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Lecture 03. Reactions of Organometallic Reagents.

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Automatisierte Medienanalyse

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In the morning well I am I am
really happy today still so this is the 1st time that I've used electronic homework 1 of the classes I it's I
was so happy when I look this morning at 9 o'clock and found virtually everybody had engaged with the homework assignments and so
much of learning organic chemistry is actively working problems and actively trying to to understand that I was really really excited to see people were coming along with me on this process of warnings and it makes me very very happy so today
we're going to continue our discussion of Chapter 20 and I'd like to introduce a again a metallic reagents and talk about their reactions with carbon yield
compounds and their reactions in general and then we're going to talk about reactions of members of the carboxyl against his family with hydride nucleophile and with Our O'Donnell metallic reagents and if there's time will conclude by talking
about the use of these reagents and these reactions in synthesis so what we were talking last time we talked about hydride reagents with key tones and
held up signs and we said sort of generically
if we have some Keatonâ Al the Hidenao all right generically just showing large groups
that could be could be aromatic they could be hydrogen so generically as he told Alden hide and we it's invasion its reaction with some hydride nucleophile there remember when I'm writing something like this
age minus in quotes of course there's no reagent that is itself a hydride nucleophile but these are things like lithium aluminum
hydride and sodium bore a hydride that serve as sources of hydride and then if we carry out a work with 8 we assassinated age 3 old class or in some cases you can use water and again I'll put this in quotes because you can't go and buy a
bottle of each Rio plus you could take sulfuric
acid and poured into water to make Hydro Neumeier uninvited sulfate ions you could take HCL in water and make H 3 0 plus and chloride ions and so you go to the stockroom and ask for 1 of those when you do that you get a reduction of all the the key tone were Al the height of impregnation like so to give an alcohol now what I'd like to to do at this point is to consider an analogous reaction again written at this point as an abstraction so again we will take our cue tone or
the and will imagine instead of adding our
hypothetical hydride Anaheim wouldn't add something that I'll say his or her mind With the loans pair of electrons meaning of carbon based an
Ireland will talk more about it not necessarily something you can get as a free
and and certainly certainly not something that you could put in a bottle on its own it would be part of an organic metallic reagent but again right now we're getting our view from 30 thousand feet and again if a your marriage some type of 8 Rios worked up with age the Rio plus now instead of adding in hydride fewer carbon mealtime contained we've added in an hour group news of Prime's and double crimes and so forth it's just my way of representing that their various groups different were the same
anyway but that again in the view from 30 thousand feet the
profound thing about this reaction as I've written it is that we formed a carbon-carbon bond in so much of organic chemistry both the practical aspects of synthesizing useful molecules and the real intellectual beauty
of the discipline is the fact that we can create greater degrees of
complexity valuable complexity medicines analogs of natural products natural products that are too scarce to get otherwise probes to probe reactions and pro biology we can do all of this group chemical system which we take a little molecules that might be able to be
purchased and build them up into big and complex and useful molecules that can cure cancer or fight disease were teach us things so now we come down to the issue of what is our AA-minus what is our source of our carbon nucleophile in the
1st really really valuable ,comma nuclear files that were developed green yard reagents developed by Victor Green yards he received the Nobel Prize in 1912 in chemistry for this and the basic idea is that you take some halide and bromide
chloride on iodide fluoride is sort of the oddball among theologians and if you go down the Periodic Table to ascertain it's not of a stable with radioactive organic chemist would never never work with it you you can't really
isolated anyway if if we take an alkyl halide such as Beutel bromide and we treated with magnesium metal if you've done 1 of these reactions in the laboratory you'll have seen your magnesium metal is kind of bright and shiny and white waited comes turnings that had been worked off a big block of magnesium with a wave your putt there with
your local here lied in a solvent the solvent will be an ether solvents either the 3rd ths
typically sometimes other ethers and used tear Japan's test high-growth year-round it's a cycling there so it's anti-terror with with a
five-member during and it has long cares it's kind of like Diana with its ears pinned back
In either of these worked well the the result is that you get a green yard reagent I started with the rule bromide here and saw all right the green yard reagent From bugle bromide we call this view magnesium bromides but she In the
ether solvents coordinates to the magnesium the magnesium doesn't have a complete architect here we have only for electrons around the 2 from the alkyl group and 2 from the bromide and so the ether
solvent the dire Felice Arteta hydro fuel ran will coordinate the magnesium and helped give it the feeling of having a complete tech anyway as I said the broader category of this is a green yard reagent
and you can make these from anything from promo benzene to Alkol bromides to methyl iodide and so
this technical a typically 1 makes a green yard reagent as part of a synthetic process there actually stable reagents you can put them in a bottle you can buy them but in the laboratory because they react with air because they react with moisture you would typically
go ahead and immediately add a carbonyl compounds so let me show you a typical synthetic carbon-carbon bond
forming sequence that 1 might do in the laboratory so we might take our fuel bromide In treated 1st with magnesium in the care of you'll often see people write a slash in equation often that slashes a way of saying the solvent is below the /slash therefore
just writing a simple line of equation we
might put a solvent field below the arrow then let's Eric carbonyl compounds and for the purposes of teaching for the purposes of this
