Notes on Nomenclature of Alkanes: Cycloalkanes and Bicycloalkanes

hello class well we&#39;re going to discuss now is nomenclature of alkanes excuse me called by cycloalkanes now we&#39;ve previously seen alkanes in a ring structure like that so that would be cyclohexane but the moment that we stick another ring on it okay so let&#39;s say if I oops added a DOT to it that right there is called a bicycle compound or a bicycle alkane and the reason why is because now this ring has two rings so what we could see here is you could see in blue right here got six membered ring right there okay but then what&#39;s on the inside looks like a five-membered ring right and so what what we have going on here is we need to be able to draw these molecules okay and so you could so let&#39;s just go back and do something simple okay let&#39;s see here we could just look at cyclohexane okay and we could take that molecule and draw it like this so just draw a little like a little bit more broader boom boom and then in like that all right so that and that represent the same thing and the reason why we drop like this is because when we add that extra carbon right there there so there&#39;s a total of seven carbons in this molecule we can represent it like this we can number that number one two three four five six now this is just for numbering purposes just so you can see what where everything is okay this numbering process that I&#39;m doing right now is not for nomenclature okay so we see carbon four has a carbon that&#39;s bonded to carbon one like that do you see how I put a little Gap so this Bond right here do you see I put a gap right there why is that so important is because if let&#39;s draw it was where I didn&#39;t just draw it like this all right what&#39;s the difference between this molecule here and this molecule here well this molecule here has seven carbons this molecule here has eight why because every Junction is a carbon so one two three four five six seven eight but here you can see one two three four five six seven that&#39;s all there is so when you draw the Rings like this you need when you draw this little triangle right there you have to uh put a little Gap in between it there all right so now what we have here is we have the molecule looking like this right so getting rid of these numbers here so this is that representing the same thing now let&#39;s talk about this by cyclo alkane what&#39;s the name of this well it has seven carbons right so we can call it a bicyclo heptane like that and in a bicycle heptane we have what&#39;s called Bridgehead carbons all right Bridgehead carbons like so and the bridge had carbons is that carbon there and that carbon there and we will get to it momentarily why do how do I know those are Bridgehead carbons right so we&#39;ll get there in a second but we have when you look at a compound it looks a little funky with two rings we call it two or more Rings we call it a bicycle heptane so the Bridgehead carbons are the carbons that join the two rings together so if we look at it in this structure right here I could view it this way I could see a ring like this there&#39;s one ring right there and then I could also see this I can see the second ring right there so I had that pink ring and that blue ring and where are they joining together they&#39;re joining together right there and so that&#39;s what we see in this structure right here this is our bridged head carbons right there now why is this important to find the Bridgehead carbons is because when you take a look at another molecule what if I draw another molecule that looks like this well what&#39;s the difference between this guy and this guy well when I look at it this is a bicycle alkane and it has seven carbons so I could call it bicycle peptane but when you look at the two structures you can clearly see that they look different but how can we how can I name them the same thing if I did how which one would you know I&#39;m talking about so that&#39;s the thing that&#39;s uh going to that&#39;s why the Bridgehead carbon is so important is because now it&#39;s going to help us figure out how to actually name it more specifically so I know exactly which one I&#39;m talking about so if I look at this one on the left the bridge carbons would be this guy right there and that guy right there because those are the carbons that are joining the two rings together now when we take these molecules we are going to now do use nomenclature to figure out what the name is okay so when we take let&#39;s look at this one here what you&#39;re going to do is you&#39;re going to identify the two Bridgehead carbons and then you&#39;re going to try to find the longest path that&#39;s connecting them all right and so you can start here and I can see I could go one two three okay so that&#39;s a path boom boom boom okay now within that path that&#39;s connecting the two Bridge carbons we count how many carbons there are in between those two Bridge carbons so we count one two there&#39;s two carbons in between this path so I I make that note mental note okay that there&#39;s two carbons in that longest path now if what if I count the other way there&#39;s going to be one two three okay there&#39;s that path you&#39;ve seen that now how many carbons are in between the two braced carbons there&#39;s one two so there&#39;s another two now I find another path between the bridge carbons from this path to that path and I see one two how many carbon atoms are in between those two Bridge carbons one so this