Preparation of Carboxylic Acids

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Video in TIB AV-Portal: Preparation of Carboxylic Acids

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Preparation of Carboxylic Acids
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2
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27
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2015
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English

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Abstract
This is the third (and final) quarter of 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: 00:43 - Oxidation of Alkyl Groups Bonded to Aromatic Rings 03:31 - Sulfonic Acids 09:33 - Reactivity of Carbonyl Compounds 11:57 - Type 1 of Carbonyl Compounds 15:01 - Type 2 of Carbonyl Compounds 16:14 - Both Type 1 and Type 2 Carbonyl Compounds are Electrophilic 32:46 - Both Type 1 and Type 2 Carbonyl compounds are weakly basic at the carbonyl oxygen and protonated by strong acids 41:07 - Both Type 1 and Type 2 carbonyl compounds are acidic 44:24 - Reactivity of the various Type 1 and Type 2 Carbonyl Compounds
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Sense District Ethylgruppe Toluene Chain (unit) Chemical property Carboxylate Resonance (chemistry) Chloride Spaltfläche Aromaticity Ethanol Electron Sodium hydroxide Human body temperature Cryogenics Benzene Potassium permanganate Conjugated system Oxide Chromium Pyridine Fatty acid methyl ester Alkane Ozonolyse Concentrate Benzyl Carbon (fiber) Alkansulfonate Aldehyde Chemical reaction Erdrutsch Hydrogen Sodium Acid Computer animation Functional group Materials science Dehydration reaction Cobaltoxide Base (chemistry)
Ionenbindung Ester Weakness Carboxylate Chloride Organische Verbindungen Chemistry Atomic orbital Reactivity (chemistry) Human subject research Lactitol Acid dissociation constant Common land Metallorganische Verbindungen Conjugated system Process (computing) Setzen <Verfahrenstechnik> Substituent Acyl Phosphorus Ketone Carbon (fiber) Carbonylverbindungen Aldehyde Addition reaction Lone pair Hydrogen Acid Computer animation Acid anhydride Functional group Etomidate Acetone Chemical structure Base (chemistry) Cobaltoxide Pipette
Resonance (chemistry) Aluminium Chloride Chlorine Atomic number Chemistry Electron Rapid Hyperpolarisierung Elimination reaction Aluminium hydride Thionylchlorid Hydride Walking Sulfur Addition reaction River source Chemical reaction Alcohol Wine tasting descriptors Lone pair Exothermie Acid Acetone Cobaltoxide Isotopenmarkierung Ionenbindung Biosynthesis Reaction mechanism Substitutionsreaktion Wursthülle Reactivity (chemistry) Tetraederstruktur Lithium Atom Process (computing) Setzen <Verfahrenstechnik> Acyl Hydrogen bond Carbon (fiber) Carbonylverbindungen Aldehyde Hybridisierung <Chemie> Protonation Electronegativity Water Hydrogen Ice Drop (liquid) Computer animation Functional group Base (chemistry)
Setzen <Verfahrenstechnik> Ionenbindung Kohlenhydratchemie Ester Resonance (chemistry) Carbon (fiber) Carbonylverbindungen Wursthülle Acid Computer animation Electron Covalent bond Cobaltoxide Base (chemistry) Conjugated system
Alkyne Ionenbindung Ester Carboxylate Sunscreen Resonance (chemistry) Carbonate Chloride Aromaticity Alpha particle Reactivity (chemistry) Electron Abbruchreaktion Derivative (chemistry) Setzen <Verfahrenstechnik> Acyl Induktiver Effekt Ketone Topicity Carbon (fiber) Carbonylverbindungen Aldehyde Protonation Chemical reaction CHARGE syndrome Food additive Hydrate Lone pair Hydrogen Combine harvester Acid Computer animation Functional group Etomidate Enol Chemical compound Cobaltoxide Base (chemistry) Isotopenmarkierung
we are going to finish up chapter 19 and start chapter 20 so I went kind of faster chapter 19 I will slow down when we get to chapter 20 because that's new material all right so we're left off
last time talking about preparation of carboxylic acids so we can do it by oxidation so that would be from chapter 12 we can oxidation aldehydes with chromium reagents we can also do oxidative cleavage using ozonolysis that was also in Chapter 12 and then in chapter 18 we talked about the fact that you can oxidize alkyl groups bonded to aromatic rings so you'll recognize if you had me last quarter you'll recognize this slide from notes last quarter alkyl group on a benzene ring can be oxidized or carboxylic acid the commonly used reagents are potassium permanganate sodium dichromate I'd the one that I use is potassium permanganate and that debt is kmno4 and base so sodium hydroxide and heat alright so here's some examples here it doesn't really matter how long the chain is the oxidizing this is a very powerful oxidizing agent it's going to oxidate it all the way down to a carboxylic acid so all of these starting materials give the same product you could have a chain that was a hundred carbons long it would still give you the