Organic Chemistry

What is Organic Chemistry?

Alkanes, Alkenes, and Alkynes: How to Name and Draw

Organic Chemistry

^[1]An organic molecule: penicillin

What is Organic Chemistry?

You learned earlier that molecules bond to complete the valence and when they bond covalently they share the valence electrons. Organic Chemistry is commonly called the chemistry of carbon molecules; carbons bonded together are the backbone of the molecule. Carbon has 4 valence electrons so it needs 4 bonds to complete the valence. Therefor a carbon chain can form single, double, and triple bonds. In this unit, we will learn how to name and draw common organic molecules and the characteristics of the different groups.

Learning Target 2.2.1: I can compare and contrast alkanes,alkenes and alkynes

Goal 2.2.1.a: I can name alkanes alkenes and alkynes

Goal 2.2.1.b: I can draw alkanes,alkenes and alkynes

Goal 2.2.1.c: I can write molecular structure given the name and or structure

Alkanes, Alkenes, and Alkynes: How to Name and Draw

We will follow the rules set by International Union of Pure and Applied Chemistry (IUPAC) to name Organic Molecules.

Recall Prior Learning:

How many sides are in a octagon? How many sides in a pentagon? Many of the prefixes you learned in an earlier Geometry class are the same prefixes you will use in naming Organic Compounds.

Below is a table with prefixes that refer to the number of carbons. Example, if you hear the name propane that refers to a carbon molecule that has 3 carbons (prop- is the prefix).

Prefix System for Naming Hydrocarbons

Alkanes

The second thing that you must pay attention to in the name of your molecule is the suffix. If the molecule has all single bonds between the carbons in the longest chain then is is classified as an alkane and the suffix -ane is used.

^[2]A molecule of propane contains 3 carbon atoms. This compound is often used as a fuel in gas grills.

A Lewis structure of butane. This compound is also used as a fuel in lighters. Notice there are four carbons and all single bonds between the carbon atoms. ^[3]

Hydrogens are placed around the carbon atoms to complete the octet and form 4 single bonds.

Carbon skeletons are a simplified way to draw straight chain organic molecules. In carbon skeletons, the hydrogen carbon bond is not written, but it is understood to be present.

The above Lewis structure of Butane

          would be drawn as a carbon skeleton as

The molecular formula for the organic molecules can be determined by examining the structure and counting the number of carbon and hydrogen atoms in the molecule. They can also be calculated with the general formula. For alkanes the general formula

where n is equal to the number of carbons atoms in the molecule.

Check for Understanding

^[4] A ball and stick model of an organic compound.

Can you name the above organic molecule? What represents the carbons? What is representing the hydrogens? Can you write the molecular formula for this compound? Answer the questions in your notebook and then check the answers.

Alkenes

If the longest chain has a double bond between 2 of the carbons in the longest chain it is classified as an alkene and the suffix -ene is used.

^[5]A Lewis structure of ethene. It has 2 carbons so the prefix eth- is used and there is a double bond so the suffix -ene is used.

The molecular formula for alkenes can be determined by examining the structural formula or they can also be determined by the general formula:

where n equals the number of carbon atoms in the molecule

Alkyne

When there is a triple bond between 2 of the carbons on the longest chain it is classified as an alkyne and the suffix -yne is used.

^[6]A Lewis structure of ethyne. The prefix eth- is used because there are 2 carbons and suffix -yne because their is a triple bond between the carbons.

The molecular formula for alkynes can be determined by examining the structural formula or they can also be determined by the general formula:

where n equals the number of carbon atoms in the molecule.

There are many more rules to understand how to draw and name alkenes and alkynes. Watch the learning video on how to name and draw alkenes and alkynes. Be sure to do the practice problems at the end of the video.

In your notes, compare and contrast Alkanes, Alkenes and Alkynes.

Practice by doing the Alkanes, Alkenes, and Alkynes Worksheet.