ranking acids and bases that'll be the topic in this lesson now we just had an introduction to acids and bases in the last lesson and now we're really going to learn uh all the different structural features that allow us to actually compare the relative acidities between two acids or the relative basicities between a couple of bases as well now this is my brand new organic chemistry playlist i'll be releasing these lessons weekly throughout the 2020-21 school year so if you don't want to miss one of these subscribe to the channel click the bell notifications you'll be notified every time i post a new video so ranking acid bases i just want to start off with a little reminder from our introduction in the last lesson that the stronger an acid the weaker its conjugate base and vice versa so if you have a stronger conjugate base you're going to have a weaker acid associated with that and so next part of that is going to be that a more stable base is a weaker base so that's the next part and then more stable base is usually going to mean lower energy electrons on the base now recall that lewis definition of base was an electron pair donor and usually lower energy electrons mean more stable electrons less reactive electrons we'll see one major exception to that but most of the time that's kind of how we're going to rank bases we're going to look at how low the energy of the electrons are and their relative stabilities associated with that so lower energy electrons more stable base more stable base weaker base all right so we're going to use a little mnemonic here and in this case i'm going to use reo so but the truth is we only use reo if we're comparing bases first off these are mnemonic for comparing bases but we only use it if we're comparing a bunch of bases that all have the same charge now and most of the time we'll be using bases that have a negative charge but this could apply to comparing bases that are all neutral in charge and things of a sort as well so so i want to want to put charge at the top of the list although it's not a part of the the proper mnemonic now other textbooks uh and professors will often use a version of this mnemonic that includes charge and they would call it cardio and induction here instead of calling it induction they might call it dipole induction so they can put the d and the i on that because cardio is just a really cool one so and it starts with charge so charge is really important we'll get into that in a little bit and and then the atom actually acting as the base and where it's located on the periodic table that'll be important in determining relative basicity uh and then resonance we you know we've learned about resonance stabilization and how that could stabilize the base and make it a weaker base as well and induction is one we haven't specifically talked about yet maybe you saw it in gen chem maybe it didn't depends on your class so but induction means do you have any electronegative atoms nearby so that might help stabilize a base it turns out having electronegative atoms are going to pull electrons towards them and lower the electron density on that base making it a more stable base less negative sort of thing uh we'll get more into that a little bit and then finally orbitals and this last one really should you know be called hybridization because it's really a difference in hybridization of the orbitals of where you find a lone pair of electrons but that wouldn't make a good mnemonic you know are or something like that you know so reo they go with orbitals but it's really a matter of hybridization but this little mnemonic is the one we're going to use and you typically follow it in order and most the time again 99 of the time you're just going to be comparing a bunch of bases that all have the same charge and so this little charge rule becomes irrelevant and that's why it really just reduces down to reo but for that one time out of a hundred i put the charge at the top of the list here so let's take a look we're gonna take an in-depth look at every single one of these rules so that you can rank acids and bases in their relative acidity or relative basicity just based on looking at their structures with no pkas provided all right so charge here so it turns out when you get a negative charge that raises the energy of the electrons and you have more electrons around that oxygen nucleus they can't get as close to the nucleus because they're repelling each other and so they spread out and the further they get out from that nucleus the higher their energy and the greater the reactivity as a base and so having a negative charge causes your electron cloud to be bigger the electrons are on average further from the nucleus and it leads to a stronger base now a positive charge is going to do the exact opposite if i was actually talking about this guy is acting like a base here that lone pair because now we have a positive formal charge in the auction with fewer electrons around the nucleus which means the remaining electrons can actually get even closer to the nucleus which lowers their energy and makes them less reactive and so in this case if we were going to look at a trend in basicity so it would be going to the left and if we want to talk about the stability of the electrons the electrons would actually be getting more stable as they went to the right so that would relate to basicity here so it turns out for charge though you could also look at this in terms of acidity in this one case and and notice we've got hydronium over here hydroxide over here we know hydronium is a strong acid we know hydroxide's a strong base