path right here so one and then I put a little like that and so the these numbers right here are going to tell us the name of the compound and so the way we actually name it is by cyclo and then we use brackets and then we put in the order the longest paths so 2 dot two dot one by cyclo heptane like that so how would we name this guy well we&#39;ve identified the Bridgehead carbons and so we we find the paths so let&#39;s go starting here one two three four so you don&#39;t count the Bridgehead carbons so from there to there I follow this path so we have a one two three four nope sorry we don&#39;t from Bridgehead to Bridgehead it&#39;s four carbons one two three four five but we only count what&#39;s in between so one two three so we have a three and then we could start here and go boom boom so that&#39;s one or I could have went boom boom and that is also one carbon in between so we would call this guy a by cyclo 3.1.1 heptane so what&#39;s the difference between the two it&#39;s the numbers inside those brackets and those are what&#39;s going to show us where the where the this these numbers right here is showing us the connectivity of these rings that&#39;s the important part now let&#39;s take a look at a bicycle alkane that has substituents on it and here we have one methyl substituent so the way I like to name these molecules I understand that we have a a bicycle how many carbons are in the ring and I count one two three four five six seven eight so that&#39;s a bicycle octane now I know that&#39;s not the correct name because I don&#39;t have the the numbering scheme for the Bridgehead carbons right so I then I need to identify the bridge head carbons I see that they&#39;re there okay now typically when you uh name a alkane you always want to give your substituents the lowest locant number and that&#39;s typically how you do it but not with by cycloalkanes what you do is you first figure out what numbers go into those parentheses all right and so the let&#39;s do it here so we&#39;ve got to find the longest the paths here so we have something let&#39;s let&#39;s do this one from this Bridgehead carbon to there what do we have one two carbons in between the two bridgeheads two but do I have a path that&#39;s longer than two what if we went this way that is one two three carbons in between and we always just pre we rank them from largest to smallest and then we see from this we can follow this path right there and there&#39;s only one carbon so 3.1 now we have to kind of memorize this three two one because we&#39;re going to follow that path in order to prioritize the locant numbers so it&#39;s telling me to go through this three path so I could start right here number that carbon one two three four five do you see how this number right here is telling me to follow that path once I stop at a Bridgehead carbon I look at the next number and that says two so follow the two path so I&#39;m going to go six seven so I&#39;m following this path back to the Bridgehead carbon effect there&#39;s my two boom boom boom and then it says now I stopped at this bridge had carbon now follow that path so right there so that would be carbon eight do you see how I&#39;m doing the numbering scheme by following the path here I&#39;ll do another example to hopefully make this makes more sense so now that I have those numbers here I see that my methyl group here is on carbon 8. so we can name it let&#39;s see here so that would be do I have enough space here let&#39;s write it here that would be it eight Dash methyl methyl right there by cyclo now I have to do the parentheses 3.2.1 [Music] close parentheses and then it would be what eight carbons so octane now I&#39;m going to run out of board space and you see that I ran out of space but that&#39;s going to say octane so 8-methyl by cyclo 3.2.1 octane now with this one we see it&#39;s a bicycle alkane we count how many carbons are in the ring there&#39;s let&#39;s start with this one one two three four five six seven eight so it&#39;s another bicycle octane now we have to figure out the paths here and so we identify that and that is our Bridge head carbon so let&#39;s look at the path there&#39;s one two three we get back there so there&#39;s three carbons in between and it&#39;s not commas it&#39;s period then we can go one two right there so that&#39;s the two and then one okay so there&#39;s our paths now we have to select here a correct path okay so let&#39;s do this in colors here What if I numbered it this way following three two one so one two three four five six seven come back here then that&#39;s eight like that okay that&#39;s one path what if why could I have not have done it this way why could I not have started here on this particular carbon one two three four five six seven eight because when I looked at the path in blue I did three two one three two one I followed that but I can also follow that in the pink weight as well watch that&#39;s the third pathway second pathway the last pathway so now we have the blue numbers in the pink numbers which ones would you choose well we want to give the substituent the lowest number if we have a tie with numbering the bicycle ring now when we&#39;re numbering the bicycle ring we have to follow this path but if there&#39;s two ways to go about this path then you give the substituent the lowest low kit number so that would be the six or the peak numbers so the name of this compound is going to be 6 methyl by cyclo parentheses 3.2.1 octane huh so that&#39;s the nomenclatures for bicycle