so we're now going to get introduced to the various acids and bases that we will see in organic chemistry and we will look at a little bit about how to talk about them um we'll also touch on a little bit of nomenclature so first let's look at carboxilic acids so you should have heard this name before because carboxilic acids are the most common organic acids that we see in organic chemistry and and some of those others that are the most common right within that family are acetic acid and formic acid so acetic acid has a methyl group here and formic acid has a hydrogen there acetic acid is the acid that's found in V vinegar and formic acid is uh responsible for ant stings so like the biting of ants and that why it stings is because it has formic acid in it and you'll notice the pka's of these carboxilic acids are fairly low they're usually five or less and so we see acetic acid with a pka of 4.76 and formic acid with a pka of 3.75 the next group to talk about are alcohols alcohols are going to be groups that have that o group on them and we see methyl alcohol and ethylalcohol as examples of compounds in this group and notice that their PKA are close to 15 so they have much less of a tendency to act as an acid than these carboxilic acids do even less than that we have amines amines are these groups that contain nitrogen so that nh2 group methylamine and ammonia are um examples of amines and the pka of amines can range anywhere from about 35 to 40 so those are very very high PKA and they really do not have a tendency to lose that hydrogen so you see that on the nitrogen you have two hydrogens here and that pka of 40 means that it is not very likely at all to be able to lose that nitrogen in fact it's more likely to act as a base to gain a hydrogen rather than it is to act as an acid and lose that hydrogen we've got a couple more things to talk about on here the first one we'll talk about is protonated alcohols and carboxilic acids and then the second one we'll talk about are protonated amines so when we talk about a protonated compound it's exactly like it sounds a protonated compound is a compound that has gained an additional proton right it has an extra hydrogen on it and the pka of protonated groups are going to be less than their nonprotonated counterparts so if we look at the pka for alcohol protonated alcohols and protonated carboxilic acids you can see that the pka for proteinated alcohols are less than zero which means that they are very willing to lose that hydrogen and it's much lower than the pka of our nonprotonated alcohols well non extra protonated alcohols I guess you could say and a protonated acetic acid is even much lower than that now which of the oxygens is going to have that extra proton right because we've got two in a Caro ilc acid the one that is proteinated is actually going to be this guy right here and that is something you'll have to remember if you'd like to know the reason why you can ask me and I can explain it to you but you don't need to know that as of this point now just because we have a protonated substance doesn't necessarily mean that it's going to be super acidic for example take protonated amines so we have protonated methylamine here and proteinated ethylamine where we have this nitrogen with an extra hydrogen on it and you can see the pka are much lower than that of am meanes but in terms of acidity it's really not that acidic still we've got protonated methylamine having a pka of 10.7 and protonated ethylamine having a pka of 11 and so that's much less than what we would expect for a strong acid strong acids remember are less than zero like we see here with the proteinated alcohols and carboxilic acids so these don't even fall in the category of weak acids they're higher than that and so just because something has an extra proton I want you to realize doesn't necessarily mean that it's going to act as an acid okay so the next thing we're going to do is we're going to take some of these different compounds and we're going to look at how they can act as acids and bases so first up is alcohols an alcohol can act as both an acid and a base and so let's see here what we can see about an alcohol acting as an acid right if it acts as an acid it gives up its hydrogen so we can see here a base coming in and grabbing a hydrogen off of that alcohol and then the pair of electrons that are between the hydrogen and the oxygen are going to remain exclusively on that oxygen when the bond breaks and so we see here the ion that's formed the methoxide ion and we have water right because we have that hydroxide that has grabbed a hydrogen from the methyl alcohol leaving the methoxide ion and water and so we've got a new Bond that's formed here and ultimately we have our acid and our conjugate base and our base and our conjugate get acid right so we can see here this reaction that's taking place where the alcohol is acting as an acid now you see these curved arrows and we're going to continue to see these curved arrows throughout organic chemistry we will go over them more in depth later but I wanted you I wanted to point out here these arrows because it's not the fir well it is the first time we're seeing them but it's not going to be the last and so the first thing I'll say about these arrows is that they always started an electron source and they always end at something that's electron deficient that's lacking electron something that's positive okay so always start at a negative and put it towards a positive so we've seen just now an alcohol being able to act as an acid but an alcohol can also act as a Bas and so we see here methyl alcohol that has a lone pair and so that lone pair can potentially accept a hydrogen and so we see our Arrow starting here at this electron source and pointed towards our hydrogen off of our hydronium ion and so that positively charged hydrogen is going to be grabbed by the alcohol and then this pair of electrons between the oxygen and the hydrogen that were forming a bond are now going to belong exclusively to that oxygen atom of the of what's now water and so we see then that hydrogen being transferred to the alcohol now