)

54. Reaction of ethanol with sodium dichromate(VI)
This reaction is used in the preparation of ethanal
Reaction conditions: heat, excess ethanol, acidified sodium dichromate(VI) solution
The aldehyde is distilled off as it is formed in order to prevent further oxidation to ethanoic acid

55. Preparation of ethanal

56. Oxidation of primary alcohols
Primary alcohols such as ethanol are oxidised to the corresponding aldehydes, which can be further oxidised to the corresponding carboxylic acids.

57. Oxidation of ethanol

58. Reaction of ethanol with sodium dichromate(VI)
This reaction is used in the preparation of ethanoic acid
Reaction conditions: heat, excess acidified sodium dichromate(VI) solution
The reaction mixture is refluxed in order to bring about oxidation to ethanoic acid

59. Preparation of ethanoic acid
Reflux followed by Distillation

60. Oxidation of secondary alcohols
Secondary alcohols such as propan-2-ol are oxidised to the corresponding ketones, such as propanone
Unlike aldehydes, ketones are not easily oxidised, and so no further oxidation takes place

61. Oxidation of propan-2-ol

62. Combustion of organic compounds
Most organic compounds burn in air, forming carbon dioxide and water
The structure of the compounds’ molecules is completely destroyed, with the carbon and hydrogen atoms in each molecule being oxidised
Combustion is exothermic, and ethanol is used as a fuel where it can be produced cheaply

63. Non-flammable organic compounds
Fully halogenated alkanes such as bromochlorodifluoromethane are non-flammable
Because of this they can be used in fire extinguishers and as flame retardants
For environmental reasons, the use of many of these substances is being phased out

64. Reduction of aldehydes and ketones
Aldehydes and ketones can be reduced to the corresponding alcohols, using hydrogen passed over the heated surface of a nickel catalyst
For example, ethanal is reduced to ethanol

65. Reduction of ethanal to ethanol

66. Reduction of propanone to propan-2-ol

67. ENERGY PROFILE one step reaction transition state TS activation
energy maximum
activation
energy Ea
obtained from
heat (collisions) E N R G Y
heat of
reaction DH
starting
material
exothermic
(releases heat)
product
opposite is
endothermic
REACTION COORDINATE
( follows the progress of the reaction )

68. Reactions as acids

69. Reactions of alcohols with sodium
Alcohols react with the reactive metal sodium, forming a sodium salt and hydrogen
For example, ethanol reacts with sodium forming sodium ethoxide and hydrogen

70. Reaction of ethanol with sodium

71. Acidic nature of the carboxylic acid group
Ethanoic acid is a far stronger acid than ethanol
This is because its anion is much more stable than that of ethanol
This enables it to lose a hydrogen ion more readily
The stability of the ethanoate ion is due to electron delocalisation (as in benzene)

72. Reactions of carboxylic acids as acids
Carboxylic acids react with:
Magnesium, forming a magnesium salt and hydrogen
Sodium hydroxide, forming a sodium salt and hydrogen
Sodium carbonate, forming a sodium salt , carbon dioxide and water

73. Reaction of ethanoic acid with magnesium
Acid + metal → salt + hydrogen
2 CH3COOH + Mg → (CH3COO)2Mg + H2
ethanoic acid magnesium ethanoate

74. Reaction of ethanoic acid with sodium hydroxide
Acid Base → Salt Water
CH3COOH + NaOH → CH3COONa + H2O
ethanoic acid sodium ethanoate

75. Reaction of ethanoic acid with sodium carbonate
Acid + Carbonate → Salt + Water + Carbon dioxide
2CH3COOH + Na2CO3 → 2CH3COONa + H2O + CO2
ethanoic acid sodium ethanoate