same product what you do need for this reaction to work is a benzylic hydrogen so here's the benzylic hydrogen here here's a benzylic hydrogen here here's a benzylic hydrogen here must have been Zilla hydrogen if you don't have a benzylic hydrogen there is no reaction so this one here as you can see this carbon has no benzylic hydrogen therefore there is no reaction so here's an in our little box on the test we would write no reaction okay no reaction if you don't have any benzylic hydrogen so that NR for no reaction all right so potassium permanganate we saw this this is a this is a chapter 18 we also saw a potassium permanganate in Chapter 12 doing something completely different and that is doing dihydroxylation I'm just just to point out that this is low temperature here so the temperature is kept low so that we don't have things like this previous reaction happening okay so we keep the temperature low for that for dihydroxylation when we're doing the above reaction we will use heat for that and the last thing I want to talk about in this chapter is sulphonic acid so phonic acids are very similar to carboxylic acids so you saw sulphonic acid s-- last quarter in dehydration reactions right okay so we use this for a dehydration we abbreviated this T Soh toluene sulphonic acid now that you've had chapter 18 now that name makes sense to you okay so that was used for dehydration used instead of concentrated h2so4 for dehydration and I'm off the edge of the paper so dehydration and that of course is chapter what is that chapter 9 chapter 9 so everything you've ever learned all year comes back in 51c alright so these guys are actually similar on this properties to carboxylic acids but much much much more acidic so I'm carboxylic acids have pk's of about 5 these fpk is around negative 7 and the reason that they're so acidic is their conjugate bases are very very highly resident resident stabilized so when you remove this acidic hydrogen with the carboxylic acid you can do localized the electrons on to two oxygens with sulphonic acid you can do localize the electrons on to three oxygens so here's oxygen number one oxygen number to an oxygen number three so more highly delocalized electrons so highly resonance stabilized because their conjugate bases are such weak bases they make great leaving groups and so we saw in chapter 9 that we can use tousle eights as a leaving group this one here is ethyl tosylate so I'm sure you recognize the name ethyl toss li you might have forgotten what at oscillate looks like and that's the danger of using abbreviations when you're doing reactions you forget what they actually look like so if we were going to abbreviate this we would write ch3 ch2 o toss so that's art oscillate and we know that they make great leaving groups so what this reaction would look like we attack carbon backside attack kick off tousle eight as a leaving group that gives us ethyl nitrile and our leaving group of course is the same one we have drawn above very highly resonance stabilized the negative charge delocalized on to three oxygens great leaving group alright remember how to make tossa lights well let's let's use our retro-synthetic arrow how do we make this we can make this from ethanol and tousle chloride pyridine so hopefully that's ringing bells here for you so although all the reactions we've ever learned come back in 51 see I try to remind you of them as we go I remind you of them and in lecture I remind you of them discussion and I remind you of you on tests to I mean I suppose okay so but what you're what you're going to start to see is that a lot of the reagents there's a certain few that we use over and over again and I call them famous reagents and there's definitely some
ones than 51b that you will use a lot more than others alright questions anybody let's start chapter 20
so who needs handouts that doesn't hasn't picked up the notes already nobody probably got a big stack in the back there okay all right
all right so here's where we start really getting into the nitty-gritty of carbonyl chemistry so in this chapter here we're going to talk about carbonyl chemistry with all of the carbonyl compounds and organometallic reagents so irreversible carbonyl addition and then in chapter 21 we talked about reversible additions of aldehydes and ketones and then in chapter 22 we talked about irreversible additions to carboxylic acids esters amides and all of that so we're very general chapter this is a chapter that you certainly do not want to get behind in because you'll feel be lost very quickly here all right so what do we know about carbonyl compounds it's an extremely important functional group in organic chemistry and in biology too it plays an important role in many biological processes so here's a carbonyl group this is a carbonyl group and what do we know about structure well structure wise we know that we have SP to oxygen and sp2 carbon