Hydride Reagents and Addition to Carbonyls Part 2

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Hydride Reagents and Addition to Carbonyls Part 2
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4
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27
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CC Attribution - ShareAlike 3.0 USA:
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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: 00:24 - Alkoxide Leaving Group 01:39 - Points about Hydride Additions to Carbonyls 06:38 - LiAlH4 adds twice to Acid Chlorides 14:32 - Exactly Reducing Acid Chlorides to Aldehydes 17:59 - LiAlH4 Reduces Carboxylic Acids to Alcohols 26:43 - Converting a Carboxylic Acid to an Aldehyde 28:18 - Reducing Amides to Amines 38:33 - Stereochemistry of Carbonyl Reduction 40:21 - Chiral Reducing Agents 45:18 - Addition of Carbon Nucleophiles: Organometallic Reagents
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Ester Reaction mechanism Aluminium Chloride Quartz Chemistry Electron Carbonylgruppe Cryogenics Lithium Aluminium hydride Dipol <1,3-> Aldehyde Dyeing Dye Hydride Ketone Walking Hydrogen bond Elektronenpaar Carbon (fiber) Chemical reaction Butyl Alcohol Thylakoid Water Korken Hydrate Lone pair Ice Hydrogen Acid Functional group Chemical compound Tablet (pharmacy) Cobaltoxide Isotopenmarkierung Hope, Arkansas Catalytic converter
Biosynthesis Ester Species Reaction mechanism Carboxylate Aluminium Acetic acid Chloride Hydroxyl Atomic number Chlorine Methoxygruppe Reactivity (chemistry) Lithiumdeuterid Electron Carbonylgruppe Redox Lithium Acetaldehyde Aluminium hydride Conjugated system Aldehyde Setzen <Verfahrenstechnik> Metal Hydride Walking Hydrogen bond Carbon (fiber) Alkoxide Chemical bond Ice front Chemical reaction River source Alcohol Electronic cigarette Lone pair Water Hydrogen Acid Functional group Azo coupling Chemical compound Cobaltoxide Base (chemistry) Thermoforming
Sense District Ester Reaction mechanism Carboxylate Resonance (chemistry) Aluminium Chemistry Molecule Lithiumdeuterid Electron Carbonylgruppe Colourant Lithium Aluminium hydride Aldehyde Stickstoffatom Walking Carbon (fiber) Alkoxide Hybridisierung <Chemie> Protonation Chemical reaction Alcohol Water Lone pair Hydrogen Acid Functional group Azo coupling Etomidate Amination Chemical structure Cobaltoxide
Enantiomere Ester Reaction mechanism Stereochemistry Aluminium Wursthülle Methoxygruppe Chemistry Methylgruppe Electron Carbonylgruppe Redox Lithium Mixture Sodium borohydride Aluminium hydride Aldehyde Stickstoffatom Hydride Doppelbindung Ketone Hydrogen bond Walking Carbon (fiber) Chemical bond Chemical reaction Lone pair Hydrate Hydrogen Functional group Racemization Amination Cobaltoxide
Enantiomere Alkyne Biosynthesis Kohlenstoff-14 Recreational drug use Activity (UML) Radiation damage Haloalkane Ibuprofen Copper Wursthülle Organische Verbindungen Chlorine Methylgruppe Ether Enzyme Electron Hyperpolarisierung Benzene Mixture Metallorganische Verbindungen Atom Halogen Metal Potenz <Homöopathie> Hydride Alkylation Carbon (fiber) Chemical bond Chemical reaction Electronegativity Wine tasting descriptors Medicalization Functional group Generic drug Racemization Lithiumcarbonat Chemical compound Boron Chemical structure Substrat <Chemie> Acetophenone
Surface finishing
good afternoon we're gonna get started oh we have that on mute don't we let's do this okay hope you guys had a great weekend are there any questions before we get started somebody stole my box again I have a box that I put the let the tablet on so that I don't get a backache going like that and so I want I'm going to be doing sinking down like this because otherwise it's gonna and I think what I need to do is make one out of cardboard that nobody wants not a nice one from Container Store like I've been buying so somebody had to help themselves two times so I'm not for buying any more of them any questions no yes say that a little louder right yeah dipole doesn't work very well for acid quartz we're using that other reagent and I'm gonna be talking about that today dye ball doesn't work very well for esters either so truth of the matter all right more questions so I'm gonna go through the mechanism here I usually don't ask the mechanism for dye ball but I want to go through it so you can see how it's happening all right okay so we're talking about the mechanism for dive ball die ball allegedly on paper reduces an ester to an aldehyde allows you to stop at the aldehyde on this reaction is run at low temperature to prevent the dye ball from adding twice but it still does anyway but we're just going to pretend we don't know that so this would be minus 78 degrees so we cool things down and so because this aluminum is different than lithium aluminum hydride remember lithium aluminum hydride has four hydrides around it and