Complex Organic Compounds in Chemistry: Types, Groups & Examples

Instructor: Adrianne Baron

Adrianne has taught high school and college biology and has a master's degree in cancer biology.

We are going to delve into the world of complex organic compounds. The four main types will be explored by looking at their general structure and some examples.

Organic Compounds

In today's world, the word 'organic' elicits thoughts of a section in the grocery store where you can buy foods that haven't been altered. You start thinking about healthy and wholesome foods when you hear or see 'organic'.

What you probably don't think about when you hear the word 'organic' is your dog, cat, fish, favorite flower, bacteria or fungi. A chemist, especially an organic chemist, would have thought about those living things at the mention of the word 'organic,' because they would think about organic compounds. Organic compounds are any molecules that are composed of the element carbon.

Diamonds are molecules of crystalline carbon.
Picture of a diamond

We are constantly surrounded by organic compounds. Diamonds are molecules of crystalline carbon. Gasoline and charcoal are also examples of simple organic compounds.

There are more complex organic compounds that make up living organisms. There is a constant circulation of carbon between living and non-living organisms called the carbon cycle. The carbon cycle contains various biogeochemical processes that are necessary for life to exist. So, you can sum it up this way: no carbon means no organic compounds, which means no life. That means that carbon is extremely important.

Complex Organic Compounds

The main reason for the value of carbon is because it can form four bonds at one time, which allows it to form complex, flexible molecules. This is ideal for life. The four main groups of carbon molecules of life are proteins, carbohydrates, lipids, and nucleic acids. These are the most complex types of organic compounds.

All right, go take a look in the mirror. Do you see the complex organic compounds? You do if you see your skin. Skin is made up of proteins. You do if you see fat. Under your skin and fat, there are many processes taking place, which all require energy in the form of carbohydrates. We can't forget the very important nucleic acids, which tell the cells in your body how to operate and reproduce.

In simple organic compounds, a carbon is bonded to just hydrogen. Complex organic compounds, especially those involved in living systems, have carbons bonded to at least hydrogen and oxygen. Let's start simple and go complex again.

Sugar is a type of carbohydrate.
Picture of different types of sugar

Carbohydrates are molecules made of carbon, hydrogen and oxygen. An example of a carbohydrate is table sugar, known as sucrose. Sucrose has the molecular formula C12H22O11. All complex organic molecules, like sucrose, are known as polymers. Polymers are complexes of repeated structural units. The structural units that make up polymers are called monomers. So essentially, polymers are complexes of monomers. Sucrose is a polymer of the monomer glucose.

Lipids, commonly referred to as fats, are also polymers. Lipids are polymers of fatty acids. The cholesterol that you work so hard to keep within certain limits is an example of a lipid. Cholesterol is one of the main components of animal cell membranes, and allows the cell to be flexible and change shape. Cholesterol has a complex structure of four linked hydrocarbon rings and a hydrocarbon tail. Cholesterol's molecular formula is C27H46O.

If you have tried to diet before, then you are aware of the two main types of lipids, saturated and unsaturated. You may have been on a diet high in unsaturated fats, or fatty acid chains with double bonds, because these are healthier. Saturated lipids are fatty acid chains that have no double bonds. Most animal fats are saturated lipids, whereas most plant and seed fats are unsaturated lipids. A few exceptions to this are some tropical plant fats, such as coconut or palm oil, which are saturated lipids.

Our next organic compound, protein, is even more complex than carbohydrates or lipids. Proteins are polymers of amino acids. Amino acids contain nitrogen, carbon, oxygen and hydrogen. Are you noticing that as we add more elements, the organic compound gets more complex? There are 20 amino acids with a wide range of chemical properties, thanks to the nitrogen they contain. Amino acids span the entire pH scale, with some being acidic, basic or neutral. Some amino acids have a charge, making them polar. This is important when it comes to how proteins fold together, as well as how they bind to other compounds.

The shape of proteins after folding determines their function. For example, an enzyme is a protein with an active site that will bring together other molecules to catalyze a reaction. Some proteins are huge due to their final shape after folding. These proteins are so big that chemists don't focus on their molecular formula; instead, they focus on their molecular weight.

DNA and RNA are complex organic compounds.
Picture of DNA diagram

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