We're now ready to start building much more complicated organic molecules. I'm going to give you my analogy of how I think about the structure of organic molecules. In my opinion, organic molecules are kind of like Christmas trees.
So whether or not you celebrate Christmas come, I don't know, October, November, you're inundated with Christmas decorations pretty much wherever you go. And one of the most common decorations is a Christmas tree. A Christmas tree really has two parts to it. You've got the actual tree structure, right? You can choose from real trees, plastic trees, you can get different kinds of trees, right?
The ones with the short needles, the ones with the long needles, scrawny Charlie Brown Christmas trees, or really full ones. There's a lot of variability, but you need that basic structure. Once you have the basic structure, then you decorate it, right? There are people that might have four or five Christmas trees in their house, and each one has a different theme, right?
One holds red, white, and blue. ornaments. One is just an angel Christmas tree, one is Disney ornaments, right? So each one has a theme based on what kinds of decorations you put on it.
Organic molecules are exactly the same way. First of all, you've got to pick your basic structure, what we call your skeleton, and then to give each organic molecule its specific functions, you have to decorate it with extra chemical groups that give that basic structure. its unique characteristics. The first thing we're going to do in this section is talk about the skeleton or that naked Christmas tree before it gets decorated. The skeleton of organic molecules, the basic tree shape is formed using carbon atoms.
These carbon chains, also called the carbon skeleton, can have a variety of lengths and shapes. On this slide, we give you some of that variability. For example, Those carbon skeletons can vary in length. We looked at ethane as a previous example. Ethane has two carbons.
You can add a third carbon to get propane. You can have a fourth carbon, butane, fifth, pentane, and so on and so forth. So they can vary in length. Once you get up to four carbons, you can start to introduce some branching, and that's shown down here. So both of these molecules, on the left we've got butane, and on the right we've got isobutane.
These molecules both have the exact same molecular formula, so same number of carbons, same number of hydrogen, they're just organized a little bit differently. Butane has all the carbons all in a row, whereas isobutane has three carbons in a row, and then that fourth one branches off the middle carbon there. All right, you can also have not just single bonds between carbons, but you can have double bonds. And depending on where you put that double bond will create a slightly different molecule.
So double bond position is another way in which you can vary that. carbon skeleton. Again here in C we've got two examples. We've got one butene on the left and two butene on the right. You'll notice again these molecules both have the same number of carbon, same number of hydrogen, they just differ in where that double bond is.
For one butene you have the double bond at the end of the molecule and for two butene you've got it right in the middle there. The last way in which those carbon skeletons can differ is through the presence of rings. So you can take that linear carbon chain and you can make it a ring. You can seal the ends. One of the most, let's say two of the most common ring structures are cyclohexane here, which shares all single covalent bonds between the carbons, and then you've got your benzene ring, where you've got alternating single and double bonds between the six carbons found in that ring.
Alright, so maybe before we move on to this slide, something that you will notice about all of the examples that we used here to show variability of the carbon skeleton, all of these molecules solely contain carbons and hydrogens. We give a very specific name to that. type of molecule.
They are all what we call hydrocarbons. Hydro for hydrogen, carbon for carbon. Right, so hydrocarbons are organic molecules that consist only of carbon and hydrogen.
Let's take one more step back. Think about the names ethane and propane and butane. Hopefully, when you hear those names, you immediately think a source of fuel. You're going to use it in your lighters, for example, or in a propane grill. Hydrocarbons, because of their molecular Arrangement of those carbons and hydrogens.
Hydrocarbons have a large capacity for storing a lot of energy. So clearly, propane, ethane, butane are really good molecules to use as fuel. Now, as living organisms, we don't necessarily produce molecules that are solely hydrocarbons, but we still have certain molecules that we do make that have hydrocarbon components to them that allow us also to store a lot of energy. What I'm alluding to here are fat molecules. We'll introduce the fat molecule here and then we'll talk a lot more about it once we get to the chapter on macromolecules.
If you look in the center of the slide here, this is an example of what a fat molecule looks like using a space-filling model. The blacks are going to be your carbons and the grays are going to be your hydrogens. You can see that this fat molecule has sort of a backbone right here.
We will learn later that this is a glycerol. And then attached to the backbone, you've got these three long hydrocarbon tails. These are your fatty acids. And this part of the fat molecule, those fatty acid tails, have the ability to store a lot of energy. And as animals, fats are the primary way in which we store our long-term energy reserves.
And those fat molecules are going to be stored here in tissue that's called adipose tissue. So this is an image taken using a microscope. of a fat cell. You can see the nucleus right here and then all of these yellow droplets are all fat droplets.
So they are made out of many many many fat molecules and the main responsibility of adipose tissue or adipose cells is simply just to store those fat molecules so we have that energy reserve waiting in case we need to store them. to use it. So again, hydrocarbons, when you break them down, they can go through these reactions that release a lot of energy. So they're a good energy storage molecule. OK.
