next thing we're going to learn in this chapter is how to name alkanes but using a systematic naming system so we've talked about the common naming system and the common naming system we talked about is great for the simplest alkanes when we get to things that are much more complicated like these guys down here right it's a lot harder to name them using just nicknames and so so IUPAC has come up with that naming system that can be used no matter what the compound is so you can just look at the structure and determine that compound's name and there are certain rules we need to follow in order to do that the first rule that you guys will be having to know is you have to identify the longest continuous carbon chain this chain is called the parent hydrocar carbon and so if you see here in this first example the longest continuous carbon chain has 1 2 3 4 five 6 seven eight carbons in it so the parent chain here is octane the name of that carbon unit that has eight carbons in a line and we can have eight carbons in a line as you can see in a straight line or be aware that these carbons can turn so the longest continuous chain in the second example here has eight carbons as well 1 2 3 4 5 6 78 but we have to turn a corner to get to those eight carbons if we just did a straight line then it would be 1 2 3 4 five six seven carbons which is not the longest chain so how I like to think of it is if I can draw my pencil without picking it up it's a continuous chain so here the longest continuous chain is octane same as here and believe it or not again same as here we've turned a corner here but we haven't picked up our pencil so 1 2 3 4 5 6 7 8 is our longest chain of octane so that's the first trick and if you don't identify the longest continuous chain correctly then you're going to have problems with the rest of the name it's not going to be correct so it's very important important to identify the longest continuous chain correctly and once we've got that base name then we've accounted for these carbons already okay so we don't need to name them again when we look at naming the rest of the molecule okay so once we've got this longest continuous chain identified the next step rule two is to number the chain in the direction that gives the substituent the lowest number Poss on the parent hydrocarbon so a substituent is something that's attached to the main chain so in this first example here we have the longest continuous chain being five carbons long 1 2 3 four five right either way we go we have five carbons here we have five carbons here so we want to number the chain in the direction that gives a substituent this guy hanging off the parent chain the lowest number that it can have and so if we number from left to right we would have that substituent on the second carbon right one two however if we numbered from right to left that substituent would be on the 1 2 3 four the fourth carbon well which numbering do we do well we want to have as low of a number as possible and so we'll number in this particular example from left to right so that way the substituent is on the second carbon rather than on the fourth carbon and we name that substituent just like we do um that we learned in the previous slides where because this has one carbon it's a methyl substituent okay methane would be the name of a carbon hydrogen a hydrocarbon that has one carbon since it's a substituent we take off the A and add y l so this is methyl and it's on the second carbon right so we put two- methyl indicating its position on the parent chain and then we have pentane at the end so to name a substance you have to identify the very Basics its parent chain identify any substituents on it write the names of those substituents and where they fall on the parent chain and put those in front of the name for the parent chain so the correct systematic name for this compound would be 2-methyl pentane so there's no space here between the methyl and the pentane it's all written as one but you do separate numbers from letters using dashes as you see here okay in the second example we have the longest continuous chain being six carbon atoms right 1 2 3 4 5 six or 1 2 3 4 5 6 right either way we go the longest chain is six carbon atoms long so our parent chain is hexane that's what we put at the end here now we have the substituent that we have left to name the substituent has two carbons and so our hydrocarbon with two carbons is ethane but since it's a substituent since it's attached to the main chain we take off the A and add y l so we have ethyl here so this is going to be ethyl hexane and then we have to say where that ethyl group is which carbon of the parent chain it's on so let's say we numbered from left to right this would be one 2 3 4 it would be on the fourth carbon if we numbered from left to right but if we number from right to left it will be on the one two three the third carbon and so because we want to number the chain in a direction that gives the substituent the lowest number possible we will number from right to left here and call this compound 3-l hexane not that four- ethyl hexane okay so I hope you're getting a little bit of the hang of it right kind of the steps rule one identify the longest chain get that name and then you're adding the substituents and where they're at on the chain to name hydrocarbon substituents right it's based off of the name of the number of carbon atoms that it has right that kind