Organic Chemistry: Hydrocarbon

1. ORGANIC CHEMISTRY
Hydrocarbons: Alkanes, Alkenes, and
Alkynes

2. Organic chemistry
 The study of carbon compounds
 The first known organic compounds were
derived from animal and vegetable sources
and were difficult to crystallize and purify.
 Swedish chemist Torbern Bergman was the
first person to express the difference between
“organic” and “inorganic” substances, and the
phrase organic chemistry soon to came to
mean “the chemistry of compounds from living
organisms”.

3. Organic Chemistry
 To many chemist at that time, their only
explanation for the difference in behavior
between organic and inorganic compounds
was that organic compounds contained a
peculiar and “vital force” (vital force theory) as
a result of their derivation from living sources.
 Michel Chevreul (1816)
Animal fat NaOH
soap + Glycerine
Soap H3O+ “fatty acids”

4. Organic Chemistry
 Friedrich Wohler (1828)
- it was possible to convert the “inorganic”
salt, ammonium cyanate, into “organic”
substance, urea.
 O
 NH4+-OCN heat
H2 N C NH2

5.  Why is Carbon special? Why is it that sets
Carbon apart from all other elements in the
periodic table?
-The unique ability of carbon to bond
together forming long chains and rings.
Carbon, alone of all elements, is able to form
an immense diversity of compounds, from the
simplest to the staggeringly complex: from
methane to DNA, which can contain hundreds
of billions.

6. Important Families of Organic
Compounds
Hydrocarbons Only C and H present
Alkanes Single bond
Alkenes Double bond
Alkynes Triple bond
Aromatic
Alcohols R O H
Ethers R O R’
O
Aldehydes
R C H
O
Ketones
R C R
O
Esters
R C OR

7. O
Carboxylic acids R C OH
R’’(H)
Amines R N R’(H)
O R
Amides R C N R

8. HYDROCARBONS
 Hydrocarbons are organic compounds that
consist of only C and H atoms.
 Hydrocarbons come in a variety of forms. They
may be gases (methane and paropane),
liquids (hexane and benzene), waxes (paraffin
wax), or polymers (polyethylene and
polystyrene).
 Hydrocarbons can be processed to create
plastics.
 They are insoluble in water.

9. HYDROCARBONS
 The simplest class of organic compounds.
 Nonpolar
 There are four main types of
hydrocarbons:
- saturated hydrocarbons (alkanes)
- unsaturated hydrocarbons (alkenes or
alkynes)
- cycloalkanes
- aromatic hydrocarbons

10. HYDROCARBONS
 SATURATED means that each carbon is
bonded to four other atoms through single
covalent bonds. Hydrogen atoms usually
occupy all available bonding positions after the
carbons have bonded to each other.
 UNSATURATED hydrocarbons contain either
double or triple bonds. Since the compound is
unsaturated with respect to hydrogen atoms,
the extra electrons are shared between 2
carbon atoms forming double or triple bonds.

11. ALKANES
 made up of only
carbon and hydrogen
atoms
 Also called “paraffins”
 single bonds only
between carbon
atoms
 general formula: CnH2n+2
(assuming non-cyclic
structures)
 name ends in "ane"

12. IUPAC Molecular Structural Boiling Melting Density
name Formula Formula Point (°C) Point (°C) (g/ml, 20°C)
Methane CH4 CH4 -161.5 -182.5
Ethane C2H6 CH3CH3 -88.6 -183.3
Propane C3H8 CH3CH2CH3 -42.1 -189.7
Butane C4H10 CH3(CH2)2CH3 -0.5 -138.4
Pentane C5H12 CH3(CH2)3CH3 36.1 -129.7 0.626
Hexane C6H14 CH3(CH2)4CH3 68.7 -95.3 0.659
Heptane C7H16 CH3(CH2)5CH3 98.4 -90.6 0.684
Octane C8H18 CH3(CH2)6CH3 125.7 -56.8 0.703
Nonane C9H20 CH3(CH2)7CH3 150.8 -53.5 0.718
Decane C10H22 CH3(CH2)8CH3 174.1 -29.7 0.730

13. Alkanes
 Many of these (alkanes) substances are familiar
because of their widespread use.
Example: Methane (CH4 ), a major component of natural
gas
- propane (C3H8), major component of bottled
gas
- butane (C4H10), used in disposable lighters
and in fuel canisters for gas camping stoves and
lanterns.
- alkanes with from 5 to 12 carbon atoms per
molecule are found in gasoline.

