Understanding Alkanes and Their Naming

Naming alkanes, aka the nomenclature of alkanes, if you want to go with the formal name, that'll be the topic of this lesson in my organic chemistry playlist. Now, this begins an entire chapter on alkanes, and the first half of this chapter will all be involved with naming alkanes. We'll name normal alkanes, and then complex substituents, and then bicyclic compounds as well. The latter half of the chapter will be dealing with the different three-dimensional conformations of alkanes. We'll have a lesson on constitutional isomers, one on what are called Newman projections, and then we'll finish it off with the confirmations of cycloalkanes, the most important of which is the chair confirmation of cyclohexane. Now, if you're new to the channel, my name is Chad. Welcome to Chad's Prep, where my goal is to make science both understandable and even enjoyable. Now, this is my brand new organic chemistry playlist. I'll be releasing these weekly throughout the 2020-21 school year. So if you don't want to miss one, subscribe to the channel, click the bell notifications. You'll be notified every time I post a new video. So naming alkanes. Now, you might recall a couple of chapters back, we learned a whole variety of different functional groups and the alkane was just the first one. In fact, we often looked at it as kind of like the absence of all the other functional groups. So just a reminder, an alkane is a molecule that has all carbons and hydrogens, nothing else and it doesn't have any carbon-carbon double bonds or any carbon-carbon triple bonds. Those would be alkenes and alkynes respectively and with just a slightly different set of rules and we'll find out that All the different functional groups, whether it be alkenes, alkynes, alcohols, amines, ketones, aldehydes, so on and so forth, are going to have a little different spin on how we name those. We're going to name them and learn how to name them throughout the year, but for now, we're going to focus just on the alkenes, and all the rules we learn how to name these here will still apply to all those other functional groups, just with a little extra rule here and there for those as well. Alright, so it turns out we're going to talk about what's called the parent chain, and the parent chain is going to be the longest continuous carbon chain in a structure. So if we look at here, I've got a bond line structure and recall that every vertex represents a carbon. So here we've got one, two, three, four, five, six, and then seven or seven. So, and then an eighth carbon. So, and what I mean by continuous chain, then it's why I kind of skipped around a little bit at the end there is that they've got to be directly bonded to each other in a link, kind of a linear chain. So one, two, three, four, five, six. And from here being six, either I go up here to seven or down to here to seven. But even though there's eight total carbons in the structure, the longest continuous chain is going to be. seven carbons and so if we kind of circle that longest continuous chain here and I had the option of either circling this as part of the longest continuous chain or this one and it is completely arbitrary wouldn't make a difference either way so but we're going to call that the parent chain So, and then anything that's not part of the parent chain, so, is going to be called a substituent. All right. So, it turns out the number of carbons in the parent chain or the number of carbons in a substituent is going to be indicated by a certain prefix. Now, when it's the parent chain of an alkane, you use a suffix A-N-E. But the... prefix that comes before that is going to be a numerical prefix that describes the number. So if we take a look at, you know, just a single carbon alkane as a parent chain, it's just simply CH4 and that's methane. So on the other hand, if we have a two carbon chain, So that's just ethane. And so meth means one, eth means two, and so on and so forth. There's a whole list on your handout there, and I'll put them up on the board here. So, but prop means three, bute means four, pent like a pentagon means five, hex like a hexagon means six, hept means seven, oct like an octagon means eight, non means nine, dec like a decade is ten years, dec means ten, undec means eleven, like... un meaning one and dec meaning 10 and 10 plus one is 11. And then dodec, two plus 10 means 12. Now, some of you guys might not be responsible for 11 or 12, but most everybody is going to be on the hook for at least one through 10 here. So, and again, if you're the parent chain, we just add A and E. And so again, one carbon chain is methane, a two carbon chain is ethane, propane with three carbons, butane with four carbons, pentane with five carbons. hexane with six carbons, heptane with seven carbons, octane with eight carbons, nonane with nine carbons, decane with ten carbons, undecane with eleven carbons, dodocane with twelve carbons. Now obviously real molecules get bigger than this but you're only on the hook for up to twelve maximum for just about any class I've ever seen. So cool. So that's for the parent chain. Now that the parent chain again always ends with that a-n-e suffix for an alkane but if you're a substituent, if you're a branch coming off the parent chain, we actually end it with a YL sound. And so in this case, this is just a single carbon right there. And so instead of calling it a methane group, we call it a meth. ethyl group. Let's draw that in red. So if you were a substituent with two carbons, it would be an ethyl group. Three carbons, a propyl group. So four carbons, butyl, and then on to pentyl, hexyl, heptyl, octyl, nonyl, dekyl, undycyl, dodycyl, so on and so forth. That's how that works. Now again, students often struggle with these. numbers from like five up for the most part. So because five pent like a pentagon and hex for a hexagon with six, so on and so forth. But the first four, and they're used a lot, are probably fairly new to you. So you got methyl ethyl propyl butyl, and I like to say meat, eat, peanut butter. So to get that mnemonic down, to get those first four down, so methyl, ethyl, propyl, butyl, me, eat, peanut, butter. So if that helps, great, and if it doesn't, well, I'm sorry. You're going to remember that forever. I apologize. All right, so now we kind of know how to name parent chains with an A-N-E ending and the substituent with a Y-L ending. So let's kind of put this together on this fairly simplistic example. The way this works is we name the substituents first and the parent chain last when we name an alkane. All right, so we're going to say methyl first, and then in this case we've got one, two, three, four, five, six, seven carbons in that longest chain. And recall that seven, the prefix is hept, and so we'll call it as a parent chain heptane. And so this is going to be called methyl heptane, but that's not good enough. And the reason it's not good enough is this methyl group could have been technically located just about anywhere on the chain. And so we now have to actually number that longest continuous chain, that parent chain. And you want to number it. In this case, I could go left to right or right to left. And the way you choose is you want your substituent to have the lowest, what we call, chain locator possible, where it's located on the parent chain, the lowest number possible. So notice if I go left to right, it'd be one, two, three, four, five. It would be attached at the sixth carbon of the parent chain. But if I number this right to left, we can see that it would be actually attached at the second carbon of the parent chain instead. And so that's how we're going to number this thing. And so before you name a substituent, you always give its chain locator first. And so instead of just saying methyl heptane, we're going to say 2-methyl and then heptane. Now one thing you should note, we always put a hyphen between a chain locator and the substituent, and we don't put a space or anything in between the substituents and the parent chain. Now in this example, we only had just one substituent, but a lot of examples we'll see, we're going to actually have multiple substituents. And the key is, there's no space, there's no hyphen in between the letters of the substituents and the beginning letters of the parent chain. It's just one big word. I like to joke with students that... The goal in organic chemistry nomenclature is to make the longest word in the world. And we'll see that there are certain rules that will ensure that the word we use, the name we give to a compound, is as long as it possibly could be. All right, but this one's just simply 2-methylheptane. But we can make this a little more challenging. So if we look at this one here, again, the first rule is to find the longest continuous chain. Let's get this out of our way here. So longest continuous chain. And I can definitely see that this is going to be part of the longest continuous chain. So we'll go... one, two, three, four, five. And the question is, do I go over here or do I go up here? Well, in this case, it'd be six, seven, or it would be like six, seven