compounds okay now we&#39;re going to shift our focus on what&#39;s called constitutional isomers of alkanes now we can have formulas for alkanes okay and I could take that formula right there and draw that molecule there&#39;s one two three four carbons and then there&#39;s 10 hydrogens but then what is a constitutional isomer then well I can draw another molecule with the same amount of carbons and hydrogens what if I drew it like this do I have the same amount of carbons let&#39;s count one two three four so four carbons how many hydrogens do I have on this molecule three six nine ten so this molecule and that molecule you can clearly see that they look different right they are different molecules they have different names they look different but what do they have in common the exact same chemical formula and that is what a constitutional isomer is the same molecular formula but different connectivity of atoms they look different you can see that we have a zigzag like this that&#39;s the connectivity but then the zigzag looks a little different on this guy so if we take a a pentane what could be one of the structures well just draw a zigzag one two three four five there&#39;s five carbons and there are 12 hydrogens but could we figure out some other could we figure out a constitutional isomer for this well what if I just took this carbon right here chopped it off and put it over here like this just stuck it right there do I have five carbons and 12 hydrogens for this molecule one two three four five carbons and there&#39;s 3 6 7 8 9 10 11 12. so that is a constitutional isomer could I draw another one What if I did this one two three four five so that&#39;s five carbons and then we have 12 hydrogens so they have three constitutional isomers here now look at this if we go to C6 h14 you know any uh constitutional isomers we have of that we have about five of them now look at how crazy this gets if we have seven carbons we&#39;re going to have nine of them now I&#39;m just going to skip down to 10. look at this 10 carbons so what&#39;s that 22 I&#39;m just double checking the numbers here look how many constitutional isomers there are 75 and the number just gets exponentially larger and larger and larger as we increase the amount of carbons so you may be thinking how do I know how to draw all the isomers there&#39;s no trick to it there&#39;s no strategy really you just start doing your zigzags making sure you have enough carbons and enough hydrogens and if it matches the chemical formula then you&#39;ve done it you&#39;ve made a constitutional isomer now the challenge that you&#39;re going to run into is when you do duplicates okay so let me show you what I mean by duplicates as you&#39;re going through all of these trying to figure out all the isomers you&#39;ll be like okay here&#39;s our hexane so we could do two three four five six oh that&#39;s a beautiful molecule okay and then you take that most simple one and then you start uh moving the atoms around and trying to uh figure something out well what if you came up with let&#39;s see here one two three four five what have you came up with uh isomer like this all right so that&#39;s one two three four five six so that one&#39;s correct or that that one&#39;s valid I&#39;m going to erase this one for a minute so you&#39;re like yeah that one looks good and then what if you draw a molecule like this and you&#39;re like one two three four five six perfect and you look at these two molecules and you&#39;re like based off a visual inspection you&#39;re like they&#39;re different they look different they&#39;re isomers of one another same chemical formula but different connectivity but oh you got to be careful oh you got to be careful and why do you have to be careful what&#39;s the common feature about a single Bond a single Bond can rotate okay they can rotate and so what is actually happened here these two molecules are not isomers of one another they are identical it&#39;s just the bonds have been Twisted to make them look different you can take this molecule right here and twist these bonds and it will match perfectly with this one so this molecule right here if we call it a is that molecule and at the beginning we call this guy B because we&#39;re like a and b are different but we&#39;ve got to be so careful because if we can twist and rotate around these bonds we will see that a actually is B so both of these molecules are the exact same they are identical they are not isomers of one another now how can you figure that out well you can rotate molecules in three-dimensional space all right so let me just show you how I I see it and some people can see it uh very well and easily so what I&#39;m going to do is I&#39;m going to take this molecule here and twist it 90 degrees and when I twist it 90 degrees so we&#39;ll go here I&#39;m going to twist it 90 degrees okay and it&#39;s going to look something more like that okay let&#39;s put it more like that okay and then I&#39;m going to take this Bond right here and just rotate it and then when I rotate it I&#39;ll rotate this carbon right there down I&#39;ll just rotate it down this carbon here is still there now do you see this matches that perfectly so they&#39;re identical now one way to help get your brain to see this is to pull out your model kits and make these molecules and put put them together just like Legos and rotate the atoms you&#39;ll see that the whole molecule can rotate now for some people that visual representation is just too difficult to see and that&#39;s