and we got water right in the middle which is neutral and so you can look at this like so cool so charge in this one example here this set of examples is you got to be careful on when it's relevant because it's not going to always be relevant now as long as you're comparing a conjugate base to a conjugate acid conjugate conjugate base that's when charge will work every time as long as you're just comparing a conjugate acid a conjugate base yes whichever one of these is more negative is the better base whichever one of these is more positive or less negative is the better acid that's when it works now if you try to compare just two totally different molecules that have a different charge maybe it'll work and maybe it won't and it's not a comparison that comes up a lot as a result because it's hard to ask you about it now if it involves one of the acids that you're supposed to memorize the pkas for one of those typical functional groups that we went through in the last lesson well the model means that's fair game and you wouldn't even need to use rules and you shouldn't use rules in that case and i'll show you a couple examples where that happens so but i just want to point out that charge is important and it's probably the most important thing however most of the time you're not going to be comparing acids or bases that have any difference in charge and so most of the time this will just be a moot point but i did want to cover my bases and i definitely want to relate it to the energies of electrons as well and again negative charge higher energy electrons positive charge lower energy electrons okay so now let's get into that mnemonic proper so once you verify that what you're comparing has the same charge you next kind of follow these this mnemonic in order so the first rule you'll consider is adam and if you don't find a difference there then you'd move on to resonance and if you still don't find the distinguishing difference there you'd move on to induction and if you still don't find the you know a distinguishing difference there you'd move on to orbitals so these are ranked kind of in like order of priority so the atom rule is the most important again after charge so but then resonance then induction then orbitals and again this is not a perfect set of rules and there is no perfect set of rules so but this will work usually you know at least 90 percent of the time this will lead you to the right conclusions as far as relative acidity and basicity and when these won't lead to the right path that's why we memorized some pkas earlier because that would kind of take care of those exceptions so before i ever use these rules if i'm ranking acids i look at pkas first the ones i've memorized so but if i don't know the appropriate pkas then i go to my rules and rank my relative acidity and basically so this atom rule the way this works if we look at relative basicity on the periodic table and i know you can't see the whole periodic table but it just needed you to be able to see the non-metals that'll show up in our organic compounds and it turns out basicity increases as you get smaller and as you get less electronegative so and there's two parts to this so the vertical part of that trend is all about size and it turns out a smaller base makes a shorter bond to an h plus ion and a shorter bond is a stronger bond and so as a result the smaller base is the stronger base so and then finally as you go from right to left within a period now if you're comparing elements within a period it's not about size anymore because they're all really close in size and it turns out to be more about electronegativity instead and it turns out the less electronegative base is the less stable base and the stronger base so as long as you're comparing in the same group your comparison is about electronegativity as long as you're comparing and i said that backwards as long as you're comparing in the same period it's about electronegativity but if you're comparing within the same group it's about size so that's kind of the deal here so you gotta remember which is which but they're both important but notice size must be more important because again if you're comparing them in the same period the more electronegative it is it's a weaker base the less electronegative the stronger base but in the same group the more electronegative is actually the stronger base that's how we know that size must be more important consideration so but again if you're comparing them in the same group it's about size if it's in the same period it's about electronegativity all right incidentally so with electronegativity you can totally correlate the energy of the electrons when you have like a negative charge let's say they're just lone pairs on a more electronegative atom on the more electronegative atom it pulls them closer to the nucleus which lowers their energy and makes them more stable in a weaker base now in size this is the one place where the energy of the electrons does not correlate with basicity so it turns out the larger atom has higher energy electrons but it's still the weaker base so because it turns out the energy of the electrons is not the whole story but most of the time it's an adequate story but this is the one example where it's not when you're comparing atoms here in the same uh group size is more important and instead of just worrying about the energy of the electrons it's also about the process of acting as a base of making a new bond to h plus and again those big atoms they just make really weak bonds to h plus and so they're not good bases it turns out and so as a result the energy the