or six, seven. But I have three different ways to get seven carbons out of this. And so when there's a tie for how you can get the longest chain, they break the tie by saying, let's make the longest word in the world. Again, I like to think about it, but they say break the tie by picking a way that has more substituents coming off the parent chain. So for example, if I just go one, two, three. four, five, six, seven, well then the only substituent would be this branch coming off the parent chain right there, just one. However, if instead of having numbered it that way, I go like six, seven, well now all of a sudden I'd have a branch coming off carbon five that's not part of the parent chain and a branch coming off carbon six that's not part of the parent chain. I'd have two substituents, which is going to guarantee we get a longer word and that's the way they break the tie. So, and in this case, I could have made this guy seven as well. It actually is arbitrary in that case, because whether I have a one carbon substituent at six on the right-hand side or the left-hand side, I'm still going to get two substituents off this thing, and they're totally equivalent. So it didn't matter in that case. All right, so now we found our longest parent chain. Now, that's not the actual way we're going to number this longest parent chain, though, as we'll see. So first thing I'm going to do is I'm going to circle that longest continuous chain, that parent chain, once again. So and then I'll circle the substituents here as well. We've got one here and we've got one here. And so this This will be the first time where we have more than one substituent, and there'll be another rule associated with how you name that. All right, but first I'm going to do is number that longest continuous chain again. And in this case, if I number this as number one, this end, it'd go one, two, three, four, five, six, seven. And what we'd see is that my first substituent that I come across in the numbering system would be located with a chain locator of five. But if I number it the other way and go one, two, three, four, five, six, seven, the first substituent I'll have... We'll be located with chain locator 2 and the lower one is better just like it was up here. And so you look for the first substituent you come across number wise and you want to get the lowest possible number. And so we'll number this starting with this end as number one. So one, two, three, four, five, six, seven. All right, so here's where things get a little bit tricky. So, but if we take a look at this, this is still a seven carbon chain. That's still gonna be called heptane. The very end of our name, the parent chain will be named heptane. But now we've got two substituents. We've got a single carbon substituent that is still called a... methyl group, but then I've got a two carbon substituent here, and that is called an ethyl group. Don't forget me eat peanut butter. One, two, three, four. All right. Well, when you've got multiple different types of substituents, we actually named them in alphabetical order. So we don't actually name them based on where their chain locators are. It turns out they decided the rule was going to be that you named them in alphabetical order and ethyl comes before methyl in the alphabet. And so we'll name ethyl before methyl. And so this is going to be some form of ethyl. ethyl methyl heptane. But again, before you ever say ethyl or methyl, you've got to give me those chain locators first. And so ethyl is going to be first here and it's located to the main chain, the parent chain from carbon three. And so we'll start this off by saying three ethyl. Alright, from there our next substituent is the methyl group and it's located at carbon 2 of the parent chain. And so we'll say 2-methyl. Notice the use of hyphens here. So our chain locators are going to be surrounded by a surrounded by hyphens. So in every case, except when they're at the very beginning, I guess they'll just have a hyphen afterwards. But if they're in the middle of the word, those chain locators are gonna be surrounded by hyphens. I like to say that we're gonna separate numbers from letters with hyphens, is the way it usually works out. But it's really that chain locators need a hyphen around them, unless they're at the beginning of the name. All right, so 2-ethyl-3-methyl, and then we've just got left the parent chain. All the substituents are named at this point, and that's just simply, again, heptane. And again, no space here, no hyphen. Just one big, long, ugly word. And again, we'd say this is 3-ethyl-2-methyl-heptane. All right, so we're making this more and more complicated as we go. So in this case, we've got to once again find the longest continuous chain. And students often struggle with this early on. And so one thing I recommend is look at your branch points, like this one right here. Look at those branch points and say, okay, in all the different directions, well, obviously, going to the right is going to be part of this. But the question is, do I go up or do I go left? Well here my longest chain going left would be 1, 2. My longest chain up would be either 1, 2 or 1, 2. And it's equal again. But I can see that I'll have more substituents if I go up, just like we did in the last example. So that'll be part of our longest continuous chain. And I'll circle that up until we get to the next branch point. And at this branch point here, I can go down and go 1, 2. Or I can go off to the right here and go 1, 2, or 1, 2, or 1, 2. Those are all three equivalent. Doesn't matter which one. But it's two carbons down. It's two carbons up to the right. And the tiebreaker, again, is going to be, does one of those get me more substituents that won't be part of the parent chain? Yeah, going off to the right will. And so in this case... So we'll go off to the right. And again, I could have circled either this carbon, this one, or this one. They would all be equivalent. It wouldn't make a difference. I just chose one at random. All right, but there's our longest continuous parent chain, and it is one, two, three, four, five, six, seven, eight carbons long. And so the parent chain here is going to be named octane at the end of the name. So, but let's take a look at all those lovely substituents. We got One here, one here, one here, one here, and one here. And all of a sudden, this got a whole lot more fun. So if you look, this guy is a methyl group. These are both. methyl groups. So and then this guy right here is an ethyl group with two carbons. And this one is an ethyl group with two carbons as well. Now when you've got multiples of the same substituent, you got to say how many of them you have. So using a numerical prefix. Now not the same numerical prefixes that tell you how many carbons something has. So but now we're gonna have some lovely numerical prefixes like mono, di, tri, so on and so forth. We don't use mono. When there's only one, you just leave that off. But the di, tri, tetra, penta, hexa, hepta, so on and so forth, we will use... So in this case, we've got three different methyl groups, so we're going to say trimethyl in the name. We've got two different ethyl groups, so we're going to say diethyl in the name. Now what you have to know, though, is that when you alphabetize the different types of substituents here, you don't include that as part of the alphabet. You only alphabetize it either under ethyl versus methyl. And ethyl is still going to win, so we're going to name the ethyls first. But when we do, we'll say diethyl. But now we've got to still number that longest chain. So if we number this from left to right, it would go 1. 2, 3, 4, 5, 6, 7, 8. But I'd see my first substituent would be chain location number 2. But if I go right to left, it'd be 1, 2. And one of my first substituents would also be located at number 2. It would be a tie. So then what do you do to break the tie? Well, then you go to the next substituent you come across. And so if I number this this way, go 1, 2, and my next substituent would be this ethyl, which would be located at chain location number 3. And so if I go to the other side, then 1, 2, but here I've actually got two substituents that are attached at carbon 2. And so not only was the first substituent attached at carbon 2, so the second one would also have a chain locator of 2, and that's going to break the tie. Your second substituent's at 2. your second substituent from this direction would be located at three instead. This is the better way. We want to get those lower numbers for the substituents when possible. And so we'll number this one right to left. So we'll go one, two, three, four, five, six, seven, and eight. All right, so now that we got the chain locations for everything, so we're going to name the ethyls first. And I can see they are located at three and six. So on the parent chain, so we're going to say 3, 6-diethyl. All right, now if you look when you've got multiple of the same substituent, between your chain locators you're going to use a comma. So your chain locators get separated by a comma, but all your chain locators get separated