4. Alkanes and Cycloalkanes
IUPAC Naming
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Alright guys, so this one was actually surprisingly tricky right from the very beginning because of the fact that there's a lot of different chains that could be the longest chain. So I think one of the obvious chains that you might have thought of would be that this would be the longest chain. Okay? So that's possible. The only thing is that there's actually other combinations as well that would also be just as long. I could also make my chain go up like this. That would be another possibility. That would also be 7. And then, this is going to get ugly, I could also do this. Okay. Do all of these make 7 carbon chains? Alright. So what I'm going to have to do is go 1 by 1 and see which one gives me the most substituents. Right? Let's go to the yellow one first. How many substituents do I get? I get 1 up here, 23. Okay. Now you guys might be wondering why did I assign that as 23 if they're coming off of the same carbon? Because they're 2 different branches. Okay. So each branch gets its own number. So this would be 3 substituents. Okay? Three branches. So that's the number to beat. Let's see if any other chains can beat that. So let's do the one that I made in blue. That would have been like that. How many substituents do I get for this one? What I get is one here and then I actually just get one really complicated one here. Is that good? No. This one's actually worse because this one just gives me 2 substituents and they both I mean and it's less than 3. So this one's not going to be my answer. So let's finally do the one that I did in purple. So I'm doing this. How many substituents do I get now? I'm actually going to get, let's see, 1, 2, 3, 4. Yikes. Okay. So this is actually going to be my longest chain because this is the one that gives me the most branches. Okay. Now this is probably the reason that you guys got this question wrong. If you got the question wrong, it's probably because you had the wrong chain from the very beginning. Okay? Now what I want to do is go ahead and start using the other rules in terms of direction. Okay? So is this going to be my one carbon or is this going to be my one carbon? Okay. Well, let's go ahead and start numbering. So my first substituent would start on 3 for red. My first substituent would start on 3 for blue. So there is a tie. Okay? But then that tie is easily broken on the next round because on the next round my next substituent would be on 4 for red, but my next substituent would still be on 3 for blue. Why? Because I have 2 substituents on the 3 position. Does that make sense? So I would start off and I would I would have that one cancel out with that one, but then I would have this one win and this one would lose. Okay, because it's closer. So blue should be my number 1. Does that make sense? Cool, so now I know that I'm numbering in this direction. That helps a lot. Now I just need to get the substituent numbers and stuff. So this would be 3, this would be 4 and this would be 5. Are you guys cool with that? So now what we have to do is put all of this together and get everything down on paper. So what's the root name? I like to separate stuff out. The root name is going to be heptane. Okay. What are the substituent names? Okay. Well, in this case, I want to put locations and substituents. Okay. So how many different types of substituents do I have? I know I have 4 substituents, but in terms of types, how many do I have? Actually, only 2 different types. I have methyl groups, which I have 3 of. I have 3 methyls. 1, 2, 3. And then I have 13 carbon chain, which is going to become what we call a propyl group. Okay? So what that means is for substituents, I actually just have a trimethyl. See how that works? I put them all together. Instead of naming them out individually, trimethyl methyl saves a lot of space. And then I'm also going to have a propyl. Okay? Now all I have to do is I have to get the number locations of all of these. Okay? So I'm going to put sub out here to give me some more space. Alright? So what are the number locations of the trimethyl? Well for trimethyl, I actually have to be explicit about every single location. Why is that? Because if I don't put exactly where each of the methyls is, what I'm going to wind up getting is a very confusing structure where I don't know where they go. So it looks like 2 of the methyls are on the 3 position and one of the methyls is on the 5. So the way this is going to look is it's going to be 3 comma 3 comma 5 dash trimethyl. Alright? Tricky, Right? But that is the way that we name it because now I know that 2 are on the 3 and one is on the 5. Now I know that one of you guys is asking, but Johnny, couldn't I just put 35? Wouldn't that be fine? Why do I have to put 335? No, you can't because then I wouldn't know where's the third one. Is it on the 5 or is it on the 3? So you need to say that 2 are on the 3 and 1 is on the 5. Alright? Then let's do the propyl. That one's easy. That one's on 4. Alright, so now I'm done with my roots. I'm done with my substituents with my root and substituents. Now all I need to do is put it together in the right name. So obviously this is going to be a long name and I have to figure out what's the correct order to say all of these. You could have all of these steps right, but if you put the name in the wrong order on your exam, you still get the question wrong. So we have to be very meticulous about each step. So now when we're ordering this, we have to go in alphabetical order and prefixes don't count. So that means what are we going to talk about first? What's going to be the first substituent that we lead off on? It's going to be trimethyl. And the reason is because of the m. K? M beats p. So that means that I'm going to say that this is 335. I'm going to run out of room probably, so I'm going to try to write a little smaller. Trimethyl. I'm actually going to take myself out of the page. Okay? 335 trimethyl. Then we've got 4 propyl because that one is the next one. Notice that every time that I have a number and a letter separated, Oops. Okay. Yeah. Every time that I have a number and a letter separated, I'm using a dash. Okay. So then the next thing would just be for propyl and then I've just got to say what the ending is and the ending is heptane without a space. So then it would just be heptane. Isn't that interesting where the m beat the p in alphabetical order? Alright, so if you got that answer, then awesome job. If you didn't, that's okay because I know that this is tricky. It's your first time. Alright, so now let's go ahead and move on to the next topic.
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