electrons not a good reflection in that one comparison again comparing different atoms in the same group but outside of that the energy the electrons and and will correspond greatly with basicity lower energy electrons weaker base one exception there all right so again bases get stronger as we go up the periodic table and as we move to the left so if we compare some make some comparisons here so in this case we're going to first compare these two and i just want you to circle on your study guide there which one is the stronger base and in this case i can see auction is smaller than sulfur they're in the same group so it's all about size and the smaller base is the stronger base so we're good to go there and in the next pair again circle in the stronger base now it's between oxygen and nitrogen so and now these are in the same period so now it's about electronegativity oxygen's more electronegative that makes him the weaker base nitrogen is less electronegative that makes him the stronger base in this pair cool now at the same breath i also want to compare and rank some acids here and the problem is is from reo here is doesn't this doesn't help you rank acids directly the rules ario here are going to be for ranking bases but this is where the idea that the stronger acid has the weaker conjugate base and vice versa comes in handy because if you're asked to compare acids and that's what i'm asking you over here now in these pairs what you're actually going to do is look back and draw out their conjugate bases if you haven't already notice this is the conjugate base of this one and this is the conjugate base of this one and so if you're comparing bases that's what the rules for you don't want to draw any conjugates out or anything like that but if you're comparing acids first thing you'd ever do is draw out the conjugate bases and you look at them and be like okay who's stronger over here well he's stronger so if this one is the stronger base well then he comes from the weaker conjugate acid and if this is the weaker base the weaker more stable base then he comes from the stronger conjugate acid and so we're not actually ranking the acids directly we're only ranking them in the context of having already ranked their conjugate bases so when you're asked to rank bases good to go that's what the rules are for but when you're asked to rank acids you're going to do it indirectly every time so well almost every time so but you're going to do it indirectly most of the time by looking at the conjugate bases instead same thing here so here we circle the stronger base and if this is the stronger base it has the weaker conjugate acid so if this was the weaker base he has the stronger conjugate acid and so a lot of times when we're ranking acids we just say okay which one of these has the weaker more stable conjugate base in this case it was sulfur and in these two if i said which one again has the weaker more stable conjugate base in this case it was oxygen now up here it was the weaker conjugate base because sulfur is bigger than oxygen and down here so the weaker more stable conjugate base was oxygen because oxygen is more electronegative than nitrogen cool that is your atom rule all right so after atom is the resonance rule and again these rules for ranking bases and resonance simply stabilizes bases that's the way it works so if you have something with resonance and something without well the thing with resin is generally going to be more stable assuming you've already done your atom rule so again we would never start out with the resonance rule we first verify that the bases we're comparing all have the same charge then we verify that they're all the same atom acting as the base and then we'd move on to resonance so if we look at the example here we're going to compare these three bases and i've drawn out all the resonance structures here and so in this case the first question would be do they have the same charge well negative charge negative charge negative charge done cool then we move on to the atom rule and say which atom actually acts as the base well it's oxygen here it's oxygen here and it's oxygen here and so we have a tie and so then we'd have to move on and go to the resonance rule so that's kind of how this works so you wouldn't start with the resonance rule unless you've already done the charge in the atom rule first all right so doing the resonance rule now we see that here the negative charge is no resonance it's on a single oxygen completely here the negative charge due to resonance is shared between two oxygen atoms that makes it more stable and a more stable base is a weaker base this is a weaker base than the first one that has no resonance and then finally this last one the negative charge is actually shared on three oxygen atoms and is even more stable and even more stable means even weaker base and so if we were to rank these as bases with one being the strongest and three being the weakest well our most stable base is our weakest base and let's do this in blue so and then our strongest base that had no resonance number one and then obviously this one that had two resonant structures sharing on two auctions was number two now something you should know about comparing resonance it's not just about the total number of resonance structures it's also about the quality of resonance structures because if you notice like here i'm sharing the negative charge on two oxygens and here it's on three options well that's an easy comparison but what if the negative charge was shared like instead of on two auctions what if it was shared on one auction and