let's draw out the structure I'm going to kind of lay this on its side perpendicular to your page so we have our pipe we have our PI bond here so these are our two unhybridized p orbitals so that's a p orbital that's a p orbital and those two orbitals overlap to make our PI bond so our PI bond an overlap of two P orbitals and then our Sigma bond is the carbon oxygen Sigma bond is right here overlap of what type of orbitals sp2 and SP 2 so now we're now we're going all the way back to chapter 1 so we're gonna we're gonna hit all those chapters and so then we also have lone pairs on oxygen let's draw in the lone pairs what type of orbitals are the lone pairs on oxygen yeah anybody Oxygen's sp2 hybridized so we with these must be an sp2 orbitals right sp2 so when we hybridize one sn2 P's we get three sp2 orbitals one of those sp2 s overlaps with carbon to make a sigma bond than the other two are how to pull two lone pairs I know we have an unhybridized p orbital which makes the PI bond okay questions I know it's been a while since we've done that substituents attached to the carbonyl strongly affect the reactivity of carbonyl compounds there's going to be I'm going to divide these into two different types I'm going to divide them into type one and type two and they the two types have different reactivity type one the acyl group so remember the acyl group so this right here that's the acyl group so an acyl group is the carbonyl with an R group attached when we're just talking about the carbonyl it's the carbonyl while we're talking about the R group attached in addition to the carbonyl that's the acyl group so acyl group is attached to a group that does not have lone pairs and cannot act as a leaving group so here we have so the acyl group is attached to a hydrogen or the acyl group is attached to another R group so this would be an aldehyde and this would be a ketone and these are both type 1 so we if we if we compare R and H the things that they have in common are is that they have no lone pair they have no lone pairs and they can't be a leaving group how do we know if something's a good leaving group or not remember that from chapter 7 what's a good leaving group weak base okay so it can't be a good leaving group so these must be strong bases so let's let's look if our left it would be our - which would have a pKa of for the conjugate acid that's how we're going to judge basicity pKa of the conjugate acid is our H our HS our conjugate acid and it has a PKA equals 50 horrible horrible leaving group not going to happen let's look at H - as a leaving group because if those groups left that would be our leaving group h minus PKA conjugate acid conjugate acid is H - and that has a pKa of 36 so also horrible leaving group okay so I'm just to remind us against let's label this good leaving groups our weak bases these are not weak bases good leaving groups our weak bases all right so that's type one aldehydes and ketones we're going to talk about them together and that's going to be the subject of chapter 21 we're also going to talk about those in this chapter and then type two acyl groups attached to a group else oh so I use el L stands for lone pair and L stands for leaving group so L leaving group and L lone pair so any any carbonyl compound that has a it that is it bonded to a group L that has a lone pair or can be a leaving group it is going to be type two and they're gonna have different chemistry than type one so here so again this is our acyl group here acyl group and it's either a good leaving group or it can be protonated to make it a good leaving room so that's the what these all have in common so here's the examples here if it's a chloride it's an acid chloride if it's a if it's an amine then it would be an amide Oh are we an ester Oh H carboxylic acid and if it's bonded to another carbon C group then that would be an anhydride so a lot of people have forgotten anhydride I'd say I noticed that in my lab class so that would be an anhydride so something something that we're gonna be talking about this quarter questions so far the two types all right so let's talk about what type one and type two carbonyls have in compound common common and what they don't have in common and I'll start with the simple ketone so here we have a ketone this is acetone
