Thank you. All right. >> Good afternoon. Exam number two coming up Thursday. We have already discussed the vast majority of what is fair game for exam number two. >> But there are a couple of profit. >> Couple of you have noticed from the practice exam that we haven't said anything about. First order of business today will be to finish off the last couple of topics for your second bitmap. >> And then for the rest of today will be moving into chapter seven, Keating, your textbook company. >> That's carboxylic acid chemistry, including hopefully some Chemistry relating to a lab experiment you're going to be doing tomorrow. >> Now one thing that a couple of people were asking about the reaction that appeared on the brand. >> Because again, pull the inaugural condensation evokes was born too late. >> If you are taking this course 30 years ago, you wouldn't have to fill up with my nasal voice. You could have taken this course for my former research advisor, Professor forks. What a rich, skinny pony in that sense, it was just a pleasure to listen to him speak, especially when the entrepreneur shoes like the canoe. >> And also it's just level. However, in so many words you've already seen that can open uncle condensation because you saw this earlier. >> This is from last time we were talking about Al, compensation, various forms, especially the one that you did in the laboratory, which looks something like this. The point is that with the crossed out all condensation that involved Dehydration of the beta hydroxy intermediate perform an alphabetic enough. Now in principle, all the keynote bonobo condensation is going out all compensation with dehydration to form an alphabet. The only difference is we start from a beta di carbonyl compound. So for point of reference in your textbook, I'll call your attention to section 18.5, which is the diode elites of beta dichotomy op amp. Let's begin by talking about what a beta dichotomy or compound is. Here's an example. This is T4 pentane diode, which we've seen before. But the point is we pick either of the carbonyl groups and then come one notch over to the alpha carbon atom here. And then one more notch over to the beta carbon end-of-year. Whoops, that's a ketone two. So this is sometimes called a beta di ketone because no matter which carbonyl carbon atom is, starts from two notches over your final meal. >> That's all we mean by a beta di carbonyl compound. >> How many alpha hydrogens are there in this compound? >> Yeah, all of them, all the hydrogens in this gone bad or on alpha program. >> So in principle, all of them are acidic, all of them to give me move my base. >> However, if you treat one mole of this compound with one mole of base, which hydrogen do you think gets removed? >> One of the end hydrogens are one of the middle hydrogens. >> Why you're right? >> Is one in the middle. >> Why it, yes, it away. >> There are two electron withdrawing groups there. Realized that the whole reason alpha hydrogens are acidic in the first place is there has to be some electron withdrawing group there, preferably a carbonyl group that can help stabilize the negative charge by resonates well, if you have two carbonyl groups next door, you have that much more chance to stabilize the negative charge by resonance. They do show a very good picture of this at the bottom of the 44 in your textbook. >> But if you look at the bottom of the page here, they show the first resonance structure where there is a negative charge and the middle apartment. >> But by moving the electrons around as shown, you can draw two other resonance structures in which that negative charge on the oxygen. And so in the hybrid structure, you have a partial negative charge on all three atoms. And the point is, the more atoms you can spread out the negative charge over, the more stable the IUD is. In fact that they point out a little bit higher up on the page. A typical alpha hydrogen has a PKA somewhere in the ballpark of about 18 to 20. By contrast, a hydrogen, that is alpha 22 carbonyl groups has a PKA somewhere around 91011 >> That's a difference of about nine pk units, which means that's a difference of about ten to the ninth. >> In terms of acidity, ten to the ninth is a billion. And so this guy, the billion times more acidic than this guy is. >> So the point is, when you take some combat like T4 pentane value and treat it with a base like hydroxide ion. >> It should come as no surprise to find that where the negative charge forms design the central carbon. And we can draw those two other resonance structures that shape your textbook other net, pretty much what you've seen before. >> So for example, we take two for pentane diode, throw in something like big Zelda, hide this. But we wind up with is an alpha-beta ino through essentially the same kind of mechanism that we showed in the previous page that we put up there a few minutes ago, leftover from last lecture last time. >> But just to walk you through the details just in case we need a little memory refreshing On the outdoor condensation, which is really all this is. Once you generate that negative charge on the carbon, carbon attacks positive carbon nucleophilic addition. >> In essence, this point, just to speed things up, I'm going to resort to bond line notations. >> But as you get something that looks like this, Meanwhile, we still have another alpha hydrogen on the middle carbon there. >> And again, we can argue about whether this is one step or two, but to save time, we will just assume that this is an improv, molecular proton transfer. Imp t is my former colleague drove it. >> So once again, you get an ion stabilized by resonance. >> And then to arrive at the final product, pick out hydroxide as you're leaving group by moving the electron, then moving hydroxide out. And hydroxide is normally a lousy leaving group, but you can get away with it in this case, because you get a very conjugated product in the process. Now the point is again, actually look very similar to what we showed you before with the previous example. We drew things out a bit more detail if resorted to the bottom line notation. >> But refer back to this page in your notes. >> If you want things grown out, waiting, bond line voltage, because the logic make sense. >> Ok? >> So bottom line, the fancy word kinome, an idol is really just an out all condensation with the dehydration. >> But starting from a beta di Carbonell **** that for more information about such compounds, C-section 18.5. All right. >> That's one thing that deserve to be cleaned up that course. >> Last time he spent a lot of time talking about reactions taking place at the alpha carbon atom and what sorts of things we can attached to the alpha carbon atom by taking advantage of I in chemistry, what we showed here, we're looking at alpha iteration, alpha-bar elimination, things like that. >> One of the things you can do is attach alkyl groups on the African, for example. >> Well, if we take a simple heat