three carbons well carbon's not as electronegative as oxygen it's not as good of a place to put a negative charge so you gotta ask yourself is it two resonant structures sharing it on two oxygens better or is four resonant structures but it's only one oxygen and three carbons better well i don't expect you to know that well it turns out sharing it on two auctions is better so but again that's one of those examples where you're just kind of until you've seen it worked out for you but you just don't know however that's exactly the situation we have when it compare carboxylic acid to a phenol but if you've memorized your pkas you'd know that a carboxylic acid has a pka of 4-5 a phenol has a pka of 10 so the carboxylic acid is stronger and you wouldn't have to rely on the rules for an example that's a little bit challenging because you've memorized some pkas so just want to point out where that might come in handy okay so here's we've ranked some bases now what if i asked you to rank these acids and so for these acids notice these are just the conjugate acids here and if you were asked to rank these acids first thing you'd want to do is draw the conjugate bases if you didn't have them already on the board like i do so we've got them on the board now and in this case you just know that the acids have the exact opposite ranking so the strongest acid has the weakest conjugate base well the weakest conjugate base was this one it was the one that was most stable due to resonance the weakest base so then this must be the strongest acid we'll make him number one and it's just the exact opposite ranking our strongest and least stable base comes from the weakest conjugate acid cool so once again you can rank bases directly that's what the reo mnemonic and the rules are for but acids we rank indirectly by looking at the conjugate bases and just knowing again the stronger the acid the weaker the conjugate base and vice versa all right the next rule in our reo mnemonic is induction so an induction deals with polarity now for now i'm going to look at things that are simply electronegative we like to call them electron withdrawing when they're electronegative because they're pulling electrons away and if you recall we talked about charge at the very beginning we said that something with a more negative charge is a stronger base whereas with a less negative charge i.e more positive charge would be a weaker base and so what an electronegative atom does is it pulls electron density away from a base making the base less negative and therefore more stable lower energy electrons and a weaker base cool we'll find out later on in the course not in this chapter that in addition to electron withdrawing groups there are also things called electron donating groups and they're not going to really have much relevance here but they will have some relevance down usually in the beginning a second semester when you study alcohols and phenols all right so let's go through our list and again we wouldn't ever start with induction as a rule we just work our way down so first thing i want to look at in comparing the first pair here i want you to circle the stronger pair or the stronger base in the pair is charge well they're both negative one then go to atom well oxygen is the base in either case the atom with the negative charge so no difference there so then we move on to resonance well these are both the conjugate bases of carboxylic acids they're both going to have two resonant structures and share the negative charge between two oxygens we still have no distinguishing difference and so now we move on to induction and so we've already identified that oxygen is the base that's the atom rule don't get that confused a lot of students confuse the atom rule in the induction rule my question now is now that we know oxygen is the base in both cases are there any electronegative atoms nearby that can act as a helpful neighbor to help stabilize the base and over here we've got chlorine and over here there's nobody electronegative around those auctions at all so again those options are sharing the negative charge by resonance they are the base and if you are the base that's what the atom rule's about and the atom rules about size and then electronegativity but induction here means you're not the base you're just a helpful neighbor and you're in the area to help that base out and it has nothing to do with size it has everything to do with just pure electronegativity pure polarity if you will and so in this case the chlorine here is going to pull electron density so away from this carbon technically which is then going to pull it away from this carbon which then pulls away from this carbon which is then going to pull some away from those oxygens eventually making those oxygens less negatively charged which makes them more stable lower energy and a weaker base so the one stabilized by induction is the weaker base okay so that's the first part so and again induction is all about electronegativity so far as we're concerned with in this lesson all right in the next example here so we're going to go through the rules again charge no difference atom oxygen in both cases no difference resonance stabilized by resonance between two auctions in both cases no difference so we make it to induction and we ask do either of these have a helpful neighbor nearby well yeah they both do and they have the same neighbor chlorine which is equal in electronegativity so however if you notice by the way the we pull electrons from the adjacent atom through the bonds based on electronegativity so if we were like a hundred carbons long