and we know that we can draw a resonance structure for acetone where we break the pi bond and we move it on to the more electronegative atom so it'd look like this this is not a great resonance structure it's not a super contributor but it does actually contribute a small amount to the hybrid and so if you look at the polarization of a carbonyl group we have partial positive charge on the carbon partial negative charge on the oxygen and so what what all of the type 1 and type 2 carbonyl compounds have in common is that the that we have the carbonyl carbon is electrophilic so it's quite electrophilic it'sit's more electrophilic as we have not only do we have residents contributors we also have the difference in electronegativity and those things add together to make that bond more polar than a typical carbon oxygen bond and so since its electrophilic and what we're going to see this is the type of reactivity that we're going to see for these guys is nucleophiles attacking the carbonyl carbon so this is what it will look like nucleophile attacks the carbonyl carbon and then we kick electrons up onto oxygen that's the reactivity that we're going to see for all of the carbonyl compounds this is an addition so that's the reactivity that we're going to see and what we're going to do is blend things like adding of adding a proton source to protonate that oxygen we'll see that coming up to make alcohol so we have a new synthesis of alcohols type 2 carbonyl compounds on the other hand are a little bit different following addition elimination occurs so it's going to be two steps now for these guys all right so the nucleophile is going to attack same as it did with with the type 1 carbonyl compounds that's going to attack except now we got to edit L here so go ahead and add that Allen I'm just going to put a little lone pair on L to show that that's a lone pair and a potential leaving group so kick electrons up onto oxygen we get negatively charged oxygen and then we have this group L that can be a leaving group so that step right there is addition same as above but because we have a group L that can be a leaving group what's going to happen is the leaving group is going to lead so electrons on oxygen are going to come down and kick off the leaving group that second step is called an elimination so if you look at what we have after that elimination we've basically replaced a nucleophile with L so it looks like it's a substitution reaction but it's not an sn1 and it's not an sn2 because it has undergoes an addition-elimination reaction so it's a completely different reaction this is the overall if we let's summarize the over let's look at the overall process here we're taking a leaving group and we're replacing it with a nucleophile so a substitution but not an sn1 not an sn2 we're going to call this an acyl substitution so nucleophilic acyl whoops sorry about that nucleophilic acyl substitution let me give you an example that we're going to be talking about in this chapter here this reagent here is aluminum reagent related to lithium aluminum hydride which are already familiar with slightly different though but in the same in the same family and it's a hydride source we have negatively charged aluminum so if you remember from chapter was that is that the that was the ox that was chapter 12 right when we talked about lithium aluminum hydride and so we're gonna use the same arrow pushing arrows gonna come from the aluminum hydrogen bond we're gonna attack the carbon eel we're gonna kick electrons up onto oxygen you're probably gonna see it here we say that attack the carbonyl carbon kick electrons up on the oxygen you're probably gonna hear me say that like a hundred two hundred times by the time we get through carbonyl chemistry so it's just so common that reactivity this is addition and then let's let's draw the addition product and then as you can see we've got chloride ion could be a possible leaving group and that's exactly what's going to happen so we have the oxygen they could differently charged oxygen we've got the chlorine here we've got the hydrogen our leaving group is not going to be hydride our leaving group is going to be chloride and so the electrons on oxygen are going to come down and kick off the leaving group chloride ion that's elimination addition elimination and what we do this reaction we've turned our acid chloride into an aldehyde so that's a reaction that we're going to be talking about in this chapter and so here's the big difference type 2 carbonyl compounds have a leaving group so so what we do is when we do the attack we get something that we call a tetrahedral intermediate why do we call that a tetrahedral intermediate if you see if you see we start off when we're sp2 carbon and then here we're sp3 so our intermediate has changed hybridization it's now sp3 and so it's tetrahedral carbon so we call this a tetrahedral carbon and the tetrahedral intermediate has a leaving group and if the tetrahedral intermediate has the leaving group the leaving group is going to leave so we're going to be able to make predictions about what carbonate what carbonyl compounds are going to do just by looking at of the groups that are attached questions so far anybody now