down like acetone, a base like hydroxide, and then throw in Denzel worldwide. >> By the way, just to clarify a point, you see the abbreviation penalty for that a benzene ring attached to something else, which would logically, you might have thought that benzene as a substituent would be called benzene, but it's not Denzel is and all of that extra CH2. So this count bad is commonly called bends or bromide. >> Anyway, throw these things together. >> The compound shown here is one possible product that can form. Now let's just take a quick look at the basics of what's going on mechanistically here, which I'm hoping based on WiFi, it should be pretty obvious. >> What's the first step in the mechanism of this reaction has to be rigorously correct on the arrows. >> I'm going to redraw this guy a little bit. But the point is hydroxide, being a strong base, was one of the alpha hydrogens. >> It would be easily ion from acetone and bed. >> What happens? >> Yeah, so the bottom line is, since bromine is the most electronegative atom in this department, it's attached to, has a partial positive charge, negative charge attacks positive, judge. >> In short, one thing that was mentioned that some point back when we were talking about everything is that benzoic halides and do as N1, N2 reactions like the lights can be primary, secondary or tertiary alkyl. >> Hey, like primary. >> So S one or S into most like what they tend to not have bandwidth could conceivably do either one because the pencil carve a cat ions resonant, stabilized. >> But let's go with authentic. The anion from acetone leaves the nucleus, oops, applicable by substitution. Much, End of story makes sense. Ok, now that much is pretty straightforward, but let's take a look at a slight variation on this theme. The only difference is instead of doing this with acetone, where all the hydrogens are aldehyde, or where did this with 2B node instead. >> Other net same conditions when the worldwide leader with a base. >> But here's what makes this case a little bit more interesting. >> Acetone is symmetrical. >> All six hydrogens are equivalent. Doesn't make any difference which one you take off, you get this as or even the alpha hydrogens down back. >> Yeah, well, the point is let's number the carbon chain here. >> Depending on whether you take off your alpha hydrogen from carbon number one or urban number three. There are two different Appalachian products you could conceivably yet Take off your alpha hydrogen from carbon number one and do the same mechanism we showed a few moments ago. You get this edge, a major product, but would you take off your alpha hydrogen number three? Same mechanism as before. You get this as a major problem. Which one strikes you as more likely? >> Why the bottom one? >> Because k. >> Now the nice part about that question was there was no way you could get that question wrong. Because actually it turns out you can manipulate condition so that either one of these could be the major product depending on what base you use and depending on what solvent. Let's call these to product a and product B. And what is the other day you said product B would be the major product are absolutely right. >> As long as the base is something reasonably normal, like hydroxide or methoxide. >> In some products, solvents like water or methanol or something like that, those conditions favor product B. But if your base is compound called LDA, about which more in a few moments. >> And the solvent is THF, which is short for tetrahedral few ran, which looks like this, which is basically just a cyclic ether. And since there are no hydrogens on the oxygen, and this isn't a product solvent, you tend to get a major product. Now let me say a word or two about what LDA is. Actually, he paid 841. >> In your textbook, section 18.4 talks about so-called lithium emulates. >> Now one way to generate lithium elites is to use LDA as your base. >> And LDA stands for lithium di isopropyl amid. >> This reaction down here shows one way of making LDA. >> You can take some alkyl lithium, lithium and react it with dye scopolamine. Alkyl lithium has a very strong case. It takes off the hydrogen and you get this guy over here. >> But the point is, if you draw up a structure of LDA And you see those two isopropyl groups on that nitrogen. >> What thought those three, or in other words, yes, this bound, bound is a strong base. >> But what else is true about it? Yeah, it's a strong and spherically hindered base. >> Now, a few moments ago, and I asked which one of these two will be the major product? >> Somebody said B, because it's more stable. >> Well, the actual product is not per se more stable than product. >> But the late IN leading up to it is, let me draw for a moment. >> Both I and that could be formed here, in other words, the inlet i. And it could be for by removing a hydrogen from farms. And one at the end could be formed by removing a hydrogen carbon number three. And I'm going to draw both resonance structures are both violates. So bear with me for a moment. They're the two resonance structures from the late Iron form by removing a hydrogen carbon. Number one. They're the two resonance structures for the elite, for my hierarchy. >> Now take a look at those two ETL 8s and maybe be easiest if you compare these two structures over here at the right. >> Which one is more stable and why? In other words, you can think about these things for a moment. >> Not as Nina lead ions, but more like our seeds. >> And it doesn't matter whether you consider the oxygen to be a substituent or not. But the point is this is a more substituted alkene. If you want to consider this being sort of like a try substituted out, that's fine, which would make this, but this is cry substituted with live die, substitute it. And the price up to date, it, alkenes are more stable. >> And I substitute it felt in terms of comparing these two for which one is more stable. >> It turns out that this is the more stable life. The more stable in late I and it's sometimes referred to as the thermodynamics. Thermodynamics is all about what's more stable than one. Now the point is, if you conduct this reaction using some strong base and some product solvent. And notice that the product solve, and I chose here, is just the conjugate acid of the base in question. In principle, the base could pull off a hydrogen from either one of these two and generate either of these. Doing this in a product solvent protocol, but can just protonate it again. >> And then the base comes along and pulls it off again, and the solver comes along and protonated again. >> And that might happen a 100 times before the Ino. It actually has to do rather other than just be protonated and deprotonated, protonated, deprotonated. >> In other words, in that situation, these two ions exist in equilibrium with each other. >> And the point is, in that situation, the one that's going to predominate is the one that's more thermodynamically stable. So, and