One more thing to take into consideration when we're looking at the skeletons of the carbon skeletons of organic molecules. Some of them can be very similar. And yet, because of the slight differences that they have, the differences confer different properties to those molecules. So we need to discuss isomers.
By definition, an isomer is going to be a compound or compounds that have the same molecular formula but different structures and therefore different properties. You didn't know it yet, but we actually already took a look at some examples of isomers. So let's take just a couple steps back. Alright, so our butane and our isobutane.
I said, hey, they have the same molecular formula, just their structure is a little different. These are isomers. The same thing goes for 1-butene and 2-butene.
Also, same number of carbons, same number of... number of hydrogens, just they're organized a little bit different. These are going to be isomers as well.
So there are different kinds of isomers. We're going to talk about three different kinds. The first is on this slide.
So we have structural isomers. These have different covalent arrangements of their atoms. So this is much like butane and isobutane. We've got pentane and then two methylbutanes.
So same number of carbons and hydrogens, but the pentane has that carbon skeleton all in a straight line. whereas a 2-methyl butane introduces a single branch. We can also have cis-trans isomers.
These are also sometimes called geometric isomers. If you'll recall, in an earlier video, we talked about how you don't necessarily have to have single bonds between carbons. You can have double bonds.
Whenever you have that double bond between the carbon, the attached atomic components or molecular components to the carbons all lie in the same plane. and there's no rotation of the molecule. So it matters where you put certain atoms or molecular components attached to those double-bonded carbons. So we've got two examples on the slide here that are cis-trans isomers. This one over here, you'll notice the two X components are on the same side.
This would be considered a cis-isomer, cis meaning same side. The Xs are on the same side of that double bond. On the other hand... This one is the trans isomer.
There's the double bond. The Xs are on opposite sides, trans meaning opposite. Because you have no rotation across that double bond, you can't turn this half of this molecule, or let's say this half of this molecule, to make it look like that one. So these are two distinct molecules.
And I have that represented using my little models here as well. So for example, if you're focusing on the two hydrogens here in the middle, in white, you'll notice that these guys are an opposite. sides of the double bond. So this would be the trans isomer and then its little friend over here is going to be the cis isomer. You've got the hydrogen's on the same side of that double bond here.
So because there's no rotation across that double bond, these two molecules are distinct. They'll have different properties associated with them. Okay, and then the last kind of isomer, these are my favorites, these are enantiomers. So enantiomers are essentially mirror images of each other, kind of like your right and your left hand, right? Your right hand is never going to fit comfortably into the mirror.
to the left hand. You can't ever rotate your right hand in any way to get it to look exactly like your left. So while they still have the same components, four fingers, a thumb, and a palm, they are two distinct components. components of your body, much like the isomers that you see down here. So these two molecules, they have the same components attached to the carbon, but there's no way you can rotate the isomer on the left here to make it look like the isomer on the right.
Two different molecules, and they have different properties. Enantimers are particularly important in the pharmaceutical industry. So the two enantimers of a drug, the mirror images of the same drug, might have different effects on a living organism.
You... Usually what happens is only one of the two isomers is actually biologically active. The other one does absolutely nothing. This shows you how sensitive bodies, living organisms are to very slight changes in chemical composition. Let's take a look at some examples.
First of all, our first example here is ibuprofen. This is probably something that everybody's taken at some point in their life. It reduces pain, reduces inflammation. In the pharmacology. pharmaceutical industry goes through the chemical reactions to make ibuprofen they make the ibuprofen as two enantiomers you've got s ibuprofen and you've got our ibuprofen the s version the s enantiomer is actually the effective enantiomer this is what reduces the inflammation and the pain it's about a hundred times more effective than the r enantiomer now to make a single enantiomer in its pure form can be very expensive for a pharmaceutical company.
So because R-ibuprofen really doesn't harm you at all, usually when you take ibuprofen, you're taking a mixture of S and R because it's cheaper for the pharmaceutical company to make. They can sell it to you cheaper. You're more likely to buy that product. And you still get the effectiveness that you need from the S-ibuprofen.
The other example here is albuterol. Albuterol is a drug that sometimes... is prescribed to asthma patients, and it's supposed to increase or open the air passages during an asthma attack.
Again, the drug comes into enantiomeric forms. R-albuterol, in this case, is the effective enantiomer, and S-albuterol is the ineffective enantiomer. The difference here between ibuprofen and albuterol is that while R-albuterol opens the air passages, S-albuterol is not necessarily ineffective.
It actually does does the opposite of R-albuterol. It actually constricts the air passages. So this is where pharmaceutical companies have to be very careful.
In this case, they have to make that single R enantiomer to make sure that they're only opening the air passages for the asthma patients. If they sold a mixture, it would likely be ineffective. Or if by chance maybe there was more S than R, you can actually kill an asthma patient because that that S-albuterol would be contributing to the construction of their air passages when the patient already can't breathe.