making it a proteinated alcohol and water remaining so we have our base our acid our conjugate acid and our conjugate base so the benefit of using these arrows is it shows you exactly what's happening in that chemical reaction it shows you exactly what electrons are being broken and exactly what bonds are being formed and so this is very helpful when you're trying to understand mechanisms of reactions and how reactions actually occur so next we have carboxilic acids and just like alcohols carboxilic acids can act as both and acid and base so we see here this carboxilic acid we see hydrogen and we see it represented as acting as an acid so we have our substance here that's doing the attacking or hydroxide that starts with some excess electrons right it has a negative charge and so those extra electrons are going to attack the substance that's positively charged this hydrogen here and so this hydrogen is now going to be bound to the oxygen a new bond is going to form between a lone pair on this Hy hydroxide and this hydrogen and these electrons that were between the hydrogen and the oxygen of the carboxilic acid are now going to remain exclusively on the oxygen of the carboxilic acid and so we have this carboxilate ion that forms and also water one bond has broken that's resulted in a lone pair and one bond that was a lone pair has now formed with between the hydrogen and the oxygen the way that a carboxilic acid can behave as a base right is by taking a hydrogen away from something that has extra hydrogens and so you see here a lone pair on the carboxilic acid acting as a base and pulling a hydrogen away from the hydronium ion and so you can see we're starting at at an electron Source we're going towards something that's positive charged and the bond between the oxygen and the hydrogen on on the hydronium ion is breaking those electrons have to go somewhere they're not going to go with the hydrogen so they're going to stick with the oxygen and so ultimately what we have here formed is water and the carboxilic acid will have a new carbon hydrogen bond or sorry an oxygen hydrogen bond from that original lone pair that was on the oxygen now forming a bond between the hydrogen and we can look at these reaction arrows and see that under this first reaction we have products favored so the reaction would go towards this way mostly and in the carboxilic acid acting in as a base we actually will go towards the reactants so the reactants are generally favored over the products so next we'll see am means being able to act as an acid or a base but one of those is more likely to occur than another and we'll actually talk about that in a minute but to give you a hint it has to do with the tendency of that substance to act as an acid and we can tell that with the pka values so first let's look at an amine behaving as an acid for an amine to behave as an acid it has a hydrogen so it has has to lose that hydrogen and so we see something like hydroxide taking its excessive electrons its lone pair and grabbing that hydrogen and using that lone pair to form a bond now the electrons that were between the nitrogen and the hydrogen are going to stick with the nitrogen and so we see here the nitrogen without its additional hydrogen and a negative charge and we see that hydroxide with that hydrogen Onin so the acid and its conjugate base and the base and its conjugate acid note that the arrows reaction arrows indicate that the reverse reaction is favored more than the forward reaction so we actually have more of a tendency to go back towards reactants than we do to form products for an amine to act as a base we have a lone pair on it that can grab a hydrogen from a protonated species something that has extra hydrogens or just something that has hydrogens in general just depending on what it's paired with so we see that lone pair now forming a new bond with this hydrogen off of the hydronium ion and so those pair of electrons went to form that new Bond because nitrogen now has four bonds to it it gets a positive charge and we see those electrons that were between the hydrogen and the oxygen now exclusively belonging to the oxygen as a lone pair and so we have this protonated amine and water that forms from the reaction of this um amine with the hydronium ion and this is going to favor products more you can see that reaction Arrow pointed more towards products than reactants so the next thing we're going to look at is PKA values understanding PKA Val values is very important to understanding when a reaction will happen and when it won't and understanding the general properties of various chemical species and so there's a very easy way to remember these approximate PKA values and it's an increment of five and so 0 five 10 15 going up by fives each time is a different category of PK values so at a pka of about zero or less we have proteinated alcohols proteinated carboxilic acids and protonated water here kind of falls under the same category as protonated alcohol so these species the proteinated alcohols and carboxilic acids have pka of less than zero these organic acids carboxilic acids have pka of about five okay so we're increasing by five now 0 five and then 10 is protonated amines and so protonated amines have a pka of around 10 and at a pka of another increment of 515 is alcohols and Waters and then finally we jump a little bit in increments of five and get to about 40 and we get the pka of an amine and so you will have to remember these PKA values they're not going away they will be on quizzes and exams I can promise you that so memorize these approximate PKA values because they're going to be very important for your grade and then also very important when we learn about the reactions of organic compounds you can also find them on the back cover of your textbook so it makes it easy to reference so how can we determine which reactant is the acid and so the answer to that is that we can predict the outcome of an acidbase reaction by looking at these PKA values because it makes sense the one with the lower PKA the one that has more tendency to act as an acid is going to be the acid and so when you're