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Lecture 07. Acid-Catalyzed Formation of Hydrates, Hemiacetals, & Acetals.

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Lecture 07. Acid-Catalyzed Formation of Hydrates, Hemiacetals, & Acetals.
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This is the third quarter course in the organic chemistry series. Topics covered include: Fundamental concepts relating to carbon compounds with emphasis on structural theory and the nature of chemical bonding, stereochemistry, reaction mechanisms, and spectroscopic, physical, and chemical properties of the principal classes of carbon compounds. Index of Topics: 1:19-Electrophilicity of Aldehydes and Ketones 5:37-Hydrates 12:17-Acid-Catalyzed Addition of Water to Acetone 21:29-Acetone Enol Example 24:01-Reverse Reaction 25:31-Energy Diagram 29:28-Reverse Reaction Mechanism 36:38-Acid-Catalyzed Acetal Formation 40:00-Hemiacetal 43:01-Strong Acid 47:23-Hemiacetal Formation Mechanism 50:52-Hemiacetal to Acetal Mechanism 1:00:52-Acid-Catalyzed Acetal Hydrolysis 1:06:12-Protecting Groups 1:12:15-Cyclic Hemiacetal
water Säuren hydrides Lecture/Conference alkyl basic conjugate chemische Reaktion alcohols
fall Carbonyl Kohlenstoff-14 Mesomerie carbon alcohols molecule water Lecture/Conference function chemical structures oxygen basic period label
species Twins Mesomerie plant hydroxyl groups case reactive molecule Table wine Lecture/Conference Kohlenstoffgruppe carbon Katalase source chemische Reaktion charge stocks water Hydration Säuren remove Hydroformylierung Hydroxyoxonorvalin <5-Hydroxy-4-oxonorvalin> chemical structures oxygen separation den
carbon source methyl man molecule water Hydration Magnetometer Lecture/Conference remove Acetaldehyd form bottles weight
Geröll Mesomerie charge methyl orbitals electron Magnetometer Lecture/Conference function Gamma Iron conjugate form
water Lecture/Conference mechanism orders of magnitude formal low temperatures remove additional chemische Reaktion man
near left concentration steps Foul carbon proton solutions chemische Reaktion man Neutralisation water lone pairs Säuren Drops age electron Lecture/Conference orders of magnitude Gamma remove basic oxygen
aldehydes oil mechanism steps hydroxyl groups proton law of mass action man water flow collection electron Lecture/Conference remove electron transfer oxygen weight
Bog Hydrologie mechanism balance steps carbon proton chemische Reaktion case OH- man molecule water Table wine Lecture/Conference yield remove Laxative
Carbonyl species mechanism formal carbon hydroxyl groups case OH- methyl chemical Heck Reactions water lithium hydride Ham Säuren Lecture/Conference orders of magnitude mixing AdoMet
aldehydes Färben type bond species chemische Reaktion case solutions methyl molecule water conditions Säuren Magnetometer Lecture/Conference remove basic conjugate stuff
molecule conditions Magnetometer Lecture/Conference remove benzene rings chemische Reaktion Materials International Space Station Experiment
transition states type progress bioactive mechanism rates multiple steps chemische Reaktion case VSEPR molecule metabolic pathway Lecture/Conference remove Imidacloprid
aldehydes type left rock mechanism steps Katalase proton chemische Reaktion source chemical man lone pairs water flow Wasserstoff electron Lecture/Conference Wollfaser Kunststoffe remove chemical structures oxygen Germinal center
sense Cyanide species perish Polyurethane mechanism Mesomerie case Essigsäureethylester Natriumhydroxid Lecture/Conference temperatures Acetaldehyd conjugate Germinal center aldehydes type Maische asset proton chemische Reaktion solutions alcohols firm water Heck Reactions conditions Säuren metabolic pathway compounds remove chemical structures oxygen bottles form methanol
aldehydes sense mechanism asset Sheet hydroxyl groups chemische Reaktion end systems water Taxis conditions Lecture/Conference function remove Acetaldehyd
Toluol species mechanism Weak chloride Emissionsgasthermoanalyse Inosite Sulfide molecule Ethanol firing electron age Lecture/Conference cell sulfuric acid benzene rings wear conjugate weight type power progress Alkyl Groups organizations Gases steps asset carbon proton chemische Reaktion alcohols water toxicity Hydration lone pairs Zulauf <Verfahrenstechnik> Wasserstoff Säuren Wasserdampfdestillation pKa remove old oxygen basic methanol
species rock steps hydroxyl groups proton chemische Reaktion man molecule flow water lone pairs electron age function By-product oxygen methanol
water islands Insulinkomabehandlung species Magnetometer Lecture/Conference function carbon Katalase chemische Reaktion
mechanism Mesomerie deformation case methyl man molecule islands Lake Lecture/Conference hydrolytic sulfuric acid Germinal center power probe Essigsäuremethylester Arginine asset steps proton chemische Reaktion source alcohols stocks water lone pairs Säuren metabolic pathway function coupling Wasserdampfdestillation compounds remove chemical structures Klinischer Tod pore oxygen methanol
biosynthesis Toluol Ethylenglykol mechanism HCl hydroxyl groups Propionaldehyd chemical man molecule solvents synthesis Lecture/Conference temperatures molar Acetaldehyd lithium Aluminium hydride processes aldehydes Färben ethane Propandiole steps carbon proton chemische Reaktion solutions alcohols stocks water toxicity systems Säuren function Wasserdampfdestillation compounds chemist methanol Dilution
Glucose sugar hydroxyl groups case chemical molecule strains Lecture/Conference active site Hexane Acetaldehyd mixture level period type Drink organizations concentration rates carbon Carbonyl Compounds chemische Reaktion firm water Vanadium Hydration Wasserstoff Säuren function compounds Harnstoff Cycloalkane chemical structures form
conformation Glucose sugar hydroxyl groups carbon chemische Reaktion case end chemical Alpha molecule Säuren Lecture/Conference coupling Kohlenstoffgruppe Hexane form
good morning you so know today
I'd like to finish it Our discussion of the reaction of about hides in the tones with various nuclear files and this is basically the content of Chapter 21 so we had started by by talking about basic nuclear files and reviewing how basic nuclear files including very basic nuclear files like alkyl nuclear files and hydride reacted without the high and the tones then we went on to other sorts of what I'd say were moderately basic nucleophile stings like a means for the future of the country get acid was on the order of 10 or 11 and now I'd like to conclude by talking about weekly basic nucleophile things that are basic formerly white alcohols and water but where the PKK of the conjugate answered is so strong that there it's