by the actual substituents using hyphens. So keep that in mind. So I like to say that we separate numbers from numbers with a comma, and numbers from letters with a hyphen, and that's usually sufficient most of the time. Alright, so 3,6-diethyl, but then we've got three methyls, so we're going to say trimethyl, and two of them are located at chain locator 2, and one of them is located at chain locator 7. Now, the truth is, and a lot of students missed this early on, is if two of them are located in the same chain location, you do have to list it twice. And so this is going to be 2,2,7-trimethyl. And then finally our parent chain of octane. Now a lot of students, when they start off, they forget one of the twos. And they just say 2, 7, trimethyl. And when I see 2, 7, trimethyl, I'm like, well, one's at 2, one's at 7, and I don't know where the third one is. So you have to explicitly say all the chain locations. So if you're going to say trimethyl. you better have three chain locators out front of it, even if one of them is being repeated to show that there are two of them attached there. So we have a couple more examples to go through here. And again, the key here is there's all these special rules for certain situations that always come up. And I wanna make sure we do at least one example of every special situation that you might come across that you've really got these rules down pat. So, all right, so this top one here, again, first rule is find your longest continuous chain of carbon atoms. So here, whether I start with either one of these carbons, it's the same length either way from this branch point, so I'll just choose this one here. And when I get to this branch point right here, I can definitely say I can get more carbons going off to the right than going up, so we'll go off to the right. And then from here, whether I go down or whether I go up to the right, it's the same distance either way, so it doesn't really matter which one you choose. In this case, that's going to leave us with three substituents. And in this case, all three identical substituents, they are all... methyl groups. Alright, now we gotta figure out which way to number that longest chain. If we go left to right, the first substituent we'll come across would be at position 2. If we go right to left, the first substituent we'd come across would also be at position 2, and it's a tie. And just like in the last example, when there's a tie, well then you go to the next substituent you encounter. And from left to right, that next substituent would be at 1, 2, 3, 4, would be at position 5. But if I go right to left, it would be at position 1, 2, 3. And that's going to be the superior method here of numbering this. So we'll number this right to left. 1, 2, 3, 4, 5, 6, and 7. And in this case, they're all methyl groups. So we'll just name them all at the same time. We'll say trimethyl for three identical methyl groups. And give, again, three chain locators to indicate where they're located. So 2, 3, and 6. So 2, 3, 6 trimethyl. And then the longest chain seven carbons is heptane and again one big word. Alright, so another example that'll iterate another special case we'll come across. So in this case, longest continuous chain from this branch point, definitely want to go off to the left here, not up. And then we'll go off to this branch point. And from here, whether I go up, it's two carbons long. Whether I go off to the right, it's two carbons long. It doesn't matter which one we choose. So, and a lot of people just like to choose right across the middle, but they get in the habit of going right across the middle and think they should always go right across the middle. So I'm just going to... choose the other one this time just so you know it doesn't have to be right across the middle left right or right to left so it is the longest continuous chain whichever way you come up with that cool and again these have been equivalent either one would have worked i just chose the other one so you can see that all right All right, so if I number this left to right, the first substituent I'll come across would be at one, two, three. But if I number it right to left, the first substituent I'll come across would be at one, two, three. So there's our two substituents that are not part of the parent chain. So it's a tie. So then we move on to the second substituent. And if I number left to right, it goes one, two, three, four, and it would be low. The second one would be at five. And if I number right to left, it would be at one, two, three, four, five. And so whether I go right to left or left to right, it's... three and five are with the substitutions are located no matter what. And when you have a tie like this, well, if they're all identical substituents, great, doesn't matter. But if they're not, and these are not identical, in this case, one's a methyl and one's an ethyl. Well, you're going to use the alphabet to break the tie in that case. Not size, so we're going to choose the ethyl to have the lower number in this case. Not because ethyl is bigger than methyl, but it comes earlier in the alphabet. So a lot of students see us work this example and they're like, okay, so we're numbering this in such a way to get the ethyl the lower number. to break the tie. And they think, oh, it's because of size. No, again, it's due to the alphabet. Ethyl comes before methyl in the alphabet. All right, so we go to name this. We're still going to name it in alphabetical order as well. So we're going to start off with the ethyl then, and we start off with three ethyl, and then five methyl. Cool, and then once again our parent chain being seven carbons long is once again heptane. And again one big long word no space. Cool, 3-ethyl-5-methyl-heptane. Alright, so now we're going to move some examples of what we call cycloalkanes, and these are alkanes that form ring structures. And so when you've got that ring structure, so typically you're going to name the ring as the parent chain in most of the examples you're going to see. But we'll definitely work an example where the ring is actually not the parent chain, and we'll see what makes the difference and stuff like this. But in these three examples, we're going to name the ring as the parent chain, and when your ring has six carbons in it, like this one does right here, Instead of calling it hexane, you put a cyclo prefix on it and you call it cyclohexane. Let's write that out over here. So one of the more common mistakes students make is when they're naming cycloalkanes is they forget to say cyclo at the beginning. So they just revert back to hexane like they would with a linear chain. So keep in mind, get that cyclo prefix on there when you're naming the parent chain as a cyclo for a cycloalkane. All right, now the first example we're going to do here is going to have a single substituent. So, and this is the first time where I've actually included a halogen as a substituent. Now you only ever name halogens as substituents. So, and you just simply, instead of saying like chlorine, bromine, iodine, fluorine, you put an O on the end for the I and E. So it would be fluoro-chloro-bromo-iodo as a substituent. So just like you'd name a methyl, ethyl, propyl butyl, pentol, so on and so forth. you give the chain locator first and then you're just going to say fluoro or chloro or bromo or iodo so and again always named as a substituent not as part of the parent chain all right now one other thing that's going to be a little strange about cycle alkanes is there's no end of the chain now when we've numbered the longest chains in the past we always started at one end or another end or something like this and that's where carbon one's going to be but on a ring there's no end and so the key here is you get to choose or at least have to figure out where carbon number one is going to be. Well, in the case where there's just a single substituent on your cycle, okay, and we call this a mono substituted cycle, okay, then your goal is to make sure that the substituent gets to be at the lowest possible number. Well, that happens if you make his location number one. And so that's where it's always going to be for a single substituent, wherever your substituent is, that's where number one has to be. and whether you go one two three four five six around clockwise or one two three four five six around counterclockwise it's the same thing either way now with only a single substituent Because it has to, by definition, in how we number things, be located with a chain locator of number one, we actually leave the one out of the name. And so instead of saying one chlorocyclohexane with just a single substituent, you just say chlorocyclohexane instead. And that's what we'll do here. And it's one big word. And again, if you say one chlorocyclohexane, it is technically wrong. So leave that one off. And again, a lot of students get confused here. So they're like, well, Chad, hey, so if I've got something like this. And I number my longest chain, 1, 2, 3, 4, 5, 6. And they say, Chad, so then this would just be chlorohexane, right? No, no, no, no. This is one chlorohexane