fine so there&#39;s other ways that we can figure this out if you&#39;re not a visual person how can I tell that both of these molecules are identical okay use the IUPAC name the thing right so let&#39;s name this guy so we find the longest carbon chain one two three four five we have a methyl group there on carbon three so that would be a three methyl pentane that&#39;s how that&#39;s named right okay now we come over here and find the longest carbon chain one two three four that&#39;s not long one two three four five okay so how do I number this do I number it from this Direction one two three four five no because we want to give our substituent right here at the lowest locant number so that&#39;ll be one two three wait am I am I lying here let&#39;s double check the locate number is at one two three okay and if I number it the other way it&#39;s that three oh so it all works out the same so what have we found that we have a substituent at cart at Carbon three so that&#39;s a three methyl and five carbons long is the longest carbon chain so that&#39;s a pentane and then I evaluate 3-methylpentane three-methylpentane boom exact same name exact same molecule they&#39;re not isomers of one another so that&#39;s one way that you can double check your cells if you&#39;re making any duplicates okay so in the energy industry we use gasoline to fuel our vehicles and we&#39;ve all heard of octane because you have the octane numbers there on the gas station gas pumps and so we have Octane and we we take octane let&#39;s represent that by this two three four five six seven eight so that&#39;s eight carbons long and if we add some oxygen okay and then we add a little spark to it we&#39;re going to combust that and that&#39;s going to turn into eight moles of carbon dioxide plus nine moles of water okay now how much oxygen does it need to make this uh balanced here it&#39;s going to need 12 and a half okay 12 and a half moles of oxygen to combust here okay but what if we looked at another an isomer of octane that looked like this all right just let&#39;s double check one two three four five six seven eight so eight carbons eight carbons and if we treat that with 12 and a half moles of oxygen put a spark that&#39;s going to combust into eight moles of carbon dioxide plus 9 moles of water okay so both of these give the same amount of carbon dioxide and water but look at this this difference right here the heat of the reaction how much heat or how much energy is given off when you take this molecule and burn it with oxygen you get a number of 5470 kilojoules per mole okay you can&#39;t see the moles part there but that&#39;s moles kilojoules per mole but if you take this isomer constitutional isomer of octane it&#39;s going to give off a different amount of heat 5452 so this is quite interesting same amount of carbons same amount of hydrogens same amount of moles of everything but one gives off more heat than the other so it looks like this octane the linear octane gives off more heat gives off more energy than a more compact a molecule with the same amount of carbons here so what this is telling us is the stability of the alkane because this is releasing more heat when it combusts and that&#39;s when we burn something we call it combustion so when this combusts it gives off more Heat and the only reason why this gives off more heat is because it&#39;s more unstable so maybe to make sense of that let&#39;s draw a diagram here to illustrate that so if I draw myself energy diagram here and what we have is our energy the heat of combustion all right that&#39;s just a not symbol there so how much energy is given off here well what&#39;s interesting is that when you combust the linear octane versus the compact octane you generate the same product and that is carbon dioxide plus water it does not matter if you burn the linear octane or the compact octane you get the same product so if we have let&#39;s draw it here in a different color now here&#39;s our linear one two three four five six seven eight okay and we&#39;ll have we&#39;ll put its energy level right there in order when it combust it released a negative 5470 kilojoules of energy kilojoules per mole that&#39;s the energy gap between the starting material and the product that energy gap but what&#39;s so interesting is this number right here is smaller and the only way that could be smaller is if the starting material is lower in energy and so this energy gap right there is a negative 5452. kilojoules per mole and so what we&#39;re learning here is this molecule right here is more stable than the linear form and so there&#39;s there&#39;s an area of research when we look at molecules do you remember from General chemistry doing calorimetry where you were doing reactions in a Colorimeter to measure the heat that&#39;s released or absorbed and in this particular case we use a calorimeter we find out how much heat is given off when you burn these different types of fuels and so from one perspective you can do these calorimetry experiments to determine which molecules are more stable so I think that&#39;s pretty pretty slick