very acidic and conversely year nuclear files are very weakly basic suggesting give you an
idea of the themes that I'm talking about if you have some generic now that provided key tone like so and maybe I'll of drawing mind long periods just to complete our structure you can think of this this Alabama Hyder a key town kind of moderately electrical lines in other words nuclear files like to to attack the group but they need to be moderately good or very good nucleophile kind of label this is moderately electric Inc now I just as water just and alcohol is but base so we base so as the oxygen of Carbondale group and you can think of the oxygen of Aqaba Hill was being able to be impregnated and if you probably made the oxygen of this the tone around the highs and the situation changes because at this point you have a full positive charge in the molecules in other words when we were thinking about how the heights in key towns we thought about it and recognize that oxygen is more electoral negative than carbon and so you could say Well there's a very minor resonance structure with a negative charge and oxygen in the fall positive charge on carbon but it's only a minor contributor as we go to a protonated carbonyl now we come up with a different situation because now you've got a full part positive charge the oxygen in the carbon atoms becomes very Elektra felt like the 1 way we can think about this is to recognize
that although often will just draw 1 resonance structure is the 2nd resonance structure and in this case are
2nd resident structure it doesn't have any negative charge in it on like we have when we had the separated charges of tone so it's even more of a contributor and now you have the positive charge on oxygen on carbon it's still minor residents structure but it's a bigger minor resonant structure greater contributed to the reactivity so while we will make me just what 1 picture very often in the back of her head will be keeping in mind that there is this component of reactivity embodied in this 2nd resonance structure that makes this extra electrical and often we will refer to this species I don't think you textbook uses this name but sometimes I will refer to it as an Oxo ,comma Bunye my hon copying is a fancy name were more proper name for cobbled Cat which you learned about previous quarters and Oxo ,comma near just tells us there's enough oxygen substituent there because the oxygen can donate in you really don't have very much of Chicago plant and character Frank put numbers on it I'd say it's sort of 18 20 in terms of the the components but nevertheless you can think of there being a little bit of this resonant structure with the other and so collectively those 2 structures will make up a picture of the molecules structure here stocks so Kirby mind really helps embody a lot of the reactivity that was going to see today and in fact were going to see reaction upon reaction in which this theme is continuously the same so let's start by talking about the reaction that occurs and for the most part we don't even pay attention to it if you have found Haida key tone again just the right this sort generically as all our COR R and you have water present let's say you dissolve it water dissolved in acid told the dissolving isn't out the hide water you have an equilibrium that in many ways you don't see in many ways it's invisible because if you distill your product that you never end up seeing this you just get back your acetone toward Europe for men or Europe ass about the height but you haven't equilibrium with this species here were now instead of having a carbon group you have to hydroxy group water has added to the cardinal rule of this species is called hydrates died of an obvious thing to call something to which you've added water sometimes you'll hear it referred to as AGM and all die all Gemini you might recall is the Zodiac character for the Twins so GM all just means that there are 2 hydroxy groups on the same card twins hydroxy groups if you well and I'll just emphasize that this
is not a stable molecules with certain exceptions in other words it's not something that you can put into a bottle in pure form so you have this equilibrium In the presence of water equilibrium will lie somewhere to the right or to the middle or to the left depending upon the exact nature of the carbon you'll come I
find it very instructive to take 3 examples your textbook uses the same examples that I think they're really embody the idea here so if you have acetone were indeed just about any key town unless you have something truly exceptional cited should the drawing methyl groups here if of acetone at just about any key town unless you have something truly exceptional would say like a trifle removal the world that equilibrium lies far to the left in other words when you dissolve acetone and water you have mostly mostly mostly acetone and just a little bit the general die all just a little bit of the hydrate the radio at equilibrium is 98 2 . 2 for Aceh now the height and indeed for Aldape hides in general that equilibrium lies more In the middle himself arrested now the height of the equilibrium lies at 42 to 58 in other words almost one-to-one no I look at this these 2 numbers and I find this really instructive to keep in mind I keep in my head not the details of the numbers but they suggest that the acetone that equilibriums weight to the left acetaldehyde is waning and in way without telling me the way it's influencing my thinking the same mold that means that the carbon Nealon height it is like a thousand times like 2 into the 3rd more Elektra filet then the carbon and acetone the Carbondale and had it the carbon Eolande acetaldehyde Hyde is much less happy being a carbon Neil it's much more willing to accept water as a nucleophile and the
main reason for this is electronic the main reason we talked about electron delegation into the cardinal group the methyl groups donate
electrons you can think of this year just thinking of methyl groups are electron donating were thinking about hyper conjugation thinking back to cobble tat irons and remembering that resonance structure where you have the charges separated tone and saying Wait a 2nd this means here we have Nepal's donating and you can also think of it a molecular orbital approach thinking about the orbitals of the CH groups overlapping with the prices start molecular work but anyway it's about a thousandfold difference if we take away this remaining methyl group and there's only 1 elder hide in this category beyond is familiar the Hyde but for Malahide you really really is unhappy and the