that situation, recent product B is favored is because that's the product form from the thermodynamic. But now let's consider the other situation using LDA. >> Thf. >> Lda is a strong spherically hindered base. In principle, it could pull off either one of these hydrogens to, but it's probably going to go after the hydrogens are number one, just because they're out on the end of the carbon chain, not buried in the middle of the carbon chain like these hydrogens are, and therefore more accessible to this big, bulky, spherically hindered things. So chances are pretty good that right off the bat you're going to get more of this enol eight. And you deal with this in a way. But if you're not doing this in a product, solve it, then you don't get a chance for that equilibrium do establish. In other words, as opposed to pull a proton off, put it back on. >> Paul wrote that I'll put it back on political thought. I'll put it back on this set of circumstances. >> You pull that proton off and that's it. In other words, whatever is formed that the fastest is going to be the one that predominates. In Chem 321. We talked about kinetic control versus thermodynamic control with reactions. >> Kinetic control refers to whatever is formed the fastest in the LDA reaction. >> This E9 is referred to as the kinetic ino it. And since we're doing this, that any product solvents present a major product here turns out to be the product form from the kinetic easily, which is formed at first glance and doesn't get a chance to equilibrate with the other one. On page 842 in your book, you will see other examples of thermodynamic versus kinetic. >> And the point is you can, as it says down here at the bottom out the way, ketones >> By way of either the thermodynamic or kinetic Italy. However you choose to set up the reaction conditions. So the fancy term here is you have control over the Riggio chemistry of this reaction. That is, you can Riggio selectively form and whichever you wish just by filling with reaction traditions. So see the top of page 843 for another example of this kind of thing that we're talking about. But is it clear what we mean by kinetic versus thermodynamic emulates what LDA is and all that kinda stuff. But the point is some big, bulky, spherically hindered base like LDA. The presence of the solvent a good choice. If you want the kinetic anoint, you can use any base your watch. If you're using a product solvent, probably going to get the thermodynamic evaluate. >> It makes sense that flask couple of topics in chapter 18, but you need to be concerned about where your exam coming up on Thursday. >> So at this point, we can pretty much draw the line in your notes. >> This is the end of what you are responsible for your second technique. >> However, let me just say one other thing now. >> If I write now there will be no spectroscopy questions like your second exam. However, we are just about at the midpoint of the second summer session, which means your final exam is just over two weeks away. And there will be spectroscopy questions on your final exam. >> So what I'm gonna do from time to time is stop what I'm doing and refresh your memory on spectroscopy as it pertains to the functional groups we've been talking about lately. >> And of course, the functional groups we've been talking about lately are aldehydes and ketones. So let's just take a look for a moment at an aldehyde, and in this case a methyl ketone. >> And talk about how some of the spectroscopic techniques we were discussing earlier semester can be used to get information about the structures of these things in the mass spectrum of aldehydes, ketones, and for that matter, any carbon containing compounds. One thing these compounds love to do is fragment somewhere near the carbonyl group. In other words, one thing that's very commonly see in the spectrum of an aldehyde is a fairly sizable m minus one peak, which comes from chopping off the hydrogen right next door to the carbonyl. And for methyl ketones, in addition to the molecular ion peak, you get a fairly sizable peak at m minus 15, which comes from chopping off the methyl group over there. >> Methyl groups, way 16. >> And also in aldehydes, you tend to get a fairly sizable p, get M over Z. 29 What piece of the molecule that you think represents 29 mass units? >> Yeah, other words, chopping the other side of the carbonyl group. >> Carbon weighs 12, oxygen weighs 16, hydrogen weighs one. >> That HCOO piece weighs 29. >> So what do you think? 43 corresponds to which they usually the tallest peak in the spectrum of mental Kitab. >> Yeah. >> Same deal with this one chapeau. If on the other side, metal sea level about weighs 43. >> What should show up prominently in the infrared spectrum of both aldehydes down, yeah, carbon oxygen double bond stretch showing up approximately where? >> T about 1701. >> Trick you can sometimes use to tell aldehydes from key towns using just the infrared spectrum. The carbon-hydrogen stretching frequency of the aldehyde functional group itself is a little bit farther to the right than most other carbon-hydrogen stretching frequencies. >> We typically see a couple of peaks, somewhere around twenty nine hundred and twenty eight hundred for the carbon-hydrogen stretching of that particular department hired proton NMR spectrum. >> Approximately where should an aldehyde hydrogen show up? >> Roughly a number between 112. >> Yeah, they get as close to 12, Not quite that far down, but it will be somewhere around nine to ten parts per million. >> Somewhere in that ballpark is typical for aldehydes. >> And I, for something like a methyl ketone live with those methyl hydrogen show up roughly the time saying, I'm not going to call it was a carboxylic acid. Yeah. >> My father appealed. >> Five is for or weights or things like that. That's closer. >> Typically about two to 2.5 parts per million. >> For a mental ketone, acetone shows up with a single peak at about 2.1. >> And then finally, carbon spectrum Where abouts in the carbon 13 spectrum, do carbonyl carbon atoms for both aldehydes, ketones would show up. Pick a number between 0229, somewhere in the ballpark of about 190 to 210 parts per million. >> That's about as far down field as we go. >> And the carbon 13 spectrum, how would you tell the difference between an aldehyde and a ketone just from the carbon-13 spectrum. >> Yeah, I mean, the point is the number of hydrogens attached is what detected splitting and the carbon-13 spectrum. >> So since there's one hydrogen attached here for the harbor GEOCARB of an aldehyde that should show up as a doublet or a ketone with no hydrogens attached to that carbon should show up. >> It makes sense, but again, not for your second nickname, but I'm going to refresh your memory from time to time because you'll need this. >> And actually there isn't a lab for too much longer. We'll say more about that. >> Alright, going on to Chapter 17, carboxylic acids and their derivatives. >> Temper 17 