of Base name it has one carbon atom it's methyl if it has two it's ethyl three propyl four buty so on and so forth okay so that's how you name name these different compounds at the very basic we're going to get into a lot more complicated things but starting off this is what we're doing so now that we've know both common and systematic names which one's right well the answer is they're both right both are different ways to name the same thing so for example this compound we could call it isohexane we learned that that's the common name for something that has these six carbons and then an ISO unit it um at the end so this is isohexane but it's also can be named systematically where we identify the longest chain that being five carbon atoms long so we call it pentane right we have pentane here and then we need to name our substituent well there's just one carbon so we call it methyl right so methyl and then where is it at okay so we have one 2 3 four yep and five well it's on the second carbon here so it would be two methyl sorry that didn't turn out well there we go we'll do it this way two methyl right two methyl pentane so both names are correct for this particular compound it's just one is its nickname and one is its kind of formal name okay so keep that in mind and also generally common names don't have numbers so if something has a number it's going to be its systematic name so if you're trying to tell the difference look for numbers if there's numbers there and there likely would be it will be a systematic name so next moving on let's say we have more than one substituent how do we deal with that well if we have more than one substituent then the chain is numbered in a direction that will produce a name that has the lowest of the possible numbers so you still put the substituents in alphabetical order and put the number to where that substituent belongs to the carbon to which that substituent belongs of the parent chain so let's do an example let's look at this guy here so here our longest chain let's identify it is going to be this guy here right this this is our longest chain even if we turn a corner we don't have any chain of carbon atoms longer than that so we have one 2 3 3 4 5 6 7 and 8 we have eight carbons in our parent chain so we're going to call this parent chain octane right that's going to be our ending here now we have two substituents we have this guy here with one carbon and we have this guy here with two carbons so the two substituents that we have are ethyl and methyl okay so we put those in front now we need to say where those groups are well if we number from left to right our first substituent falls on the third carbon okay if we go from right to left our first substituent falls on the fourth carbon okay so because three is a lower number than four we're going to number from left to right so here this will be on the third carbon and thus this ethyl group will be on the fifth carbon so we say the methyl group is on the third carbon and the ethyl group is on the fifth carbon so putting that all together in a name you have arranged alphabetically and separating the numbers from the letters with dashes you have 5- E-3 D methyl octane okay so it's not too complicated it's just remembering and identifying the longest chain naming the substituents and putting them in front and then labeling their positions on the parent chain separating the letters from numbers with dashes so what if you have multiple substituents of the same type it's actually pretty nice because what you can do is you can instead of saying methyl methyl in each of their numbers you can say the positions of where those substituents are that are the same put the numbers where they are at and then put a a prefix in front that indicates how many of them you have so for example this guy here this first example the longest continuous chain of carbon atoms is six carbon atoms long right 1 2 3 4 five six six carbon atoms long and we have two substituents one here and one here but those are both methyls right we have two methyl groups so instead of saying two methyl form methyl what we can do is we can say dimethyl okay there's two methyl groups attached to that chain and then we can indicate the positions of where those methyl groups are at so numbering in a direction that gives you the lowest number will go from left to right and put the first methyl group on the second carbon and the second methyl group on the fourth carbon so when you're labeling multiple positions on Carbon 2 and on carbon 4 for the same type of substituent you separate those numbers from each other with a comma so you'll go to comma 4 and then your dash dimethyl um when you are arranging these alphabetically you actually do not alphabetize the D TR or if you have Tetra SEC TT those prefixes are not alphabetized but the only one that is is ISO so you will alphabetize ISO but you will ignore the prefixes for the most part when it comes to arranging these substituents alphabetically you can see that reflected here we have three ethyl substituents 1 2 and three so we've called this substance trieth for the substituents but notice that this still comes before the methyl because the T here is not alphabetized we're still alphabetizing based on the E of ethyl so look through these other examples and make sure you understand how this name was obtained okay because you will have to be doing this even with these complicated guys right