CSUS – CH6B
Hydrocarbons
Instructor: J.T., P 1
Hydrocarbons:
1)
2)
`
Saturated hydrocarbons
alkanes:
CnH2n + 2
i.e.: CH3 – CH3
ethane
Unsaturated hydrocarbons:
a)
alkenes:
CnH2n
i.e.: CH2 = CH2
ethene
alkynes:
CnH2n-2
i.e.: CH ≡ CH
ethyne
b)
3)
4)
Cycloalkanes:
i.e.:
CnH2n
CH2
CH2
CH2
CH2
cyclobutane
Aromatic hydrocarbons (arene):
i.e.:
Benzene
Definition of aromatic compounds includes only those with a benzene ring.
CSUS – CH6B
Hydrocarbons
Instructor: J.T., P 2
Notes:
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You need to be able to translate the name of an organic compound
into its structural formula.
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You need to be able to name a compound from its given formula.
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You need to remember that each line represents a pair of shared
electrons!
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Make the total number of bonds on each carbon up to 4.
Carbon forms 4 bonds with other atoms.
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Hydrogen and Halogens (F, Cl, Br, I) are terminal
an organic formula.
elements in
Alkane Nomenclature
Choose the longest carbon chain.
Count the number of the carbons.
1 carbon:
2 carbons:
3 carbons:
4 carbons
5 carbons
6 carbons
7 carbons
8 carbons
9 carbons
10 carbons
meth
Eth
Prop
But
Pent
Hex
Hept
Oct
non
Dec
+ ane
+ ane
+ ane
+ ane
+ ane
+ ane
+ ane
+ ane
+ ane
+ ane
If another chain of carbon atoms starts out of the main carbon
chain, it is referred to as branching.
The positions of the substituent alkyl groups ('branches') are
denoted by using the lowest possible number(s) e.g. 2, 3 etc. for the
associated carbon atoms in the main chain, where the 1st carbon atom in
the chain is considered as C atom 1.
CSUS – CH6B
Hydrocarbons
Instructor: J.T., P 3
...But what are alkyl groups?
In chemistry, radicals (often referred to as free radicals) are atomic or
molecular species with unpaired electrons.
An alkyl is a univalent radical containing only carbon and hydrogen atoms
arranged in a chain.
The general formula CnH2n+1.
Examples:
Methyl:
Butyl:
Alkane
methane
ethane
propane
butane
CH3·
(derived from methane)
C4H9·
(derived from butane).
Formula
CH4
CH3CH3
CH3CH2CH3
CH3CH2CH2CH3
Alkyl group
methyl group
ethyl group
n-propyl group
n-butyl group
Formula
·CH3
·CH2CH3
·CH2CH2CH3
·CH2CH2CH2CH3
Example:
Pay attention to the:
Skeletal formula
Alkyl name
Lowest number position
in the name. Hence,
2- rather than 5-.
CH3
4
6
5
3
2 1
2- methyl hexane
3
1
2
Wrong!
CH3
4 5
5- methyl hexane
6
CSUS – CH6B
Hydrocarbons
Instructor: J.T., P 4
Combustion or burning is a complex sequence of exothermic chemical
reactions between a fuel and an oxidant.
Natural Gas combustion:
CH4 + 2O2 → CO2 + 2H2O + Energy
2 C2H2 + 5 02
→
4 CO2 + 2 H2O
In general Combustion of Alkane:
Cn H2n + 2 +
3n +1
O2 → n CO2 +
2
(n +1) H2O
Example: for n=2
C2H6 + (7/2)O2
2 CO2 + 3 H2O
In general Combustion of Alkene:
Cn H2n
⎛3n⎞
+ ⎜ ⎟ O2 → n CO2 + n H2O
⎝ 2⎠
CSUS – CH6B
Hydrocarbons
Instructor: J.T., P 5
Chemical Reactions of Hydrocarbons
1) Substitution:
Replace a flat tire with a spear tire!
UV
CH3-CH2-CH3 + Cl2
→
CH3-CH2-CH2Cl + HCl
2) Addition:
Flower in pot!
CH3-CH2-CH=CH2 + HBr → CH3-CH2-CHBr-CH2H
CH3
CH
Where, X= Cl, Br, I
CH2 + X2
CH3
CH
CH2
X
X
CSUS – CH6B
Hydrocarbons
Instructor: J.T., P 6
3) RedOx (Reduction-Oxidation)
I.
OXIDANT:
A substance that gains electrons in a chemical reaction.
Mr. Oxidant begging for electron
OXIDANT
Or: A chemical compound that readily
transfers oxygen atoms.
II.
Reductant (or reducer) that donates electrons in a redox reaction.
You can recognize oxidation-reduction reactions in organic chemistry as:
Oxidation:
a) When hydrogen atoms are removed from a carbon atom.
Example:
An alcohol oxidize to an aldehyde
b) When an oxygen atom is added to a carbon atom.
Example:
An aldehyde is oxidized to a carboxylic acid.
Reduction:
a) When hydrogen atoms are added to a carbon atom
Example:
An alkene is reduced when it react with hydrogen to form
an alkane.
b) When an oxygen atom is removed from a carbon atom.
CSUS – CH6B
Hydrocarbons
Instructor: J.T., P 7
Examples of Redox reactions:
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CH2
Basic Media:
Dark green solution formation.
CH2 +
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5 CH2
2MnO4-
2OH-
CH2
CH2 + 2MnO4=
OH
OH
Acidic Media:
CH2 +
2MnO4-
6H+
2H2O
5CH2
OH
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C
CH2 + 2Mn++
OH
Neutral Media (Baeyer Test):
Brown solid formation
C
+ KMnO4
H2O
C
C
OH OH
+ MnO2