and then there was just a chlorine way over here do you think the other side of the molecule would even know there's a chlorine down there no and so proximity is really important as well typically the closer it is the bigger the impact it's going to have in terms of stabilization so in this case the chlorine is closer to these oxygens it's only one two and then three bonds away whereas this one is one two three four bonds away from the oxygens and so the closer it is the more stabilizing of an impact the greater its stabilization due to induction and so that makes this the more stable base and the more is the weaker base so the one that's less stabilized is the stronger base all right so now we've learned having an electronegative atom in the area is helpful and the closer it is the more helpful it is and so now what if we have two different helpful neighbors uh carrying out inductive stabilization here so once again charge no difference atom auction auction no difference resonance shared between two oxygen two resonant structures on both no difference so then we make it to induction and now there is a difference now they're in the same location they're the same distance away from the oxygens from the bases but one's chlorine and one's fluorine and this is the most one of the most common mistakes students make is they say okay but chad you just told me that fluorine was a better base than chlorine no no no i told you when fluorine is the base is the atom acting as the base that it's a better base but again here fluorine and chlorine they're not the base in either one of these the oxygens have the negative charge they're the base fluorine and chlorine are not acting as the base at all but they can help stabilize the oxygens who are acting as the base and again your ability to help stabilize those auctions has nothing to do with how big you are only with how electronegative you are and fluorine is more electronegative than chlorine and as fluorine is more electronegative than chlorine this will be a more stabilized base that negative charge will be diminished more on these auctions than on the auctions on the molecule next door and so as a result the more stable base on the right here is the weaker base more stabilized by induction so the one on the left is the stronger base cool can't emphasize this enough though so the difference between the atom rule and induction the atom rule is you're examining the atom that's acting as the base which in our case was oxygens in both cases no difference induction though is you're looking for a helpful neighbor who's near to the base and it's all about electronegativity so the atom rule is about size first and then electronegativity are you the base then we're going to talk about your size and then your electronegativity but if we're talking about induction and you're not the base you're just nearby you're in the neighborhood it's purely about your electronegativity your size is irrelevant all right finally last example here and in this case same comparisons same charge same atom same resonance comes down to induction again and two fluorines is better than one so to speak so two fluorines two electronegative atoms will have even more of a stabilizing impact than one flooring so this will be the even more stable base and therefore the weaker base therefore this one is the stronger base cool so now i've given you an example of every kind of comparison you might see and again we only compared two at a time you might get three or four of these and be asked to rank them in order well everything that's important just came up do you have an electron you know withdrawing group and one doesn't do you have both the same electronic group but one's closer and one's further or do you have two different ones and one's more electronegative one's less less or negative or do you have more electron withdrawing groups versus another those are the typical comparisons you're likely to see okay so i didn't want to clutter up the board initially so but in addition to comparing these lovely bases now we're going to go compare their conjugate acids and again the key is again the rules are for bases and we just jumped right into comparing the bases but if you had been asked to compare any of these pairs of conjugate acids first instead well the first thing to realize is like oh they're asking me to compare acids i don't compare acids i would draw out their conjugate bases and then compare those and fortunately we can already take advantage of the fact that we've done that and so we're already ready to compare these because we've already compared the conjugate bases and so in this case in the first example in these two conjugate acids i would again draw out their conjugate bases i'd realize that this one is the more stable conjugate base the more stable conjugate base is the weaker conjugate base and the more stable weaker conjugate base comes from the stronger conjugate acid so now we're circling the stronger conjugate acid same thing in the next example we already figured out again in comparing these two acids we already figured out the relative basicities of the conjugate bases so this had the chlorine closer which had a more stabilizing influence by induction and the more stable base is the weaker base and the weaker base comes from the stronger conjugate acid cool next comparison again we're comparing these two acids first thing you do is draw these two conjugate bases and here fluorine was more electronegative than chlorine and so fluorine is going to pull more electrons away from the oxygens making them less negative and more stable and