even with these crazy things here um on quizzes exams and homework so if the more practice you get with naming the better it's going to be for you when you're asked to name them on quizzes and exams now what do we do if no matter which direction we go in a parent chain you get the same number for the substituent let's look at this first example so here we have a longest chain of five carbon atoms right 1 two 3 4 five and no matter which direction you go if you go from left to right one two or if you go from right to left one two you have the first substituent in both cases falling on the second carbon so how do you address that what do you do in that case when it comes to naming well the fourth rule is that when both names have the same lowest number you you look at the next substituent and you give that one the next lowest number that you can so looking at the purple numbers going from right to left we see the first substituent falling on the second carbon and the next substituent not coming until the fourth carbon okay but going from left to right we see the first substituent falling on the second carbon and then the next substituent we name would also be on the second carbon and so going from left to right is more appropriate when we talk about naming because right you're going to get overall lower numbers for the next substituent when you number from left to right and so we' call this compound 224 trimethyl pentane because there's three methyl groups so we indicate that with a prefix Tri we put the numbers there that those methyl groups are on separated by commas and then the dash separating the number from the name and because we've gotten overall lower numbers going from left to right that is the most appropriate name what if no matter where you go they both have the same number okay well rule five says that when the same numbers are obtained in both directions on the parent chain the first group that's listed gets the lower number okay so take for example this guy up here we have a chain of four carbon atoms right so butane is the name of the parent chain of that compound and we've got two substituents we've got a chloro substituent and a bromo substituent okay for chlorine and bromine and the halogens they are indicated as substituents and you take off the ending the I ne E ending like for Florine bromine iodine right those sorts of things you remove that and you add an O so the correct substituent name for a hallogen is something like bromo or chloro or iodo or floro those sorts of things okay so be aware of that and be aware that they are substituents they do go in front of the name okay so back to kind of what we're getting at here if I go and number left to right I get the chlorine on the two and the bromine on the three or if I go from right to left I get the bromine on the two and the chlorine on the three I'm getting two or three either way so which name is right well when you alphabetize the B comes before the C so just by virtue of that fact the bromine is going to get the two and the chlorine is going to get the three okay so the first group that's listed gets the lower number let's go on to rule six and as you can see we're adding more and more things we're getting more and more complicated and it is just going to take practice for you guys to kind of get this and understand so don't be upset if it takes a minute you have to think about it that's why we're doing the practice problems in class because the more practice you get the better you're going to get it naming okay and you won't see Branch substituents too often but let's say we have this long parent chain right for example this first guy here we have this long parent chain and then coming off of it we have another chain like what in the world how are we going to deal with this kind of chain within a chain and actually the answer is that's exactly how we deal with it so when you are doing systematic names for branched substituents you number the alkal substituent starting at the carbon that's attached to the parent hydrocarbon so for example we've got this longest chain of heptane there's seven carbons here 1 2 3 4 five 6 s so that's our parent chain we've got heptane but then looking at the substituent looking at the substituent we have a branched substituent where there's kind of multiple pieces here so if we're naming this this carbon that's attached to the parent chain the C here always gets the one okay you always number that the one and then you number the longest chain in that so in this case the longest chain is two carbon atoms so this is always carbon one and then this would be Carbon 2 if there's a third carbon here that's attached to that longest chain within the substituent we call it carbon 3 okay and then you say well off of carbon one I have this methyl group so this substituent name takes into account the quote unquote small parent chain of ethane there's two there and also the substituent off of that little chain which is methyl and that's off the first carbon so we call this branched group this Branch substituent one- methyl ethyl because it's still a substituent instead of ethane we say ethyl okay and so that name goes in parentheses before the name of the parent chain and we still have to indicate where that branch substituent falls on the parent chain so that would be the fourth carbon in in either direction we go so four dash parentheses that Branch name where we've numbered a new kind