looking for which is the reactant the one with the lower PKA value is going to be the acid so if we look between HCL and water we can see that HCL has a pka of -7 and water has a pka of 15. seven so the one with the lower PKA value is HCl therefore HCL is the acid and water is going to be the base and additionally here you saw water being able to act as the acid right so when we look at ammonia in water we can look at the ammonia that has a pka of 36 and water that has that pka of 15.7 so water here has that lower PKA value and so that means that water is going to have the stronger tendency to act as an acid and our ammonia is going to act as the base so looking back retrospectively at a lot of these reactions we've talked about in this chapter what I want you to see is that when you go back multiple reactants can act as the acid or base because usually we have usually each of the reactants has a lone pair and usually each of the reactants has a hydrogen and so theoretically both reactants could potentially act as an acid and both could potentially act as a base but now you know that you can look at PKA values and find the one that acts as the acid because that's the one that's going to have the lower PKA value now does that mean that the reaction is going to happen that we're actually going to go towards products well no not necessarily because there we're talking about the equilibrium of the reaction rather than which of the reactants is going to act as a product act as an acid or and which one is going to act as a base so if we do want to determine the position of equilibrium we have to look at the pka values of the acids on each side so you need to look at the reactants and determine which one will act as the acid and you need to look at the products and determine which one will act as the acid from there you can say well the reaction is going to favor formation of the weaker acid the one that has the less tendency to act as the acid so if we look here we have a carboxilic acid and we have ammonia the carboxilic acid has a PKA value of about five ammonia has one of about 35 so on the reactant side the carboxilic acid will act as our acid over here we don't have a hydrogen so that's our conjugate base and so therefore this is going to be our acid on the product side now here this is a protonated amine and so it's going to have a pka of about 10 so our acid on our reactant side is a pka of about eight and our acid on our product side has a pka of about 10 because this has the higher PKA the reaction is going to favor formation of products it's going to favor formation of that weaker acid the one that doesn't have as strong of a tendency to act as an acid okay we could see that in this example too looking at our reactants we first need to determine which one is going to act as the acid so we have an alcohol that has a pka of about 50 and an amine that has a pka of about 40 so the acid in this case is the lower PKA that would be about 15 that would be the alcohol on the product side right we have a something with a negative charge that's not going to want to lose a hydrogen at all because it's already negative it'd have to become more negative so the thing that would be an acid more willing to lose a hydrogen is going to be our protonated amine and that has a pka of about 10 so comparing the pka of our acids and on our product side this protonated amine of about 10 and the alcohol about 15 this one's actually the weaker acid the alcohol is the weaker acid and so that means our reactants are actually going to be favored because our weaker acid is a reactant right so the reaction the equilibrium favors formation of the weaker acid the one with a higher PKA value and you can see those reaction arrows reflecting that particular statement right it makes sense if we're comparing two compounds the stronger one the stronger acid is going to be more willing to give up its proton than the other one and so the reaction will favor forming that weaker acid and something else that's really cool is we can actually calculate the equilibrium constant and we can calculate the equilibrium constant by taking well we can calculate I suppose the PK equilibrium by taking the pka of our reactant acid and subtracting the pka of our product acid so for example on the previous slide we saw a reaction between acetic acid and ammonia our reactant's acid was acetic acid our product AED was the ammonium ion right that ated ammonium and we have our pka of the acetic acid 4.8 minus 9.4 that will give us a PK equilibrium of 9.6 and then if we transform that if we take 10^ the ne 4.86 we get the equilibrium value to be 4.0 * 10 4 notice it's big right it's greater than one which indicates that products are favor in that second reaction on the previous slide we had ethyl alcohol and we reacted it with methylamine we said ethyl alcohol would be our acid because it had the lower PKA value but we also said that the reaction was going to favor reactants because the ethy alcohol was a weaker acid than our protonated amine that was on the other side of that reaction Arrow so we had our PK equilibrium equal to our reactant acid which is ethyl alcohol subtracting the pka of our product acid the product acid was the protonated methylamine and we get a value of 5.2 and so transforming that getting rid of the P here just going back towards the um actual K equilibrium that value we take 10 to the 5.2 right because it's we take 10 to the negative and if it a negative it' become positive like we saw up here so 10^ the 5.2 will give you 6.3 * 10^ the -6 and that is much less than one right which means that the bottom of our equation is going to be bigger so we're going to have more reactants than products at equilibrium and so the reactants are going to be favored at equilibrium and so we can see here we can actually determine these equilibrium values from knowing our PKA and so these PKA values are quite important because it tells us about the extent of the reaction and about very important pieces of how the reaction is going to happen so we'll go through these problems in class um please let me know if you have any questions