![]() The IUPAC system treats the shorter alkyl group as a substituent located on position “N” with the remainder of the name based upon what it would be without this substituent. To my knowledge there are no equivalent names that treat the amino group as a substituent. Having said this, it could be easy to mistake methylpropylamine for 1-methylpropylamine. In these cases, the traditional method is perhaps a little simpler where the alkyl groups are straight chains, simply name them in alphabetical order using di and tri if there is more than one of the same type. Secondary amines have two carbon atoms attached to nitrogen and tertiary have three carbon atoms attached to nitrogen. As you can see, the traditional names for more complicated branched molecules start to get a bit ridiculous whereas the IUPAC preferred names seem somewhat more rational. The straight chain and branched isomers of six carbon atom containing amines are summarised in the following table. This is a personal opinion, but I think I see why IUPAC prefer their method. But what about their traditional analogues? 1-methyl-n-butylamine and 1-ethyl-n-propylamine, often written without the “-n-“. We know where we stand with pentan-2-amine and pentan-3-amine (or 2-aminopentane and 3-aminopentane if you prefer). The traditional name for butan-2-amine is sec-butylamine or 1-methylpropylamine (which could be easily confused with methylpropylamine, you will see why in the next section). Isobutylamine would be the equivalent to 2-methylpropan-1-amine (CH 3CH(CH 3)CH 2NH 2). So it must stand to reason that the molecule that IUPAC would prefer to call butan-2-amine (CH 3CH(NH 2)CH 2CH 3) must have the old name isobutylamine? I’m afraid not. However, using the traditional naming system for this molecule would conjure up the somewhat archaic isopropylamine. You could instead call it 2-aminopropane which also makes sense if you use halogenoalkanes as a frame of reference. If you can name alcohols confidently then this won’t present a problem. For example, if I was to ask you to draw propan-2-amine then I would expect most A Level Chemistry students to be able to work out that this is a three carbon molecule with an amino group on the middle carbon atom i.e. This is where I think it is better to move away from the traditional naming system. Other primary amines and branched primary amines Straight chain primary amines with the amino group at the end of the chain are summarised in the following table. Incidentally, for amines of this type containing three or more carbon atoms, the traditional system uses an “n-” before the name. The drawback is that it can get a bit confusing when the functional group moves or you have secondary, tertiary or branched amines. So which is best? I guess the obvious answer is that we should stick close to the convention that the exam board favours. The third way is aminomethane, aminoethane, 1-aminopropane which, in terms of nomenclature, treats amines like halogenoalkanes. The IUPAC names for the corresponding molecules would be methanamine, ethanamine, propan-1-amine. This is the old, traditional method for naming them but not the preferred IUPAC system. Examples include methylamine (CH 3NH 2), ethylamine (CH 3CH 2NH 2) and propylamine (CH 3CH 2CH 2NH 2) and so on. This is the system that you will probably see in text books and on exam paper questions. Straight chain primary amines with amino group at the end of the chainĪll the exam boards seem to favour the “alkylamine” system of naming amines. In this blog post I detail the three most common naming systems and discuss their relative merits. This is because there are many naming conventions that can be used. Of all the functional groups investigated in A Level Chemistry, amines are the trickiest to name. ![]()
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