because when it's on a linear chain, that chlorine could be located attached to carbon 2 instead or attached to carbon 3 instead. And on a linear chain, you have to give me the chain locator because I don't know where it is otherwise. It's only on a ring with only one substituent. that it has to be located at one by default. And notice it doesn't mean that the top's one. I could have put the chlorine over here and then we would have just defined that to be carbon one instead. So it's only for our cycloalkanes with one substituent that it's by default going to be have to located at position one. Not true for our linear systems. So don't get that wrong. Common mistake students make at this stage. All right. Now, if you've got a disubstituted cyclohexane in this case, so well then your goal is to get the lowest possible numbers. But if you notice, you can number this, let's say, we'll put where the chlorine is at number one, and that would put where the methyl group here is at number two. and our substituents will be located at positions one and two. But we could just as well have put the methyl group at number one and the chlorine at number two. And so whether I number it this way clockwise or this way counterclockwise, my two substituents are located at exactly the same numbers, the same chain locators, one and two, either way. And so we have a tie. And if you recall, the tiebreaker is the alphabet. And so once again, this is our chloro substituent. This is our methyl substituent and chloro comes first in the alphabet. And so we'll do it clockwise here with the chloro being at number one and the methyl being at number two. And when you've got more than one substituent, now you'll include all your chain locators. It's only with just a single substituent that you'll leave out the chain locator because it has to be at one. But here, you've got to let me know where they're at. And so in this case, we'll name this still in alphabetical order. So we'll do one chloro and then the two methyl. So, and then again, big mistake students make is they'll just say hexane and forget that they need to say cyclohexane for the ring. Cool. So one chloro, two methyl, cyclohexane in this example. Now students take what they've gleaned from a disubstituted cyclohexane, and then that often causes them to make a mistake when they get to a trisubstituted cyclohexane. And so in this case, they look and say, oh, let's see, we've got a chloro, we've got a methyl, and we've got a bromo for our substituents. Well, bromo comes first in the alphabet. We'll make him number one. Well, again, we only ever revert to relying on the alphabet to break a tie. And we We haven't verified that all the numbers are the same at all. And so notice we could, in fact, make bromo number one. And when you do this, you always want a number in such a way, clockwise or counterclockwise, that you encounter the next substituent with a lower number possible. So notice if I go around clockwise and he's one, it'd be two, three, four for the next one. Whereas if I start with him as number one, it would be two, three. And so we do it this way. That would be one, three. and four for those chain locators. Well, notice, what if I start with the chlorine as number one? Well, if I start with him as number one, I definitely want to go clockwise because then my next chain locator for where a substituent's located would be two, and then three, and then the bromo would be at four. And so notice, we'd be comparing... 1, 3, and 4. 2, 1, 2, and 4. And in this case, there's no tie with all the numbers, and we don't have to revert to the alphabet at all. There's a tie at 1, but 2 is going to beat three and so that's out. Okay, well we had one other option for where we could put number one. Number one either had to be where one of these three substituents is located, so I guess the other one we could have tried is putting the one where the methyl group is located. And if we make him number one then we're definitely going to want to go counterclockwise so that the next substituent we see would be located at two and then three four and the bromine would be located at five in this case instead. And so we can see our substituents would now be at one 2 and 5. And so for the first position, we definitely have a tie at 1. For the second substituent, we have a tie at two, but for the third substituent, four is going to beat five. And so the numbering system we've outlined in blue here is going to be the right one. So let's go back and take some of these off. But notice we did not have to revert to the alphabet. And that's a big mistake students make here is they often revert to the alphabet on a triceps like this before they've ever verified that the numbers are all the same. It's only when all the substituents have exactly the same chain locators. that you then revert to the alphabet to break the tie. We never had a tie here. One, two, and four was going to be the best possible numbers we could have. All right, so now we've got the right numbering system, but when we go to name this, we still name our substituents in alphabetical order, and so not by number order. And so bromo is going to come first in the alphabet, then chloro, and then methyl. So that's another thing students screw up is they, you know, We didn't use the alphabet to get the right numbers here, but then they forget that they need to name them in alphabetical order when they list the substituents. So that's what we need to do here. So we'll start off with 4-bromo. Move on to 1-chloro. So then to 2-methyl. And then our parent chain again is cyclohexane. So once again, 4-bromo-1-chloro-2-methyl-cyclohexane. Now I alluded to the fact that we'd name one where the cyclo part of it was not the parent chain. So in the last examples, it always was. But in this case, it's not going to be the case because we have a straight chain here that is 6 carbons long. And our ring is... only consisting of four carbons in this case. So, and the way it works is if you're, you know, typically if one of them is longer or more complex with more substitutions coming off, that's what you're going to make the parent chain. Well, in this case, if I name the straight chain as the parent chain, it's six carbons along with one substituent, the ring. If I name the ring as the parent chain, it's four carbons long with one substituent, the straight chain. And so I'll pick a longer parent chain in that case. Now a lot of students make the mistake and they ask me the question or they'll say, well Chad I can get a longer chain. I can go one, two, three, four, five, six, seven, eight, nine, ten and keep numbering through the ring. Well the rules say you can't do that. So either your parent chain is the ring or it's not the ring. but you can't include the knot ring and the ring combined in some sort of longer parent chain doesn't work. So in this case, it's just the knot ring. And so our parent chain is this guy, and our substituent... are those four carbons right there. Now our parent chain is six carbons long so we'll call it hexane and we'll number it in such a way that our substituents located at the lowest possible number so we're definitely going to number this right to left. Cool, and as you recall, so if this had just been a parent chain, we would call it cyclobutane. Bute means four carbons. So, but in this case, because it's a substituent, recall that when you do the parent chain, you have like methane, ethane, propane, butane, pentane. But if it's a parent chain, you have like methane, ethane, propane, butane, pentane. the substituent it's methyl ethyl propyl butyl pentol with a yl sand in so this case and again instead of being cyclobutane it's going to be a cyclobutyl group and in this case it's located at position one and so when we name this we'll say one cyclobutyl and then the parent chain is just straight up you hexane. Now I know some of you are thinking, you're like, hey Chad, you got to give the one. Oh, I do got to give the one. It's only again when it's attached, when a substituent's attached, and it's the only substituent to a ring. Well, in this case, my parent chain is not even a ring. And again, I could have had six carbons and I could have had this cyclobutane attached. at carbon two or the cyclobutyl group, I really probably say it could have been at carbon one, two instead. And so if I don't say one cyclobutyl hexane, I just say cyclobutyl hexane. Well, then was it located at position one or position two or position three? I don't know. It definitely has to be stated in this case. So when you have a single substituent on a ring parent chain, that's when you don't include the one. So, but again, in this case, we have a single substituent attached to carbon one of a straight chain. You definitely got to include the one in that case. Now if you found this lesson helpful, please consider giving me a like and a share. Pretty much the best thing you can do to support the channel. And if you're looking for the study guides that go with these lessons, or if you're looking for practice problems on naming alkanes, so please check out my premium course on chadsprep.com.

