1. ALKANES, ALKENES, ALKYNES
NOMENCLATURE, STRUCTURES AND ISOMERISM

2. Alkanes = CnH2n+2
Alkenes = CnH2n
Alkynes = CnH2n-2

3. ALKANES, ALKENES, ALKYNES AND CYCLOALKANES ARE HYDROCARBONS (COMPOUNDS CONTAINING ONLY CARBON AND HYDROGEN).
EACH OF THESE FORM A HOMOLOGOUS SERIES (A GROUP OF ORGANIC COMPOUNDS HAVING A COMMON GENERAL FORMULA/ OR IN WHICH EACH MEMBER FIFFERS FROM THE NEXT BY A – CH2)

4. THE HYDROCARBONS MAY BE SATURATED (CONTAINS ONLY SINGLE BONDS BETWEEN CARBON-CARBON ATOMS/ CARBON ATOMS BONDED TO THE MAXIMUM NUMBER OF HYDROGENS)
OR UNSATURATED (CONTAINS AT LEAST A DOUBLE BOND BETWEEN C-C ATOMS)

6. ALKANES: NOMENCLATURE
Also called paraffins. A group of saturated hydrocarbons with the general formula Cn H2n+2 . They form a homologous series. Straight chain alkanes have their carbon atoms bonded together to give a single chain Alkanes may also be branched.
ALKANES: NOMENCLATURE

7. Hydrocarbon names are based on: 1) type, 2) # of carbons, 3) side chain type and position
1) name will end in -ane, -ene, or -yne
2) the number of carbons is given by a “prefix”
1 meth- 2 eth prop- 4 but pent hex hept- 8 oct non dec-
Actually, all end in a, but a is dropped when next to a vowel. E.g. a 6 C alkene is hexene
NAMING (GENERAL)

8. Determine the longest continuous chain (not always straight) in the molecule. The base name of the hydrocarbon is the name of the longest chain.

9. IUPAC system

10. Name any chain branching off the longest chain as an alkyl group (e. g
Name any chain branching off the longest chain as an alkyl group (e.g., methyl, ethyl etc)
The complete name of a branch requires a number that locates the branch on the longest chain.
Therefore number the chain in whichever direction gives the smaller number for all branches.
IUPAC SYSTEM

12. When two or more branches are identical, use prefixes (di-, tri-, etc
When two or more branches are identical, use prefixes (di-, tri-, etc.) (e.g. 2,4-dimethylhexane). Numbers are separated with commas. Prefixes are ignored when determining alphabetical order. (e.g. 2,3,5-trimethyl-4-propylheptane)
When identical groups are on the same carbon, repeat the number of this carbon in the name. (e.g. 2,2-dimethylhexane)

13. Where there are two or more different alkyl branches, the name of each branch, with its position number precedes the name. the branch names are placed in alphabetical order.

14. Alkenes and alkynes Both groups are unsaturated hydrocarbons.
Each group is a homologous series.
The main chain is defined as the chain containing the greatest number of double/tripple bonds
We number the position of the double/tripple bond so that it has the lowest numbers.
Alkenes and alkynes

15. ALKENES

16. alkynes

17. Naming side chains Example: name the following structure
Step 1 – Identify the correct functional group

18. Naming side chains
Step 2 - find the longest chain

19. Naming side chains
Step 3 - add the prefix naming the longest chain

20. Naming side chains
Step 4 - number the longest chain with the lowest number closest to the double bond

21. Naming side chains
Step 5 - add that number to the name

22. Naming side chains
ethyl
methyl
methyl
Step 6 - Name the side chains

23. Naming side chains ethyl methyl methyl
Step 7 - Place the side chains in alphabetical order & name the compound

24. name the following

25. 1 2 4 3

26. 9 10 11

28. A GOOD TIME TO INTRODUCE ISOMERS (COMPOUNDS WITH THE SAME MOLECULAR FORMULA BUT DIFFERENT STRUCTURAL FORMULAE)
TRY THE FOLLOWING:
ISOMERS

29. Reactions of alkanes & alkenes
We study three particular reaction cases:
Substitution
Addition
Elimination
Combustion
Reactions of alkanes & alkenes

30. Substitution (of H, commonly by Cl or Br) Combustion (conversion to CO2 & H2O)
Reactions of alkanes

31. Combustion
When alkanes are heated in a plentiful supply of air, combustion occurs
Alkanes are energetically unstable with respect to water and carbon dioxide
They only burn when they are in the gaseous state
Explain what happens when a candle burns!