held form it prefers to exist as trigeminal all Foreman again the number from your textbook or indeed from anywhere else East Cleveland to 190
million we now find another words now we've got another 3 orders of magnitude in the direction of favoring the hydrates and if you want to put this in energetic terms remember for every order of magnitude in equilibrium at low temperatures you have about 1 . 3 6 kcal per mole Siew can sort of think of this an energy diagram where and how the height is like 5 kcal per mole more high in energy or more reactive than a key tone and formaldehyde is like another 5 still account
for more just to give you sort of a ballpark on the numbers are at this
point I want us to be able to look at how we get at the mechanism because this is going to become a big theme here at the mechanism of how we get From the elder rider from which the tone to the German although all so what we're gonna do and this is going to be an archetype for all the other mechanisms to reseed today what I'm gonna do is right out again as the catalyze the mechanism of additional water and main point here is that acetone is not on its own Super electoral delight in other words an acetone and water is not on its own Super nucleophilic so what really speeds up this reaction what really makes it go
is a massive you can add some acid to the
water if you do this in neutral water of course you should remember that even you draw water has a little bit of acid present because neutral water has taken to the negative 7th smaller fighter only a mile or so you always have to Leicester and basic solution you always have some small concentrations of age the Rio Plus and will just imagine adding a few drops of 8 reassesses safely estate water so the 1st step of this reaction is in equilibrium Bronstad acid-base equilibrium and for the moment at least I'm going to be good about writing Kerberos later on we may get a little faster a little bit sloppy here but we can
envision electrons flowing from the lone pair on the
acetone to 1 of the protons on the Hydro mind they're all the same you know I'm a right 1 or the other can electrons flowing back onto the oxygen atom to give us admitted acetone but speech so if you wanna get a feeling for where this equilibrium lies we know what the PKA of Hydro Neumeier is of grown in minus the strongest acid you can have in waters PGA Ronnie Milo is negative 1 . 7 acid tones that was basic then water is this equilibrium is going to liability to the left you're going to have protons going on and off the features of protonated acetone isn't about negative 7 and in general my rule of thumb is if within about 10 orders of magnitude you have a difference of PKA protons can transfer back and forth are equilibriums come alive waved to the left but will have a significant and a sufficiently appreciable concentration of protonated acetone for it to react ah let's move on to the next step because what happens in this that is we bumped up the electoral felicity of the carbon Hill by protein-a together to make the oxen ,comma near my house
now at this point water
is good enough nucleophile to attack so here's opportunity acetone there is no water electrons flow from the thing that has electrons to this thing that once electrons from the nuclear file to the electrify all the flow of oil into oxygen again we have an equilibrium but the but but the but like so and finally protons come off protons go on you have 55 Moeller water mass action basically dictating most of the time the protons are going to be on the water instead of I'm that hydroxy group and so our final step in this mechanism in this three-step mechanism is brutal and transfer to water In addition it doesn't matter which Proton die right here which won't here I use over here so our final status of the equilibrium is that we have original dial the intifada high during an interview or collective weight at these 3 steps you really see the embodiment of catalysis In other words the catalyst is
taking intimate partner reactions in the 1st step of the reaction the hydrology Miami that's catalyzing this reaction is being consumed and we know a catalyst isn't consumed the destroyed in a reaction which means in the last step of the reactants doesn't have to be the last step but in this case it is the last step in the last step were getting it back in other words the entire balance equation has been embodied in the addition of 1 molecule of water to the acetone but that
reaction has gone easier In the presence of a catalyst I could also write a mechanism for this reaction that was base-catalyzed and your textbook does it hydroxide is a good enough nucleophile to add to the carbon yield you would envision hydroxide adding to the carbon to given Oxy and I and the axiom and I'm putting up a proton from water to give you back hydroxide now technically I could write on catalyze mechanism in the case of acetone that
mechanism probably doesn't occur to a heck of a lot In the case of formaldehyde which is remember about 10
kcal per mole about let's say about 2 6 orders of magnitude more electrify felt like formaldehyde need be you can have an on catalyze mechanism will water attacks the formaldehyde that we're going to skip over that because basically that's sort of is the exception and we really set up the theme for the class the theme is basically a good nucleophile like hydroxide or enemy in the war Mathilde Group methyl lithium hydride can attack and on activated carbon Yeo a week nucleophile like
the water workouts all generally requires presentation of
carbonyl last month I think there are but if you add too much acid would you program made the OH group and dehydrated now we're going to see and interesting mix of chemistry coming up and so right now we have learned to species that are can be present we've seen our acetone and we've seen our
German die all it's not stable and we've seen a
