1. Dr Manal F. AbouTaleb Alkanes 1 Introduction 2 Nomenclature of Alkanes
3 Physical Properties of Alkanes
4 Preparation of Alkanes
5 Reactions of Alkanes
Dr Manal F. AbouTaleb

2. Alkanes Alkanes are the hydrocarbons of aliphatic row.
Alkanes are hydrocarbons in which all the bonds are single covalent bonds (-bonds).
Alkanes are called saturated hydrocarbons.
The simplest one, methane (CH4), is also the most abundant.
All carbon atoms are sp3-hybridized
All bond angles are 109.5°

3. Alkyl groups
Alkyl groups are formed by loss of a hydrogen atom from the corresponding alkane . General formula of alkyl group : CnH2n+1
( e.g. CH4 Methane – 1 H = -CH3 Methyl group )
Alkyl groups are named by dropping the -ane suffix of the alkanes and adding the suffix -yl. Methane becomes a methyl group, ethane an ethyl group, etc.

4. Unbranched alkyl groups

5. Nomenclature Of Branched Alkyl Groups
Three-Carbon Groups
- Methylethyl is the systematic name; isopropyl is a common name.
- Numbering always begins at the point where the group is attached to the main chain.

6. Propane
Butane

7. 2. Four-Carbon Groups

8. 2. Four-Carbon Groups

9. IUPAC Nomenclature
IUPAC (International Union of Pure and Applied Chemistry) names:
1- The unbranched alkanes (homologous series)
2- Branched alkanes
Suffix of Alkanes added ane

10. 1. Straight-Chain Alkanes
Nomenclature of Alkanes
1. Straight-Chain Alkanes
Name
Number of carbon atoms
Structure
Methane
Ethane
Propane
Butane
Pentane
Hexane
Heptane
Octane
Nonane
Decane 1 2 3 4 5 6 7 8 9 10
CH4
CH3CH3
CH3CH2CH3
CH3(CH2)2CH3
CH3(CH2)3CH3
CH3(CH2)4CH3
CH3(CH2)5CH3
CH3(CH2)6CH3
CH3(CH2)7CH3
CH3(CH2)8CH3

11. Alkanes are either acyclic or cyclic.
Nomenclature of Alkanes
Alkanes
Alkanes are molecules(hydrocarbons) that contain only C-C and C-H  bonds.
Alkanes are either acyclic or cyclic.
Acyclic alkanes (not cyclic) have the formula
CnH2n+2 (where n = an integer)

12. 2. Branched-Chain Alkanes
Nomenclature of Alkanes
2. Branched-Chain Alkanes
1. Select the longest possible straight chain; this gives the parent name for the alkane
2. Number the parent chain beginning with the end of the chain nearer the branched chain
3. Use the number obtained by application of rule 2 to designate the position of the branched chain
When two or more branched chains are present, give each branched chain a number corresponding to its position on the parent chain
When two or more branched chains are identical, indicate this by the use of the prefixes ‘di-’, ‘tri-’, ‘tetra-’, and so on

13. Nomenclature of Alkanes
1. Select the longest possible straight chain; this gives the parent name for the alkane
2- methyl hexane
3,4- dimethyl heptane
3- methyl heptane
2. Number the parent chain beginning with the end of the chain nearer the branched chain
4- ايثيل –3- ميثيل هبتان
4-ethyl-3- methyl heptane

14. Nomenclature of Alkanes
3- Use the numbers obtained by application of rule 2 to designate the position of the branched chain
In writing the full name the root name is placed last; the substituent group, preceded by the number indicating its location on the chain, is placed first. 14 14

15. Nomenclature of Alkanes
4. When two or more substituents are present, give each substituent a number corresponding to its location on the longest chain.
- The substituent groups are listed alphabetically.
5. When two substituents are present on the same carbon, use the number twice.

16. Nomenclature of Alkanes
6. When two or more branched chains are identical, indicate this by the use of the prefixes ‘di-’, ‘tri-’, ‘tetra-’, and so on. e.g.

17. 3,3- Dimethyl hexane 2,7,8-Trimethyl decane 1 2 3 4 5 6
Nomenclature of Alkanes
3,3- Dimethyl hexane
2,7,8-Trimethyl decane

18. Nomenclature of Alkanes
7. When two chains of equal length compete for selection as the parent chain, choose the chain with the greater number of substituents.

19. Nomenclature of Alkanes
8. When branching first occurs at an equal distance from either end of the longest chain, choose the name that gives the lower number at the first point of difference.