more stable means weaker base and the weaker base again comes from the stronger conjugate acid and finally in the last example we found out that two fluorines was more stabilizing than one fluorine so this was the more stable base the more stable base comes once again from the stronger conjugate acid cool so obviously very fortunate that we already had the conjugate bases on the board and we already had them ranked but if we hadn't that would have been the first thing we'd have to do so the last rule in our mnemonic is orbital so the o here and once again you wouldn't just jump into using this rule you'd first have to verify that there's no distinction made between the rest of the rules and the comparison that you're making so and again it's orbitals here if the o for orbitals but again it really refers to a difference in the hybridization of your basic atom so if we take a look here at comparing these three lovely bases here first thing we do is say do they all have the same charge yep negative one negative one negative one okay no difference there then we move on to talk about the basic atom and it's carbon compared to carbon compared to carbon okay atom rule doesn't help us either so we'd move on to resonance and it turns out none of these are stabilized by resonance so if you look you might go chad wait a minute load about like this guy well again when your lone pair of electrons is exactly one bond away from the pi electrons ie like allilic or benzylic that's when you can expect resonance but here it's not one bond away it's right where the pi electrons are so no resonance in any of these so move on to induction are there any electronegative atoms in the area to help stabilize this nope not in any of the cases so finally we move on to orbitals and we say is there a difference in the hybridization of the basic atom in all these cases and there is indeed a difference so this carbon right here is only two electron domains it's bonded to one atom and has one lone pair so it's going to be sp hybridized so this carbon right here is bonded to two atoms a carbon and a hydrogen maybe i'll draw that hydrogen in to make this a little more obvious so it bonded to two atoms one lone pair three electron domains sp2 hybridized and then finally this one right here is bonded to three atoms a carbon two hydrogens and it has a lone pair four domains is going to be sp3 hybridized so there is a difference in hybridization and it turns out that's a significant thing now if you kind of look at the difference between an sp and sp2 and sp3 so your sp is 50 s 50 p we'd say 50 s character and probably looks like something like this your sp2 is now only 33 percent s one third s two thirds p and resembling more like a p orbital now only 33 s character it's a little longer and the electrons are going to be a little further from the nucleus at the node there than they would be if they were not sp hybrid orbital so having a lone pair and an sp as compared to having a lone pair in an sp2 they're going to be on average closer to the nucleus in an sp hybrid than an sp2 and then finally in an sp3 hybrid orbital it's even elongated even further and so the electrons on average are going to be even further from the nucleus and be even higher energy and less stable in an sp3 and so the idea then is that your lone pair is going to be most stable on an sp hybridized carbon as compared to an sp2 or an sp3 and if here it's most stable that makes him the weakest base which we'll put number three in this case and then here on the sp3 hybridized atom that lone pair is going to be the least stable which in our case is going to mean the strongest space and then this guy's in the middle and so that's our trend for basicity that's the orbital rule really a difference in hybridization and so if you were asked to compare the conjugate acids instead well again you'd realize that i'm not comparing acids and first thing you do is draw out all the conjugate bases go through the rules and come up with this relative basicity which would then allow you to come up with exactly the opposite trend in acidity for the conjugate acids so the most stable and weakest conjugate base has the strongest conjugate acid so on and so forth this rule doesn't come up very often but it is something you're probably going to see at least once or twice between your homeworks and your tests so now we've made it completely through the mnemonic and we've kind of gone step by step and you know we kind of knew what comparisons were coming because we were going in order so now i want to work three examples and with these three examples we're going to do specifically comparing acidity so and we're going to keep in mind the pkas we're supposed to know as well as all these lovely rules all right so we've got three different comparisons here and the first one's going to be this lovely species versus this one and first thing you should do is keep in mind what pkas do you know well this is a carboxylic acid and his pka is in the four to five range usually it's pretty typical whereas this is an alcohol and its pka is usually in the range of like 16. now the truth is this one's got a chlorine that's going to inductively stabilize the conjugate base which is going to ultimately make the conjugate base weaker and this acid a stronger acid but 16 versus four to five it's not going to make it down that low not a chance and so in this case technically you could just be like yeah there's my stronger acid i circled it life is good so but if you didn't you know recall your pkas or didn't categorize these correctly again you could always just draw their