protonated species along the way that the hot to probe native species that are very high energy we said in acetone we have . 2 per cent when you dissolve acetone and water you have . 2 per cent as the German dial later on we're going to see that there are other species present also in small amounts so what you will see I think it's in the coming chapter and maybe even the ones following that will be this species here of the acetone in all that will enter into our consideration this terrorism is unstable and hiring energy like the German all die now the practical implications of this this is this stuff including a little bit of acetone in all this is the stuff that's going to be present in a water solution of acetone or even with a little bit of arson it won't take a lot of acid you actually even just with the tend to the negative 7 more were aged 3 0 loss in water we are going to have all 3 of these present in equilibrium later on we're going to start to learn about new reactions like the Algol reaction and you're gonna see that if you really cook the acetone or indeed if you cook other sorts of key tones and now the heights together that they will start to react in carbon-carbon bond forming reactions that can be promoted by days were by acid called the Algol reaction will be 1 of the babies that we're learning about sales and that will go either through the Union all were in the case of base catalysis the conjugate base you know like in practice if you take acetone and expose it to certain types of acid long enough you will find species were 2 molecules of acetone have come together to form a the elbow product or even under special conditions for the molecules to form a benzene product 1 3 5 try methyl
benzene called Miss Italy and you can catch TA is in the office hours to to discuss how the molecules of acetone incumbent invisible Our well there's something else that's
very very cool about this reaction and we know it's an equilibrium so we know that there is a reverse reaction equilibria have forward or reverse reaction and I wanted to give you a big big overarching principle here and I'll give it a fancy name and 2nd the reverse reaction must go through the exact same halfway that the forward reaction went through under these conditions but in reverse in other words in said the reverse
reaction which were about the see in 2nd must go through the same mechanism but there is a
fancy name for this idea of the principle of microscopic irreversibility of like so many things that have fancy names they really come down to to a very very simple ideas so we look at the reaction uptake the reaction we had here but we believe this is universal so we can't take any immediately after Manginelli action energy diagram you've seen these in earlier chapters of the text of the another word something will remember energy on the 1 hand axes and we have some type of the reaction coordinate of for you can think of it as the progress of the reaction on the x-axis and imagine a scenario in which we go from reactants Jew intermediate and on product and in this particular case I'll give us an example of a slightly uphill reaction just as there acetone for unified rate was slightly up here but that's not what we make a diagram for a reaction like this what we're really doing is is diagramming out the lowest energy pathway for the reaction in other words there may be other halfway ways through this reaction there may be a pathway that where up to you but it's going to be high on energy and the basic premise for a reaction is that as we proceed from reactants 2 intermediate step products over a 1st transition state over a 2nd transition state if we have multiple transition states we go on over a series of energy barriers and we're going to take the lowest energy fare well if this is the lowest energy panel in the forward direction then it's also going to be the lowest energy in the reverse direction if there were even lower energy had they would have gone through that pathway because it would have taken less activation energy to go over those barriers here molecules would have gone over that pathway In the revert in that are in the forward reaction and this principle this idea of microscopic irreversibility then tells us exactly what must be happening in the reverse reaction for even a reaction you haven't seen before now
we're gonna start with something pretty simple and it should be easy to win your way through this reaction even without any high fancy high-polluting fancy principles of microscopic reversible because of all this chemistry is just about protons going on protons coming off and the formation of rocks ,comma you might so let's of managing
the reverse reaction at this point and here's our general denial and we're going to get ourselves and that they have some of the idea that has to be the same as the 1st reaction in other words the last act of the formation of the German dial it involves a loss of a proton from the Germinal dialog so the 1st step of the reverse reaction has to be putting time onto the chairman of guy IOC soldiers are aged Rio plastic and again it's going to be acid catalyzed so we put a proton Poland can general guy all electrons flow from the lone pair to the Proton from the hydrogen bottom to the hydrogen back onto the oxygen I think that with the help of the the and for now at least I'm going to be a good person and write everything out step by step linger on Ogden wool investor will make a little bit quicker and expect you to follow along but in our next step of the mechanism now you can just envision the water getting pushed out by a lone pair of electrons and so we put push out and we get protonated acetone and it doesn't particularly matter whether I have the protons in office To the left or to the right In the final step but the mechanism were in water there's lots of water protons go on protons come off just about everything would alone bear the to it'll take a long way around here home off my Proton but but but but but but but but but but but but but but it it is we get our Geneva vote and back and so the mechanism of the reverse reaction looks identical to the mechanism of the the forward reaction but in reverse some students might wonder why don't we just drop water leaving here and we could draw cat and the answer is there is no difference I've written 1 residents form I've written the more important residents form if you were to write it 1 way in the forward in the forward reaction I try right the same way in the reverse reaction but in the back of our head just as I said at the start of the lecture in the back of our he is the idea that embodied in this structure are 2
different structures to different species to different resonance one-third of saved to different pictures of the same thing thoughts of questions at this point great question does the reverse ability it's applying to the saying the same