hello class well we&amp;#39;re going to discuss now is nomenclature of alkanes excuse me called by cycloalkanes now we&amp;#39;ve previously seen alkanes in a ring structure like that so that would be cyclohexane but the moment that we stick another ring on it okay so let&amp;#39;s say if I oops added a DOT to it that right there is called a bicycle compound or a bicycle alkane and the reason why is because now this ring has two rings so what we could see here is you could see in blue right here got six membered ring right there okay but then what&amp;#39;s on the inside looks like a five-membered ring right and so what what we have going on here is we need to be able to draw these molecules okay and so you could so let&amp;#39;s just go back and do something simple okay let&amp;#39;s see here we could just look at cyclohexane okay and we could take that molecule and draw it like this so just draw a little like a little bit more broader boom boom and then in like that all right so that and that represent the same thing and the reason why we drop like this is because when we add that extra carbon right there there so there&amp;#39;s a total of seven carbons in this molecule we can represent it like this we can number that number one two three four five six now this is just for numbering purposes just so you can see what where everything is okay this numbering process that I&amp;#39;m doing right now is not for nomenclature okay so we see carbon four has a carbon that&amp;#39;s bonded to carbon one like that do you see how I put a little Gap so this Bond right here do you see I put a gap right there why is that so important is because if let&amp;#39;s draw it was where I didn&amp;#39;t just draw it like this all right what&amp;#39;s the difference between this molecule here and this molecule here well this molecule here has seven carbons this molecule here has eight why because every Junction is a carbon so one two three four five six seven eight but here you can see one two three four five six seven that&amp;#39;s all there is so when you draw the Rings like this you need when you draw this little triangle right there you have to uh put a little Gap in between it there all right so now what we have here is we have the molecule looking like this right so getting rid of these numbers here so this is that representing the same thing now let&amp;#39;s talk about this by cyclo alkane what&amp;#39;s the name of this well it has seven carbons right so we can call it a bicyclo heptane like that and in a bicycle heptane we have what&amp;#39;s called Bridgehead carbons all right Bridgehead carbons like so and the bridge had carbons is that carbon there and that carbon there and we will get to it momentarily why do how do I know those are Bridgehead carbons right so we&amp;#39;ll get there in a second but we have when you look at a compound it looks a little funky with two rings we call it two or more Rings we call it a bicycle heptane so the Bridgehead carbons are the carbons that join the two rings together so if we look at it in this structure right here I could view it this way I could see a ring like this there&amp;#39;s one ring right there and then I could also see this I can see the second ring right there so I had that pink ring and that blue ring and where are they joining together they&amp;#39;re joining together right there and so that&amp;#39;s what we see in this structure right here this is our bridged head carbons right there now why is this important to find the Bridgehead carbons is because when you take a look at another molecule what if I draw another molecule that looks like this well what&amp;#39;s the difference between this guy and this guy well when I look at it this is a bicycle alkane and it has seven carbons so I could call it bicycle peptane but when you look at the two structures you can clearly see that they look different but how can we how can I name them the same thing if I did how which one would you know I&amp;#39;m talking about so that&amp;#39;s the thing that&amp;#39;s uh going to that&amp;#39;s why the Bridgehead carbon is so important is because now it&amp;#39;s going to help us figure out how to actually name it more specifically so I know exactly which one I&amp;#39;m talking about so if I look at this one on the left the bridge carbons would be this guy right there and that guy right there because those are the carbons that are joining the two rings together now when we take these molecules we are going to now do use nomenclature to figure out what the name is okay so when we take let&amp;#39;s look at this one here what you&amp;#39;re going to do is you&amp;#39;re going to identify the two Bridgehead carbons and then you&amp;#39;re going to try to find the longest path that&amp;#39;s connecting them all right and so you can start here and I can see I could go one two three okay so that&amp;#39;s a path boom boom boom okay now within that path that&amp;#39;s connecting the two Bridge carbons we count how many carbons there are in between those two Bridge carbons so we count one two there&amp;#39;s two carbons in between this path so I I make that note mental note okay that there&amp;#39;s two carbons in that longest path now if what if I count the other way there&amp;#39;s going to be one two three okay there&amp;#39;s that path you&amp;#39;ve seen that now how many carbons are in between the two braced carbons there&amp;#39;s one two so there&amp;#39;s another two now I find another path between the bridge carbons from this path to that path and I see one two how many carbon atoms are in between those two Bridge carbons one so this path right here so one and then I put a little like that and so the these numbers right here are going to tell us the name of the compound and so the way we actually name it is by cyclo and then we use brackets and then we put in the order the longest paths so 2 dot two dot one by cyclo heptane like that so how would