a negative charge this one doesn't this has one hydride and two ice isobutyl groups and so because aluminum only has six electrons it wants to accept an electron pair and so the oxygen of the carbonyl is going to attack it and it's going to look like this after that so now the oxygen is going to have a positive charge and a lone pair we've got our aluminum here with two isobutyl groups again I will not be testing you on the dive ball mechanism and in fact I'm going to give you an alternative to this that works a little bit better so here's our ester so now we've got the aluminum with four groups around it and let's label the previous step here so this is di dye ball H so that either H is referring to this hydrogen what's going to be transferred and I should have that all caps but you can write it like that also Lewis acid accepts an electron pair from oxygen and that's what then what's going to happen is an intramolecular hydrated ition that's white and this is all this is gonna this throw students off a little bit so that's where if we're not going to test on this one let's see what we get after that we go from sp2 carbon to sp3 so a tetrahedral intermediate so it looks like that and I'm going to put brackets around this because this is stable at minus 78 and so basically once all of the esters converted into that in a stable intermediate that's stable at minus 78 then you add we do a second step where we add we protonate so we add water and then we get another comp compound here and these guys are also not very stable so this is what we call a hemiacetal we're gonna learn about those in chapter 21 so hemiacetal unstable converts to aldehyde so it's kind of like the emails that we saw in chapter 11 where the emails are not stable and so they convert into the ketone remember that from chapter 11 this is like that this is a hemiacetal and it's also unstable it's going to convert to the aldehyde so I'm going to put a reversible arrow long arrow here this is a reversible error short arrow back and we're gonna get the aldehyde we will actually learn this mechanism in chapter 21 so when we get back to chapter 21 we'll talk about this mechanism but this is one of the reasons why I don't ask this mechanism chapter 21 chemistry for this last part here the hemiacetal going into an aldehyde all right so that reaction doesn't work very well because this stable intermediate that's supposed to be stable at minus 78 is not very stable and so another way to do this and especially if you don't want to memorize the eyeball itself is that you can Musa lithium aluminum hydride reduce the ester all the way down to an alcohol we showed that mechanism already and then PCC will take you to the aldehyde so just as easy to turn this into two steps rather than one questions so far anybody all right looking Luna no hydrate also adds twice to acid chlorides that's scrolling not correctly that should be on the next page it also adds twice to acid cards to give alcohols so let's go through that mechanism we're gonna follow it each step of the way and then we're gonna make decisions based on what we see what the intermediates look like all right so we have lithium oh no hydride so aluminum with four hydrogen's around it and a negative charge and the electrons are going to come from one of those aluminum hydrogen bonds it doesn't matter which one the pair of electrons the lumen of hydrogen bond is going to break and the pair of electrons are going to go on to carbon and then we're going to kick electrons up onto oxygen so we've already seen that a number of times we've got a tetrahedral intermediate
that has a leaving group when we did esters we had a methoxy leaving group that was not as good chloride ions a fantastic leaving group okay so this is gonna come off very very quickly electrons are gonna come from by one of the lone pairs on oxygen so if you haven't happy before I'm pretty strict on mechanisms I want a lone pairs on all reacting atoms and arrows should come from lone pairs or a bond and so since I'm pushing electrons on to chlorine we want the lone pairs on chlorine we also want the lone pairs on oxygen all right so what's our product there after that step acetaldehyde now what's more reactive and aldehyde or an acid chloride acid chloride we should be able to stop there right technically the product is less reactive than what we started with however luteum aluminum hydride is just too powerful to stop it will add again you cannot stop after one addition okay so let's write that down aldehydes are less reactive than acid chlorides should be able to stop here but you can't and the reason you can't is that lithium aluminum hydride it's just too powerful to stop so why lithium aluminum hydride too strong okay so it's not going to stop there what we're gonna do is we're gonna add lithium aluminum hydride again and so we're gonna find