Transcript Slide 1

Organic Chemistry
Hydrocarbons
Introduction

Organic species can be classified into 2 groups

There are many more organic compounds than
inorganic. This is because:
– Inorganic compounds
– Organic compounds: contain hydrogen and carbon and
have a carbon-hydrogen bond
– i) Carbon atoms can bond together to form chains.
The number of carbon atoms in a chain varies
enormously. This is called polymerization.
– ii) The bonds between the carbons are covalent – each
carbon atom must share 4 bonds.
 The bonds between the carbon atoms may be single, double,
or triple.
– iii) It is possible for the same number of atoms of
carbon to form more than one different structure –
the structures could have the same chemical formula,
but different structures. This is called isomerism.
UNIT A
I. The Abundant Hydrocarbons
All living things contain carbon
 All foods are organic compounds –
carbohydrates, proteins, and fats (this stems
back to photosynthesis)

– When plants convert energy from
the sun to food, they take in carbon
dioxide and produce glucose.

When all living things die, they become
trapped and buried in the earth.
– As a result of intense heat and pressure, they are
converted to fossil fuels.
II. Classifications of Hydrocarbons

Hydrocarbons can be classified as follows:

Aliphatics are those that contain chains of
carbon atoms

These chains can be branched…
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These chains can contain single…
ALKANE
…double…
…or triple bonds.
ALKENE
ALKYNE
III. Types of Formulas

There are three types of molecular formulas that
are used to represent hydrocarbons.
– 1) Molecular Formulas: condensed symbols that display
the number of each type of atom in the compound.
 Ex. C3H8(g) (propane)
– 2) Condensed structural formulas: show the number of
hydrogen atoms bonded to each carbon atom.
 Ex. CH3 – CH2 – CH3
– 3) Structural formulas: indicate how many hydrogen and
carbon atoms are bonded together. A dash (-) represents
a bond between two atoms.
 Ex.
IV. Nomenclature of Hydrocarbons
There are a tremendous number of
hydrocarbons.
 This poses a problem when naming the
hydrocarbons.
 Hydrocarbons are composed of a stem and may
contain branches

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The following chart needs to be memorized. It will be
used for naming organic compounds”
Number of
Carbon Atoms
Stem Name
Branch Name
(Alkyl Group)
1
meth
methyl
2
eth
ethyl
3
prop
propyl
4
but
butyl
5
pent
pentyl
6
hex
hexyl
7
hept
heptyl
8
oct
octyl
V. Nomenclature of Alkanes
Alkanes contain only single bonds.
 Alkanes can be named by using the prefixes
outlined above.

– If the chain has one carbon, the name would be
methane.
– If the chain has two carbons, the name would be
ethane
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They have the general formula CnH2n+2
Chemical Formula
Chemical Name
CH4
methane
C2 H 6
ethane
THE RULES!!!
1)
For straight chain alkanes, name the longest chain of
carbon atoms with the ending –ane.
2)
For branched chains, number the carbon atoms of the
longest chain closest to the branching.
Locate the branch by indicating the number of the
carbon atom to which it is attached to the stem (main)
chain.
Name the branch. The branches are called alkyl groups –
named by using the appropriate stem plus the suffix –yl.
The position and name of the branches is given first in
the name.
If more than one of the same alkyl groups are present
as branches, the number of these branches is indicated
by the prefix multipliers di, tri, tetra, etc.
If there are different types of branches attached to
the stem, then they are to be listed in the name in
alphabetical order.
3)
4)
5)
6)
Examples:
Structural Formula
Chemical Name
H H H H H H H H
H C C C C C C C C H
H H H H H H H H
propane
H
HCH
H
H
H C C C H
H H H
2,3-dimethylbutane
4-ethyloctane
H
HCH
H
H H
H C C C C H
H H H H
3-ethyl-2,4dimethylhexane
H
H C H
H H H
H C C C C H
H H H H
3-ethylhexane
H H H H H
H C C C C C H
H H H
H
HCH
H C H
H
2,2,3,3,4pentamethylpentane
H
H C
H
H
C
HCH
HCH
H
H
C
H
H
C
H C H
H
H
C
H
H
C
H C H
H CH
H
H
C H
H
VI. Nomenclature of Alkenes
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
Alkenes are hydrocarbons that have a double bond
between two of the carbon atoms.
Similar rules for naming alkanes apply to naming alkenes.
The general formula for alkenes is CnH2n
 Hydrocarbons that contain the
maximum number of hydrogen
atoms are called saturated.
 Since alkenes contain a double
bond rather than all
carbon-hydrogen bonds, they
are said to be unsaturated.


