Introduction to Organic Molecules I: Functional Groups

If you've ever wondered what gives vinegar that sour flavor, you may not realize that you have contemplated functional groups. View this lesson for an introduction to organic chemistry, functional groups and how they are part of your daily life.

What Is Organic Chemistry?

What do you think of when you think of when you hear the word organic? Do you think of the baby carrots that you saw in the grocery store the other day or do you think of something entirely different?

When we talk about organic foods, we mean that they were grown using only natural fertilizers. Now, what does this have to do with chemistry? Well, it turns out that for a long time chemists have been studying the molecules that make up living things, and for a long time they called this organic chemistry.

To them, organic chemistry was the study of molecules that came from living things and from formerly living things. These molecules included sugars (such as glucose), proteins and the amino acids that make them up (such as glycine), fats and also hydrocarbons (such as methane - which you know is natural gas - and octane - which is a component of gasoline) which are molecules that came from things that used to be living.

At some point, scientists decided that they were going to start making these types of molecules synthetically. So the old definition no longer fit. Organic chemistry could not just be the study of molecules that came from living things, but it needed to be a little bit broader. So, scientists looked at the different kinds of molecules from living things and found that they all contain carbon.

This leads us to our new definition of organic chemistry, which is the study of molecules that contain carbon.

What are Functional Groups?

Now, if all these molecules were like methane and octane (containing only carbon and hydrogen), life wouldn't be exciting. In fact, life probably wouldn't exist, since these molecules mostly sit around interacting with other like molecules. Unless oxygen and fire come along - in which case, they burn and turn into carbon dioxide and water. Since we're not running around as flaming people, this means there must be a little more to the story. It turns out, this is true.

While organic chemistry is the study of molecules that contain carbon, they also contain other atoms. So, organic molecules can contain carbon, hydrogen, oxygen, nitrogen, phosphorus and sulfur. All of these atoms come together to make what we call functional groups.

Functional Groups - 1

Functional groups are groups of atoms that we often find together that have a specific behavior. They're also a really good way to help you recognize different classes of molecules, because different types of molecules contain different functional groups.

Now, think of it as if you're going to go on an okcupid.com or a match.com date. You've never met this person before, so you need to remember what he or she looks like. So you look at the profile and say: this person whose name is ChemistryIsAwesome has glasses, brown hair and he or she is about 5-foot, 8-inches. All of this information gives you some idea of what this person looks like and how you will recognize him or her. That is exactly what functional groups do for us when we meet new biological molecules.

So, as we meet new biological molecules, functional groups can help us to recognize them because each of the different types of biological molecules has a characteristic set of functional groups. So, we're going to go meet the functional groups now.

Hydroxyl Group

The first functional group we're going to meet is the alcohol or hydroxyl group. Now, looking at the name hydroxyl you might think this thing probably contains hydrogen and oxygen. If that's what you're thinking right now, you're right.

A hydroxyl group is an oxygen atom that is single-bonded to hydrogen and is also single-bonded to a carbon-containing group. A common alcohol that you probably know is ethanol, which can be used as a cleaner and is the alcohol that is found in alcoholic beverages.

So the general picture of an alcohol is that it is a group that contains carbon attached to oxygen, which is single-bonded to hydrogen. A lot of times, chemists use the short hand R to talk about something that contains carbon. In some cases it can be carbon or hydrogen, but in the case of an alcohol it's always a carbon, because if it was not a carbon-containing group than it would be water.

Amine Group

The next functional group I'd like to introduce you to is the amine. The simplest amine is ammonia and is often found in bathroom cleaners. It has a very simple chemical structure which it a nitrogen atom that is bonded to three hydrogen atoms. It's quite small and quite volatile, and that's why it has a very pungent smell.

More generally, amines are a nitrogen atom that is single-bonded to three different groups that contain either hydrogen or carbon. So, in the case of amines in our group, it can be either hydrogen or carbon and it doesn't matter. Amines are found in amino acids and are very important in biological systems because they are basic and they can accept protons from more acid substances.

Functional Groups - 2

Ether Group

The next functional group that I'd like to introduce you to is the ether, which is found in sugars. The ether group consists of oxygen that is single-bonded to two different carbon atoms. An example that you might be familiar with is diethyl ether, which was used as an anesthetic for a long time. So, if you've ever seen a movie where someone is going in for a surgery and they put a cloth over their face, it contained diethyl ether and was meant to knock them out.

A more general version of ether would be an oxygen atom with any two carbon-containing groups on either side of it.

Carbonyl Group

The next functional group is the carbonyl. A carbonyl is a carbon that is double-bonded to oxygen. A carbonyl-containing molecule that you're already familiar with is acetone, which is found in nail polish remover. Carbonyls are found fairly often in biological systems.

A carbonyl-containing functional group is the carboxylic acid. When you look at the word carboxylic you probably see carb, as in carbonyl, and oxyl, as in hydroxyl. It turns out this is the structure of the carboxylic acid. It consists of a carbon that is double-bonded to an oxygen, and single-bonded to an oxygen that is single-bonded to a hydrogen (which we know is a hydroxyl group). So it is a carbon that is both a carbonyl and bonded to a hydroxyl group. These are found in amino acids and fatty acids in our body. One that you may be familiar with is acetic acid, the major component of vinegar and what gives it that lovely pungent smell.Ester Group

The last functional group that I'd like to introduce you to today is the ester. Esters consist of a carbon atom double-bonded to an oxygen atom that is single-bonded to an oxygen atom that is attached to a carbon atom. So, you have a carbonyl where the carbon is also part of an ether, and we call this an ester.

Esters are important in biological systems because they hold fats together. They bond fatty acids to glycerol to form mono-, di- and triglycerides. In addition, esters are one of the things that make fruits smell really nice.

We've reached the end of our lesson and I hope that you've enjoyed learning a little bit about organic chemistry and also meeting some of the different functional groups that we'll be encountering as we meet new molecules.

Functional Groups - 3