Hydrocarbons

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Hydrocarbons
Alkanes
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Learning Objectives
Define and/or describe the following terms
Hydrocarbon Alkane
Straight-chain alkane Branched-chain alkane
Isomers Constitutional isomers
Condensed structures Conformation
Recognize and name the straight-chain alkanes
composed of up to 6 carbon atoms.
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Learning Objectives
Recognize and name the branched-chain alkanes
composed of up to 6 carbon atoms.
Recognize and name the cycloalkanes composed of 3
to 6 carbons.
Identify the two main conformations of butane
(anti and eclipsed), and explain why the anti
conformation is lower in potential energy.
Describe the combustion of alkanes using a
balanced, chemical equation.
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Definitions
Hydrocarbon an organic compound that contains
only carbon and hydrogen. Alkane a hydrocarbon
that has only single bonds. Straight-chain
alkane an alkane that has all its carbons
connected in a row. Branched-chain alkane an
alkane that has at least one branching
connections of carbons. Isomers compounds with
the same molecular formula but different
structures.
Constitutional isomers compounds with the same
molecular formula but different connections among
their atoms.
Conformation the specific three-dimensional
arrangement of atoms in a molecule at a given
instant.
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Alkanes
Alkanes are hydrocarbons that contain only single
carbon-carbon bonds.
C
C
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Methane CH4
Ethane CH3CH3
Propane CH3CH2CH3
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n-butane
CH3CH2CH2CH3
n-pentane
CH3CH2CH2CH2CH3
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Straight-chain alkanes
Number of carbons
Condensed structures
1 CH4 methane 2 CH3CH3 ethane 3 CH3CH2CH3 p
ropane 4 CH3CH2CH2CH3 butane 5 CH3CH2CH2CH2CH3 p
entane 6 CH3CH2CH2CH2CH2CH3 hexane
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Names of common alkyl groups
Name
Condensed structural formula
methyl CH3 ethyl CH2CH3 propyl
CH2CH2CH3
isopropyl
CHCH3
CH3
CH2CH2CH2CH3
butyl
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Branched-chain Alkanes
Branched-chain alkanes an alkane that has at
least one branching connection of carbons.
Constitutional isomerism in alkanes
Constitutional isomers compounds with the same
molecular formula but different connections among
their atoms.
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C4H10
butane
2-methylpropane
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C5H12
pentane
2-methylbutane
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C5H12
2,2-dimethylpropane
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Naming branched-chain alkanes
(1) Name the main chain the longest chain of
carbon-carbon bonded atoms.
(2) Number the carbon atoms in the main chain,
beginning at the end nearer the first branch
point.
(3) Identify the branching substituent, and
number each according to its point of attachment
to the main chain.
(4) Write the name as a single word.
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Conformation the specific three-dimensional
arrangement of atoms in a molecule at a given
instant.
This type of structural arrangement of atoms
depends upon bond rotation.
Any three-dimensional arrangement of atoms that
results from rotation about single bonds is
called a conformation.
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Conformations of butane
CH3
anti
CH2
CH2
CH3
gauche
eclipsed
CH3
CH3
CH2
CH2
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Cycloalkanes
Cycloalkane an alkane that contains a ring of
carbon atoms.
cyclopropane
cyclobutane
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cyclohexane
cyclopentane
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Chemical Reactions Combustion
All organic matter (any material that is composed
of carbon such as wood or other plant material)
will burn if heated to a high enough temperature.
Inorganic materials usually will not burn,
however, some metals (steel wool) will.
Burning is a combustion reaction a reaction in
which a substance reacts with oxygen, usually
with the rapid release of heat to produce a
flame. Organic compounds usually burn in oxygen
or air to yield carbon dioxide. If the organic
compound also contains hydrogen (and almost all
do), then water is also a product.
CH4 2 O2
CO2 6 H2O heat
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Glucose is an organic compound composed of
carbon, hydrogen, and oxygen C6H12O6.
Combustion reaction of glucose
C6H12O6 6 O2
6 CO2 6 H2O heat
This reaction occurs when glucose is heated to
its combustion temperature in the presence of
oxygen. This same overall reaction takes place in
living cells except it does not occur all at
once, and most of the energy is conserved (put
into other compounds) instead of being given off
as heat.