mechanism in the forward reaction and the reverse applying 2 other reactions as well absolutely and so we sort Sianna Hydra information on Tuesday a week ago and we didn't talk about sigh and a hydrant decomposition but the base-catalyzed form a decomposition of a hydrants back to hides and cyanide goes by the exact same mechanism in reverse and discussion section this week you'll be seeing that reactions were also going to be seeing some examples in the homework of acetaldehyde decomposition and other sorts of reactions and yet that idea applies and it doesn't apply just because I said it in applies for this fundamental principle that the lowest energy path in 1 direction is indeed the lowest center if a path in 1 direction is indeed the lowest energy panel that is of course the same in the reverse direction so yes it's universal care you were to change the condition and say they are right now imagine I throw in a handful of sodium hydroxide into my acetone solution and asked How is my German although all decompose now up we just change the conditions then it's going to be a base-catalyzed mechanism that it's going to be polling approach on all getting enough oxygen and I'm kicking out hydroxide but as long as the conditions are the same as long as you have the same species present the same conditions of create the same forward other questions good question you know this is an interesting reaction he does so this reaction will go at room temperature it'll go at higher temperature you're not going to shift that equilibrium there is essentially nothing you can do to isolate a bottle of acetone Jim old all or a bottle of asks about the high gym an old guy all they are that equilibrium essentially giver take a little bit stays right where it is regardless of temperature so yet no way you can drive that now I'm going to now introduce us to something where instead of forming an unstable species to species that you can't isolate or put the body in a bottle we're going to see the formation of a stable species and acid house and so that's where we're going to go next and we will invoke list shall liaise principle to drive reaction but but but but but but but but it's so alcohols How alcohols in a way the cousin a lot of the cousin in the sense that they are alike they fall far hydroxyl like compounds they both have similar PKA is in the case of the conjugate assets and they both can give up a proton the big difference with water Is it has the 2nd Proton to give up OK so that means they're going to be many reactions that look a heck of a lot alike so let's take our friend as it's known here and let's imagine instead of treating our acetone With water basically dissolving your acetone and water retreated with all right this is a major plus for for now and I ain't plus I mean a strong acid catalyst and some methanol we specifically don't want it's 3 real cost because we're going to be seeing a reaction in which water is the product of reaction we wanted drive that reaction by getting rid of the water you don't want to do this reaction in 8 winners answered in the product of the reaction is and what's called an answer talent in this particular 1 is called acetone .period I'm ethyl acetate and the assets unlike the Germinal dial it is stable the other productivity reaction is water so you want to go ahead and write this reaction by getting rid of the water which is why I said we want to use anything but
a four-year sentences for the reaction and the reaction is going to proceed so this no way is sort about cousin all our general dial and cousin in the sense that it has I'm a taxi group and thoughts group instead of a hydroxy group and hydroxy group and the reaction is going to go by way of an intermediate that is sort of a sister of
the German old and that's by way of an MIS at 2 Kamiah means have been so I him alliances Tal of means at have offensive tower in other words it's something where you have 1 group that's an outcome the group and 1 group that's a hydroxy group and my acetaldehyde general is unstable but then a saying right now that at the end of today's lecture and perhaps even in your backpacks right now there is we will see stable Hi my ass italso circumstances can make a special condition ever going to see how this reaction goes now by the way there's an older system of nomenclature you may see it it may have even popped up in the sampling costs sometimes you will see the term sheet shall use fallen out of usage but you'll sometimes see the term sheet shall use the talents and Athens Taliban tone so sometimes you'll see this referred to as acetone dime Apple key Talbot these days as talents preferred and simmer away sometimes you'll see this referred to as at might keep him out and a pledge both of these terms in parentheses so we don't worry about them but if you hear them either crossed my lips in the course of our discussions were you see immunity of where you read that's what you're going to see all the textbooks tend to use them and as I said they may not have described out of out of saplings the IRS so before we move on to the mechanism let's take a moment to talk about the asset so the strongest asset you can have in water is H 3 of
in other words if I dissolve in water I don't have HCL and water approach makes the water dissolves sulfuric acid in water similarly it's nice to have in mind some idea of what constitutes a strong acid in general a strong acid is anything that's got a PKA that's lower than that of the solvent that you're thinking of so Gates CL PKA of negative 7 H 2 SO for sulfuric acid PKO farthest-right negative 300 need 1 popular 1 that use of Cl dissolves
in methanol just great HCl doesn't dissolve and see benzene so well it's not so soluble and say solvent like benzene which is good because we learn that benzene is good solvent for removing watery learned about the CIA Tropic distillation which is often important in driving reactions like acid to help formation that are equilibria so another popular as insisted that organic chemists like to use his parrot toluene telephonic acid parrot toluene sulfide aggressive looks a lot like sulfuric acid right sulfuric acid is H 2 SO for HOS tho H O S O Old Age and top power toluene sulfide gas it just has benzene benzene actually electron MacDraw into the feeding of toxic gasses is about of the flight your TSO wages are you usually see abbreviated which is a fancy name for Parra told you insult upon offensive anyway peaking at negative 7 again a very strong so if we imagine for a moment say taking methanol and dissolving like Gates CDL reached U.S. for a or toxic gasses in the you have an equilibrium