depending on who you had last quarter this reaction this addition elimination is going to look very familiar to you we've already seen it so this type of substitution via addition elimination twice in Chapter nine way back to the beginning of 51b here's the first time alcohol sino chloride attacks thionyl chloride we check the sulfur we kick electrons up onto oxygen that's addition and as you can see now we're going we can label that as a tetrahedral intermediate really not tetrahedral because we've got extra electrons here but I negatively charged oxygen and a second chlorine here and then in the next step the electrons on oxygen came down and kicked off the leaving group chloride so your book does this mechanism a little bit differently most of the professor's here do follow this addition elimination mechanism for thionyl chloride so again it depends on who you had for 51a throw that positive charge on oxygen so everybody remember that from chapter 9 and so what we're going to see is and that and that's kind of why I made a point of emphasizing this reaction is because I knew that this was going to be important for carbonyl chemistry so that's what that looks like after that kicks off the chloride that's the first time we saw it in chapter 9 the second time we saw it in chapter 9 was for doing at oscillate making it oscillate so alcohol Plus tousle chloride so hopefully this is all coming streaming back to you right now all right so in the book they did straight they had the electrons come from oxygen and kick off the chloride in one step it doesn't happen in one step it's an addition-elimination so the electrons on oxygen come and attack the sulfur we kick electrons up onto oxygen that's addition and then after addition because the sulfur has a chloride which can act as a leaving group it's going to do just like carbonyls do so if negatively charged oxygen what else do we have we have a chloride here we have toluene ring attached here and we have a second oxygen so a lot of groups around carbon I mean around sulfur and then we had the electrons on oxygen come down and kick off our leaving group chloride ion all right so that second step of course is elimination so let's label that and I need to label this up here go back and label this up here elimination and what do we get overall substitution so same idea here so atoms that are not sp2 3 hybridized undergoes substitution via addition elimination okay so that's the take-home point here all right so um we've already seen this before it's a little simpler actually with carbonyl compounds type one compounds on the other hand do not contain a group that's either a good leaving group or may convert it into a good leaving group by protonation so only addition can occur so here's an example of a reaction that we'll be talking about in this chapter of what happens when you take and this you'll recognize lithium aluminum hydride from chapter 12 and we saw that this can attack up oxides and open them up it can also attack carbonyls so let's draw an aldehyde very rapid reaction with aldehydes arrow comes from the aluminum hydrogen bond attacks the electrophilic carbon we kick electrons up onto oxygen just like that and that of course is addition which all are just abbreviate with ad and we get a tetrahedral intermediate why is it a tetrahedral intermediate it's the same same thing as before this is sp2 and after we do the addition it's now sp3 so therefore tetrahedral so the in this case the tetrahedral intermediate has no leaving group our minus can't leave because it's too strong of a base h- can't leave because it's too strong of a base so it's stuck with addition there is no elimination and so what we normally do with these guys as we add a proton source in the second step now your book kind of uses different proton sources sometimes they use water sometimes they use hydronium ion I don't want you to worry about that okay so in truth when you do this reaction if you're actually doing this reaction this very exothermic reaction with water so you cool your reaction down in an ice bath you add a drop of water you wait for the exothermic reaction to subside you add water first and then you put everything in a set bundle and you shake it up with a little acid so I'm gonna let you so I'm saying proton source in the second step and I'm gonna pretty much I'm gonna allow H 2 to H 2 O or h3o plus is fine with me for exam so you could use either one in other words I'm choosing not to make a big deal about this whether you use water or hydronium wine and so you can see we get a completely different product here we get an addition product not a substitution product all right so type 2 on carbonyl compounds do acyl substitution type 1 carbonyl compounds do additions alright questions so far anybody all right so
that's that's there so a little bit