we name this guy well we&amp;#39;ve identified the Bridgehead carbons and so we we find the paths so let&amp;#39;s go starting here one two three four so you don&amp;#39;t count the Bridgehead carbons so from there to there I follow this path so we have a one two three four nope sorry we don&amp;#39;t from Bridgehead to Bridgehead it&amp;#39;s four carbons one two three four five but we only count what&amp;#39;s in between so one two three so we have a three and then we could start here and go boom boom so that&amp;#39;s one or I could have went boom boom and that is also one carbon in between so we would call this guy a by cyclo 3.1.1 heptane so what&amp;#39;s the difference between the two it&amp;#39;s the numbers inside those brackets and those are what&amp;#39;s going to show us where the where the this these numbers right here is showing us the connectivity of these rings that&amp;#39;s the important part now let&amp;#39;s take a look at a bicycle alkane that has substituents on it and here we have one methyl substituent so the way I like to name these molecules I understand that we have a a bicycle how many carbons are in the ring and I count one two three four five six seven eight so that&amp;#39;s a bicycle octane now I know that&amp;#39;s not the correct name because I don&amp;#39;t have the the numbering scheme for the Bridgehead carbons right so I then I need to identify the bridge head carbons I see that they&amp;#39;re there okay now typically when you uh name a alkane you always want to give your substituents the lowest locant number and that&amp;#39;s typically how you do it but not with by cycloalkanes what you do is you first figure out what numbers go into those parentheses all right and so the let&amp;#39;s do it here so we&amp;#39;ve got to find the longest the paths here so we have something let&amp;#39;s let&amp;#39;s do this one from this Bridgehead carbon to there what do we have one two carbons in between the two bridgeheads two but do I have a path that&amp;#39;s longer than two what if we went this way that is one two three carbons in between and we always just pre we rank them from largest to smallest and then we see from this we can follow this path right there and there&amp;#39;s only one carbon so 3.1 now we have to kind of memorize this three two one because we&amp;#39;re going to follow that path in order to prioritize the locant numbers so it&amp;#39;s telling me to go through this three path so I could start right here number that carbon one two three four five do you see how this number right here is telling me to follow that path once I stop at a Bridgehead carbon I look at the next number and that says two so follow the two path so I&amp;#39;m going to go six seven so I&amp;#39;m following this path back to the Bridgehead carbon effect there&amp;#39;s my two boom boom boom and then it says now I stopped at this bridge had carbon now follow that path so right there so that would be carbon eight do you see how I&amp;#39;m doing the numbering scheme by following the path here I&amp;#39;ll do another example to hopefully make this makes more sense so now that I have those numbers here I see that my methyl group here is on carbon 8. so we can name it let&amp;#39;s see here so that would be do I have enough space here let&amp;#39;s write it here that would be it eight Dash methyl methyl right there by cyclo now I have to do the parentheses 3.2.1 [Music] close parentheses and then it would be what eight carbons so octane now I&amp;#39;m going to run out of board space and you see that I ran out of space but that&amp;#39;s going to say octane so 8-methyl by cyclo 3.2.1 octane now with this one we see it&amp;#39;s a bicycle alkane we count how many carbons are in the ring there&amp;#39;s let&amp;#39;s start with this one one two three four five six seven eight so it&amp;#39;s another bicycle octane now we have to figure out the paths here and so we identify that and that is our Bridge head carbon so let&amp;#39;s look at the path there&amp;#39;s one two three we get back there so there&amp;#39;s three carbons in between and it&amp;#39;s not commas it&amp;#39;s period then we can go one two right there so that&amp;#39;s the two and then one okay so there&amp;#39;s our paths now we have to select here a correct path okay so let&amp;#39;s do this in colors here What if I numbered it this way following three two one so one two three four five six seven come back here then that&amp;#39;s eight like that okay that&amp;#39;s one path what if why could I have not have done it this way why could I not have started here on this particular carbon one two three four five six seven eight because when I looked at the path in blue I did three two one three two one I followed that but I can also follow that in the pink weight as well watch that&amp;#39;s the third pathway second pathway the last pathway so now we have the blue numbers in the pink numbers which ones would you choose well we want to give the substituent the lowest number if we have a tie with numbering the bicycle ring now when we&amp;#39;re numbering the bicycle ring we have to follow this path but if there&amp;#39;s two ways to go about this path then you give the substituent the lowest low kit number so that would be the six or the peak numbers so the name of this compound is going to be 6 methyl by cyclo parentheses 3.2.1 octane huh so that&amp;#39;s the nomenclatures for bicycle compounds okay now we&amp;#39;re going to shift our focus on what&amp;#39;s called constitutional isomers of