but that equilibrium gonna weight to the right you're going to program a methanol coordinated methanol is the strongest species that can exist in methanol the strongest acidic species that can exist in methanol and of course your of chloride this equilibrium lies to the right you can think of methanol as being very much like water in other words the PKK protonated methanol it's just about the same as the PKK about drawing mind is as the hair lower its negative to which you want wanted the exact in general you can think of an alcohol on need for having a P K of the conjugate asset of about negative 2 were negative free the alkyl groups the will of the electorate donating so what we imagine assets how formation when I imagine reaction here it would be an asset like Gatesy light H 2 SO 4 dissolved in ethanol but I think of my asset and the mechanism of probably think of it as a prorated methanol because that's going to be the strongest species that can occur there firing so I I wanted to take us I wanted to take us to the mechanism of acetone di methyl ester town formation in the mechanism is going to be identical To the mechanism we software hydrate formation but it's going to occur at whites now it's identical in the way that you have to think a little bit broadly in that you have to think that well methanol can react analogous to water protonated methanol can enact react analogously 2 of the mile and then everything is the same toxic hobby of mine on formation is the same everything else is the same except it's that you're going to have half of the expresses what mean because you don't actually have to know anything to write a all you have to to do is be able to think you are we've got acetone here and we have appropriated definitely in there said protons go on an all or just about anything with a lone pair of electrons we follow our electrons world Our carbon From Lewis bases are very weak I'm sorry advanced database to the Bronstad asset of the progress made methanol just as we had gone with the nations from the hydrangea Meyer a good but now you end up with the self-same Oxo hard being a mile and we've seen before the self-same protonated acetone so we know that we can have an attack occurred them a goal a little bit I the goggles a little bit faster here and so in the next step L Elskamp Kerberos because by this point you should be be able to do this is the next step methanol attacked and what's we still have a proton on it I don't want to get that fast so in the next step on methanol the attacks and then in our next step a molecule of methanol comes along and calls on off the proton energy and I'm going to skip the Kerberos you can imagine electrons flowing from the long tail To the hydrogen electrons flowing back on to the oxygen and cell and that point we have to catalyze the formation of the him answers how intermediate and so far and I'll go ahead and write write this out here you know mechanisms and so far everything is identical to what we wrote inositol for vacation or in hydrate formation I wanted to to take us on at this point to the formation of our asses held from our him I answered fell to wear acetone and everything is going to be identical to what we've seen In
Sn protons go on protons come off everything
with a lone pair of electrons so here we are at our him I ascertain how of the here's our program needed methanol don't go through a little bit more slowly along that more carefully now we will put a proton onto the hydroxy group it's the electrons flow from the lone pair to the protons and electrons flow from the protons back onto the oxygen atom but but but but but but but but but but but but but but but but but but but but but but but but but but but but but but but but but but but but but now the next step we're going to kick out a water molecule to form another rocks a hobby being mine should electrons flow from the oxygen pushed down push out the the water molecule doesn't matter which lone pair of electrons I used the bold this same of electrons well-balanced kind to the all age groups the push out the water molecule we go through the exit from being mine on solar water byproduct of reaction now another molecule of methanol tax taxes is Guenna electrons flow from this species with electrons to the species that once electrons free push-up up electrons onto the oxygen doesn't matter which way I at 1st and to the left after to the right as long as they go from the Bible on them to the oxygen of unit our final step now we have Watson lots of methanol protons go on approach guns come along and we recover officiated methanol catalyst but the electrons flow back onto the oxygen of but if you look of at but but but but but but but but but but but but but but but but but but but but but but but but but but but but but we get appropriated 1 of them Our Europe
old question OK 1 great question why doesn't it methanol and attack this intermediate and kicked out water in an essay 2 reactions anyone so OK so the 2 sort of questions here you just mentioned ,comma Cat Island that I hold that for a 2nd because I wanna come back to that 2 we the nuclear file OK we're getting on the right track what we know about us into reactions it said tertiary carbon and in general we don't have s into displacement editor shared carbon and indeed only very good very few nuclear files even do too
well at a secondary center so yes it's too weak to to be at a secondary center it's a tertiary center we essentially never us into it tertiary and you mentioned Cat Island and the reaction he is indeed an S N 1 reaction because if you think about it remember the leaving of water as a leading group to form this species this is just a cargo can and adjust the other residents structured the 1 and the same the Oxo Caribbean
island is bold the cargo can and like resonance structure and this residents structures so the substitution that we see here is indeed an asset and 1 tight reactions and indeed not finesse and 2 other questions great questions exactly what you should be thinking at this point this is all yes to actually look at the top of the group 1 power another question exactly that I planted people in the audience that these are the questions that all of you should be asking I'm really happy to be hearing this because these are the questions I hear every time from beginning students on this