tries to accomplish a lot because there's a lot of derivatives of carboxylic acid. So we're going to be spending a fair amount of time in chapter seven. But what a lot of it boils down to is nucleophilic addition, elimination. Sometimes golf nucleophilic substitution at the a sole carbon. Hopefully by the time we're done today or I don't know what that means, but hopefully see how it applies to the reaction you'll be doing in lab tomorrow. >> But first, let's begin where we usually do with a discussion of how these compounds get their names. >> First of all, I trust at this point that everybody is aware what a carboxylic acid is, looks like that sometimes abbreviated either our COOH or our CO2H by type setters. >> You'd like to get all of this stuff on one line. >> So you see those abbreviations here? Textbook. >> That's what they hear is the simplest possible carboxylic acid. >> Iupac system says the two main carboxylic acid is, take the name of the corresponding alkane, methane. Drop the e tack on the suffix OIC acid. >> So this can be called meta-analytic acid >> Hardly anybody calls it that. What most people call it this formic acid from a Latin for mica, which means it, if anybody here has ever been sufficiently unlucky to have been bitten by a red and part of the edge that results comes from the secretion of formic acid into the form. >> In formic acid refers to this part of the molecule, as I may have mentioned earlier, name this time-bound by any reasonable method. I know IUPAC system acetic epidemic acid, more common name. >> Acetic acid, still more common name. What do most people call this? Combat? Yep, you ought to buy some acetic acid at the food store. >> Well, find yourself a bottle with vinegar, which is basically just an aqueous solution of acetic acid. >> The ACGT refers to this part of the molecule. >> As I mentioned, I named this care about. >> Yeah. Alright, three fennel and the rest of that. First of all, you don't need one because the carboxylic acid functional group must come at the end of the carbon chain. >> So by definition, that's target number one. Then how many carbons in the chain? >> Not counting the phenol. >> So butanoic acid. Ok, certainly one way you could go, or as we've seen, we can get out the Greek letters again and call this beta phenol. >> Only probable is reusing the Greek letters. >> You have to use the Latin name of the acid, butyric acid, again from the Latin theorem, which means by her name, this camp out yet >> Or if you had to use a Greek letter to show where that OH, was, what Greek letter? >> Which of course, I suppose just for completeness, I should put in the numbers, but the other way of naming it. >> So let's put in the numbers on both of those examples. >> Yeah. >> Now getting there so happens that the common name for the five carbon acid is a lyric. >> Awesome. >> However, we are not going to make, you know, common themes for the acid formic acid. Acetic acid. >> Publicly quit, wants to go manage, want to stick with the IUPAC system. That's fine. >> But I point this out as an example of an alpha hydroxy acid. Has anybody ever heard of these things before? Middleware and the pharmacy fiber. >> Yeah. >> I'm sorry. >> I didn't hear what you think you may be, right? >> I'm thinking of something else. >> Mostly we find these things and face creams supposedly dab on some alpha hydroxy acids, maintain your youthful appearance for decades to come, you died, but at this point, you get three miles. You start worrying about things like this is a compound called Bly colic acid, which is essentially alpha hydroxy acetic acid, which is commonly found in these things that promised eternal you computing. >> Okay? And this guy hijacks the benzoic acid. >> You saw benzoic acid before when we were talking about aromatic compounds in general, this would be of course, ortho hydroxy or hydroxy benzoic acid. However, this one is definitely now, and more commonly by another name, if I know what salicylic acid is mostly used for. >> Yeah, yeah. >> By far the major use of this Kanban is by the Bayer Company to make aspirin, which is used for many purposes because yeah, now I'm worried, well, put it this way. >> Aspirin is not salicylic acid. It's an ester derived from salicylic acid. But we'll say more about that when we talk more about, as matter of fact, you're gonna be making aspirin at the laboratories. >> You're going to find out exactly what afterwards. >> Don't ingest the aspirin. Any other questions about any of these examples? I would say that if these make sense, the other examples you see in your book would make sense too. But here's a grand total of the other examples they show you. >> So not too much of an introduction here, although you should be able to handle problems 17.1 and maybe these other acids over here without too much difficulty. >> And let me just say one other thing. Compounds like this one, which have two carboxylic acid functional groups. >> The suffix is di OIC acid. >> So this Ka band is called propane. >> Di OIC acid. >> Don't need to say 13, because the carboxylic acid groups must come at the ends of the carbon chains. And the common name for this compound is Melodic Acid. We're going to say a lot more later on about the chemistry of Melodic Acid and derivatives thereof. But if these examples make sense, then I hope you should be able to handle those to be nomenclature problems that you will see in your textbook. There's a very brief discussion of the physical properties of the carboxylic acids in your book. And I think part of the problem with the way Chapter 17 laid out, do they try to do too much, too fast and shove too much in the one chapter. >> And so sometimes gets short shrift. >> But let me just say one thing about the physical properties of carboxylic acids. Now, when you just look at the essential structure of the carboxylic acid functional group. What kind of intermolecular attractive forces I think are going to be most important. >> Yeah, we have an, OH me, I'm a hydrogen attached to an oxygen. >> Anytime you have a good chance for hydrogen bonding. And it turns out to be even more important in carboxylic acids than it is for other compounds like alcohols, it turns out. But one thing carboxylic acids can do, it's sort of skipped two molecules together, something like this, with each partially positive hydrogen of one being attracted to the carbonyl oxygen. And the other point is, when you stick two molecules together like this, what you've really done, somebody words, is to take eight dimer, this molecule effectively doubling its molecular weight, which tends to crank up the boiling points of these things considerably. >> Even formic acid, the smallest carboxylic acid, has a boiling point higher than the boiling point of water, one degree celsius. >> Acetic acid boils at about a 180 degrees Celsius. >> So on. Alright. >> Oh, and just to back up for one quick moment, most of the smaller molecular weight carboxylic