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Video transcript

- [Voiceover] A functional group is a group of atoms that has a predictable chemical behavior. And there are many functional groups in organic chemistry. And I'm gonna cover some of the more common ones, the ones you'd have to know for your class. So we start with an alkene. An alkene has a carbon-carbon double bond in it, so here is a carbon-carbon double bond. R refers to the rest of the compound, or the remainder of the compound, and normally we're talking about carbons and hydrogens. Let's look at an example of an alkene. So over here on the right we can see that this molecule contains a carbon-carbon double bond so this is an alkene. So how do we name this? Well if we had a four-carbon alkane, let me go ahead and write out a four-carbon alkane here. So one, two, three, four, we already know we should call that butane, so this one should be called butane. And since we have a four-carbon alkene, we're gonna lose our ending here "a-n-e" and we're gonna add on "e-n-e", the ending for an alkene. So the name name of this molecule is butene. I'm gonna go ahead and write that out here. So this is butene. And if we number this molecule, we start with the double bond and we give this carbon right here a number one, and then we have a number two right here, and a number three for this carbon, and a number four for this carbon. Our double bond starts at carbon one, so we put a one in front here and we call this 1-butene. Let's look at another example of an alkene. If we drew out a ring like this, we already know this is called cyclohexane. If we put in a double bond now it's cyclohexene. And you can see that this has a carbon-carbon double bond and so does this molecule. So they both contain an alkene functional group, and therefore both these molecules will undergo the same types of reactions. They have predictable chemical behaviors. And that's the usefulness of grouping functional groups, of identifying functional groups on molecules. Our next example of a functional group is an alkyne. So this times it's a carbon-carbon triple bond. Here you can see the carbon-carbon triple bond in an alkyne. So if you look at the right here's our example. And we number our carbons, we can call this carbon one, this is carbon two, carbon three, and carbon four. So when you're drawing an alkyne we know that this is linear, this portion of the molecule, this bond angle, is linear. So that's why it's drawn in a straight line. So four carbons, so we would use "but", and we have a "y-n-e" ending for an alkyne. So this is butyne, so let me write out butyne here. And our triple-bond starts at carbon two, so here is where our triple-bond starts. So we could write 2-butyne for the IUPAC name. Next we're looking at an arene, also called an aromatic ring, and you're looking for this. You're looking for a six-carbon ring, and you have alternating single-double bonds, so a total of three double bonds. Now just because it says double bonds, this doesn't mean it's going to be an alkene. Actually arenes react in different ways from alkenes and that's why this is a separate functional group. So on the right here's an example of an arene, or an aromatic ring, and this right here, this portion of the molecule would be a benzene. So let's write out that, so benzene's a very famous organic chemistry molecule. And then we have a methyl group coming off of our benzene ring. So one name for this would be methyl benzene. That's not the name you would usually see, normally you will hear this molecule called toluene. So it's so common that toluene is used most often. So toluene is an example of an arene. It contains an arene functional group and so toluene would react in similar ways to benzene. Alright let's look at our next functional group here. This is an alkyl halide, so halide refers to halogen, so over here on the right we have our halogen, so X could be a halogen like chlorine or bromine. And R will be our alkyl group. For the example on the right, let me get a little more room down here, our halogen is chlorine. And our alkyl group here would be an ethyl group. We have a CH2 and a CH3. So one possible name for this molecule would be ethyl chloride. You could also call this something like chloro ethane. Alright next functional group is an alcohol. So an alcohol has an OH, an OH right here and an R for the rest of the molecule. As an example here's an OH or a hydroxyl group, and then we have a CH2 and a CH3. So we have two carbons in this molecule, and we know two carbons is "eth". And for the full name this would be ethanol. So a very famous molecule obviously. So this is ethanol. Next we have an ether. So an ether has an oxygen, with an R group on either side. So I'm sorry for the bad joke but if it helps you remember that you have an R group on either side of your oxygen, it's worth putting in a bad joke into this video. So these R groups could be the same R groups or they could be different R groups. For the example on the right we have R groups that happen to be the same. So here's our oxygen and here's an R group and here's an R group. Both of those R groups are ethyl groups. So we call this diethyl ether. So diethyl ether is the most famous ether. It's so famous that usually it's just referred to as ether. But diethyl ether would be one way to name this molecule. Next we're gonna look at a thiol. So a thiol is similar to an alcohol, instead of an OH though we have an SH, so we have sulfur instead of an oxygen. So for the example of a thiol over here on the right, we have an SH here, then we have an ethyl group. So one name for this would be ethane thiol. So I'm gonna write this out here, so "ethane thiol" is one possible name for this molecule. Next we have a sulfide. So a sulfide is similar to an ether, remember for an ether we had R-O-R, for a sulfide we have R-S-R. So it's completely analogous to an ether. So on the right here's our sulfur, and again we have two ethyl groups, so you can call this diethyl sulfide. So let me write that out here, so this is "diethyl sulfide." And finally, for this video, one more functional group. So this is an amine. So for this amine we have nitrogen and then we have three R groups attached to nitrogen, or you could be talking about hydrogens here. So any of these could be hydrogens as well. So on the right is an example of an amine, we have a nitrogen with a lone pair of electrons. This one has two ethyl groups and one of our groups here is a hydrogen, so one name for this is diethyl amine. Let me write out that one, so you could call this "diethyl amine." Alright, so we'll look at more functional groups in the next video.