different there but all the carbonyl compounds are electrophilic what else do they have in common type 1 and type 2 carbonyl compounds are weakly basic at the carbonyl oxygen and are protonated by strong acids so let's draw that and I'll just use I'll choose an ester here so if we had a strong acid to an ester the carbonyl oxygen which is this one that's part of the double bond that's the carbonyl oxygen is weakly basic but if you put a strong acid in there it will be protonated by the strong acid this is what the conjugate base would look like a protonated ester and this one is this protonated ester is resonance stabilized so let's draw some resonance structures for it we can move electrons we could break this pi bond and move electrons onto oxygen to relieve that positive charge we can do that that of course is not going to be a major resonance structure because we if we do that we leave carbon without an octet so we've got a carbo cation there but we also have another resonance structure where these electrons on oxygen here can come kick in and help stabilize that in this case that's the conjugate acid can help stabilize the conjugate acid so that is a resonance stabilized conjugate acid yes an intermediate it can I'm just showing you the three possible resonance structures for that protonated yeah so on resonance resonance stabilized conjugate acid now you might have thought to yourself well why would we protonate on that carbon i'm not oxygen why are we protonate here why don't we protonate here right we've got two possible oxygens can we ever protonate here instead of here so let's look at that that's on the next page turns out that you you don't you only get pronation at the carbonyl oxygen
when you do protonate the carbonyl oxygen you greatly enhance the electro felicity of the carbonyl compound okay so that's a big deal and so acid catalysis almost used to all often used to enhance the electro felicity of the carbonyl carbon so that more easily attacked by weak nucleophiles so we're we're going to see this is in chapter 21 and chapter 22 we're not going to really see acid catalyzed reactions in this chapter in chapter 20 but again I want to go back to the point of why does protonation occur at the carbonyl oxygen not the carboxylate oxygen let's draw the product if you protonate let's let's let's compare the two we have this which we drew on the previous page protonation on the carbonyl carbon and we can compare that with protonation at the other oxygen and probably if i if i sent around if i did had you do a little pre quiz on this most people would protonate oh my why I'm just drawing the same thing again most people would protonate on the other oxygen so let's see why that doesn't happen okay looks reasonable right all right we've already shown and so here here's why we've already shown that this one has a resonance stabilized conjugate acid we get three resonance structures for this well this one here is not resonance stabilized so if you're thinking to yourself well yeah of course that's resonance stabilized um I can just do this I'm gonna write that I'm gonna do this in purple what you don't want to do I can just go like this right can't I do that and let's see why you can't do that so let's draw the product of that were you thinking okay know that I can draw this resonance structure and then tell me what's wrong with this resonance structure hmm what's the charge on oxygen two plus and I don't know however you add 451 a when my class I said never draw any resonance structures that have a two plus or two minus charge okay so that's oxygen you've never seen oxygen with four bonds and that's for a good reason okay so you don't want to try this so let's cross that out all right and the other thing is is that we have the we also know that the the carbonyl is electron withdrawing so you remember from chapter 18 that carbonyl compounds bonded directly to the aromatic ring where electron withdrawing groups and so it turns out that the also the inductive effect of the carbonyl is destabilizing and we know we're used to seeing inductive effect being stabilizing the inductive effect can be destabilizing so if you look right here if this is an electron withdrawing group pulling electron density away this oxygen is positively charged right it's going to make it more positive it's pulling more electron density away and so when you have a positive charge inductive effect is destabilizing so so that's what's going on here with this one we have electrons pulling towards the the carbon eel like that which is going to make that less stable okay so for all of those reasons we see protonation on the carbonyl oxygen not the the other oxygen all right so that's going to really come back so you want to review this when we start chapter 21 and 22 so that's really going to come back in chapter 21 and 22 the other thing is that the other reactivity for carbonyls both type 1 and type 2 carbonyl compounds are acidic the hydrogen atoms on the alpha carbon of some type 1 and type 2 carbonyl compounds are acidic deprotonation gives rise to resonance stabilized analytes so let me give you an example here and I'm going to emphasize the word some you can't do this with all of them but some of them type 1 and type 2 so this is what we're talking