Amines: Introduction

00:01 In the previous lecture, we talked about the reactions of amines with carboxylic acid derivatives so that we could form amides, a very important functional group, both in terms of chemistry and also in biology. But, it’s important that we actually deal with amines on their own to some extent, not least because they form some… they form some of the most important chemicals within our body. Okay. So, let’s first and foremost look at the nomenclature. First and foremost, where we have an amine, which consists of an alkyl or aryl group, represented here as “R”, we use the longest chain, as we do in all cases.

00:37 So, in other words, if it was two carbon units, it would be ether; three would be propyl; four would be butyl; and so on and so forth. And then we remove the “e” at the end, and we attach the suffix “-amine”. There is sometimes a number prefix to indicate the position of the amine on the chain by the lowest possible number. What does that actually mean? Well, let’s have a look at a couple of examples. If we look at 2-pentylamine, you can see what I said before. When you have a substituent on a long chain, as you’ve seen here, where you’ve got a pentane chain, five carbons in length, what we need to do is find the carbon to which the hetero atom is attached. In the case of alcohols, it is OH. In the case of haloalkanes, it is chlorine, bromine or fluorine. And in the case of amines, it is nitrogen. Nitrogen has an atomic mass of 14, carbon of 12, therefore, nitrogen takes priority. When, of course, the nitrogen is in a terminal position, then of course, it is that carbon to which it’s attached that takes the number 1.

01:45 However, when we’re looking at a nitrogen which is substituted in the middle or close to the end of a long chain, we need to consider the terminal and call that “1”. So what that affectively means is that the amine, the NH2 group in 2-pentylamine, is in the second position, hence the name “2-pentylamine.” It’s also worthy of note that when you’ve actually got substitution on the nitrogens themselves, note we have here NH2, those Hs can be replaced by other alkyl or aryl groups, as in the case of N,N-dimethylethylamine.

02:23 Note the location of each of the components. The bottom right hand corner, you see that abbreviated formula: CH2CH3. This is the origin of your ethylamine. The fact that we have a substitution on the nitrogen by two methyl groups means that it is N,N-dimethyl, where we have on a single nitrogen, two dimethyl groups substituted.

02:49 Sometimes you’ll actually see where we have more than one nitrogen: an N and an N’, indicating the awareness that we have that there are two nitrogens in our system.

03:00 In terms of nomenclature, it’s also important to realise that there are different types of substitution and they refer to primary, secondary or tertiary depending on the number of carbons attached. The simplest possible arrangement is ammonia where we have a nitrogen to which we have covalent bonds, sigma bonds, to three hydrogen atoms, shown here. And that is the simplest possible nitrogen base. The next one up is where we have substitution of one of those hydrogens with either an alkyl or an aryl group, thus leaving NH2. This is a primary amine. Further substitution by another alkyl or aryl group, shown in this case as R’, would be a secondary amine. And then finally, substituting all three hydrogens results in a tertiary amine where, in this case, the final hydrogen has been replaced with what we’ve designated here as R’’. Bear in mind that just because we’ve given these different denotations in terms of R, R’ and R’’, they could all be the same alkyl or aryl group; it’s just for the sake of clarity.