Handbooks are notorious for listing compounds according to their common names. One gives the name “sec -isoamyl alcohol” for a compound that could be called 1,2-dimethylpropyl alcohol according to the IUPAC functional class rules. The best name for this compound is the substitutive IUPAC name. What is it?
Hey everyone. So, for this question we were given the functional class name for a compound, it being 1,2-dimethyl propyl alcohol. Now, notice that was the functional class IUPAC name but it wants us to give the substituted IUPAC name and you may be wondering what's the difference, while I went ahead and actually drew out the compound for you and its structural formula and what you'll notice is, let's analyze what I drew. So, the name they gave us was 1-2-dimethyl propyl alcohol, so it would be good to know how is this functional class name given, so the difference between functional class and substituted is that in substituted that's the one we're used to doing, where we're going to name the longest chain starting closest to our substituent but the difference in functional class is they actually start naming the longest chain starting at the substituent. So, here we know this is going to be an alcohol group, right? And you can see that highlighed right here, so notice that the name they gave 1,2-dimethyl propyl alcohol, so it started numbering right here and so this was carbon one, this was carbon two and carbon three, so what you'll notice is that at carbons 1 and 2 we actually have a methyl group, okay? So this is how we are able to draw the compound for 1,2-dimethyl propyl alcohol, okay? So, how do we give it a substituted name? Well, let's actually convert this to a bond line. So, notice we're going to have a methyl group and then off this next carbon we're going to have in an OH and then we're going to go to the next carbon, we're going to have another methyl. Remember, we're going to end with a methyl, so this is actually the compound that we were given, so what would be the regular substituted IUPAC name that you would give it? Well, we see that we have an alcohol group, we know that would get priority, but we want to get our actual longest chain now right? So we would start numbering over here, okay? And give that alcohol group that priority, would be at carbon 2, this would be carbon 3 and this would be carbon 4, okay? So, do we have any substituents? Well, we still have that alcohol, so it's going to actually affect our root name, right? It's going to be a modifier and then the other substituent we have is just one methyl group now, okay? So, how are we going to name this? the longest chain is four carbons, so we're going to say it's going to be some kind of butane, right? But here we have an alcohol group so that's going to modify this and make it butanol, we need to indicate the position of our alcohol, so we're going to call it a 2-butanol and then if we move this a little bit up we're going to name our substituent, it's going to be at carbon three. So, our name is going to become 3-methyl 2-butanol, okay? So this would be our substituted name, so let's actually move that there, okay? So now you guys know the difference between a functional class IUPAC name and our substituted name, so hopefully that makes sense, let me know if you have any questions.