so they should be going through your mind and I'm very happy to have people brave enough to ask your question is why doesn't that approach made here and indeed it dies and that takes us on the path back so that we go over upon reacted the intermediate stops products in June general we don't deserve to the the move disapproves of rule ended early action astounding held eventually we end up there and so indeed that occurs along the reverse pathway and if you're trying to make a nascent talent size it you drop by that reaction as best as possible by kicking out the water in some cases it's just by use of a large excess of methanol which Saturday's principle in some cases we really push it would deem stock distillation to drive the water out doesn't work so well with methanol because of boiling point of methanol works with other alcohols in some cases we had a compound that reacts with the water for example Mathilde opera penal war odd try try worth of lawmakers to react irreversibly with the water and suck it up and in some cases 1 answer drying agent and dehydrating agent flight July Keeler said I wanted to take us on in a a couple of directions before we finish up our discussion of acid house him my answer channels and hydrates B and 1 of the things I wanted to take us on is the reverse reaction so as I said all of these reactions are equilibria all of these reactions can be driven by the use of excess art methanol and in turn all of these reactions can be driven in the reverse reactions so if we go ahead and carry out hydrolysis with lots and lots of water we can break down arrests there are ascertained In general that's going to mean just changing our solvent and keeping arrested so so let's take a acetone dire methyl acetate call and I think at this point I'm going to avoid writing the fight I will write the methyl groups 1 last time here but I expect you to be able to understand them and so on edge and a source of acid in water a police ACL Lake Weir sulfuric acid and lots and lots of water then arrested Talal breaks down looks back to acetone and if I feel in the mood to to balance my equation 2 molecules of methanol no at this point I expect you to be able to think your way through the mechanism a great exercise you should do it yourself I'm going to give you the gist of it in shorthand suggests that the mechanism involves probe nation I'm just going to draw out a series of intermediates here maybe maybe with a few lone pairs to help us don't keep track of things the gist of the reverse mechanism it's the exact reverse 1st steps it is the same as the last step 1st step for made on oxygen next steps kick out methanol next intermediates is our arts part a mind on the next step is attacked I wonder of this the next step is to remove a proton deform unstable Germinal are unstable him my acid town the next step is to reprogram a on the math at all protons come all off protons go on all different places all different lone pairs next step is really push out the methanol the next step is I can ultimately intermediate opera mated acetone loses approach can so they're there and they're not shell is
the embodiment of the entire mechanism of acetaldehyde rolesis in reverse and indeed this is the only mechanism you're really gonna say in all of this acid catalyzed chemistry with slightly different wrinkles intramolecular intermolecular but no huge differences question only 1 of 4 Our OK good question should we get coordinated methanol we're in a you'd see a water we have 55 Moeller arranged too well and we we've dissolved out there Imola half molar of our compound most of the H 3 up most of the protons are gonna be on water Our let's take a look at it a few more common examples and a little bit of synthetic chemistry but does your text textbook because the a nice job with this so I think I'll I'll conclude by borrowing a few examples that you text invoked so what we've already learned that at certain points in
synthesis it's necessary to hide grew to render 1 group so we can react we saw off for example that in carrying out certain reactions we would want to to hide in alcohol so the OH-group isn't available by protecting it as a TBD amassing protected as a sign acid towels are often used to hide at the toner Al the functionality so for example and this comes straight from your taxable because I think it's a good relevant example for example your textbook poses the question of how could we selectively take this subpoena last year and reduce it to its legal alcohol and obviously you see the conundrum you you'll look at this reaction and immediately you say Well OK I know there are plenty of reducing agents that I can use the blast down and Esther basically we've learned in the course lithium aluminum hydride nukes any carbon medial down to analysis that down to an alcohol and yet we recognize the problem that we treat this compound with the powerful reducing agent like lithium aluminum hydride were not going we're also going to reduce the other cardinals were also going to reduce acute and the solution to this is to go ahead aid to take this compound is Peter last year and a half I the key Tomba when you can do so selectively by making an ass Tower Out of the key group and so if you envision also tend to make it particularly as at houses the tones particularly for the ones I referred to as she tells because key towns are much less reactive than the hides often you have to work really hard to make that reaction and 1 way to make it 2 1 to do that to push the reaction is to make it go from molecular weight to have 2 out of groups in the same molecule so ethylene glycol 1 to die hydroxy ethane and propylene glycol 1 3 or 1 in 3 of the top propane guy all 2 at the dial are often used as protecting groups for key towns and so if 1 Treves With catalytic toxic acid which as I said is often used in organic solvents often with stock distillation to drive out water often envisions senior toluene if 1 treats the key towns and ethylene glycol With catalytic asks you can selectively protect you can collide the key to as the acid house and now you can envision a three-step process where your 1st step is to protect your 2nd step is to reduce and lithium aluminum hydride followed by workout with water and I'll say or aged Rio blossomed in a comeback in common you know that I like to to work out my with him aluminum hydride reactions with acid usually that just means adding a lasted to the reactions and if you just add a little bit of massive without really talking things out without reading them In general tally isn't going to break out and generally you went out to really break down the key tells the break down your as Intel's Dean general need water and asks in the little bit of the I'm at this point we're learning that a get bent out of shape over these differences here you should just realize if you go into the laboratory if you pour a little bit of dilute acid in at this point you're probably not going to Ligety talent you can enter your secretary final isolated right over Mac sulfate if you then take it in water well it up with make with HCl higher temperatures longer reaction time and so forth you will indeed protect you will remove the protected with an inoculate influenced system costs ethylene glycol although it did you would get a chemist is probably going to forget about that very quickly so
