2/23/2009
Science 30 Unit B – Organic
Chemistry
Name: _______
Date: _______
The things we find on earth can be placed into two categories: Inorganic: rocks, sand,
metals, etc, and organic: plant life, animals, plastics, etc.
The simplest organic compounds are made up of only two elements: carbon and
hydrogen. Compounds such as these are called hydrocarbons.
There is an extremely large number of hydrocarbons known to science. As a result, a
classification scheme has been set (below):
Hydrocarbons
Alkanes
Aliphatics
Alicyclics
Alkenes
Alkynes
Aromatics
Aliphatic hydrocarbons contain chains of carbon atoms, like propane:
CH3 - CH2 - CH3
These chains do not have to be straight lines: they may have branches coming off of the
main chain, like 2-methyl propane.
CH3 - CH2 - CH3
CH3
Alicyclic hydrocarbons contain loops, like cyclopropane. In an alicyclic compound, all
the carbon-carbon bonds are single bonds.
CH2
H2C
CH2
Aromatic hydrocarbons also form loops, but these loops contain some carbon-carbon
double bonds. The classic example of an aromatic hydrocarbon is benzene.
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2/23/2009
Types of Formulas
There are 3 types of formulas used to represent hydrocarbons:
1) Molecular Formula: only shows the number of each type of atom in a compound.
2) Condensed Formula: shows the number of hydrogens on each carbon atom.
3) Structural Formula: Shows how the compound is put together (dashes indicate
chemical bonds)
Nomenclature of Alkanes
Organic compounds are named chiefly on how many carbons they possess in their chain.
The number of carbons corresponds to a prefix, as shown below.
Number of Carbon Atoms
1
2
3
4
5
6
7
8
9
10
Stem Name
methyl
ethyl
propyl
butyl
pentyl
hexyl
heptyl
octyl
nonyl
decyl
When naming an alkane, we start by counting the number of carbons in the longest chain
in the compound. We then match the number of carbons to a prefix, and add the suffix
“ane”, indicating we have an alkane.
Ex) Name the following compound.
CH3CH2CH2CH3
This compound has 4 carbons in it. It must have a prefix of “butyl”. Since all of the
carbons are single bonded, it must be an alkane. So the name of this compound is
“butane” (notice we drop the “yl” on any aliphatics).
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2/23/2009
Practice: Name the following compounds:
a) CH3CH2CH3
b) CH4
c) CH3CH2CH2CH2CH2CH3
d) CH3CH3
e) CH3CH2CH2CH2CH2CH2CH2CH2CH2CH3
Practice: Write out compressed structural formulas for each alkane.
a) butane
b) octane
c) heptane
d) nonane
Sometimes, alkanes do not form a perfectly straight chain. When there are branches off
the chain, we must name the longest chain first, then name the branches.
Ex)
CH3CH2CHCH3
CH3
A compound like this has a main chain made up of three carbons. It also has an extra
branch with one carbon in it.
We name the main chain butane, because it has 4 carbons in it and all the carbon-carbon
bonds are single. We name the branch a methyl branch, since there is only one carbon in
the branch.
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2/23/2009
We will also use the number 3 in the name, to indicate the methyl group is on the third
carbon of the main chain.
So the name of this compound
CH3CH2CHCH3
CH3
is 3-methyl-butane.
*Note how hyphens separate the numbers and the methyl group*.
The different branches with a chain can have, and their names, are the same as the
prefixes listed on the 2nd page of this handout.
Note: this could also be named: 2-methyl-butane if we were to count the carbons from the
right moving to the left.
When naming hydrocarbons, this is actually the preferred method for naming: always
name in a way using the smallest numbers possible.
Sometimes you won't count in a straight line to find
the longest chain! (See diagram to the right.)
Ex) Draw a compressed structural diagram of each
alkane.
a) 2-methyl-pentane
b) 3-ethyl-butane
c) 2,2-dimethyl propane
d) 3-butyl-octane
Line Diagrams
ex) CH3CH2CH2CH2CH3
An even faster way of drawing this compound is to use line structural diagrams. In these
diagrams, no hydrogens are drawn in and the points in the drawing correspond to the
positions of the carbons.
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Review: Write the following condensed structural formulas as line diagrams.
Nomenclature of Alkenes and Alkynes
Alkene Nomenclature
An alkene is any compound containing a carbon to carbon double bond. Alkenes end in
"ene".
Naming an alkene is just like naming an alkane, except you need to indicate the position
of the double bond.
ex) Name the compound.
2. Indicate the location of the double bond. Write that number in
between of the prefix and suffix.
Practice: Name the following compounds:
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Practice: Write the following as condensed structural diagrams.
a) 2-methyl-pent-4-ene
b) 2, 3-diethyl-oct-6-ene
Alkyene Nomenclature
Naming an alkyne is the same as naming an alkene, except the suffix is "yne" and the
compounds now contain double bonds.
ex) Name the following compounds.
Practice: write condensed structural diagrams for the following alkynes.
a) 2-methyl-pent-3-yne
b) 4, 4-dipropyl-non-7-yne
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