Aspirin has been used for centuries to relieve all kinds of pain and inflammation. Today, people take aspirin to reduce a fever, to stop a headache, to reduce swelling, and sometimes to prevent heart disease.

The chemical name for aspirin is acetylsalicylic acid. Its chemical formula is C-9, H-8, O-4. Acetylsalicylic acid is an example of an organic compound, which means it contains carbon.

Life on Earth is based on a vast array of organic compounds. All species of plants and animals use carbon-based molecules for structure and biological functioning. Even soil contains many different organic molecules because it's made up mostly of decomposed plants and animals.

Carbon is unique among the known elements. It's a nonmetal so it forms covalent bonds. Carbon is able to form four bonds, so it can bond to several other atoms in many different ways. As a result, most chemicals now known are organic. Many are found in nature, but in the lab, chemists have also synthesized millions of organic compounds not found in nature.

What about aspirin? Is acetylsalicylic acid natural or synthetic? A related molecule called salicylic acid comes from the bark of willow trees, a natural source. Acetylsalicylic acid is similar to salicylic acid except that it has a few extra atoms. These atoms help make the molecule less irritating to the stomach. Chemists add this group of atoms in the laboratory. Therefore, acetylsalicylic acid is neither completely natural nor completely synthetic.

Since aspirin is a fairly simple molecule, it's amazing that it has so many biological effects. Many drugs, including aspirin, take part in chemical reactions in the body. Recall that chemical reactions convert reactants into products that have different chemical properties and composition. An organic reaction is a chemical reaction involving organic molecules. When you take an aspirin, it participates in an organic reaction in your body. The products of this reaction are what give aspirin its biological effects.

We're going to explore the structures of organic molecules, particularly those involved in biological processes. We'll start with an overview of organic chemistry. Next we'll explore some of the organic molecules in the foods we eat. Then we'll discuss two groups of organic molecules that contain nitrogen: amino acids and nucleotides. By the time we finish, we'll return to our discussion of acetylsalicylic acid, so we can see how aspirin has many of its biological effects.

Copyright 2006 The Regents of the University of California and Monterey Institute for Technology and Education