is we're gonna end up getting the same product that we got with an ester so acid chlorides with lithium aluminum hydride gives the same products as esters do which is an alcohol so no Santino's I'm throwing a lone pairs on oxygen because I'm gonna be doing arrow pushing involving oxygen I'm going to attack the carbonyl carbon kick electrons up onto oxygen so if we've turned that type one carbon eel into a type we turn that type two carbonyl into a type one so it's going to add again alright so are we or are we out of leaving groups here definitely out of leaving groups okay so it's going to stop here because there's no leaving groups so it will wait a wait patiently until you add water in a second step and when you do that you get alcohol so same exact alcohol that you got with the Esther so no difference here I got that hydrogen let's move that hydrogen over a little bit okay if we you want to just if you want to just add one hydride to go from an acid chloride to an aldehyde you're going to have to use a different reagent so there's a special reagent that's just for that lithium tri tert-butyl aluminum hydride it's use exclusively to reduce acid chlorides to aldehydes so here's what it looks like we already saw I already actually showed this that towards the beginning of the chapter and so we're going to do is this is just like lithium aluminum hydride except it has three tert-butoxide roots attached that way tones down the reactivity here we have a negative charge on aluminum and we're going to do the same thing arrows going to come from the aluminum hydrogen bond we're going to attack the carbonyl carbon kick electrons up onto oxygen okay that gives us the acid chloride the fact that we only have one hydride on the aluminum is going to help us out the fact that we have the Turkey Toxie groups is also going to help to help us out to prevent this reaction from going again so we have our acid chloride we have our tetrahedral intermediate that has a leaving group so the leaving group is going to leave so notice I'm throwing electrons on the chlorine electrons on oxygen are going to come down and we're going to kick off the chlorine as chloride ion all right and that enable us they enables us to stop at the aldehyde so stops here and so still aldehyde is is Lexx electrophilic oh my gosh what am I doing here aldehyde less electrophilic than an acid chloride see how that reactivity is helping us out here less electrophilic than an acid chloride and we have a mellower reagent okay so it's not as powerful and so the luteum try turkey talks the aluminum hydride li al h with and just have three turkey Toxie groups here is mild enough to stop now if that's not an 8 every agent that you want to remember for synthesis and I understand it's going to be harder to remember that one you can also do a similar you can reduce the acid chloride with lithium aluminum hydride all the way down to an alcohol then you can use PCC so alternative to remembering this reagent is to take the acid chloride use lithium aluminum hydride followed by water to get the alcohol and then you can use PCC to go to the aldehydes so maybe that's a little easier for you to remember alright questions anybody yes well what's water used for in waters the water is used to for a couple different things if you look up here we've got
usually when you use lithium aluminum hydride you use a little bit of excess so we want to protonate all the excess lithium aluminum hydride we want to put that so here it's protonating the alkoxide not by much though we're just we're actually getting rid of the excess aluminum and then we're going to put in a set funnel and add acid to it to make sure that all of the alcohol is all of the alkoxide is protonated okay so whenever we use these metals like this we always have water we always add water all right more questions anybody yes yes well now and we didn't really show that but now that lithium aluminum hydride that's for hydride spur aluminum and it actually can transfer more than one so even if you use one equivalent which we assume if we just don't write anything in front of it you still have plenty of it around to add twice right because there's actually four of them it gets a lot more complicated showing the other forms of lithium or hydride but we have plenty of it so you don't have to worry about equivalents for that one okay all right lithium aluminum hydride reserve reared and reduced this carboxylic acids to alcohol so we're now going to be doing the two most difficult mechanisms in this chapter lithium aluminum hydride plus an al plus a carboxylic acid and lithium aluminum hydride plus an damnit and I will put one of the two of those mechanisms on midterm one and these are the hardest mechanism I would say probably the hardest mechanisms all year I would think maybe once you see it you won't think it's that bad