32. 2 C4H10(g) + 13 O2(g) 8 CO2(g) + 10 H2O(g)
2 C8H18(l) + 25 O2(g) 16 CO2(g) H2O(g)

33. SUBSTITUTION Reactions with chlorine
Alkanes only react with chlorine when a mixture of the two is exposed to sunlight or ultraviolet light
The light provides the energy required to break the very strong bonds
This is an example of a substitution reaction
SUBSTITUTION

34. In the presence of light, or at high temperatures, alkanes react with halogens to form alkyl halides. Reaction with chlorine gives an alkyl chloride.
CH4(g) + Cl2(g) CH3Cl(g) + HCl(g)

35. Cracking happens when alkanes are heated in the absence of air
The products of the cracking of long-chain hydrocarbons are shorter chain molecules
Ethane is cracked industrially to produce ethene
Cracking

36. Alkanes are non polar so they are insoluble in water but soluble in each other.
Low molecular alkanes are gases.
Boiling points increase with increasing chain length (molecular weight) for the first few members
Boiling points decrease with increasing number of branches.(Explain this in terms of Van der Waals’ forces and surface area.
PHYSICAL PROPERTIES

37. Melting and boiling points increase with increased molecular weight (Methane bp.
-164°C, decane bp. 174°C)
While boiling point decrease with chain branching (decrease in surface area), melting
points increase
· Alkanes are less dense than water and swim on top of water

38. alkenes: preparation and reactions

39. Alkenes: Preparation and reactions
Two ways of making alkenes:
1. Heat a concentrated solution of potasium /sodium hydroxide in alcohol (alcoholic KOH) with a haloalkane (halogenoalkane)
This is dehydrohalogenation (removal of hydrogen and halogen)
2. Heat concentrated sulphuric acid with the alcohol- dehydration. THE ACID IS A DEHYDRATING AGENT
Alkenes: Preparation and reactions

40. i) Dehydration of alcohols
conc. H2SO4
R-CH2-CH2-OH
R-CH=CH2 + H2O
ii) Dehydrohalogenation of haloalkanes
NaOH/ethanol
R-CH2-CH2-X
R-CH=CH2 + HX
reflux
NaOH can be replaced by KOH

41. LEARNERS MUST KNOW MAJOR PRODUCTS IN ALL CASES AND REACTION CONDITIONS
Dehydration of alcohols
Dehydrohalogenation of haloalkanes
LEARNERS MUST KNOW MAJOR PRODUCTS IN ALL CASES AND REACTION CONDITIONS

42. REACTIONS OF ALKENES (VIP)

43. Plantinum (Pt) and palladium (Pd) – Catalysts
Catalytic hydrogenation:
- hydrogenation: addition of hydrogen to a double bond and triple bond to yield saturated product.
- alkenes will combine with hydrogen in the present to catalyst to form alkanes.
Plantinum (Pt) and palladium (Pd) – Catalysts
Pt and Pd: temperature 25-90oC
Nickel can also used as a catalyst, but a higher temperature of 140oC – 200oC is needed.

44. Addition of halogens:
i) In inert solvent:
- alkenes react with halogens at room temperature and in dark.
- the halogens is usually dissolved in an inert solvent such as dichloromethane (CH2Cl2) and tetrachloromethane (CCl4).
- Iodine will not react with alkenes because it is less reactive than chlorine and bromine.
- Fluorine is very reactive. The reaction will produce explosion.

45. EXAMPLES:

46. Hydrohalogenation

47. MARKOVNIKOV’S RULE ( A statement of the rule is not needed)
There are 2 possible products when hydrogen halides react with an unsymmetrical alkene.
It is because hydrogen halide molecule can add to the C=C bond in two different ways.

48. Markovnikov’s rules (Not for examination)
- the addition of HX to an unsymmetrical alkene, the hydrogen atom attaches itself to the carbon atom (of the double bond) with the larger number of hydrogen atoms.