that's a that's a nice example elsewhere as a talented very useful instead distress and where they can be used to achieve a goal selectively which as I said is really 1 of the big things about organic chemistry it's that I want to make this molecule not that molecule I don't wanna make a mixture of molecules I don't wanna make a mixture of dire streamers and in some cases I don't want to make a mixture of vanadium MBAs 1 single of and this is all with these tools about but I kind of have dropped and that intramolecular parody ends up giving you a special relationship a member of the water it's 55 Moeller in other words when a reaction occurs with water say the formation of a hydrate like we saw on acetaldehyde where the equilibrium where right in the middle essentially at 1 2 1 at 42 to 58 that equilibrium lies in the middle cousin 55 water there's only a certain amount of water president to pushing hydroxy group but if you have the hydroxy group lighten the molecule you can have that carbonyl group seeing an even higher concentration of water in other
words the effective ilarity instead of being 50 Moeller 55 Moeller water can be a hundred or a thousand or 10 thousand where that hydroxy group is just staring the top group in your face in the face in the text that gives too nice examples that are relevant to the chemistry of carbohydrates which is where I will find we conclude 1 of these is hydroxy now derivative and the other is a hydroxy Newton now derivative and both of these compounds exist in equilibrium with their genital dialog with the there about him I as child but and those equilibrium now my toward the right inside the some make my error a little bit longer in the former case you have a hydroxy take the hydropower ran type of structure now the hydroxy group has cyclist into the carbon city of examined all got to give a as towel and in the other cases do you have any hydroxy urea and structure but and now because that hydroxy group is staring in in the face your equilibrium as a said lies to the right it's 6 thousand 94 in the case of the former and its 11 to 18 In the case of the latter in other words if it were just water there were just water just even methanol you have halfway roughly for the equilibrium India have half of the German although I also have to be out of the hide were methanol you'd have half of the him acid house half of the elder but by the time you have the hydroxy group in the molecule can form of Bolivar six-member growing then you will have to be much higher effective malaria the hydroxy groups steering the cardinal in the face the equilibrium lies To the right six-member ratings are good because they're on strange five-member rings are good because they're smaller but you get a little bit of bringing straying from eclipsing remember the ring strain and cyclo hexane is effectively free the ring strain encyclopedia about 6 kcal per mole so higher effective malaria of hydroxy group in the 2nd case and the hydroxyl you now but simmering straightened out alright now where there's really ends up coming into play and why I said you probably have this sitting in your backpack and certainly you have to sit in the new bodies is the sugar molecules and a free market and a molecule like glucose in and didn't want 1 way which I think is a little bit closer to what we're seeing here and then all another way so this molecule With all of these hydroxy groups on it it is glucose or more specifically what's called a meeting of the Group of how data tells us about the Syria chemistry at this position the OH proved disappointing founded as details about the theory chemistry up advanced positions but the main thing is this is a sugar that should be familiar to you if you're drinking on honestly if you're breaking out what if I have to go .period Europe you've got glucose in there eating soups gross it's part of the molecule that infuriating Haifa just corn sugar it's been broken open if you look at Kandy were glucose is been it's there as well now if you notice here amidst all of these hydroxy groups is a carbon that is an acid test this program is and how the Hyde hiding Japan just as our carbon is over here and haven't won in the hydrogen but of course there's a hydrogen here and there's a hydrogen here which means just as our hydroxy painted now exists in equilibrium with the cycle like forms are hydroxy view now Our glucose exists in equilibrium and that equilibrium is way way way in favor of the site .period form even more then she 6 it's like 99 . something 99 . 9 9 something and yet there is a teeny tiny amounts of the Al the form and drawing hydrogen here just because tonight and will clearly likes them at 1st the United just to keep a consistent level drawn in the besieged and so on particularly with the presence of a little
bit of acid to catalyze the reaction your equilibrium will go back and forth between the close form and the open form in this case there are a couple of reasons why this equilibrium is further toward the site with former 1 of them is stare is conformational the hydroxy is just just perfectly organized the molecules form a nice stable chair
cycle hexane you'll often see evaded Daegu Coast written in its chair conformation life so in all of the hydroxy groups with far Ecuador at all 1 is really all of the hydroxy groups track which oratory of the other reason is electronic your hydroxy groups particularly the alpha hydroxy group is inductively electron withdrawing it holds electron density away from the carbon group and so it makes the carbon of glucose even more Elektra felt like the end of the the high carbon meals it's even more problems 2 react and I think this is where I'm going to her wrap up our chemistry and you will get a very nice example of some sugar chemistry in the latter homework problems from Smith and I urge you to take a look at them and very nice exercise our rights we will pick up with our next chapter on Thursday