acids, like formic acid, acetic acid, diapsids like Melodic Acid are soluble in water. Most of the larger molecular weight carboxylic acids, like say three penalty, you'd milk acid, not particularly water-soluble, although we'll talk later on about ways to make them more water-soluble, Need to make themselves. >> But what I want to talk about Nacht is the fact that as the name suggests, carboxylic acids are acids. >> So I want to talk about their acidity not only relative to each other, but relative to other functional groups who talked about. But that is a somewhat lengthy discussion. So this would be a good time to take a short break. >> Yeah, you're already pretty good. Right. Thank you. I'm like, no, I agree with you. I think it's done like that. They are thinking about running Chuck deal with completely aqua therapy. Let's go back to that, right? Yeah. Ok. They're very, very interesting. Yeah. No. Right. >> Yeah. Okay. Open quiets down faster than gone. Alright, the name suggests carboxylic acids. >> Are acids generally more acidic than most other organic? If the late IN chemistry we've been talking about relatively recently is that hopefully it'll make more sense as to why carboxylic acids are acidic. Because of course, if we take something like a methyl ketone, like we did at the beginning of this class period with acetone and use a base to pull off one of the alpha hydrogens, we get this. But the reason this works is that this enol eight ion is stabilized by resonance. So we can draw out a couple of different resonance structures here. >> But this is nothing more or less than the an-ion chemistry we've been looking at up to this point. >> Well, all we have to do is change this carbon atom to an oxygen atom. >> Now it's a carboxylic acid, but it still has a quote unquote alpha hydrogen atom on it. >> That is to say a hydrogen atom on the atom next door that can be removed by a base. And part of the reason that that works as well as it does is because the conjugate base of the carboxylic acid can also be stabilized by the main difference here is terminology. The conjugate base of an aldehyde or ketone is colon late in. The conjugate base of a carboxylic acid is called a carboxyl eight. >> And I now look at all four resonance structures here. >> Which one strikes you as least important for contributing to the overall bonding picture of its species. >> And one, what's the worst resonance structure? >> Okay, yeah, the one on the top left, because he felt that the negative charges, I'm carpet in all of these other structures, the negative charges on oxygen, always a good idea to get negative charges on the electronegative atoms. The point is, it's always a good idea to spread out a charge over more than one atom. So both the ina late ion and the carboxyl with ion are stabilized by resonance. But it's an even better idea to spread out that negative charge over as many oxygens because you can't, the net effect is significant. As we said earlier, a typical PKA for typical aldehyde or ketone and serve as a removing an alpha hydrogen is about 80 for carboxylic acid, typical pK values is somewhere in the ballpark of five. Now again, remember that p and PKA means take the negative logarithm out of these are logarithmic scales. A difference of 13 pk units is a difference of ten to the 13th. And see what is that. That's like 10 trillion in terms of the relative acidity. So a typical carboxylic acid is 10 trillion times more acidic and a typical aldehyde or ketone. Carboxylic acids that are water soluble, like formic acid or acetic acid, are acidic enough to make aqueous solutions whose pH is less than five. >> Yeah, that's about KFC Section 17.2, especially Part C. >> And your textbook, page 781, talks a little bit more about this. They show the carboxyl iodine over here. And they point out that, for example, for something like benzoic acid that is insoluble in water, treating it with something like sodium hydroxide or sodium bicarbonate that will react with this thing makes it water-soluble. >> So they need to get this thing into solution, somehow converting it into its carboxyl eat salt help solubilize it. >> By the way, sodium bicarbonate, baking soda, it is usually a good enough base to deprotonate our carboxylic acid. And many of you have done that experiment in the kitchen where you take vinegar and baking soda and mix it together just to see that that's basically what that is. Carboxylic acid reacting with silicon bipolar. Now, when I say the typical carboxylic acid has a PKA somewhere around five. >> That's fine. >> But carboxylic acids can vary in PKA depending on what else is attached. Which do you think would be the stronger acid, acetic acid or chloro acetic acid. >> Why do you get the chance for which one? >> The hard part. Why? >> Yes, you're right. It's speculation as to why electromagnets >> As he said up here, part of the reason this thing has such a lower PKA compared to this thing. You can spread out the charge over electronegative atoms. If you have other electronegative atoms at somewhere near the acidic functional group that tends to spread out the negative charge that much more. That's something called the inductive effect. You have electro-negative atom has or groups somewhere near the acidic functional group tends to increase the acidity by pulling negative charge towards that electronegative atoms, spreading out that negative charge that much more, stabilizing the conjugate base, that much more, making it that much more likely that the proton will be donated. I would try chloro acetic acid. Compare with the other two in terms of SIP? >> The strongest answer them a bunch weakest answered him a bunch somewhere in the middle of a bunch. >> If one nearby chlorine atom increases the acidity, two or three nearby chlorine atoms has that much greater effect. And actually we have information on these particular compounds in your textbook. If you look up here, about the middle of page 782, they list all of these compounds with their PKA values. Acetic acid that 4.76, chlorella acetic acid that 2.86. Try chloro C2C acid, 0.70. And I'll throw one more at you and you think, try flora acetic acid would compare the others are still, fluorine is more electronegative than chlorine. The more electronegative atom is, the stronger its effect is quite Florida acetic acid has a PKA of about 0.23. These last two almost quantify as strong acids, truly strong acid like HCl or sulfuric acid. >> At negative, He's got pretty close. >> Makes sense. >> Let's call these compound a, B, C, and D. This is butanoic acid to chloral butanoic acid. Butanoic acid, perchloric acid, which one strikes you as the weakest acid. >> And y dy, because no electronegative atoms other than the oxygens that are part of the carboxylic acid itself. >> Dij is the weakest acid. Which one strikes you as the strongest acid? >> Yeah, a, because it's wagons here. >> Yep. >> My previous piece of paper, the magic word, was nearby. The closer