conjugate bases and be like and use your reo mnemonic here so in this case you go through and say do they have the same charge yep negative one negative one for comparing your bases then you'd say okay adam rule auction's the base and auction's the base it's a tie adam rule didn't help me so move on to the resonance rule and we'd see that the one on the left has resonance and the one on the right does not have resonance and so the one with resonance is more stable and a more stable base is a weaker base and a weaker base comes from the stronger conjugate acid the rules would have led us to the same place cool moving on to the next one here and this is one i brought up earlier so we've got a carboxylic acid here and again pka of a typical carboxylic acid is in the four to five range and this is a phenol and pka of a typical phenol is in the 10 range and so we can say yep we've got our stronger acid right here because we memorized some pkas now this is the tricky one had you not memorized those pkas you'd had a tough time with this one until you came across it somewhere along the way and we've seen a carboxylic acid it's got two resonant structures shares the negative charge on two oxygen atoms here but the phenol we haven't actually drawn out specifically but the conjugate base actually shares the negative charge between the auction and then it turns out three of the carbon atoms in the ring i'm going to draw these out but i'm not going to actually show you how to get there i'll leave that on you for now and finally one more you know what i'm going to be a little nicer than i said i was going to be so and here lone pair comes down low pair comes out onto that atom here lone pair goes into form a pi bond pi bond becomes a lone pair getting you here here lone pair becomes a pi bond pi bond becomes a lone pair getting you here all right so the question got to ask yourself a lot of students get this one wrong because here they're all more resonant structures more resonance more stable base more stable based weaker base weaker base comes from the stronger acid but we saw that wasn't the case at all but we're not comparing apples to apples here so you can't just compare the absolute number of resonance structures unless the negative charge is just being shared on the same atom every time well that would that would work so but here sharing the negative charge on two options as compared to sharing the negative charge on one action and three carbons and there's no intuitive way to just be like well i have a hunch so it really does come down to either having seen this example before or just knowing those pkas super helpful in this case it turns out sharing it on two auctions was more stable that was the weaker base which came from our stronger acid all right finally this last one this last one is a super tricky example but you might remember pka's here and pka of a terminal alkyne here was right around 26. so and we didn't cover this guy's pka explicitly but we did cover a very similar molecule and that similar molecule was ammonia and we said ammonius pka was right around 38. and so whether you deprotonate neutral nitrogen ammonia or a neutral nitrogen on an amine it's going to be around a pka of 38 and i can see that my lower pka is definitely this guy and he's going to be our stronger acid cool and i brought this one up on purpose because this is a tricky example if you try to follow the mnemonic here you're going to get hosed and let's see why so if we draw those conjugate bases so said at the beginning of this lesson that there's no perfect set of rules because there are always exceptions like this one so if we look here and we start with charge like negative one negative one life is good so we move on to atom we're like carbon versus nitrogen well carbon and nitrogen are in the same period which means it's going to be about electronegativity and as nitrogen is more electronegative we'd think oh more electronegative more stable more stable base weaker base weaker base comes from the stronger acid and we totally got the opposite determination from our pka values that we knew so what's going on here so well it turns out this is usually the order of priority as far as it you know what distinguishes two bases and comparing them and order importance so however so there's two differences here it is a difference in atom but it's also a difference in hybridization of the orbitals so it's not just comparing carbon to nitrogen and that's the only difference it's an sp hybridized carbon versus an sp3 hybridized nitrogen and it just so turns out that the sp so is more stable the sp carbon is more stable than the sp3 nitrogen now there's no intuitive way to have known that but because we knew the pkas we didn't get hosed by this exception from our rules so like i said there's usually two or three comparisons you can make where the rules are going to lead you astray but if you know all your pkas those can't get you cool this is asked in bases and ranking them and again understanding relative acidity and basically basicity is really going to be key to understanding relative reactivity when we start talking about chemical reactions later i can't stress how important this is for getting a good working understanding of how the world works from an organic chemistry perspective but how chemical reactions work if you have found this lesson helpful consider giving me a like and a share that's again the best thing you can do to support the channel and if you're looking for practice problems on asks bases or the study guides that go with this check out my premium course on chatsprep.com