of small parent chain and indicated where substituents are at on that new small chain tricky part to remember here is this carbon that's attached to the parent chain always gets the one doesn't matter if a substituent's way down here and you a long chain always gets the one either way okay the other thing that's a little bit different in these branched chains that I want to note for you guys is that in these branched chains you do include the D or ISO in the alphabetization there so looking at this third example here remember we always have the one as the carbon attached to the parent chain so that's the first carbon so we always are starting here and then we can only go with the two carbons so our parent chain there is ethane and we have these two methyl substituents okay so we'd call this dimethyl ethyl and these two dimethyl groups are both both on the first carbon so total parenthetical name here is 1 one dimethy ethyl again it's in parentheses and like I said where this gets a little weird is that now because it's a parenthetical name this D is going to be alphatia tized within the name so the D would come before the E and we would then put that together with the rest of our name now something you'll notice hopefully for all of these examples is that we have this parenthetical name which will always work but in these three cases we actually do have a common name this is isopropyl this is isob we see that ch3 ch3 CH and this is tbal so because they do have a common name that we can recognize we can put that instead so instead of saying for parentheses one methyl ethyl heptane we could just say for isopropyl heptane or for example on this last one we could say five tbal 3L octane now here the T of course isn't going to be capitalized or isn't going to be alphabetized excuse me so keep that in mind as well but it might be a lot easier just to realize that we have these names that are common names but that can be used in systematic nomenclature because they are used so frequently but if it doesn't have a common name then you have to use the parenthetical name these are pretty complicated examples right we've got some long chains of carbon atoms here this is the longest chain that's decking here you can see there's 10 carbons and this guy the substituent doesn't have a common name we look at it there's five there we go five carbons within there but we do not know a common name for that guy so we have to use its parenthetical name right we start our numbering on the carbon that's attached to the parent chain so this guy always gets the one and then the longest chain within there is going to be three carbons long right so one two and three you can't go farther than that off of the first carbon okay you have to start at the first carbon you can't include this one and say there's four that's not allowed because you'd have to pick up your chain to go back here you'd have to pick up your pen to go back here so this is a substituent and this is a substituent off of the first carbon of the little parent chain and off of the second carbon of the little parent chain because they're both methyls we can say 1 comma 2 dimethyl and then the little parent chain is three carbon so we call it propane but since it's a substituent we have the y l because it's a parenthetical name it's in parenthesis and we do include the D in the alphabetization okay so complicated but that's the idea there um again look through these examples try to make sure you understand how they got the names because we are going to be working through these in class these ex well not the examples but but homework related to naming these different branch substituents and the branch substituents are going to be the most complicated ones probably that you're going to run into now our last rule rule seven here is that if two or more chains have the same length then the parent hydrocarbon is going to be the one with the most substituents okay so let's take this example our longest continuous chain is six carbon atoms we could have this being the longest continuous chain of six carbon atoms guys see that that's six as well 1 2 3 4 5 six but then if that's the longest chain we only have one substituent we have another chain and I'm going to go this way harder to to see but that is also six carbons long okay if we count 1 2 3 4 5 6 six carbons long and in that case we have one and two substituents so we have six being the longest chain we could either go this way or we could go this way since going from bottom to side here going this way gives gives us more substituents gives us two substituents that's the one that's actually going to be our longest chain our parent chain okay so it's going to be the one in green because it gives us more substituents two substituents versus just one when we go this other direction okay I know that was a lot but it's important to be able to apply these rules to naming so that way you can just look at a compound and be able to determine its name just from the structure okay and it's complicated because organic compounds are complicated right um otherwise we just have common names for everything so we'll do the in-class problems I'd also recommend working through the online naming via that website it's very useful and gives you some very good practice this especially with skeletal structure naming so please let me know if you have any questions and we'll work through these problems and naming in class