the electronegative atoms are to the acidic functional group, the stronger their effect is that you can visualize, for example, 20 carbon chain with a carboxylic acid group at one end, the other end, that is going to have much of effect. >> And it turns out these compounds are listed in your textbook too. Okay, for compound a, 2.85, compound B, 0.05, compound C, 0.50. >> And I don't have a listing for this one, but it's probably about 4.8 or somewhere. >> And then see the bottom of pay 70 to go again to the concepts make sense? >> Alright, one more example. >> All right, for ease of reference, what's called these compounds, V, W, X, Y, and Z. >> These are all substituted. >> Benzoic acid is compound B, has benzoic acid itself. The others have various substituents. The Para positions. Let's list these. >> From strongest to weakest acid. Which of these compounds? Right? >> She was most likely to be the strongest acid. >> The N1. >> Yes, he's not a bad guess. >> Y w. Now we do have a chlorine atom attached there. What is electronegative? >> So w is one of the stronger acids up there, but it actually comes in second. There's one asset up there that stronger yes, x, y, x. Now oxygen is electronegative. >> Yes. >> However, I'm bad. >> X actually turns out to be the weakest acid up there. We'll say more about why in a few moments, but other speculation for which one might be the strongest depth y prime. The nitro group is very electron withdrawing. That's part of what makes compound. Why a stronger acid than in fact any of the others that are up there. Okay? So at this point of established which won the strongest, which ones, we, just matter of fact, we only have two left to consider, and that's B, and see which one of those two strikes you as stronger. >> Yeah, tell me a little bit in lecture. >> That's correct. >> Let's think back for a moment to whenever we're talking about ortho para versus meta directing groups and activating versus deactivating leafs. >> Let's consider each of these chlorine that's so important, whether it's ortho pair directing, what's think activating or deactivating, which is boring flooring is slightly deactivated about the methoxy group strongly debating nitro group, strongly deactivating methyl group, slightly activated when we were talking about electric Tillich, aromatic substitution. >> What makes one substituent activating or deactivating, is its tendency to donate or withdraw electrons. Electron donating groups tend to be activating groups. Electron withdrawing groups tend to be deactivated groups. The two strongest acids up here, Y and W, have substituents that are electron withdrawing. >> These things tend to be deactivated goods. >> The two weakest acids up here, the ones with the CH3, CH3 substituents are the weakest acid because those substituents tend to be electron donating, especially by resonance, even though the oxygen here is electronegative, but relatively strong tendency of those lone pairs on the oxygen to donate towards the ring by resonance tends to make that the weakest acid. So there are two things to worry about here. One is the inductive effect, which we described before as being based on electronegativity. And that certainly is an important factor. The other factor that comes into play, especially for these aromatic acid fear, is referred to as the resonance effect. And in the case of resonance, what we're talking about is how the electrons move around. Things tend to be electron donating or electron withdrawing. So a more general way of expressing what I said before about the inductive effect is to say that electron withdrawing groups increases. >> And if you want the converse statement, change withdrawing to donating change, increase or decrease electron withdrawing groups, increased acidity, electron donating groups decrease. >> And if you're not sure which is which, just go back to that activating versus deactivating thing. Activating groups tend to be electron donating, deactivated groups that make sense. >> Okay, try problem 17.3 on page 1783. >> At some juncture, it just asks you to compare two acids and decide which one is the stronger acid based on the principles we've talked about so far. Now at this point, I'm going to skip forward in chapter 17 a little bit. I will call your attention to Section 17.3, how to make carboxylic acids. Now at this point, we actually have seen a fair number of these reactions. Probably the most obvious way of making carboxylic acids by oxidation of aldehydes and primary alcohols. We've seen how to do that, but as you page through Section 17.3, you'll encounter other reactions we've seen before, such as oxidation of the side chain on aromatic rings or reacting, renew our reagents with CO2. We've seen all these reactions before. >> There are some things in there that we haven't talked about yet, but we'll get around to it now. >> Section 17.4 is really what this chapter is all about. Nucleophilic substitution, nucleophilic addition, elimination accurately. >> So carbon. >> So we're going to spend a lot of time talking about that mechanism. But what I want to do for at least right now, for the little bit of time we have left. Say something about how this applies to the experiment you're going to be doing labs. Section 17.7 is briefly entitled esters. So all about estrogen. Section 17.7, Section 70.7, a synthesis of esters, esterification. >> Esterification is a fancy word that means to make an ester. >> And if you look at the examples here, which is a carboxylic acid reacting with an alcohol. >> Now let me just say a little bit more about that we're actually going to be doing in lab is called the Fischer esterification file_name. >> Fisher, who worked on it, worked on a lot of other aspects of chemistry to put the Fischer esterification reaction perspective, let me just call your attention to what may quite possibly have been the very first reaction that was ever discussed in any chemistry course. >> You ever took HCl Sodium Hydroxide products? >> It's not a trick question. >> Yeah. >> Saltwater in HCl and H2O. >> In other words, take h from HCl and OH from sodium hydroxide together. >> Water, whatever's left is your other product, the old switch, the partners game. >> The Fischer esterification is sort of the organic equivalent to that. >> You can take a simple carboxylic acid like acetic acid and a simple alcohol like ethanol, and throw them together in the presence of an acid catalyst. Then one way of thinking about what goes on in this reaction is to take each from the acid and OH, and the alcohol and get them together and make water and then hook up whatever's left. >> Look up whatever's left, you get this, which is what functional group? >> Now, if all you want to know is what the product of the reaction looks like. That's all you gotta do. >> Take away hydrogen from the acid or LH, from the alcohol. >> That's the water. >> Connect up. What >> That regard Fischer esterification reaction three is where it