The latter half of the chapter will be dealing with the different three-dimensional conformations of alkanes. We'll have a lesson on constitutional isomers, one on what are called Newman projections, and then we'll finish it off with the confirmations of cycloalkanes, the most important of which is the chair confirmation of cyclohexane. Now, if you're new to the channel, my name is Chad. Welcome to Chad's Prep, where my goal is to make science both understandable and even enjoyable. Now, this is my brand new organic chemistry playlist.

I'll be releasing these weekly throughout the 2020-21 school year. So if you don't want to miss one, subscribe to the channel, click the bell notifications. You'll be notified every time I post a new video.

So naming alkanes. Now, you might recall a couple of chapters back, we learned a whole variety of different functional groups and the alkane was just the first one. In fact, we often looked at it as kind of like the absence of all the other functional groups.

So just a reminder, an alkane is a molecule that has all carbons and hydrogens, nothing else and it doesn't have any carbon-carbon double bonds or any carbon-carbon triple bonds. Those would be alkenes and alkynes respectively and with just a slightly different set of rules and we'll find out that All the different functional groups, whether it be alkenes, alkynes, alcohols, amines, ketones, aldehydes, so on and so forth, are going to have a little different spin on how we name those. We're going to name them and learn how to name them throughout the year, but for now, we're going to focus just on the alkenes, and all the rules we learn how to name these here will still apply to all those other functional groups, just with a little extra rule here and there for those as well.

Alright, so it turns out we're going to talk about what's called the parent chain, and the parent chain is going to be the longest continuous carbon chain in a structure. So if we look at here, I've got a bond line structure and recall that every vertex represents a carbon. So here we've got one, two, three, four, five, six, and then seven or seven.

So, and then an eighth carbon. So, and what I mean by continuous chain, then it's why I kind of skipped around a little bit at the end there is that they've got to be directly bonded to each other in a link, kind of a linear chain. So one, two, three, four, five, six. And from here being six, either I go up here to seven or down to here to seven.

But even though there's eight total carbons in the structure, the longest continuous chain is going to be. seven carbons and so if we kind of circle that longest continuous chain here and I had the option of either circling this as part of the longest continuous chain or this one and it is completely arbitrary wouldn't make a difference either way so but we're going to call that the parent chain So, and then anything that's not part of the parent chain, so, is going to be called a substituent. All right. So, it turns out the number of carbons in the parent chain or the number of carbons in a substituent is going to be indicated by a certain prefix.

Now, when it's the parent chain of an alkane, you use a suffix A-N-E. But the... prefix that comes before that is going to be a numerical prefix that describes the number.

So if we take a look at, you know, just a single carbon alkane as a parent chain, it's just simply CH4 and that's methane. So on the other hand, if we have a two carbon chain, So that's just ethane. And so meth means one, eth means two, and so on and so forth.

There's a whole list on your handout there, and I'll put them up on the board here. So, but prop means three, bute means four, pent like a pentagon means five, hex like a hexagon means six, hept means seven, oct like an octagon means eight, non means nine, dec like a decade is ten years, dec means ten, undec means eleven, like... un meaning one and dec meaning 10 and 10 plus one is 11. And then dodec, two plus 10 means 12. Now, some of you guys might not be responsible for 11 or 12, but most everybody is going to be on the hook for at least one through 10 here. So, and again, if you're the parent chain, we just add A and E.

And so again, one carbon chain is methane, a two carbon chain is ethane, propane with three carbons, butane with four carbons, pentane with five carbons. hexane with six carbons, heptane with seven carbons, octane with eight carbons, nonane with nine carbons, decane with ten carbons, undecane with eleven carbons, dodocane with twelve carbons. Now obviously real molecules get bigger than this but you're only on the hook for up to twelve maximum for just about any class I've ever seen. So cool.

So that's for the parent chain. Now that the parent chain again always ends with that a-n-e suffix for an alkane but if you're a substituent, if you're a branch coming off the parent chain, we actually end it with a YL sound. And so in this case, this is just a single carbon right there. And so instead of calling it a methane group, we call it a meth.

ethyl group. Let's draw that in red. So if you were a substituent with two carbons, it would be an ethyl group.

Three carbons, a propyl group. So four carbons, butyl, and then on to pentyl, hexyl, heptyl, octyl, nonyl, dekyl, undycyl, dodycyl, so on and so forth. That's how that works. Now again, students often struggle with these. numbers from like five up for the most part.

So because five pent like a pentagon and hex for a hexagon with six, so on and so forth. But the first four, and they're used a lot, are probably fairly new to you. So you got methyl ethyl propyl butyl, and I like to say meat, eat, peanut butter. So to get that mnemonic down, to get those first four down, so methyl, ethyl, propyl, butyl, me, eat, peanut, butter.

So if that helps, great, and if it doesn't, well, I'm sorry. You're going to remember that forever. I apologize.

All right, so now we kind of know how to name parent chains with an A-N-E ending and the substituent with a Y-L ending. So let's kind of put this together on this fairly simplistic example. The way this works is we name the substituents first and the parent chain last when we name an alkane. All right, so we're going to say methyl first, and then in this case we've got one, two, three, four, five, six, seven carbons in that longest chain.

And recall that seven, the prefix is hept, and so we'll call it as a parent chain heptane. And so this is going to be called methyl heptane, but that's not good enough. And the reason it's not good enough is this methyl group could have been technically located just about anywhere on the chain.

And so we now have to actually number that longest continuous chain, that parent chain. And you want to number it. In this case, I could go left to right or right to left. And the way you choose is you want your substituent to have the lowest, what we call, chain locator possible, where it's located on the parent chain, the lowest number possible.

So notice if I go left to right, it'd be one, two, three, four, five. It would be attached at the sixth carbon of the parent chain. But if I number this right to left, we can see that it would be actually attached at the second carbon of the parent chain instead.

And so that's how we're going to number this thing. And so before you name a substituent, you always give its chain locator first. And so instead of just saying methyl heptane, we're going to say 2-methyl and then heptane.

Now one thing you should note, we always put a hyphen between a chain locator and the substituent, and we don't put a space or anything in between the substituents and the parent chain. Now in this example, we only had just one substituent, but a lot of examples we'll see, we're going to actually have multiple substituents. And the key is, there's no space, there's no hyphen in between the letters of the substituents and the beginning letters of the parent chain. It's just one big word.

I like to joke with students that... The goal in organic chemistry nomenclature is to make the longest word in the world. And we'll see that there are certain rules that will ensure that the word we use, the name we give to a compound, is as long as it possibly could be. All right, but this one's just simply 2-methylheptane.

But we can make this a little more challenging. So if we look at this one here, again, the first rule is to find the longest continuous chain. Let's get this out of our way here.

So longest continuous chain. And I can definitely see that this is going to be part of the longest continuous chain. So we'll go...

one, two, three, four, five. And the question is, do I go over here or do I go up here? Well, in this case, it'd be six, seven, or it would be like six, seven or six, seven. But I have three different ways to get seven carbons out of this.