alkanes now we can have formulas for alkanes okay and I could take that formula right there and draw that molecule there&amp;#39;s one two three four carbons and then there&amp;#39;s 10 hydrogens but then what is a constitutional isomer then well I can draw another molecule with the same amount of carbons and hydrogens what if I drew it like this do I have the same amount of carbons let&amp;#39;s count one two three four so four carbons how many hydrogens do I have on this molecule three six nine ten so this molecule and that molecule you can clearly see that they look different right they are different molecules they have different names they look different but what do they have in common the exact same chemical formula and that is what a constitutional isomer is the same molecular formula but different connectivity of atoms they look different you can see that we have a zigzag like this that&amp;#39;s the connectivity but then the zigzag looks a little different on this guy so if we take a a pentane what could be one of the structures well just draw a zigzag one two three four five there&amp;#39;s five carbons and there are 12 hydrogens but could we figure out some other could we figure out a constitutional isomer for this well what if I just took this carbon right here chopped it off and put it over here like this just stuck it right there do I have five carbons and 12 hydrogens for this molecule one two three four five carbons and there&amp;#39;s 3 6 7 8 9 10 11 12. so that is a constitutional isomer could I draw another one What if I did this one two three four five so that&amp;#39;s five carbons and then we have 12 hydrogens so they have three constitutional isomers here now look at this if we go to C6 h14 you know any uh constitutional isomers we have of that we have about five of them now look at how crazy this gets if we have seven carbons we&amp;#39;re going to have nine of them now I&amp;#39;m just going to skip down to 10. look at this 10 carbons so what&amp;#39;s that 22 I&amp;#39;m just double checking the numbers here look how many constitutional isomers there are 75 and the number just gets exponentially larger and larger and larger as we increase the amount of carbons so you may be thinking how do I know how to draw all the isomers there&amp;#39;s no trick to it there&amp;#39;s no strategy really you just start doing your zigzags making sure you have enough carbons and enough hydrogens and if it matches the chemical formula then you&amp;#39;ve done it you&amp;#39;ve made a constitutional isomer now the challenge that you&amp;#39;re going to run into is when you do duplicates okay so let me show you what I mean by duplicates as you&amp;#39;re going through all of these trying to figure out all the isomers you&amp;#39;ll be like okay here&amp;#39;s our hexane so we could do two three four five six oh that&amp;#39;s a beautiful molecule okay and then you take that most simple one and then you start uh moving the atoms around and trying to uh figure something out well what if you came up with let&amp;#39;s see here one two three four five what have you came up with uh isomer like this all right so that&amp;#39;s one two three four five six so that one&amp;#39;s correct or that that one&amp;#39;s valid I&amp;#39;m going to erase this one for a minute so you&amp;#39;re like yeah that one looks good and then what if you draw a molecule like this and you&amp;#39;re like one two three four five six perfect and you look at these two molecules and you&amp;#39;re like based off a visual inspection you&amp;#39;re like they&amp;#39;re different they look different they&amp;#39;re isomers of one another same chemical formula but different connectivity but oh you got to be careful oh you got to be careful and why do you have to be careful what&amp;#39;s the common feature about a single Bond a single Bond can rotate okay they can rotate and so what is actually happened here these two molecules are not isomers of one another they are identical it&amp;#39;s just the bonds have been Twisted to make them look different you can take this molecule right here and twist these bonds and it will match perfectly with this one so this molecule right here if we call it a is that molecule and at the beginning we call this guy B because we&amp;#39;re like a and b are different but we&amp;#39;ve got to be so careful because if we can twist and rotate around these bonds we will see that a actually is B so both of these molecules are the exact same they are identical they are not isomers of one another now how can you figure that out well you can rotate molecules in three-dimensional space all right so let me just show you how I I see it and some people can see it uh very well and easily so what I&amp;#39;m going to do is I&amp;#39;m going to take this molecule here and twist it 90 degrees and when I twist it 90 degrees so we&amp;#39;ll go here I&amp;#39;m going to twist it 90 degrees okay and it&amp;#39;s going to look something more like that okay let&amp;#39;s put it more like that okay and then I&amp;#39;m going to take this Bond right here and just rotate it and then when I rotate it I&amp;#39;ll rotate this carbon right there down I&amp;#39;ll just rotate it down this carbon here is still there now do you see this matches that perfectly so they&amp;#39;re identical now one way to help get your brain to see this is to pull out your model kits and make these molecules and put put them together just like Legos and rotate the atoms you&amp;#39;ll see that the whole molecule can rotate now