Welcome to part one of the organic chemistry introduction. I'm Melissa Marabou, your personal tutor, and the most important element for organic chemistry is carbon. Remember, carbon has four valence electrons, which means it could have four bonds. Knowing this, let's go over the four different ways a molecule can be represented.
The first way is the typical molecular formula. The second way is the structural formula. which looks like a typical Lewis structure. The third way is called a condensed structural formula.
To write this formula, we looked at the structural formula, where on the first carbon to the left there are three hydrogens attached. This is why we have CH3. Next, the middle carbon only has two hydrogens, so CH2. And the last carbon to the right has three hydrogens, so CH3. The fourth way is what you will most commonly see throughout the entire semester.
It is the skeletal formula, also referred to as a line diagram, where each point represents a carbon and the hydrogens are not shown. This is where knowing that carbon wants four bonds is going to be very important. This is what the structure would look like if we drew in the hydrogens. At this carbon, We already have one bond, so we are missing three more bonds, which must be three hydrogens.
Next, the middle carbon already has two bonds, so we need two more, so we have two hydrogens. And this last carbon already has one bond, so we need three more bonds, so three more hydrogens. To make sure you get this down and don't miss anything on your exam, make sure to pause the video and try this question out, and we'll go over the answers together.
Okay, here are the answers. The structural formula consists of four carbons and ten hydrogens. So this first carbon needs three hydrogens. Next carbon has two bonds, so it needs two hydrogens.
Same goes for this carbon. And this last carbon has one bond, so it needs three hydrogens. So this is our structural formula. Using the structural formula, we'll write the condensed structural formula.
Where this first carbon has three hydrogen, so CH3, the next carbon has two hydrogen, so CH2, same for the next carbon, so CH2, and the last carbon has three hydrogen, so CH3. This is our condensed structural formula. Now for the skeletal formula. Since there are four carbons, we need four points. There is a trick to drawing this right each time.
If you were to count... one, two, three, four, we actually drew too many carbons. We drew one, two, three, four, five, but we just wanted four. So if you count to one less carbon than what you're originally looking for, then you will draw the correct amount of carbons each time. So in our case, we will count to three when drawing the lines.
So one, two, three, and we really have one, two, three, four carbons. This is the correct skeletal formula. These molecules that we are working with are called hydrocarbons.
A hydrocarbon consists of only hydrogens and carbons. There are different types of hydrocarbons. This is based on the type of bonds that are between the carbon atoms. Alkanes have single bonds.
Alkenes have at least one double bond and alkynes have at least one triple bond. You will later get into naming different types of structures, so know that the ending is very important. If something ends in"-ene", it's an alkane, meaning it only has single bonds. The ending"-ene", means it's an alkene, which has a double bond. And the ending of"-yne", makes it an alkyn, which means it's a triple bond.
This all is talking about the major carbon chain or longest carbon chain. But we can also have something known as a substituent, which is an atom or groups of atoms that replaces a hydrogen and gets attached to the carbon in the longest carbon chain. Think of it this way, the longest carbon chain is like the body of a person, and the substituents are the arms or legs, because that's what's sticking out of the body. Here's a list of the most common substituents you will first see. These specific substituents are also referred to as alkyl groups.
An alkyl group is made up of only carbons and hydrogens. It is also defined as an alkane that is missing one hydrogen. The first alkyl group is methyl.
This has only one carbon. Next is ethyl. This has two carbons.
then propyl has three carbons, and butyl has four carbons. You will definitely be tested on functional groups, which is what I'll be covering in part two. You can find that right over here.
And remember, stay determined. You can do this.