All alkenes have the suffix –ene to indicate the
presence of a double bond.
Chemical Formula
Chemical Name
C2 H 4
ethene
C3 H 6
propene
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To name these compounds, first indicate the position
of the double bond with the number of the carbon
that proceeds the bond.
Numbering closest to the
double bond overrides
numbering closest to the
first branch.
It is possible to have two or more double bonds in an
alkene.
To name alkenes, you must indicate the positions of
the double bonds, and place a multiplier in the suffix.
Ex. CH3-CH=CH-CH2-CH3 → 2-pentene
Ex. CH3-CH=CH-CH2=CH2 → 1,3-pentadiene
Chemical Name
Molecular Formula
H
HC H
HHC H
H C C C C H
H H H H
methylpropene
H
H H H C H
H C C C C
H H H H
3,5-dimethyl-2-hexene
H
H H H H CH3
H C C C C C C C C H
H H CH3 H H H H H
5-ethyl-4-propyl-2,3heptadiene
H
H C H
H C H
H C C
H
H
C
H
HCH
H
C
H
H H H
C C C H
H H H
5-ethyl-4-methyl-2heptene
H
C
H
H
H
C
C
C
C
C
C
C
H
H
H
H
H
H
H
H
VII. Nomenclature of Alkynes
Contain at least 1 triple bond.
 Alkynes are similar to alkenes in that they are
unsaturated.
 The general formula for an alkyne is CnH2n-2
 The suffix –yne represents
a triple carbon-carbon bond.

Chemical Formula
Chemical Name
C2 H 2
ethyne
C3 H 4
propyne
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The rules for naming alkynes are similar to naming
alkenes.
i) Count the carbons present in the longest
chain. This will be the alkyne name.
ii) Number the carbons starting at the end
closest to the triple bond. Place the number of
the leading carbon of the triple bond in front
of the alkyne name.
iii) Name any groups as methyl, ethyl, propyl, etc.
Be sure to indicate which carbon the branch
stems from.
Ex. CH = C-CH2-CH2-CH3
Ex. CH = C-C =C-CH3
→ 1-pentyne
→ 1,3-pentadiyne
VIII. Physical Properties of
Hydrocarbons
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Melting and boiling points of hydrocarbons increase
as the number of carbon atoms in the chain increase.
– The London forces that hold the hydrocarbons
together increase as the number of atoms
increase.
– The more forces holding together the larger
molecules, the more energy needed to break the
intermolecular bonds.
Hydrocarbons are not soluble in water, but they
are soluble in other hydrocarbons.
– Ex. Methane will dissolve in ethane, etc.
IX. Combustion Reactions
All hydrocarbons burn by combining with
oxygen.
 The general equation for combustion is as
follows:

CxHy(g) + O2(g) → CO2(g) + H2O(l) + heat
X. Stability of Hydrocarbons
*Remember* Hydrocarbons that contain the
maximum number of hydrogen atoms are called
saturated.
Hydrocarbons that contain double or triple bonds
are unsaturated.

Saturated hydrocarbons are more stable than
unsaturated hydrocarbons.
– Alkanes are more stable than alkenes. Alkenes are
more stable than alkynes.
Unsaturated hydrocarbons react readily with
small diatomic molecules, such as hydrogen.
 This type of reaction is called an addition
reaction.
 Reaction with a sufficient quantity of
hydrogen (hydrogenation) converts
unsaturated hydrocarbons to saturated ones.
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XI. Cracking


As the name suggests, cracking is a chemical reaction
in which a longer carbon chain is cracked or broken
into smaller carbon chains.
When alkanes are heated in the absence of air, some
of the carbon-carbon bonds will break.
XII. Polymerization
Polymerization is the adding together of
many units to create a long chain
 This creates polymers
 The polymerization of ethene (ethylene)
to produce polyethene (polyethylene)
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XIII. Fractional Distillation and
the Petrochemical Industry
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Computer assignment