Concept: Concept: Naming Primary Amines7m
Hey guys, in these next few videos we're going to focus on how to name amines.
So you might recall from prior videos that amines can exist as several different degree states. You can have primary, secondary, tertiary and even quaternary amines. And unlike other functional groups where you pretty much always have the same naming system for all of the molecules in that functional group, amines are different because the type of name that you assign is going to depend on the degree of the amine.
So before we can even talk about IUPAC names, let's refresh on what the different degree systems for amines are. Remember that the degree of the amine is going to be dependent on directly how many R groups are attached to the nitrogen. In this case, this first amine that we're looking at would be a primary amine because it is attached to only one R group.
As you look at the second example, the second example is now a secondary amine because I've got an R here. I've got an R here. That is a secondary amine.
So then we go up to tertiary. Tertiary means, as you guys remember, they don't have any hydrogens because it's just all R groups.
And then finally we have quaternary amines. Now a quaternary amine by definition is always going to have a positive charge. Why? Because that nitrogen does not like to have four bonds. This is going to have a formal charge and we're not going to focus on these for this lesson since it's in an ionized state. We're only going to focus on the neutral versions of nitrogen.
Let's go ahead and talk about the simplest type of amine which is a primary amine. They way to name primary amines is pretty straight forward. What we're going to do is we're going to add the suffix -amine to the name of the alkyl substituent. So we look at the alkyl group, and like we did for other functional groups, we'd say this is a modifier. So we'd change the 'e' in the alkene for amine at the end. Other than that it's like naming a regular alkane.
So we can look at this first version here, this first molecule, and we could say how do we name that R group just as the R group itself and then we just have to add amine towards the end. Let's just go ahead and do this one together.
What we're going to notice is that the longest chain is three carbons. What we notice is that there's really no preference for 1, 2, and 3 here in terms of the locations because it's symmetrical. So I'm just going to make this one 1, this one 2, and this one 3. What that means is that we have two things going on on that 2. We have a methyl group. That's a methyl. And we have the amine. Right? Awesome.
So if we put that all together what is that name going to be? Well, we would just name it as an R group then with the amine at the end. So what you would say is that this is going to be a 2-methyl. 2-methyl and then 2-propanamine. So this name got a little bit longer than the line underneath it, but I hope you guys were able to fit that in.
Basically, what we're doing is we're just naming the longest carbon chain. We're naming the methyl as a substituent and then I'm adding the amine part at the end. I'm taking off the 'e.' I'm adding amine because it's on the second carbon so that's why it's a 2-propanamine. All right. Got it?
So let's go ahead and do the next one. Let's look at the next one. So this next one the R group is, in this case, a ring. So how is that going to change the name? Well, we're going to have to name it as a cycloalkane substituent. In this case, if I were just to kind of ignore the nitrogen, what would I be looking at? I'd be looking at a methyl group again, but, in this case, my R group is cyclobutane.
Now in terms of priority, we do have to ask ourselves a question here. If you were looking at the ring, which one would have the higher priority. Would the 1 go on the methyl or would the 1 go on the amine. That's because you could either name it as the amino group, whatever, the amine on the 1 and the methyl on 2 or you could name the methyl on the 1 and the amine on the 2.
What's your suspicion? Which one do you think is going to get the higher priority? You've got it. Amine is a modifier and as a general rule, anything that modifies the root name is going to have higher priority than a methyl group. That means I'm going to choose to have my amine as my 1 and my methyl as my 2.
Putting that all together, what would we get? Again, I think I'm going to run out of space here. I'll try to write it a little smaller. But what I'm going to get is something that looks like this 2-methyl-1-cyclobutamine. Why is that? Let's just break that down a little bit. The reason for that name is that we've got the methyl group on the two. We've got a cyclobutane.
Oh, I'm sorry. It should have been butanamine that is my bad because we're only supposed to exchange the last 'e'. So what I should have actually written was – let's get our erasers out – butanamine.1-cyclobutanamine because I'm taking out the last 'e' and I'm replacing it with amine. And why is there a 1 there? Because I'm giving priority to the amino group. Awesome guys.
So then we've got one last example. You guys might remember this molecule from our aromatics chapter. What do you guys think the name of this one is? All right, so this one doesn't get an IUPAC name because it is one of the common names for benzene that you guys are supposed to be familiar with already. So I'll just go ahead and write it down. The name for this one is going to be aniline.
So aniline is also a primary amine, guys. But it's one that we're going to prefer to use the common name for because it's benzene and we know that benzene molecules are some of the oldest ones in organic chemistry, so we always tend to go with those common names.
All right? So, guys, I hope that made sense how to name primary amines. Now let's go ahead and flip the page and talk about secondary and tertiary amines.
Concept: Concept: Primary Amines as Substituents3m
All right guys, so one more thing before we move on to secondary and tertiaries, what happens if you have a primary amine, so we've got a primary amine here, but it is not the highest priority group? What if a higher priority functional group is present? Because we just talked about how amines are higher than alkyl groups, but you guys might recall that carbonyls are some of the highest priority groups in nomenclature. So what happens if I have a primary amine, but I have a carboxylic acid or some other kind of carbonyl, aldehyde, ketone, etcetera? Well, then how would we name this?
Well, when that happens, you're going to change the suffix -amine. You're not going to use that anymore and you're going to replace it with the prefix amino-. So you're going to name it as a substituent because the root is now going to be given to the higher priority group. So that means that now this is your root, this is your modifier. Remember that we keep referring to a modifier as anything that changes the parent chain name. And then the amine is now going to be the substituent.
Now how do you name an amine as a substituent? Well, you don't name it amine anymore. Now we call it amino. If you've ever heard of amino acid. An amino acid is going to be a carboxylic acid with amine as a substituent. That's why it's called an amino. That's beyond the scope of this lesson, but just letting you know that you've heard of this term before.
In this case, what's going to be the root name for this molecule? The root name or the common name would actually be benzoic acid. This is going to be benzoic acid. You guys might recall from our aromatics chapter. Benzoic acid. And that means that my NH2 is going to be named as an amino. And it's going to be on which position? What number? Three. So this would be on the 3 position. So what you could call this is you could say that this is 3-amino-1-benzoic acid.
And you guys might recall that we actually have other types of nomenclature to denote these 1,2, 1,3, and 1,4 relationships. This would also be probably more commonly referred to as m-, meta, aminobenzoic acid. Remember that when you use the words meta, ortho, and para, they're just stand-ins for 1,2, 1,3, 1,4. Awesome guys.
So I hope that that made sense. So now let's go ahead and talk about secondaries and tertiaries.
Concept: Concept: Naming Secondary and Tertiary Amines3m
Example: Example: Name the following amines3m
a. Draw the structure of 3-quinuclidinone.
b. What is the approximate pKa of its conjugate acid?
c. Which has a lower pKa value, the conjugate acid of 3-bromoquinuclidine or the conjugateacid of 3-chloroquinuclidine?
Draw the structure for N-methylcyclohexylamine.