Chemistry 20 Unit 6 – Organic Chemistry - LD Industries



Chemistry 30 Unit 3 – Organic Chemistry

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):

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.

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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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.

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2) Condensed Formula: shows the number of hydrogens on each carbon atom.

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3) Structural Formula: Shows how the compound is put together (dashes indicate chemical bonds)

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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 |Stem Name |

|1 |methyl |

|2 |ethyl |

|3 |propyl |

|4 |butyl |

|5 |pentyl |

|6 |hexyl |

|7 |heptyl |

|8 |octyl |

|9 |nonyl |

|10 |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).

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.

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-heptane

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.

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.

*Name so that the numbers

on the double bond are the

smallest possible!

Practice: Name the following compounds:

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Practice: Write the following as condensed structural diagrams, then write the correct name.

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.

[pic]

Practice: write condensed structural diagrams for the following alkynes.

a) 3-methyl-pent-2-yne

b) 7, 7-dipropyl-non-4-yne

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Name: _______

Date: _______

Hydrocarbons

Aliphatics

Alicyclics

Aromatics

Alkanes

Alkenes

Alkynes

CH2

H2C

CH2

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