about here so when we get to that when we get to the nomenclature podcast you'll see this that carbon that's adjacent to a carbonyl is an alpha carbon so let's label that this is an alpha carbon right there adjacent to the carbonyl base can come in remove that alpha hydrogen not used to seeing hydrogen's being removed from carbon too much except when we have in a terminal alkyne right so that might look a little unusual to you this is not super acidic but has a pKa of about 20 and if we remove that acidic hydrogen we form a resonance stabilized enolate ion so now here we can delocalized electrons onto oxygen so this is closely related to the enol that you talked we talked about back in 51b remember in the alkynes chapter we talked about enol and keto tautomer ization all right so this is really similar except now we have a deprotonated version okay but we do blue so what we call this is a resonance stabilized to enolate ion good news is is that this we're not going to really talk about this until chapter 23 so this is the topic of chapter 23 and 24 so the good news is this chapter we're going to come back to these this chapter we're basically going to talk about how carbonyl compounds electrophilic and the types of products that you get when you take carbonyl compounds and and react them with very strong nucleophiles all right but first
things first we need to we want to be able to predict reactivity and so we have all these different types of carbonyl compounds away what we want to know is which is more reactive which is less reactive and be able to explain why so acid chlorides in an hydrates are more electrophilic than aldehydes and ketones and carboxylic acids esters and amides are less reactive than aldehydes and ketones and between ketones and aldehydes aldehydes are more reactive than ketones so you definitely need to know this this order of reactivity but I also want you to understand why it is and be able to explain it if you're asked to do that alright so we want to be able to explain that because I know you guys don't want to just memorize that right wouldn't you rather understand it there's only so much room in your brain for memorization so at some point you have to if you understand it then you don't have to memorize it that gives you more room for other classes where you have to do more memorization okay so that's that's sort of the idea here alright so in the last three minutes we'll talk about this and see if we can explain this all right relative reactivities have found the relative stability of each acyl derivative the stability is dependent on two factors the inductive effects and resonance effects okay so we're going to talk about both of those there's a combination of the two so let's see let's talk about type 2 right now so groups where we have an L bonded to the carbonyl L bonded to the acyl group and so as L becomes more electronegative what's going to happen what we're doing what we're basically doing here is we're gonna look at how the charge on that carbonyl carbon is changing as we make changes in L so what happens is so L and if we're talking about inductive effect as L becomes more electronegative what's that going to do to the carbonyl carbon it's gonna make it more reactive or less reactive it's good it already has a partial positive charge it's gonna make it more positive it's gonna pull like more electron density away from the carbonyl so L pulls electron density away from the carbonyl carbon this makes carbon more positive and therefore less stable if carbonate is more positive than nucleophiles are going to be more likely to attack it right if it's more positive it's more electron deficient that makes it less stable it's going to be more reactive and so more partial positive charge on the carbonyl carbon means more electrophilic so more partial positive charge on the carbonyl carbon equals more electrophilic and more electrophilic is more reactive so that's inductive effect so inductive effect is destabilizing what about resonance effects so let's see what happens and we'll come back to aldehydes and ketones but let's see what happens when we talk about how L can donate that lone pair that it has so once again we're still looking at the partial positive partial negative so what happens as L feeds in electron density push it is up on two oxygen is that stabilizing or destabilizing we're actually adding electron density to that carbonyl aren't we so resonance effect adds electron density to the carbonyl carbon this makes carbon less positive and therefore more stable so less less partial positive charge on carbonyl carbon equals less electrophilic so we have two factors that are working in opposite directions and so what that means is we're going to have to weigh these two factors to see which is more important to be able to explain reactivity and we'll do that next time
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