49. Addition reaction with concentrated sulfuric acid: hydration of alkenes
- the alkene is absorbed slowly when it passed through concentrated sulfuric acid in the cold (0-15oC

50. Addition reaction with acidified water (H3O+): hydration of alkenes
Hydration: The addition of H atoms and –OH groups from water molecules to a multiple bond.
Reverse of the dehydration reaction.
Direct hydration of ethene:
- passing a mixture of ethene and steam over phosphoric (v) acid (H3PO4) absorbed on silica pellets at 300oC and a pressure of 60 atmospheres.
- H3PO4 is a catalyst.
Addition reaction with acidified water (H3O+): hydration of alkenes

53. Oxidation (Combustion of alkenes)
The alkenes are highly flammable and burn readily in air, forming carbon dioxide and water.
For example, ethene burns as follows :
C2H4 + 3O2 → 2CO2 + 2H2O
Oxidation (Combustion of alkenes)

54. HALOGENOALKANES Halogenoalkanes are compounds in which one
or more hydrogen atoms in an alkane have
been replaced by halogen atoms (fluorine,
chlorine, bromine or iodine).

55. Functional group = halogen
Ex. Fluorine = fluoro
Number by which carbon attached to, put in alphabetical order
Ex.
Bromoethane

56. Halogenoalkanes fall into different classes depending on how the halogen atom is positioned on the chain of carbon atoms. There are some chemical differences between the various types.
Primary
Secondary
Tertiary

57. Primary (1°) – carbon carrying halogen is attached to only one carbon alkyl group
Secondary (2°)– carbon carrying halogen is attached to two other alkyl groups
Tertiary (3°) – carbon carrying halogen is attached to three alkyl groups

58. Reactions of the halogenoalkanes
Substitution:In a substitution reaction, one atom or group of atoms, takes the place of another in a molecule.
Elimination: Halogenoalkanes also undergo elimination reactions in the presence of sodium or potassium hydroxide which is
dissolved in ethanol.
Reactions of the halogenoalkanes

59. Example of substitution
When an aqueous solution of NaOH or KOH is added to haloalkane an alcohol is produced.
propan-2-ol
Example of substitution

60. Example of elimination what conditions are needed?

61. Preparation and properties
ALCOHOLS (CnH2n+1OH)
Preparation and properties

62. Select the longest chain which contains the OH group and number so that the OH group has the smallest number. See the examples below
nomenclature

63. In a primary (1°) alcohol, the carbon which carries the -OH group is only attached to one alkyl group.
In a secondary (2°) alcohol, the carbon with the -OH group attached is joined directly to two alkyl groups, which may be the same or different.
Classification

64. In a tertiary (3°) alcohol, the carbon atom holding the -OH group is attached directly to three alkyl groups, which may be any combination of same or different.
See the examples below

66. Alcohols are classified as primary, secondary or Tertiary

67. Alcohols contain an –OH group covalently bonded to a carbon atom.
We need know:
the esterification reaction
Substitution and
elimination
Reactions of alcohols

68. Preparation and reactions
1. By hydration of alkanes
The acid is absorbed in conc sulphuric acid and then the acid is diluted.
Preparation and reactions

69. 2. Hydrolysis of halogenoalkanes
The halogen of the halogenoalkane is replaced by an OH group Refer to Halogenoalkanes

70. Classic example for learners to write

71. esterification Acid + Alcohol yields Ester + Water
Sulfuric acid is a catalyst.
Each step is reversible.
=>
esterification

72. Acid + Alcohol yields Ester + Water Sulfuric acid is a catalyst.
Each step is reversible.
=>
Chapter 11

73. Aldehydes and Ketones (Know the functional groups)
Nomenclature of Aldehydes:
Select the longest carbon chain containing the
carbonyl carbon.
• The -e ending of the parent alkane name is replaced
by the suffix -al.
• The carbonyl carbon is always numbered “1.” (It is
not necessary to include the number in the name.)
• Name the substituents attached to the chain in the
usual way
Aldehydes and Ketones (Know the functional groups)

75. Nomenclature of Ketones

76. No reactions. Just naming

77. SOME FUNCTIONAL GROUPS TO KNOW