14. IUPAC NOMENCLATURE
Key Concepts:
 - Name and number the longest carbon chain as for
a straight chain alkane
 Identify each of the branches (side-chains).
 Use the lowest number combinations for the branches
(side-chains).
 Name each branch or side-chain (alkyl group) :
methyl CH3
ethyl C2H5
propyl C3H7

15. Nomenclature
 For more than 1 of the same alkyl group use:
di = 2
tri = 3
tetra = 4
 Use commas between numbers, eg, 1,2 or 2,3
 Use hyphens between numbers and words, eg, 2-methyl
or 2,3-dimethyl
 If there is more than 1 type of branch or side-chain,
arrange their names alphabetically,
ie, ethyl groups are named before methyl groups which
are named before propyl groups

16. Structural Isomers
 Isomers
- compounds with the same molecular formula
but
different in structures.
EXAMPLE: C4H10
H H H H H H H
H - C – C – C - C- H H-C–C–C–H
H H H H H H
(CH3CH2CH2CH3 ) CH3

17. Sample exercises
 Name the following alkane:
1. CH3 CH3
CH3CH – CHCH2CH2CH3
2. CH3
CH3 - CH2 – CH2 – CH2 – CH – CH2 – CH3

18. Sample Exercises:
 Write the structural formula for?
1. 3-ethyl,3-methylheptane
2. 2-methylbutane
3. 2,2-dimethylpropane

19. Reaction of Alkane
 Combustion
Alkane reacts with O2 to produce CO2 and
Water
CH4 + 2 O2 → 2 H2O + CO2 + Energy
C3H8 + 5 O2 → 4 H2O + 3 CO2 + Energy

20. ALKENES
 containing a carbon-
carbon double bond
 Also called as
“Olefins”
 More reactive than
alkanes
 General formula:
CnH2n
(where n is any
integer)

21. Naming Alkenes and Alkynes
 Name the longest carbon chain that contains the double
or triple bond (see table).
 The name for the alkenes ends in ene instead of –
ane.
 The name for the alkynes ends in –yne instead of –
ane.
 Number the main chain from the end nearest the double
or triple bond.
 Indicate the position of the double or triple bond with
the number of the first unsaturated carbon.
 Place the number and names of substituents in front of
the alkene or alkyne name.

22. Alkenes
The simplest alkenes are ethylene and
propylene.
They are the two most important organic
chemicals produced industrially.
Ethylene is a plant hormone. It plays important
roles in seed germination and ripening of
fruits.
For alkenes with four or more carbon atoms,
several isomers (same formula but different
structures) exist for each molecular formula.

23. Alkenes
For example: C4H8
H3C CH3 H3C H
C=C C=C
H H H 3C H
cis-2-butene 2-methylpropene
CH3 H2C H H3C H
C=C C=C
H H H CH3
1-butene trans-2-butene

24. Geometric Isomers (cis and trans)
- compounds that have the same
molecular formula and the same groups
bonded to one another but differ in the spatial
arrangement of these groups.

25. Sample Exercises:
Give the name of the ff. alkenes:
1. CH3
CH3 - CH2 – CH2– CH – CH = CH - CH3
2. Br
CH3 CH2 CH=CCH3

26. Sample Exercises
 Give the structural formula for:
1. 1,4-pentadiene
2. 3-ethyl-1-hexene
3. tra ns -2,3-dichloro-2-butene
4. 1,3,5-hexatriene

27. ALKYNES
 C C bonds
 More reactive than
alkanes and alkenes
 General formula:
CnH2n-2
 Highly reactive
molecules

28. Alkynes
 C2H2, ethyne or acetylene is the most simplest
alkyne and it is highly reactive molecule.
When acetylene is burned in a stream of
oxygen in an oxyacetylene torch, the flame
reaches a very high temperature, about 3200
K.

29. Nomenclature of Alkynes
 Sa m e with A ne s … . .
lke
 However, when there is a choice in
numbering, d o uble bo nd s re c e ive lo we r
num be rs tha n trip le bo nd s …..
Example:
CH3CH CHC CCH2CH3
2-heptene-4-yne

30. Sample Exercises
 Name the ff. compounds:
1.
CH3 - CH2 – CH2– CH –C CH - CH2 CH3
CH2 CH3
5-ethyl-3-octyne

31. 2 HC C - C(CH3)2CH2C CH
CH3
3. HC C – C CH3
CH3
Answer: 2. 3,3-dimethyl-1,5-hexediyne
3. 3,3-dimethyl-1-butyne

32. 4.
CH3CH CHCH CHC CCH3
2,4-Octadiene-6-yne

33. Organic Chemistry
Reported by:
Maria Crsitina d.L. Payofelin
Selected Topics in Chemistry