An organic molecule (hydrocarbon) is formed when carbon bonds to hydrogen.  The simplest hydrocarbon consists of 4 hydrogen atoms bonded to a carbon atom (called methane):

In addition to binding to hydrogen, carbon can also bind to other carbon atoms, as illustrated below:

In fact the uniqueness of carbon comes from the fact that it can bind to itself.  Carbon atoms can form long chains:

branched chains:

rings:

in fact, there appears to be almost no limit to the number of different structures that carbon can form.  To add to the complexity of organic chemistry, neighboring carbon atoms can form double and triple bonds in addition to single carbon-carbon bonds:
 

Table I

A carbon-carbon single bond

A carbon-carbon double bond

A carbon-carbon triple bond

Keep in mind that each carbon atom forms 4 bonds.  As you increase the number of bonds between carbon atoms, the number of hydrogen atoms in the molecule decreases (as can be seen in the table above).

Nomenclature (naming compounds):
        The simplest hydrocarbons are those that contain only carbon and hydrogen.  As we have seen, these come in three varieties: 1) alkanes, molecules with only single bonds, 2) alkenes, those with one or more double bond and 3) alkynes, those with one or more triple bond.  Basic organic chemistry can be thought of as a molecular Erector Set, if you know the number of carbon atoms and the type of bonds in a molecule, you can build the molecular structure.  To describe the number of carbon atoms in a hydrocarbon, chemists use prefixes in the molecule's name.  The first 10 prefixes used in organic chemistry are shown below.  To complete the hydrocarbon name, the prefix is attached to the ending of the root word (drop the alk- from the words alkane, alkene or alkyne) to describe the type of bonding on the molecule.  The hydrocarbon names (also called nomenclature) is described in Table II using the first 10 alkanes as examples.

Table II
		ie.: Alkanes
Hydrocarbon prefix	# of carbon atoms	name	formula	structure*
Meth	1	methane	CH4
Eth	2	ethane	C2H6
Prop	3	propane	C3H8
But	4	butane	C4H10
Pent	5	pentane	C5H12
Hex	6	hexane	C6H14
Hept	7	heptane	C7H16
Oct	8	octane	C8H18
Non	9	nonane	C9H20
Dec	10	decane	C10H22

As we have discussed, each carbon atom has 4 bonds.  As you add carbon to a molecule, the empty carbon bonds are filled with hydrogen atoms (or other elements, as we will soon see).  You can calculate the number of H atoms in the simple alkanes.  The number of H atoms in a simple alkane equals two times the number of carbon atoms plus 2, or (2n + 2), where n is the number of carbon atoms in the molecule.  The simple alkenes have 1 double bond and 2 fewer H atoms in the molecule; the number of H atoms in the simple alkenes = (2n).  Simple alkynes contain 1 triple bond 2 fewer H atoms than the alkene, or (2n - 2) H atoms.

        The simple hydrocarbons are fairly common.  Methane, for example, is released by decaying organic matter and is the main compound in natural gas.  These chemicals are generally gases or liquids in nature and are very flammable.  Butane is used in cigarette lighters.  Ethyne, also known as acetylene, is used in welding.

        In addition to carbon and hydrogen, hydrocarbons can also contain other elements.  The alcohols, for example, are a group of hydrocarbons in which a hydroxol (-OH) group is bound to a carbon skeleton.  These compounds are named like the simple hydrocarbons, a prefix attached to a root ending (-anol for the alcohols).  Thus ethanol, is a 2 carbon alcohol with the structure:

Most people are familiar with this organic compound as it is the active ingredient in "alcoholic" beverages such as beer and wine.

        While the simple hydrocarbons are important, they do not themselves commonly occur in living organisms (except for during the occasional bout of methane flatulence).  The simple hydrocarbons are the building blocks of more complex molecules that make up living organisms.  In the next lesson, we will introduce some of these molecules and their biochemistry, the chemistry of life.

There are several good sites on the Web for exploring organic chemistry in further detail.  The one hitch with many of these sites is that most require you to have some type of molecule-viewing software.  One choice of software available for free is the Chemscape Chime 2.0 viewing software.  Once you have installed this plug-in, you can may want to visit some of the sites below for more information on organic chemistry:

• The Internet Science Room has a good introduction to simple hydrocarbons (Chime not required).
• The Smith College, Department of Chemistry has drawn some 3-D organic structures (Chime required).
• The Okanagan Department of Chemistry has put together a good introduction to organic chemistry that includes interactive 3-D molecular drawings that you can click on and rotate (Chime required).

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