gets a little bit more interesting, is figuring out what's going on mechanistically. Suppose we were to do our HCl Sodium hydroxide reaction using radioactive sodium hydroxide. And specifically the atom that's radioactive is the oxygen. >> At oxygen 18 is the radioactive isotope of oxygen. >> If we do this with radioactive sodium hydroxide, which of our products, sodium chloride or water, should be radioactive water, of course. Well, if you carry out the Fischer esterification with radioactive ethanol, which the oxygen is oxygen 18. And whatever you do, don't bring radioactive ethanol. Turns out the radioactive oxygen winds up in the aster. So that's just something we need to consider as we ponder what a reasonable mechanism for this reaction might look like. Now, based on the idea that this is in fact an acid catalyzed reaction. >> Based on this DMB song we gave out in class today is to propose a reasonable mechanism for the Fischer esterification shown here. Ginsberg, yeah, I'm sorry. >> You do not treat it with a base, you're treating it with an acid. >> Hold. >> That thought, because we have a little bit of time, we may say a little bit more about how you can make yesterday the phase. But in this case we're making you yesterday. What happens first? >> Yeah, yeah, you could conceivably protonate this oxygen with the idea that you're going to leave that as a water molecule problem. >> Is it do where does the radioactive oxygen wind up? >> In the water where it lines up? >> Yes. Protonate the oxygen. But which yes. Okay. Which what top or bottom? Bottom. It's not a bad guess. Probable is we do that puts a positive charge on that oxygen, which is right next to the partial positive charge on that carbon free. >> It's improper folks boats, boats. Dmb song gave out the bumps on I will not sing to you. >> You can sing this to yourself in the shower or wherever. >> But the party begins with a Ruby carbon. >> Neil mentioned we're trying to give you Specifically, we're going to protonate the sp2 hybridized oxygen of the carboxylic acid. When we do, we get an ox, sodium ion that looks like this. And if it helps any, you can draw the other resonance structure for this species. >> Actually, there's a couple of other resonance structures we choose, but one of them looks like this. >> And if we wind up with a positive charge on the carbon atom also. So step one, protonate the oxygen. >> But yes, you do have to figure out which one, what happens next. >> So let me just back up for just a moment. >> Suppose instead of an OH, group right here, this was just a hydrogen atom. >> What functional group with that bit? >> That would be an aldehyde. If you go back in your notes to what we were talking about, how aldehydes react with alcohols. Back to the part about forming ME answer. Towels and asset out and take a look at what's going on mechanistically there. What we're doing here, the first couple of steps of the Fischer esterification looks very much like what happened when we were forming an Emmy acetone. After we protonate the oxygen, the alcohol attaches itself to the carbon, carbon. >> And we now have something that looks like this. Alright, so far so good. Let's keep telling what happened next. Yeah, well, we aren't going to eventually have to lose a molecule of water. >> In general, we're not going to slap another proton on there because that's going to give us something with a net positive two charge. But you're right, we do want to eventually protonate one of those other oxygen. >> What do we have any first, yeah, I lose the one that's already there. >> So in other words, picking up on both of these ideas, lose this proton, then put a proton back on one of the other oxygens. Now, again, we can quibble about whether that's a two-step process or a one-step process just to save time. >> And since all of these things are in equilibrium with each other anyway, intramolecular proton transfer, which is a fancy way of saying proton falls off the one, oxygen winds up on the other. >> Okay, so now we have this. >> And now what happens? >> You lose water and now we have this. And the final step is yes, as you see in many times in acid catalyzed reactions, would attach a proton at the beginning, we lose a proton. >> At the end of that proton goes is probably do another molecule, dicarboxylic acid, to start the whole process. Now this mechanism is presented in your textbook at the bottom of page 98. But when you look at that mechanism, you will see that each step in the process is an equilibrium where the overall reaction is in equilibrium. And since the forward and reverse reactions go under the same conditions, which is to say acidic conditions. And the principle of microscopic reversibility kicks in. And we just gave you two mechanisms for the price of one, because in the forward direction it's the mechanism for Fischer esterification, but in the reverse direction. It's the mechanism for hydrolysis of an ester to give us the original carboxylic acid and an alcohol. If each individual step clear. >> Alright, lets just check one thing. >> If this is the correct mechanism, it should explain the radioactivity results. So let's follow our radioactive oxygen as it makes its way through the mechanism does indeed wind up where it should, and it appears that index. So that's one reason people like this mechanism for this reaction that does explain the radioactivity. >> For the experiment you're going to do in the lab, you're gonna be using acetic acid with ISO pencil alcohol. >> Point of the experiment is going to be to make an ester that smells like bananas. Esters in general are pleasant smelling compounds. The experiment is working at little lamps or smell like bananas. Have fun making banana oil at the lab. Are there any questions about victory ridership? >> All right, let me just wrap up for today with a couple of other variations on the theme that can be used to make esters. >> I pick up on your idea from before. >> He's basic conditions is that let me take a simple carboxylic acid like benzoic acid with sodium hydroxide throw in purple bromide fester, suggest a plausible mechanism. >> What happens? >> Yeah, carbon, it can conceivably behave as an equally file and go after the carbonyl carbon here. >> But bearing in mind that this is a carboxylic acid, what's this base more likely to do to its first director? Well though, after the acidic hydrogen, Yeah, the hydrogen on the oxygen, there is an alpha carbon over here, but it has no hydrogen. >> Thought it, yeah, point is bases pull off protons. >> So one thing hydroxide can do is pull up a proton here and generate the carboxylase, which then does what? Yep. In other words, since this is what kind of bromide, primary, secondary or tertiary primary, most likely happens when there's negative oxygen goes after partially positive carbon will kick that bromide leaving group. >> What kind of reactions that batter into primary substrate reacting with an aqueous S and D