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 in the first half of the chapter we'll 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 confirmations 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 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 uh 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 can be carbon-carbon triple bonds those would be alkenes and alkynes respectively and we built 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'll name them and learn how to name them throughout the year but for now we're going to focus just on the alkanes 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 all right 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 carbonyl so and what i mean by continuous chain then so 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 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 a 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 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 f means two and so on and so forth there's a whole list on your hand out there and i'll put them up on the board here so but probe means three butte means four pence like a pentagon means five hex like a hexagon means six hept means seven act like an octagon means eight none means nine dec like a decade is ten years dec means ten undec means uh eleven like un meaning one and deck meaning ten and ten plus one is eleven and then dodec two plus ten 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 nonine with nine carbons decane with 10 carbons undecane with 11 carbons dota cane with 12 carbons now obviously real molecules get bigger than this but you're only on the hook for up to 12 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 and 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 methyl 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 onto pentyl hexyl heptal octal nonaldecyl undical doticle 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 ane ending and the substituent with a yl 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 hepdane 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 so and the parent chain now in this example we only had just one substituent so but a lot of examples we'll see we're gonna 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-methyl heptane 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 the 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 gonna number this longest parent chain though as we'll see so first thing i'm gonna do is i'm gonna 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 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 is 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 will be located with chain locator two 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 we take a look at this this is still a seven carbon chain that's still going to 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 name 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 name 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 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 3 and so we'll start this off by saying 3-ethyl all right from there our next substituent is the methyl group and it's located uh at carbon two of the parent chain and some will say two methyl notice the use of hyphens here so our chain locators are gonna be 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 of the name all right so two ethyl three 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-ethyl2-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 so 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 go left well here my longest chain going left would be one two my longest chain up would be either one two or one two 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 one two or i can go off to the right here and go one two or one two or one two 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 gonna 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've 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 going to have some lovely numerical prefixes like mono di tri so on and so forth and we don't use mono when there's only one you just leave that off but the di tri tetra penta hexa hexahepta so on and so forth we will use those so in this case like 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's still going to win so we're going to name the ethyls first so but when we do we'll say diethyl but now we got to still number that longest chain so if we number this from left to right it would go one two three four five six seven eight but i'd see my first substituent would be chain location number two but if i go right to left it'd be one two and one on my first substituents would also be located at number two 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 one two and my next substituent would be this ethyl which would be located at chain location number three and so if i go to the other side then one two but here i've actually got two substituents that are attached at carbon two and so not only was the first substituent attached at carbon two so the second one would also have a chain locator of two and that's going to break the tie as your second substitution is at two your second substituent from this direction will 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 gonna name the ethyls first and i can see they are located at 3 and 6 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 all right so 36 diethyl but then we've got three methyls so we're going to say trimethyl and two of them are located at chain locator two and one of them is located at chain locator seven now the truth is 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 227 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 two seven trimethyl and when i see two seven trimethyl i'm like well one's at two ones at seven and i don't know where the third one is so you have to explicitly state all the chain locations so if you're gonna 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 and again the key here is there's all these special rules for you know certain situations that always come up and i want to 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 and 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 all right 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 two if we go right to left the first substituent we'd come across would also be at position two 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 one two three four would be at position five but if i go right to left it would be at position one two three 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 two three and six so two comma three comma six trimethyl and then the longest chain seven carbons is heptane and again one big word all right 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 and whether go off to the right it's two carbons long it doesn't matter which one we choose so 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 gonna choose the other one this time just so you know it doesn't have to be right across the middle left to 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 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 substitution 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 or right it's three and five are where 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 becomes 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 3-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 three ethyl five methyl heptane all right so now we're gonna move some examples of what we call cycloalkanes and these are uh 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 we'll see what makes the difference in stuff like this so 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 so keep in mind get that cyclo prefix on there when you're naming the parent chain as a cyclo for a cycle alkane 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 ine so it would be fluorochlorobromoiodo as a substituent so just like you'd name a methyl ethyl propyl butyl pentyl 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 cycloalkanes 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 was where carbon 1 is 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 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 then because it has to by definition and 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 one two three four five six and they say chad so then this would just be chlorohexane right no no no this is one chlorohexane because when it's on a linear chain that chlorine could be located attached to carbon two instead or attached to carbon three 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 you know 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 gonna be have to locate it at position one not true for our linear system 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 could number this let's say we'll put the where the chlorine is at number one and that would put where the methyl group here is at number two and our substitution would 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 so 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 only uh that you'll leave out this 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 2-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 chloro2 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 tri-substituted 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 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 to 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 where if i start with him as number one it would be two three and so we do it this way and that would be one three and four for those chain locators well notice what if i start with the chlorine is 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 substituent's located would be two and then three and then the bromo would be at four and so notice we'd be comparing one three and four to one two and four 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 one but two 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 substitutions 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 two and five and so for the first position we definitely have a tie at one for the second substituent we have a tie at two but for the third substituent four is going to be 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 tri-substitute 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 but 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 four bromo one chloro2 methyl cyclohexane now i alluded to the fact that we 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 six 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 gonna make the parent chain well in this case if i name the straight chain as the parent chain it's six carbons long 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 1 2 3 4 5 6 7 8 9 10 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 and 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 gonna number this right to left cool and as you recall so if this had just been a parent chain we would call it cyclobutane butte means four carbons so but in this case because it's a substituent recall that when you do the parent chain you like methane ethane propane butane pentane but if it's the substituent it's methyl ethyl propyl butyl pentyl with a yl sound and 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 hexane now i know some of you are thinking you're like hey chad you got to give the one well 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 cycle butyl group i really probably say it could have been at carbon one two instead and so if i don't say one cyclobutyl hexane if 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 chatsprep.com