In this video, we will take a look at isomers in the context of organic chemistry. The first thing that you need to know is structural isomers. So what is a structural isomer?
Now, this is the definition. Structural isomers are organic molecules with the same molecular formula, but different structural formulas. So on the screen, you can see two different organic compounds, one on the left one on the right they have very very different structural formulas. They're both alkanes, but this is a straight chain alkane over here, and its name is butane. Okay, four carbons, butane.
And on the right, we have a branched alkane. It is 2-methylpropane. So they're both alkanes, okay, different structural formulas, But the molecular formula... So C4H10, both of them have the same molecular formula.
Count the number of carbons in both. Count the number of hydrogens in both. You will come to the same molecular formula.
So we can also take a look at something like this. Very different organic molecules, very different compounds. They have different structural formulas.
This one is actually an aldehyde. This one is actually a ketone. However, different structural formulas, but the exact same molecular formula C3H6O.
So that's a basic idea of what a structural isomer is. But we're going to be looking at three different types of structural isomers. Positional isomers, chain isomers, and functional group isomers. Now, what I like about the different types of structural isomers is the name explains what it is. So if we take a look at number one, positional.
isomers positional isomers they have the same molecular formula but different positions so positions you understand what positions are of the side chain substituent so this is basically your branch or functional group on the parent chain so if you look at my first compound over here. I have one, two, three, four, five carbons. Okay.
So C5H. H11, 11 hydrogens and chlorine. But take a look at where chlorine is positioned. It's positioned on the first carbon.
Remember, you would number the carbons like that from right to left. Just like that, chlorine is on the first carbon. However, the molecule on the right has exactly the same molecular formula, but the chlorine, the halogen substituent, this is a halogen, it's a substituent, and it has moved to the second.
carbon. It's no longer on the first carbon. So these two are called positional isomers.
Then we have chain isomers. Now chain isomers, same molecular formula, but different types of chains. So this one is a straight chain.
You can see six carbons, hexane. So that would be C6H14. The compound on the right is also C6H14.
So that's what we mean by same molecular formula, but different types of chains. So this one has five carbons in the main chain and then a methyl branch on the second carbon. So it's no longer a straight chain alkane, it's a branched alkane, but same molecular formula.
Then the third type of structural isomer that people struggle with is called the functional group isomer. Now functional group, when you think of functional group. That definition is the bond, the atom, or group of atoms. That determines the physical or chemical properties of a group of organic compounds.
So remember, different homologous series have different functional groups. So alcohols versus carboxylic acids versus ketones, each of these different homologous series have their own functional groups. So functional group isomers, they have the same molecular formula, but different functional groups, which means that these isomers belong to completely different homologous series.
So if you take a look at the two isomers on the screen, I know that these are functional group isomers because first of all they have the same molecular formula. So count the number of carbons in both of them. We've got one, two carbons here, same thing here, one, two carbons.
Number of hydrogens, one, two, three, four. Same thing in this one, one, two, three, four. So same molecular formula for now.
And then their oxygens, one, two. Same thing in this one. One, two.
However, but this compound on the left over here, I hope you can identify what homologous series it belongs to. This compound over here is an ester. And its functional group is as follows. In my ester video, I talk about cocoa being the functional group. So this is an ester.
This is methyl, methanoate, just in case you were wondering. And then this compound over here down below me. This is a carboxylic acid, and I can tell that it's a carboxylic acid based on its functional group, which is this over here. Can you see that the highlighted bits for each molecule is very different?
So although they have the same molecular formula, they're very different functional groups, and therefore they are functional group isomers. This carboxylic acid is called ethanoic acid, just by the way. So what two homologous series go together and are...
functional group isomers. I like to think of functional group isomers like cousins, okay? Like two family members that have similar genetic makeup, same molecular formula, but they're very different structural formulas, okay? So take a look at these two, ketones and aldehydes.
Those two are functional group isomers. So if I give you a ketone and I tell you or I ask you to draw its functional group isomer, you will draw an aldehyde for me. The reason that those two are considered functional group isomers is because their general formula, they have the same general formula CnH2nO. So here's an example of that. We've got propanol, okay, propanol, which is an aldehyde, and propan-1.
This would actually be propan-2-1, indicating the position of... the double bond oxygen and these are functional group isomers. If we actually count the number of carbons in each of them we get three. The number of hydrogens will be double the number of carbons.
You can see two times n which is six and if you count on the picture it is and then o. They have the same molecular formula but you can see different functional groups and very different structural formulas. So for now, I want you to remember that ketones and aldehydes always go together.
Then we have esters and carboxylic acids. So they always go together. The reason why is because my general formula, which you have to learn for both of them, is CNH2NO2.
So for example, what I showed you earlier over here, these are functional group isomers, exactly the same molecular formula, different functional groups, different structural formulas. different homologous series. That one's an ester, that one's a carboxylic acid.
So that's how it works. In the very next video, I will go over some more detailed examples of structural isomers, especially functional group isomers. So I'll see you there.