1. Department of Chemistry Universiti Teknologi Malaysia
DR. NORAZAH BASAR
Department of Chemistry
Faculty of Science
Universiti Teknologi Malaysia

2. Hydrocarbons Aliphatic Aromatic (Arenes) Alkane Alkene Alkyne Benzene
& derivatives

3. Alkanes all bonds are single bonds (C-C and C-H,  bonds)
Known as saturated hydrocarbons
Categorized as acyclic or cyclic
General formula for acyclic alkanes:
CnH2n+2
General formula for cyclic alkanes:
CnH2n

4. Acyclic alkanes contain only linear and
branched chains of carbons atoms.

5. Cyclic alkanes are also known as
cycloalkanes.

6. Alkanes Homolog Number of Carbon Atoms Methane 1 Ethane 2 Propane 3
Butane 4
Pentane 5
Hexane 6
Heptane 7
Octane 8
Nonane 9
Decane 10

7. Cycloalkanes Homolog Number of Carbon Atoms Cyclopropane 3
Cyclobutane 4
Cyclopentane 5
Cyclohexane 6
Cycloheptane 7

8. Types of Carbons and Hydrogens
C - primary (1), secondary (2), tertiary (3) &
quaternary (4)
H - primary (1), secondary (2) & tertiary (3)

9. Try this !!!

10. Alkyl Groups removing one hydrogen atom from the alkane
substituent groups
The symbol is R.
Alkane
Alkyl group
Abbreviation
CH3-H
methane
CH3-
methyl
Me-
CH3CH2-H
ethane
CH3CH2-
ethyl
Et-

11. Propyl (remove 1 H from propane) Isopropyl (remove 2 H from propane)
CH3CH2CH3
propane
Isopropyl (remove 2 H from propane)

12. n- Butyl (remove 1 H from butane) sec-Butyl (remove 2 H from butane)
CH3CH2CH2CH3
n-butane
sec-Butyl (remove 2 H from butane)

13. (remove 1 H from isobutane) (remove 3 H from isobutane)
isobutyl
(remove 1 H from isobutane)
isobutane
tert-butyl or t-butyl
(remove 3 H from isobutane)

14. International Union of Pure and Applied Chemistry
IUPAC NAMES
International Union of Pure and Applied Chemistry
Rule 1: Determine the main chain
Find the longest continuous chain of carbon atoms, and
name it.
Use the chain with greater number of substituents as the
main chain.
Substituents can be an alkyl groups, hydroxyl groups
(-OH), halogen (-Cl,-Br,-I,-F), phenyl groups etc.

15. 4. Determine the chain with the greater number of
substituents

17. 2-methylpentane (IUPAC) isohexane (common name)
Rule 2 & 3: Numbering the Main Chain and naming the
alkyl groups
Number the longest chain, start with the end of the
chain nearest to a substituent
2. Substituted carbons always get the lowest possible
number
2-methylpentane (IUPAC)
isohexane (common name)

18. 3-ethyl-2,4,5-trimethylheptane

19. 5-ethyl-2,3-dimethylheptane
Rule 4: Organizing multiple groups
when two or more substituents are present, list them in
alphabetical order.
when two or more of the same alkyl groups
(or other substituent) are present, use the prefixes
di-, tri-, tetra-, hexa- etc.
follow the alphabet of the alkyl groups, NOT the prefixes
di-, tri-, tetra- (IGNORE alphabet of the prefixes)
5-ethyl-2,3-dimethylheptane

20. 3,3,6-triethyl-7-methyldecane
5-ethyl-3-methyloctane

21. When both directions lead to the same lowest number for
one of the substituents, choose the direction that gives
the lowest possible number to the remaining substituents.

23. If the same number is obtained in both directions, follow
the alphabet of the substituent.

25. Certain common names are still used in the IUPAC system Eg.
Isopropyl Isobutyl

27. Cycloalkanes Rings of carbon atoms (CH2 groups) Formula: CnH2n
Nonpolar, insoluble in water
Compact shape
Melting and boiling points similar to
branched alkanes with same number
of carbons

28. Nomenclature of Cycloalkane
no number is needed for a single substituent on a ring
methylcycloheptane chlorocyclohexane

29. May be cycloalkyl attachment to chain.

30. if more than one substituent, arrange in alphabetical order
give number to the carbon of the ring
choose the “best” combination of numbers

32. Isomerism
Molecules which have the same molecular formula, but differ in the arrangement of their atoms, are called isomers.
Constitutional (or structural) isomers differ in their bonding sequence.
Stereoisomers differ only in the arrangement of the atoms in space (in alkene).

33. Structural Isomers
C4H10
C2H6O

34. Geometric Isomerism in Cycloalkanes
The lack of free rotation of single-bonded carbons in a ring produces a kind of isomerism called geometric isomerism.

35. Source of alkanes Natural gas methane (60%-80%)
ethane, propane and butane
2. Petroleum
gasoline C5H12-C12H26
kerosene C12H26-C16H34
diesel fuel C15H32-C18H38

36. Physical Properties of Alkanes
Alkanes from C1 to C4 are gasses
C5 to C17 are liquids
>C18 are wax-like solids
2. Alkanes are nonpolar compounds.
Their characteristic known as “like dissolves like” rule.
Nonpolar compounds are soluble in other nonpolar solvents.
Alkanes are soluble in organic solvents.
Alkanes are insoluble in water. Why ???

37. - no hydrogen bonding between R-H and H2O
- not soluble in water
What is “hydrogen bonding”?
a strong dipole-dipole attraction
Hydrogen atom bonded to O, N, or F
Electrostatically attracted to a lone pair of
electrons on an O, N or F atom in another molecule.

38. hydrogen bonding (strong)
3. Boiling Points (bp)
a. Alkanes have low bp’s compared to more polar compounds of comparable size
CH3CH2CH3
CH3CH2OH
MW = 46
BP=79oC
hydrogen bonding (strong)
MW= 44
BP= -42oC
Van der Wall
forces (weak)
MW =44
BP=21oC
dipole-dipole
attraction

39. b. Boiling points (b.p) increases as the numbers of carbons increases because of increased surface area
CH3CH2CH2CH b.p = 0oC
CH3CH2CH2CH2CH b.p = 36oC
CH3CH2CH2CH2CH2CH3 b.p = 69oC

40. The b.p of isomers decrease with branching
because of decreased surface area
Branched alkanes are more compact, less surface contact between molecules, less van der Waals attractions.
b.p = 36C
b.p = 28C
b.p =10C

41. Synthesis of Alkanes 1. Hydrogenation of Alkenes Alkene + H2  Alkane
Catalyst required, usually Pt, Pd, or Ni.

42. Reactions of Alkanes 1. Combustion
2. Cracking and hydrocracking (industrial)
3. Halogenation

43. Mechanism of Halogenation
Step 1 (Initial Step)
Homolytic cleavage of the chlorine molecule
Step 2 (Propagation Step)
i) Chlorin radical attack alkane molecule to form alkyl radical
Alkyl radical will attack chlorine molecule to produce
chlorine radical

44. Halogenation will give mixtures of products because
Step 3 (Termination Step)
Free radicals will combine or transfer its electrons to form a molecule
Halogenation will give mixtures of products because
there are more than one atom of hydrogen that will
be substituted.

45. Try This !!!
Propose the mechanism for the following reaction. Which compound is the major product. Explain your answer.