And so when there's a tie for how you can get the longest chain, they break the tie by saying, let's make the longest word in the world. Again, I like to think about it, but they say break the tie by picking a way that has more substituents coming off the parent chain. So for example, if I just go one, two, three.

four, five, six, seven, well then the only substituent would be this branch coming off the parent chain right there, just one. However, if instead of having numbered it that way, I go like six, seven, well now all of a sudden I'd have a branch coming off carbon five that's not part of the parent chain and a branch coming off carbon six that's not part of the parent chain. I'd have two substituents, which is going to guarantee we get a longer word and that's the way they break the tie. So, and in this case, I could have made this guy seven as well.

It actually is arbitrary in that case, because whether I have a one carbon substituent at six on the right-hand side or the left-hand side, I'm still going to get two substituents off this thing, and they're totally equivalent. So it didn't matter in that case. All right, so now we found our longest parent chain.

Now, that's not the actual way we're going to number this longest parent chain, though, as we'll see. So first thing I'm going to do is I'm going to circle that longest continuous chain, that parent chain, once again. So and then I'll circle the substituents here as well.

We've got one here and we've got one here. And so this This will be the first time where we have more than one substituent, and there'll be another rule associated with how you name that. All right, but first I'm going to do is number that longest continuous chain again. And in this case, if I number this as number one, this end, it'd go one, two, three, four, five, six, seven.

And what we'd see is that my first substituent that I come across in the numbering system would be located with a chain locator of five. But if I number it the other way and go one, two, three, four, five, six, seven, the first substituent I'll have... We'll be located with chain locator 2 and the lower one is better just like it was up here. And so you look for the first substituent you come across number wise and you want to get the lowest possible number. And so we'll number this starting with this end as number one.

So one, two, three, four, five, six, seven. All right, so here's where things get a little bit tricky. So, but if we take a look at this, this is still a seven carbon chain. That's still gonna be called heptane. The very end of our name, the parent chain will be named heptane.

But now we've got two substituents. We've got a single carbon substituent that is still called a... methyl group, but then I've got a two carbon substituent here, and that is called an ethyl group. Don't forget me eat peanut butter.

One, two, three, four. All right. Well, when you've got multiple different types of substituents, we actually named them in alphabetical order.

So we don't actually name them based on where their chain locators are. It turns out they decided the rule was going to be that you named them in alphabetical order and ethyl comes before methyl in the alphabet. And so we'll name ethyl before methyl. And so this is going to be some form of ethyl. ethyl methyl heptane.

But again, before you ever say ethyl or methyl, you've got to give me those chain locators first. And so ethyl is going to be first here and it's located to the main chain, the parent chain from carbon three. And so we'll start this off by saying three ethyl. Alright, from there our next substituent is the methyl group and it's located at carbon 2 of the parent chain. And so we'll say 2-methyl.

Notice the use of hyphens here. So our chain locators are going to be surrounded by a surrounded by hyphens. So in every case, except when they're at the very beginning, I guess they'll just have a hyphen afterwards. But if they're in the middle of the word, those chain locators are gonna be surrounded by hyphens.

I like to say that we're gonna separate numbers from letters with hyphens, is the way it usually works out. But it's really that chain locators need a hyphen around them, unless they're at the beginning of the name. All right, so 2-ethyl-3-methyl, and then we've just got left the parent chain. All the substituents are named at this point, and that's just simply, again, heptane. And again, no space here, no hyphen.

Just one big, long, ugly word. And again, we'd say this is 3-ethyl-2-methyl-heptane. All right, so we're making this more and more complicated as we go.

So in this case, we've got to once again find the longest continuous chain. And students often struggle with this early on. And so one thing I recommend is look at your branch points, like this one right here.

Look at those branch points and say, okay, in all the different directions, well, obviously, going to the right is going to be part of this. But the question is, do I go up or do I go left? Well here my longest chain going left would be 1, 2. My longest chain up would be either 1, 2 or 1, 2. And it's equal again.

But I can see that I'll have more substituents if I go up, just like we did in the last example. So that'll be part of our longest continuous chain. And I'll circle that up until we get to the next branch point. And at this branch point here, I can go down and go 1, 2. Or I can go off to the right here and go 1, 2, or 1, 2, or 1, 2. Those are all three equivalent. Doesn't matter which one.

But it's two carbons down. It's two carbons up to the right. And the tiebreaker, again, is going to be, does one of those get me more substituents that won't be part of the parent chain?

Yeah, going off to the right will. And so in this case... So we'll go off to the right. And again, I could have circled either this carbon, this one, or this one.

They would all be equivalent. It wouldn't make a difference. I just chose one at random. All right, but there's our longest continuous parent chain, and it is one, two, three, four, five, six, seven, eight carbons long. And so the parent chain here is going to be named octane at the end of the name.

So, but let's take a look at all those lovely substituents. We got One here, one here, one here, one here, and one here. And all of a sudden, this got a whole lot more fun.

So if you look, this guy is a methyl group. These are both. methyl groups. So and then this guy right here is an ethyl group with two carbons. And this one is an ethyl group with two carbons as well.

Now when you've got multiples of the same substituent, you got to say how many of them you have. So using a numerical prefix. Now not the same numerical prefixes that tell you how many carbons something has.

So but now we're gonna have some lovely numerical prefixes like mono, di, tri, so on and so forth. We don't use mono. When there's only one, you just leave that off.

But the di, tri, tetra, penta, hexa, hepta, so on and so forth, we will use... So in this case, we've got three different methyl groups, so we're going to say trimethyl in the name. We've got two different ethyl groups, so we're going to say diethyl in the name. Now what you have to know, though, is that when you alphabetize the different types of substituents here, you don't include that as part of the alphabet. You only alphabetize it either under ethyl versus methyl.

And ethyl is still going to win, so we're going to name the ethyls first. But when we do, we'll say diethyl. But now we've got to still number that longest chain.

So if we number this from left to right, it would go 1. 2, 3, 4, 5, 6, 7, 8. But I'd see my first substituent would be chain location number 2. But if I go right to left, it'd be 1, 2. And one of my first substituents would also be located at number 2. It would be a tie. So then what do you do to break the tie? Well, then you go to the next substituent you come across.

And so if I number this this way, go 1, 2, and my next substituent would be this ethyl, which would be located at chain location number 3. And so if I go to the other side, then 1, 2, but here I've actually got two substituents that are attached at carbon 2. And so not only was the first substituent attached at carbon 2, so the second one would also have a chain locator of 2, and that's going to break the tie. Your second substituent's at 2. your second substituent from this direction would be located at three instead. This is the better way.

We want to get those lower numbers for the substituents when possible. And so we'll number this one right to left. So we'll go one, two, three, four, five, six, seven, and eight. All right, so now that we got the chain locations for everything, so we're going to name the ethyls first.

And I can see they are located at three and six. So on the parent chain, so we're going to say 3, 6-diethyl. All right, now if you look when you've got multiple of the same substituent, between your chain locators you're going to use a comma. So your chain locators get separated by a comma, but all your chain locators get separated by the actual substituents using hyphens. So keep that in mind.