but you know I think it is you can tell me if I'm completely wrong you can tell me at the end of the class and say you know you were wrong about those little thing a little hydride mechanism this one's much harder okay so I'm certainly open to that so let's see what this looks like so the key thing to remember here is that lithium aluminum hydride is a hydride source it's an extremely strong base so if we mix an extremely strong base with the carboxylic acid what's the very first thing that's going to happen it's going to deprotonate okay most students forget about that so you know in Chapter two we say Oh carboxylic acids are acidic unit you think to yourself oh yeah of course they're called carboxylic acids and then in chapter 19 we say oh yeah by the way carboxylic acids are acidic in your high already know that their carboxylic acid they're acidic but probably half the class will forget to deprotonate that oxygen when they see this and when they see this mechanism on the test so you you got to always remind yourself yeah let's and let's not get so caught up with what's happening with the carbonyl that we forget about that acidic hydrogen on oxygen it's just a really easy thing to forget as somebody will see when you get midterm two back okay so extremely strong base we're going to deprotonate first let's see what that looks like all right so I'm going to do arrow pushing involving this hydroxyl group here so I'm putting lone pairs on the hydroxyl I don't need to put lone pairs on the carbonyl because this step is not going to involve the carbonyl so that's sort of the way that works and so the arrow is going to come from one of the aluminum hydrogen bonds I'm going to grab this hydrogen I'm going to break the hydrogen oxygen bond so that's just an acid-base arrow pushing okay what's that look like now conjugate base of acetic acid right carboxylate ion so we have that and then let's we usually ignore these aluminum species but we also have this left over once we tranche once we transfer that heíd right now aluminum only has three bonds to hydrogen so what's going to happen it doesn't have an octet so what's it's looking for lone pairs right okay so the lone pairs on and the negatively charged oxygen are going to come and attack the aluminum so first things first these these lewis acid-base reactions the bronsted acid base reactions are faster here all right so that's a little that's a little bit whoa what did I what - what did I just do that's a little bit strange looking right so what I want you to realize about this is that this group right here is going to behave like a methoxy group in all the reactions in the rest of this mechanism that's going to behave like a methoxy group so just think of it as a methoxy group if that's a methoxy group then what's the functional group here it's if I mean if this going to behave like a methoxy group this whole compound is going to behave like an ester right so from here on out through the rest of this mechanism this is going to look exactly like the lithium hydride attacking an ester except the only thing is of course that this is not really a methoxy group but it's going to behave like one so what that means is that the lithium aluminum hydride is going to attack again and I'm going to be attacking the carbonyl so notice I'm throwing lone pairs on the carbonyl I'm going to have the arrow come from any one of these four lithium aluminum hydrogen aluminum hydrogen bonds lithium aluminum hydride aluminum hydrogen bonds there okay so behaving like an ester so if that group is behaving like a methoxy group then what's the next thing that's gonna happen we're gonna we're gonna keep this off as a leaving group aren't we so just exactly like we did with an ester we're gonna kick this whole group off and now things are looking very familiar now we have an aldehyde we know that aldehydes are more electrophilic than carboxylic acids right so we will not be able to stop here so aldehyde more electrophilic then and then a carboxylic acid so you can't stop here all right so then again this is going to
look just like the ester now it looks exactly like the ester here so look people lunar hydras going to add again so since I'm attacking the carbonyl throwing lone pairs on the carbonyl oxygen we're going to attack the carbonyl carbon kick electrons up onto oxygen we'll take a look at what happens here we've already seen this step a couple times at least three times do are we out of leaving groups we're out of leaving groups okay so tetrahedral intermediate has no leaving group so this this molecule is going to wait around patiently for all the rest of the molecules to react then it's going to wait for you to add water in a second step so when you add water in a second step we're just gonna protonate that's going to get rid of all of the that's going to take care of all the excess