for some people that visual representation is just too difficult to see and that&amp;#39;s fine so there&amp;#39;s other ways that we can figure this out if you&amp;#39;re not a visual person how can I tell that both of these molecules are identical okay use the IUPAC name the thing right so let&amp;#39;s name this guy so we find the longest carbon chain one two three four five we have a methyl group there on carbon three so that would be a three methyl pentane that&amp;#39;s how that&amp;#39;s named right okay now we come over here and find the longest carbon chain one two three four that&amp;#39;s not long one two three four five okay so how do I number this do I number it from this Direction one two three four five no because we want to give our substituent right here at the lowest locant number so that&amp;#39;ll be one two three wait am I am I lying here let&amp;#39;s double check the locate number is at one two three okay and if I number it the other way it&amp;#39;s that three oh so it all works out the same so what have we found that we have a substituent at cart at Carbon three so that&amp;#39;s a three methyl and five carbons long is the longest carbon chain so that&amp;#39;s a pentane and then I evaluate 3-methylpentane three-methylpentane boom exact same name exact same molecule they&amp;#39;re not isomers of one another so that&amp;#39;s one way that you can double check your cells if you&amp;#39;re making any duplicates okay so in the energy industry we use gasoline to fuel our vehicles and we&amp;#39;ve all heard of octane because you have the octane numbers there on the gas station gas pumps and so we have Octane and we we take octane let&amp;#39;s represent that by this two three four five six seven eight so that&amp;#39;s eight carbons long and if we add some oxygen okay and then we add a little spark to it we&amp;#39;re going to combust that and that&amp;#39;s going to turn into eight moles of carbon dioxide plus nine moles of water okay now how much oxygen does it need to make this uh balanced here it&amp;#39;s going to need 12 and a half okay 12 and a half moles of oxygen to combust here okay but what if we looked at another an isomer of octane that looked like this all right just let&amp;#39;s double check one two three four five six seven eight so eight carbons eight carbons and if we treat that with 12 and a half moles of oxygen put a spark that&amp;#39;s going to combust into eight moles of carbon dioxide plus 9 moles of water okay so both of these give the same amount of carbon dioxide and water but look at this this difference right here the heat of the reaction how much heat or how much energy is given off when you take this molecule and burn it with oxygen you get a number of 5470 kilojoules per mole okay you can&amp;#39;t see the moles part there but that&amp;#39;s moles kilojoules per mole but if you take this isomer constitutional isomer of octane it&amp;#39;s going to give off a different amount of heat 5452 so this is quite interesting same amount of carbons same amount of hydrogens same amount of moles of everything but one gives off more heat than the other so it looks like this octane the linear octane gives off more heat gives off more energy than a more compact a molecule with the same amount of carbons here so what this is telling us is the stability of the alkane because this is releasing more heat when it combusts and that&amp;#39;s when we burn something we call it combustion so when this combusts it gives off more Heat and the only reason why this gives off more heat is because it&amp;#39;s more unstable so maybe to make sense of that let&amp;#39;s draw a diagram here to illustrate that so if I draw myself energy diagram here and what we have is our energy the heat of combustion all right that&amp;#39;s just a not symbol there so how much energy is given off here well what&amp;#39;s interesting is that when you combust the linear octane versus the compact octane you generate the same product and that is carbon dioxide plus water it does not matter if you burn the linear octane or the compact octane you get the same product so if we have let&amp;#39;s draw it here in a different color now here&amp;#39;s our linear one two three four five six seven eight okay and we&amp;#39;ll have we&amp;#39;ll put its energy level right there in order when it combust it released a negative 5470 kilojoules of energy kilojoules per mole that&amp;#39;s the energy gap between the starting material and the product that energy gap but what&amp;#39;s so interesting is this number right here is smaller and the only way that could be smaller is if the starting material is lower in energy and so this energy gap right there is a negative 5452. kilojoules per mole and so what we&amp;#39;re learning here is this molecule right here is more stable than the linear form and so there&amp;#39;s there&amp;#39;s an area of research when we look at molecules do you remember from General chemistry doing calorimetry where you were doing reactions in a Colorimeter to measure the heat that&amp;#39;s released or absorbed and in this particular case we use a calorimeter we find out how much heat is given off when you burn these different types of fuels and so from one perspective you can do these calorimetry experiments to determine which molecules are more stable so I think that&amp;#39;s pretty pretty slick

Transcript for:Notes on Nomenclature of Alkanes: Cycloalkanes and Bicycloalkanes

Transcript for:
Notes on Nomenclature of Alkanes: Cycloalkanes and Bicycloalkanes