So I like to say that we separate numbers from numbers with a comma, and numbers from letters with a hyphen, and that's usually sufficient most of the time. Alright, so 3,6-diethyl, but then we've got three methyls, so we're going to say trimethyl, and two of them are located at chain locator 2, and one of them is located at chain locator 7. Now, the truth is, and a lot of students missed this early on, is if two of them are located in the same chain location, you do have to list it twice. And so this is going to be 2,2,7-trimethyl. And then finally our parent chain of octane. Now a lot of students, when they start off, they forget one of the twos.

And they just say 2, 7, trimethyl. And when I see 2, 7, trimethyl, I'm like, well, one's at 2, one's at 7, and I don't know where the third one is. So you have to explicitly say all the chain locations. So if you're going to say trimethyl.

you better have three chain locators out front of it, even if one of them is being repeated to show that there are two of them attached there. So we have a couple more examples to go through here. And again, the key here is there's all these special rules for certain situations that always come up. And I wanna make sure we do at least one example of every special situation that you might come across that you've really got these rules down pat.

So, all right, so this top one here, again, first rule is find your longest continuous chain of carbon atoms. So here, whether I start with either one of these carbons, it's the same length either way from this branch point, so I'll just choose this one here. And when I get to this branch point right here, I can definitely say I can get more carbons going off to the right than going up, so we'll go off to the right. And then from here, whether I go down or whether I go up to the right, it's the same distance either way, so it doesn't really matter which one you choose.

In this case, that's going to leave us with three substituents. And in this case, all three identical substituents, they are all... methyl groups.

Alright, now we gotta figure out which way to number that longest chain. If we go left to right, the first substituent we'll come across would be at position 2. If we go right to left, the first substituent we'd come across would also be at position 2, and it's a tie. And just like in the last example, when there's a tie, well then you go to the next substituent you encounter. And from left to right, that next substituent would be at 1, 2, 3, 4, would be at position 5. But if I go right to left, it would be at position 1, 2, 3. And that's going to be the superior method here of numbering this.

So we'll number this right to left. 1, 2, 3, 4, 5, 6, and 7. And in this case, they're all methyl groups. So we'll just name them all at the same time.

We'll say trimethyl for three identical methyl groups. And give, again, three chain locators to indicate where they're located. So 2, 3, and 6. So 2, 3, 6 trimethyl.

And then the longest chain seven carbons is heptane and again one big word. Alright, so another example that'll iterate another special case we'll come across. So in this case, longest continuous chain from this branch point, definitely want to go off to the left here, not up.

And then we'll go off to this branch point. And from here, whether I go up, it's two carbons long. Whether I go off to the right, it's two carbons long.

It doesn't matter which one we choose. So, and a lot of people just like to choose right across the middle, but they get in the habit of going right across the middle and think they should always go right across the middle. So I'm just going to... choose the other one this time just so you know it doesn't have to be right across the middle left right or right to left so it is the longest continuous chain whichever way you come up with that cool and again these have been equivalent either one would have worked i just chose the other one so you can see that all right All right, so if I number this left to right, the first substituent I'll come across would be at one, two, three.

But if I number it right to left, the first substituent I'll come across would be at one, two, three. So there's our two substituents that are not part of the parent chain. So it's a tie.

So then we move on to the second substituent. And if I number left to right, it goes one, two, three, four, and it would be low. The second one would be at five. And if I number right to left, it would be at one, two, three, four, five.

And so whether I go right to left or left to right, it's... three and five are with the substitutions are located no matter what. And when you have a tie like this, well, if they're all identical substituents, great, doesn't matter.

But if they're not, and these are not identical, in this case, one's a methyl and one's an ethyl. Well, you're going to use the alphabet to break the tie in that case. Not size, so we're going to choose the ethyl to have the lower number in this case.

Not because ethyl is bigger than methyl, but it comes earlier in the alphabet. So a lot of students see us work this example and they're like, okay, so we're numbering this in such a way to get the ethyl the lower number. to break the tie. And they think, oh, it's because of size. No, again, it's due to the alphabet.

Ethyl comes before methyl in the alphabet. All right, so we go to name this. We're still going to name it in alphabetical order as well.

So we're going to start off with the ethyl then, and we start off with three ethyl, and then five methyl. Cool, and then once again our parent chain being seven carbons long is once again heptane. And again one big long word no space.

Cool, 3-ethyl-5-methyl-heptane. Alright, so now we're going to move some examples of what we call cycloalkanes, and these are alkanes that form ring structures. And so when you've got that ring structure, so typically you're going to name the ring as the parent chain in most of the examples you're going to see. But we'll definitely work an example where the ring is actually not the parent chain, and we'll see what makes the difference and stuff like this.

But in these three examples, we're going to name the ring as the parent chain, and when your ring has six carbons in it, like this one does right here, Instead of calling it hexane, you put a cyclo prefix on it and you call it cyclohexane. Let's write that out over here. So one of the more common mistakes students make is when they're naming cycloalkanes is they forget to say cyclo at the beginning. So they just revert back to hexane like they would with a linear chain.

So keep in mind, get that cyclo prefix on there when you're naming the parent chain as a cyclo for a cycloalkane. All right, now the first example we're going to do here is going to have a single substituent. So, and this is the first time where I've actually included a halogen as a substituent. Now you only ever name halogens as substituents. So, and you just simply, instead of saying like chlorine, bromine, iodine, fluorine, you put an O on the end for the I and E.

So it would be fluoro-chloro-bromo-iodo as a substituent. So just like you'd name a methyl, ethyl, propyl butyl, pentol, so on and so forth. you give the chain locator first and then you're just going to say fluoro or chloro or bromo or iodo so and again always named as a substituent not as part of the parent chain all right now one other thing that's going to be a little strange about cycle alkanes is there's no end of the chain now when we've numbered the longest chains in the past we always started at one end or another end or something like this and that's where carbon one's going to be but on a ring there's no end and so the key here is you get to choose or at least have to figure out where carbon number one is going to be. Well, in the case where there's just a single substituent on your cycle, okay, and we call this a mono substituted cycle, okay, then your goal is to make sure that the substituent gets to be at the lowest possible number.

Well, that happens if you make his location number one. And so that's where it's always going to be for a single substituent, wherever your substituent is, that's where number one has to be. and whether you go one two three four five six around clockwise or one two three four five six around counterclockwise it's the same thing either way now with only a single substituent Because it has to, by definition, in how we number things, be located with a chain locator of number one, we actually leave the one out of the name.

And so instead of saying one chlorocyclohexane with just a single substituent, you just say chlorocyclohexane instead. And that's what we'll do here. And it's one big word. And again, if you say one chlorocyclohexane, it is technically wrong. So leave that one off.

And again, a lot of students get confused here. So they're like, well, Chad, hey, so if I've got something like this. And I number my longest chain, 1, 2, 3, 4, 5, 6. And they say, Chad, so then this would just be chlorohexane, right? No, no, no, no. This is one chlorohexane because when it's on a linear chain, that chlorine could be located attached to carbon 2 instead or attached to carbon 3 instead.