aluminum in here and then of course we're gonna put this in a set final and we're gonna add acid to protonate this alkoxide completely questions anybody on that mechanism okay so that's difficult mechanism number one and you can certainly if you will if you can't go directly to a car buck from a carboxylic acid to an amide so it's gonna have to be two steps and so let me give you two ways to do this if we want to take a carboxylic acid and convert it into an aldehyde we're gonna have to do a different way so number one reduce all the way down to an alcohol then oxidize with PCC that's always an option so lithium aluminum hydride we just showed the mechanism here lithium hydride followed by water again sometimes the book uses water sometimes they use acid we're not we've decided we're not going to make an issue about that okay we're just I'm going to accept water or acid here that gives us the alcohol and then we can use PCC to go to the aldehyde alternatively I'm you can convert the carboxylic acid to an ester then used eyeball and so what that would look like is we have the carboxylic acid and using chapter 22 chemistry which we don't know yet this is for you when you go back and study this when we're already done chapter 22 it will make more sense we can convert that carboxylic acid into an ester and then we can used eyeball that will also give us the aldehyde questions anybody on lithium aluminum hydride plus a carboxylic acid okay Luthi one hydrates reduces Hamid's to amines okay difficult mechanism number two now we have a similar situation that we had with the carboxylic acid the hydrogen that's bonded to nitrogen is acidic the first thing remember an acid-base reaction is extremely fast the first thing that's going to happen is that nitrogen is going to be deprotonated so this has a lot of similarities to the carboxylic acid one don't forget the acidic hydrogen on nitrogen so that acid-base reaction to remove one of those two protons is going to be faster than lithium aluminum hydride attacking the carbonyl alright so let's do that we'll just we'll just deprotonate this nitrogen this hydrogen right here we're going to take that and we're gonna push electrons on to nitrogen now in the book in your book they take this they deprotonate that nitrogen and they push those electrons all the way up onto oxygen you can also do it that way okay but I want you to kind of look at what's happening here rather than blindly doing that I want you to think about what happens after we do protonate that nitrogen after we do protonate that nitrogen we have a negative charge on nitrogen and we can certainly do localize those electrons on nitrogen we can push those electrons on to the carbonyl oxygen right so we can go like this boom right here then go all the way up onto oxygen we know nitrogen is really basic it's especially basic when it's deprotonated so that it's really going to want to do that all right so now that we've drawn the second resonance structure which other one of those resident structures is the best first or second second one's the best we'd rather have the negative charge on oxygen right so this is the best resonance structure that means that this resonance structure is going to contribute to the most of the hybrid that means that most of the negative charge in this molecule and the hybrid is going to be on oxygen so what the oxygen is going to do is it's going to attack the alh 3 that we have left over after the first step so it's going to go like that so rather than the nitrogen attacking the alh 3 it's the oxygen that's going to attach the attack the alh 3 so we have olh three again so we have a very strange-looking molecule that we don't have a name for with the functional group is but we have two parts to it and so let's let me just point out the two parts here we already know that this group behaves like a methoxy right the other group that we have here I'll do it in a different color here this carbon nitrogen double
bond behaves like a carbonyl hey it's it's less electrophilic than a carbonyl right because nitrogen's less electronegative than oxygen but it is electrophilic and we have we happen to have an extremely powerful nucleophile here so the nucleophile the lucila Hydra doesn't care if that's an oxygen or nitrogen it's going to attack that just like it would as if it was a carbonyl we're gonna learn about on this functional group in chapter 21 alright so so that means then where we're gonna put it I'll put it up here you could find a good spot on your page where however you've drawn this lithium aluminum hydride is going to add again so the first thing it did was it deprotonated the second thing it does is it's going to attack the carbon nitrogen double bond because again that's like a carbonyl so it's going to go here and then we're going to kick electrons up on to nitrogen just like that so we're gonna have tetrahedral intermediate the nitrogen has to note lone pairs on a negative charge and then we have this o al a ch3 group that's going to behave like a methoxy group negative charge on aluminum and so if the nitrogen is behaving like an oxygen then what's going to happen if that was an oxygen and it gives will be charged oxygen we do this right we go boom like that we'd have the we have the electrons go down we'd kick off our leaving group that's what we would do if we had an ester this is going to behave like an ester like it like a tetrahedral intermediate that you get from an ester so that's what happens whoops want to do that it's no longer a tetrahedral intermediate is it
