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 singlebonded 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