And on a linear chain, you have to give me the chain locator because I don't know where it is otherwise. It's only on a ring with only one substituent. that it has to be located at one by default. And notice it doesn't mean that the top's one.

I could have put the chlorine over here and then we would have just defined that to be carbon one instead. So it's only for our cycloalkanes with one substituent that it's by default going to be have to located at position one. Not true for our linear systems. So don't get that wrong. Common mistake students make at this stage.

All right. Now, if you've got a disubstituted cyclohexane in this case, so well then your goal is to get the lowest possible numbers. But if you notice, you can number this, let's say, we'll put where the chlorine is at number one, and that would put where the methyl group here is at number two.

and our substituents will be located at positions one and two. But we could just as well have put the methyl group at number one and the chlorine at number two. And so whether I number it this way clockwise or this way counterclockwise, my two substituents are located at exactly the same numbers, the same chain locators, one and two, either way.

And so we have a tie. And if you recall, the tiebreaker is the alphabet. And so once again, this is our chloro substituent. This is our methyl substituent and chloro comes first in the alphabet. And so we'll do it clockwise here with the chloro being at number one and the methyl being at number two.

And when you've got more than one substituent, now you'll include all your chain locators. It's only with just a single substituent that you'll leave out the chain locator because it has to be at one. But here, you've got to let me know where they're at. And so in this case, we'll name this still in alphabetical order.

So we'll do one chloro and then the two methyl. So, and then again, big mistake students make is they'll just say hexane and forget that they need to say cyclohexane for the ring. Cool.

So one chloro, two methyl, cyclohexane in this example. Now students take what they've gleaned from a disubstituted cyclohexane, and then that often causes them to make a mistake when they get to a trisubstituted cyclohexane. And so in this case, they look and say, oh, let's see, we've got a chloro, we've got a methyl, and we've got a bromo for our substituents. Well, bromo comes first in the alphabet.

We'll make him number one. Well, again, we only ever revert to relying on the alphabet to break a tie. And we We haven't verified that all the numbers are the same at all.

And so notice we could, in fact, make bromo number one. And when you do this, you always want a number in such a way, clockwise or counterclockwise, that you encounter the next substituent with a lower number possible. So notice if I go around clockwise and he's one, it'd be two, three, four for the next one. Whereas if I start with him as number one, it would be two, three.

And so we do it this way. That would be one, three. and four for those chain locators. Well, notice, what if I start with the chlorine as number one? Well, if I start with him as number one, I definitely want to go clockwise because then my next chain locator for where a substituent's located would be two, and then three, and then the bromo would be at four.

And so notice, we'd be comparing... 1, 3, and 4. 2, 1, 2, and 4. And in this case, there's no tie with all the numbers, and we don't have to revert to the alphabet at all. There's a tie at 1, but 2 is going to beat three and so that's out. Okay, well we had one other option for where we could put number one.

Number one either had to be where one of these three substituents is located, so I guess the other one we could have tried is putting the one where the methyl group is located. And if we make him number one then we're definitely going to want to go counterclockwise so that the next substituent we see would be located at two and then three four and the bromine would be located at five in this case instead. And so we can see our substituents would now be at one 2 and 5. And so for the first position, we definitely have a tie at 1. For the second substituent, we have a tie at two, but for the third substituent, four is going to beat five. And so the numbering system we've outlined in blue here is going to be the right one.

So let's go back and take some of these off. But notice we did not have to revert to the alphabet. And that's a big mistake students make here is they often revert to the alphabet on a triceps like this before they've ever verified that the numbers are all the same.

It's only when all the substituents have exactly the same chain locators. that you then revert to the alphabet to break the tie. We never had a tie here. One, two, and four was going to be the best possible numbers we could have.

All right, so now we've got the right numbering system, but when we go to name this, we still name our substituents in alphabetical order, and so not by number order. And so bromo is going to come first in the alphabet, then chloro, and then methyl. So that's another thing students screw up is they, you know, We didn't use the alphabet to get the right numbers here, but then they forget that they need to name them in alphabetical order when they list the substituents. So that's what we need to do here. So we'll start off with 4-bromo.

Move on to 1-chloro. So then to 2-methyl. And then our parent chain again is cyclohexane.

So once again, 4-bromo-1-chloro-2-methyl-cyclohexane. Now I alluded to the fact that we'd name one where the cyclo part of it was not the parent chain. So in the last examples, it always was. But in this case, it's not going to be the case because we have a straight chain here that is 6 carbons long.

And our ring is... only consisting of four carbons in this case. So, and the way it works is if you're, you know, typically if one of them is longer or more complex with more substitutions coming off, that's what you're going to make the parent chain.

Well, in this case, if I name the straight chain as the parent chain, it's six carbons along with one substituent, the ring. If I name the ring as the parent chain, it's four carbons long with one substituent, the straight chain. And so I'll pick a longer parent chain in that case.

Now a lot of students make the mistake and they ask me the question or they'll say, well Chad I can get a longer chain. I can go one, two, three, four, five, six, seven, eight, nine, ten and keep numbering through the ring. Well the rules say you can't do that. So either your parent chain is the ring or it's not the ring.

but you can't include the knot ring and the ring combined in some sort of longer parent chain doesn't work. So in this case, it's just the knot ring. And so our parent chain is this guy, and our substituent... are those four carbons right there. Now our parent chain is six carbons long so we'll call it hexane and we'll number it in such a way that our substituents located at the lowest possible number so we're definitely going to number this right to left.

Cool, and as you recall, so if this had just been a parent chain, we would call it cyclobutane. Bute means four carbons. So, but in this case, because it's a substituent, recall that when you do the parent chain, you have like methane, ethane, propane, butane, pentane. But if it's a parent chain, you have like methane, ethane, propane, butane, pentane.

the substituent it's methyl ethyl propyl butyl pentol with a yl sand in so this case and again instead of being cyclobutane it's going to be a cyclobutyl group and in this case it's located at position one and so when we name this we'll say one cyclobutyl and then the parent chain is just straight up you hexane. Now I know some of you are thinking, you're like, hey Chad, you got to give the one. Oh, I do got to give the one. It's only again when it's attached, when a substituent's attached, and it's the only substituent to a ring. Well, in this case, my parent chain is not even a ring.

And again, I could have had six carbons and I could have had this cyclobutane attached. at carbon two or the cyclobutyl group, I really probably say it could have been at carbon one, two instead. And so if I don't say one cyclobutyl hexane, I just say cyclobutyl hexane.

Well, then was it located at position one or position two or position three? I don't know. It definitely has to be stated in this case.

So when you have a single substituent on a ring parent chain, that's when you don't include the one. So, but again, in this case, we have a single substituent attached to carbon one of a straight chain. You definitely got to include the one in that case. Now if you found this lesson helpful, please consider giving me a like and a share.

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Transcript for:Understanding Alkanes and Their Naming

Transcript for:
Understanding Alkanes and Their Naming