once we do that we have something that looks like this and that is a functional group that we're going to be learning about in chapter 21 that is an amine so that will be chapter 21 when we learned about amines so the amine is electrophilic like a carbonyl not as electrophilic as a carbonyl but electrophilic nonetheless so that's gonna behave like an aldehyde isn't it it's that nitrogen is behaving like an oxygen it's gonna behave like an aldehyde so what that means is that the losing one hydride is going to attack again if we had an aldehyde the lithium woman hydrate could not stop itself from attacking an aldehyde and the same with an amine all right so I'm arrow comes from one of these aluminum hydrogen bonds we're going to attack the carbon that's doubly bonded to nitrogen you fix that a little bit we're missing my arrow here okay that looks a little better and then we're going to kick electrons up on the nitrogen rather than oxygen in this case after we do that we get another tetrahedral intermediate with two hydrogens bonded and a negatively charged nitrogen do we have any leaving groups there are no leaving groups hydride can't be a leaving group the methyl anion can't be a leaving group and so it's going to stop here no leaving group stops here and then you're going to add water and in this second step and our product is an amine so this is the way that we would convert an damid to an amine and that's going to be a really useful reaction we're going to use that a lot in chapter 25 and we'll also use it in this chapter questions on that mechanism so do you think that's your most difficult mechanism so far yeah exactly it would if it left it would be in h2 - wouldn't it be yeah so we don't want to do that all right stereochemistry carbonyl reduction all we were having so much fun not doing stereochemistry now we have to think about stereochemistry again stereochemistry of carbondale reduction follows the same principles we have previously learned of karl reagents react to form a new stereocenter the result will be a racemic mixture so it's really the same as what we've been talking about so if you did a sodium borohydride action of this particular ketone you are going to get a racemic mixture because we are forming a new stereocenter and unless you have a chiral influence on this in this reaction you will get a pair of enantiomers now there are ways to reduce ketones asymmetrically where you just form one an answer but that uses a chiral reagent and we're actually going to be doing that in my lab this week so I'm pretty excited about that most of the time we're not worrying about stereochemistry when we do carbonyl chemistry but definitely we want to keep
this in mind so racemic mixture and that's going to be and that's because we have a new stereo Center we started with a card well reagents and we have a new stereo Center all right so there is a chiral reducing agent that they talked about in your book this is what we're going to be using its called CBS reagent feel free to use the abbreviation but if you write NBC or CNN on the test you won't get it right okay I've seen that before all right so if we want to just get one in answer row we have to use the power e agent so these are the two chiral reagents we're going to talk about there's more these are not the only ones but these are the ones we're going to talk about and so there's scbs reagent and our CVS reagent and so if you have this is a acetophenone if you use a scbs reagent you get about 98 to 99 percent of a single enantiomer and then you'll have 1% of the other but it's actually very nancial selective all right so you a CVS reagent you also use this also uses boron so bh3 and so let's add pH three to both of these if use the are CVS reagent you can get the other enantiomer now I don't want you to get the idea that scbs reagent always gives you the S enantiomer and are always gives you the R an answer where that's not the case but they will give you a single enantiomer yeah usually like I said depends on this on the substrate that you use but usually really in the high 90 90 s of a single enantiomer alright questions anybody yes why it's say that one more time