20. Nomenclature Of Cycloalkanes
Monocyclic Compounds
1. Cycloalkanes with only one ring:

21. Substituted cycloalkanes:
1) Number the ring beginning with the substituent first in the alphabet, and number in the direction that gives the next substituent the lower number possible.
2) When three or more substituents are present, begin at the substituent that leads to the lowest set of locants.

23. Physical Properties Of Alkanes and Cycloalkanes
1. A series of compounds, where each member differs from the next member by a constant unit, is called a homologous series. Members of a homologous series are called homologs.
2. At room temperature ( 25 °C) and 1 atm pressure, the C1-C4 unbranched alkanes are gases; the C5-C17 unbranched alkanes are liquids; the unbranched alkanes with 18 or more carbon atoms are solids.

24. Boiling Point Higher members have higher boiling points Reason:
Physical Properties of Alkanes
Boiling Point
Higher members have higher boiling points
Reason:
Increase in molecular mass
Increase in intermolecular force

25. Physical Properties of Alkanes
Branched-chain alkanes have lower boiling points than straight-chain alkanes
∵ molecule is more compact  surface area   van der Waals’ force   boiling point 

26. Higher members have higher melting points
Physical Properties of Alkanes
Melting Point
Higher members have higher melting points
Reason:
Increase in molecular mass
Increase in intermolecular force

27. insoluble in water and highly polar solvents
Physical Properties of Alkanes
Solubility
Alkanes:
non-polar compounds
insoluble in water and highly polar solvents
soluble in non-polar solvents like benzene, 1,1,1-trichloroethane
Density
All alkanes and cycloalkanes have densities less than 1 g cm–3 at 20°C.
 Petroleum floats on water surface
Alkanes are less dense than water and swim on top of water

28. Preparation of alkanes Catalytic Hydrogenation
From Alkyl Halides
Gringard reagent
Reduction
Wartz Reaction
From Alkenes & Alkynes
Catalytic Hydrogenation

29. From Alkenes & Alkynes
Hydrogenation of unsaturated hydrocarbon:

31. A) Reduction of alkyl halides
2) From alkyl Halides
A) Reduction of alkyl halides

33. B) Hydrolysis of Grignard Reagent
Grignard reagent is an alkyl magnesium halide compound, R-Mg-X
- The Grignard reagent is formed when a solution of an Alkyl Halide (R-X) is allowed to stand over a metallic magnesium in the presence of dry ether
- Then Grignard reagent react with water or alcohol to form alkane

34. C) Wurtz Reaction تفاعل فورتز
This is the reaction of two alkyl halides (R-X) with metallic sodium to give symmetrical alkanes.
The wurtz reaction is a poor method for the preparation of unsymmetrical alkanes 

35. Preparation of Alkanes
Reforming
Reforming is a process in which straight-chain alkanes are heated under pressure in the presence of a platinum catalyst. The chains break up and reform to give branched-chain molecules.

36. Combustion Complete combustion :
29.5 Reactions of Alkanes
Combustion
Complete combustion :
Alkanes react with sufficient oxygen to give carbon dioxide and water through a complex series of reaction with the release of a large amount of energy.
General formula:

37. incomplete combustion
CH3-CH2-CH O2 ——>  CO2   + 2 CO   +  4 H2O   + heat

38. Reactions of Alkanes
Chlorination
Methane reacts with chlorine under diffuse sunlight or heating but not in dark
A mixture of products (CH3Cl, CH2Cl2, CHCl3, CCl4) is formed with the replacement of hydrogen by one or more chlorine atom
If methane is in excess, CH3Cl is major product
If chlorine is in excess, CCl4 is major product

39. Reaction Mechanism: Free Radical Substitution Reaction
Reactions of Alkanes
Reaction Mechanism: Free Radical Substitution Reaction
Mechanism of reaction :
1. Chain initiation
homolytic fission of chlorine molecules by heat or light into two chlorine radicals Step 1:

40. Reactions of Alkanes
2. Chain propagation
Step 2:
Step 3:
steps 2 and 3 repeat hundreds or thousands of time due to formation of the reactive intermediate in each step  chain reaction

41. Reactions of Alkanes
Further substitution occurs:

42. Reactions of Alkanes

43. Reactions of Alkanes

44. two free radicals combine to form a neutral molecule
Reactions of Alkanes
3. Chain termination
two free radicals combine to form a neutral molecule
the chain reaction is terminated

45. The reaction mechanism is shown as follows: 1. Chain initiation
Reactions of Alkanes
Example
Write down the reaction mechanism involved in the chlorination of ethane in the presence of diffuse sunlight.
Answer
Solution:
The reaction mechanism is shown as follows:
1. Chain initiation
Chain propagation

46. Reactions of Alkanes
Solution:
Chain termination

47. Mechanism For the Radical Halogenation of Methane