reaction. Mechanistically, a whole lot simpler way to make an ester, but the Fischer esterification, Wordsworth, there's another interesting variation on the same theme, and we'll make this the last reaction today. >> Do you think a carboxylic acid and allow it to react with dyes methane, what you get is the corresponding methyl ester. >> Now in Chemistry 21, we saw that dies o methane can be used to generate a car bean, which can then add across a double bond. This, however, is not a car being reaction. Before I asked you to propose a reasonable mechanism by which this reaction takes place. >> It might be helpful if we were to draw out a more detailed structure for days or method, this is the way the dyes are. >> Methane structure is usually draw. This is the most stable resonant structure for die. But there are other resonance structures possible, and here's one of them. And the point is, bearing in mind not just the chemistry we just talked about, but also the possible resonance structures with eyes suggest a plausible first step in the mechanism by which dies of methane reacts with benzoic acid. >> Yes. >> Okay. >> Let's back or I mean, yeah. >> Okay. >> Yeah, negative ad, it's like an attack another negative atom, but it could attack a positive m. However, as opposed to the nitrogen attacking that hydrogen, then bind where that hydrogen is eventually going to wind up. >> What's another possibility? >> Again, the carbon atom also has a negative charge. And what starts out life as a CH2 is eventually going to become a CH3, but don't have the carbon atom do the dirty work. >> If we use this resonant structure for dies of methane, that negative carbon, to pull off the proton and once again we get the same benzoate i. And as we got before, only this time the byproduct is the protonated methane. And then what happens is, in other words, what happens next is once again an f n2 reaction. >> Because the by-product of this reaction simply elemental nitrogen, nitrogen gas, which bubbles out of solution and joins all the other nitrogen in the atmosphere. One thing that people like about this reaction to the fact that the by-product just leaves the reaction mixture. So when you're done, you have an ester that doesn't need a whole lot of purification. But mechanistically, these two reactions are very similar to each other. There's only one catch to working with dyes of methane, regardless of whether you're using it randomly esters or do the carbine thing or whatever. And that is you do have to keep days oh, methane cold, because if you warm it up, it has a tendency to decompose, generate nitrogen, gas. And if you haven't still inside the bottle, it means the bottle tends to blow up. Here's a true story from my graduate school days based on what we saw this weekend. The weather wise, we know what the summers like, you get hot, humid days amend. Those cold fronts move through two-dimensional rainstorms, thunder and lightning, sometimes loss of power. Back when I was a graduate student in the lab down the hall from mine, we had a big thunderstorm ONE summer night, lost power. So happened that this research group down the hall from me had a bottle of dyes or methane in the refrigerator. The refrigerator is good place for it. But when the power goes out, refrigerator warms up. Well, suffice to say to people came in the lab the next day and found the refrigerator door was wide open and shrapnel from the exploded dies on methane bottle all over the lab. >> So suffice to say it was a good thing that nobody was there when the refrigerator bullet, so he buys a methane coal. >> Other networks, morula will stop here for today. We will talk more about chemistry in the first hour tomorrow, and then say in the second hour for whatever questions you add pertaining to your exam on Thursday. >> Okay? Hello. I'm passionate about my cognitive. >> That's not the same thing that they're above a point. >> Well, let's put it this way for the time being, I'm going to let that's technically speaking, that is why you get the most important part for at the end of the semester, nearly 1 away from the next diode re, met back in crowd. Our warning, right? >> Well, in other words, you analyze the spectrum reasonably well and you did come to the right conclusion about which compound it was. When you identify this thing here as being the carbon-carbon triple bond stretch that narrowed down to one of these two. The question is, did you just flip a coin or did you actually realized that it was this one because of this carbon-hydrogen stretching right here. So that was the only reason they took over point, because at that time they're thinking, well, this C-H stretching is four sp3 hybridized C-H stretching. >> And all of these moments that doesn't tell you very much. >> This is specifically for the carbon-hydrogen stretching for hydrogen attach would SP, hybridized carbon. I'll go back to that handout we gave out little speck, brought it and look at the spectrum of the alkyne we added there. It looks very much like that. >> Okay. And our wander away think ranks. >> Well, give you saw the, you saw the answer peek, Yeah, the Educating. >> All right, well, with that, alright, first of all, you had to show this bond breaking or get the break. >> That thought at some point also didn't draw that arrow, that cluster point. >> Mostly what you lost was for not showing the other resonance structure fitting, a silly show all the resonance structures, that's perfectly good structure, but it also has other resonance for that. >> And then the only other criticism I add is once you attach this thing, you get different resonance structures. Do the resonance structures very well, but yet to show how the electrons move, you get from one them together. >> So we're not putting in those arrows at the bottom right. I feel like I let me let me just say this about notation. >> If you had just drawn line, line, no carbon, I wouldn't giving you full credit for that because that's Fabula, yes. But if you're going to draw the carbon, you need to draw the hydrogens to, especially since the whole point of this problem was to remove the oxygen and put onto hydrogen. So either bond line notation or draw everything out and thinking problem here, you have to show the hydrogen on that oxygen. Ok, so just throw out the whole structure of the molecule. >> But under the mat had the right basic idea, get rid of the oxygen. Okay. I know I got bad news. >> I might think like join them. Like, yeah, I know, but I think actually I think I put it on my picture. >> I probably happier grade. >> I don't remember what it is the top of my head because I don't have my landlord my gradebook in fun. >> I'll look it up what it is tomorrow. I'm sure it's good. >> Otherwise it wouldn't know, right? >> Yeah, I would worry about emojis. >> Okay. Thank you. Yeah. Yeah, yeah. Yeah. No. Oh,
Lecture from Jul 27, 2010
From Dana Chatellier March 03, 2020
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