you get a single enantiomer rather than a racemic mixture yeah exactly right why do we want to make a single enantiomer if you think about all the enzymes in your body they all respond to a single enantiomer so if you can make a drug that has a single enantiomer rather than a racemic mixture it's going to be much more effective and so if you you know a lot of the drugs that we take like ibuprofen are a racemic mixture because it's very expensive to make single enantiomers and for ibuprofen only one enantiomer is effective in your body the other one is just excreted but there are other medications where the the non active enantiomer causes damage in your body so it's really important to be able to do to make enantiomeric ly pure compounds alright so that's the long answer to your simple question yes question it's going to know it that's not always the case it depends on remember priorities of the groups so yeah like for example if I put a chlorine on this methyl right here see where I'm pointing I did I left my laser printer in the car then that's going to have a different priority than the benzene ring so it's going to be different yeah so it's it's not always the case the way that they have you draw it in the book is that if you draw the benzene ring on the left then the hydride is coming in from the top with s and it's coming in from the bottom with r okay and that's the way to draw the right product all right so we're done with hydride reagents we're going to start talking about our gain metallic reagents now and what they can do very powerful reagents in organic synthesis because organometallic reagents make new carbon-carbon bonds and anytime you can make new carbon-carbon bonds you can build up carbon skeletons so if you think back to 51 a what's the carbon-carbon bond forming reaction that we used a lot which chapter was that from remember that we used it in a lot of synthesis you remember chapter 11 reamer deprotonated terminal alkyne and then you treat it with an alkyl halide that's a carbon-carbon bond we use that a lot green then so organometallic reagents we're also going to use a lot
to build up carbon skeletons question yep are they backwards so what I thought and that's the point on that's why I chose this example the RCBS does not always give you our product the scbs doesn't always give you the s product it depends on the structure of the compound that you're doing okay so that's why they're not matching and they're not intended to match okay all right okay so we're ganna metallic regions alcohols ethers alkyl halides all contain a carbon atom that's bonded to a more electronegative atom that's what we're normally used to seeing so if you think about all the alkyl halides we talked about we've got carbon at two point five electronegativity see an electronegativity and the halogens greater than two point five so what we're normally used to seeing with polarity is electrons flowing towards the group bonded to carbon and because of that that means that the carbons partial positive and this group is partial negative right that's what we've seen over and over again through 51 a and 51 B so on what we have here is electrophilic carbon and that's the most common scenario that we've seen electrophilic carbon reacts with electron rich nucleophiles all right so here's our y- is our generic electron rich nucleophile and so the why attacks the carbon we kick off X as a leaving group and we get ch3 ch2 y plus our leaving group X minus so that was chapter 7 alright so that's what we're used to seeing but ya know metallic reagents are different we're actually switching the polarity so that we have electron rich carbon instead and so how we do that is that we have electronegativity of carbon still 2.5 but if we attach that to a metal with electronegativity less than 2.5 then we've we've done we've switched the polarity so now the electrons are flowing towards carbon which are not used to seeing and so now carbon is partial negative and the metal is partial positive okay so now we have electron rich carbon if we can make new tweak and so we can react that with electron poor electrophiles and so now what we're going to get is ch3 ch2 e so now we're bonded to an electrophile rather than a nucleophile and then we get our metal on the side here so this is electron rich carbon so I like to enrich carbon also known as nucleophilic carbon reacts with electron for nucleophiles so this allows us to do many more reactions by switching the polarity of that bond alright so let's take a look on the next page there are a lot of organometallic reagents we're going to be talking about only three these are the only three carbon bond is a lithium carbon bonded to magnesium and carbon bonded to copper and that's time so
we'll finish well we'll talk about this on Wednesday you
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