Naming Thiols

Now let's talk about the nomenclature of sulfur containing compounds. It turns out that sulfur-containing compounds are going to be named very similar to oxygen compounds because of its placement on the periodic table. If you remember, oxygen is on the second row and sulfur is right below it on the third row. What that means is that many of the compounds that you've seen made with oxygens, for example, alcohols and ethers, can also be made with sulfur, but obviously, they're going to have different names.
What I've done here is I've made this nice chart that seems kind of confusing at first, but it really lists out every single possibility of a sulfur-containing compound that you could have. It turns out that there are two main functional groups that we learned to name for oxygen. That would be alcohols, where you have a terminal OH, a terminal oxygen. Notice that it's at the end of the carbon chain. And we also have, well, if you move that oxygen inside the carbon chain, it becomes an internal oxygen or what we call an ether.
Hopefully, these two names should be familiar to you guys at this point because these are oxygen-containing compounds. We usually discuss these a lot before we talk about sulfur.
But it turns out that sometimes these substituents may not always get – or these oxygens may not always get the highest priority. Sometimes oxygens are actually named as substituents. What we found is that when alcohol is named as a substituent, that means it actually has a higher priority group other than the alcohol present.
Now just so you know, side note, you haven't seen a lot of these yet in this course. But let me just give you an example. A carboxylic acid would get a higher priority than an alcohol. We're going to do more of that in orgo two where we name an alcohol and a carboxylic acid on the same chain. For right now I told you guys alcohol beats all because it almost always does in orgo one. But later on in orgo two, we will find exceptions to that.
Anyway, let's say that the alcohol is a substituent. Instead of calling it alcohol, we call it hydroxy. That makes sense. We'd say it's a 1-hydroxy, 2-hydroxy, etcetera. We're naming it as a substituent. In the same way, ether can also be named as a substituent. If you recall, the way that we name ethers in the IUPAC way is to name a long carbon chain and then to name the ether part as an alkoxy substituent.
Now we've just covered everything about oxygen. Now what we're going to do is we're going to shift over here to sulfur and I'm going to show you guys how it's really the same thing. So it turns out that sulfur can also have two possibilities. It can form on the terminal so that means it's at the very end. It only has one H. Or it can form on the internal part of a chain, meaning that it has R groups on both sides.
So what you can see is that the sulfur at the top is a lot like an alcohol. The sulfur at the bottom is a lot like an ether. But, like I said, these are not going to get the same names because then it would – that would be very confusing. They're going to get different names.
When a sulfur is on the terminal end and it's the root, just like alcohol is the root of the name, then we're going to name it a thiol. You can think of alcohol and thiol go together.
Now how about if the sulfur is there, but I have another high-priority group present, for example, like a carboxylic acid over here. Let's say that I had a carboxylic acid. What that means is that now my SH is not getting top priority. That means it's being named as a substituent. Well, in that case, instead of calling it thiol, we're going to name it mercapto.
I know that sounds really weird. That's a word that actually comes from the Latin and they just stuck with it. Mercapto means sulfur in Latin. But all we need to think is that mercapto is similar to hydroxy. If there's a situation where I use hydroxy as a substituent, I would also use mercapto as the name of the substituent. You're only going to use mercapto if there's higher priority group present on the chain.
Now finally, let's go to the ether analog. For ether of a sulfur, a sulfur ether, what we're going to name it is as a sulfide. Just think that ether is ROR, sulfide is RSR. I'm just going to even write that right here. RSR, just so you guys can see that it's very similar to ether.
But sometimes we don't name it as the common system. Remember that in the common system we just name it as ether or sulfide, but sometimes we're going to use the IUPAC system. In the IUPAC system, we would name it as a substituent. In that case, we name it as an alkylthiol, which is very similar to alkoxy, just instead of oxy, it's thiol.
I know that was a lot to walk through but hopefully by thinking of sulfur in the context of oxygen, what you already know from oxygen, that's going to make it easier for you to get a grasp on it. The only thing is there's just some funky words we have to remember.
Now we have some practice problems that I want you to go ahead and do from this chart. Try to get the exact name for this first one. Try to do the whole thing. Then I'll go ahead and give you the answer. One more thing, just keep in mind that alcohol actually has higher priority than thiols. That should be giving you an idea of which one to name as the substituent and which one to name as the root. So go for it.