example all take acetone as our carbon you'll compound and finally let's do
indicate when work out and I'll give us all Jews and answered here let's say a curious 8 Cl as the acid I would choose and the product that this reaction now is the carbon-carbon bond forming out actress and adults with a new carbon-carbon bond if you wanted to name the compound we've now form the 6 carbon chain so it's to methyl 2 hacks and all as a proper so this is a very powerful because now we've taken some
small compounds that you can buy and we've made a more complex molecule that you might not be able to buy many molecules with this type of structure these types of structures like alcohols with long chains on them are Insect Fair amounts for example so some of these types of synthetic products are used to
make tracks for insects like Japanese beetles were that will be fair will lower the inspected the trapped and then all falling in guide alright so I wanna talk a little bit about the the properties of green yard reagents and O'Donnell metallic reagents in general so settles
medals of course are
much more electoral positive then carbon so any
bond between a metal and carbon is either going to be a polar covalent bond or an ionic bonds if you want an index value or tennis like the keeper of Elektra negativity values in their head it's a useful way of assessing the degree of polarity of upon magnesium has an elector negativity of 1 . 3 carbon
about 2 . 5 at 2 . 5 5 so you can think of the bond between magnesium and carbon as the polar
covalent bonds in other words you can think of this as having developed a minus a partial negative charge carbon In a partial positive charge on
oxygen on magnesium
sometimes if you're writing a mechanism and you want to be quick about it you could say Well all right and nonbonded resonance structure even tho I know it's primarily
a covalent bond that can write 1998 bond
resonance structure so we can think of it is this maybe I'll put this in quotes here just to remind us this is sort of our sort of thinking and so if I'm thinking about this from a mechanistic point of view 1 way we could think about this I'll take our acetone and our Riyadh reagent written generically 1 way we can think about this is that our organic metallic reagents serves as a nucleophile and of course we draw Walker a barrel mechanism we help think about the flow of electrons in bond funds by starting an arrow at the long period at the available electrons either as a lone pair arena bonds and then moving to the thing that once a electoral files in other words from the nuclear file to the electoral filed as we did in thinking about hydride mechanisms we can't go ahead and now have 5 pairs of electrons around this carbon atoms so concurrently as the nucleophile moves in electrons move up on oxygen and
so we continue our glamor if you will
of writing our Kerberos mechanism now writing a product in which we have a negative charge and if I want to be good then chemists are good we love to throw away things that aren't necessary in our thinking that if I want to be good ol brought the magnesium counter there we can also think of this just as we did with lithium aluminum hydride maybe a little more correctly you're certainly alone more sophisticated place we can think of our covalent bond and keep in the back of our mind that it's a polar covalent bonds and write occurred there mechanism in which would simply go ahead and now take the electrons from Marathon move it in like so and again Chinatown to the self-same products so these are good ways of thinking sound ways of thinking about the mechanism of the reaction so 1
thing to keep in mind about green yard
reagents and indeed about most organic metallic reagents particularly ones in which there is a large difference in Electra negativity between the carbon and the metal is better than no
metallic reagents like when you're free agents in
general acts as very strong bases we can think about basis today in terms of the PKA of the conjugate and I'm so if you have Beutel magnesium bromide to conjugated and I corresponds to an al-Khaimah know the words we're in time to get acid and you have a CSP 3 carbon is bound to a hydrogen the PTA for such a hydrogen is about 50 cents about at the very end of the basis of
the scale that's about is as basic as you can get for Cobb and I have a few have an AL team but now you
have a S 2 carbon down to a hydrogen the electrons are tell the more tightly on in this type of type of structure the PKK now news about 40 to 1 way of thinking of this is since the electrons are a little more stabilized held more tightly in orbital that has more arrests characterized as feed too has 33 per cent as character as 3 has 25 per cent as character as you hold
electrons more tightly the CH
bond is more willing to give up age plus and give you a car ban I'm someone else came as a little bit more acidic then in allocating these are all compounds I called very weak acids and I usually put quotes around the acid because you would not get any evidence of acidity from the compound say dissolving it in water and testing it with a pH meter and yet in a Lewis acid Lewis base reaction you
can think of and keen say as a proton donor under certain circumstances now by the time you get
to an alkaline now you've got 50 per cent character in your C H 5 and now these are reasonable lady acidic there still very weak acids the PKK is only 25 that's really really really weak still it's not even like water which you think about is an acid forming hydroxide and I'm it's still a very
weak acid or alcohol forming an is giving up a proton informing them and Alcott's side and and yet PKN it is about
25 also you and implication of that and just just a moment when we start to talk a little more about Alcan's the point that this comes back to what I was saying before her about carbon about green yard reagents being very reactive toward water the green yacht reagent acts as a base with water and so if you expose a graveyard reagent like magnesium bromide to water the water acts like the lowest acts like a bronze answered and you get butane and Bromo magnesium hydroxide and mix Mix salt here so this is a list of Bronstad acid Bronstad days reaction if you think
about it we have water acting as
a had acid on the left have side of the equation we have our al-Khaimah as an asset on the right side of the equation and because the PKA differences so humongous the PKK water is 15 . 7 the PKK butane is about 50 I don't even bother to write an equilibrium react arrow the equilibrium constant is the 30 forthright it's tend to the difference in PKA that reaction life so far to the right that there's just no component to the
left on it and it just as much Cho whether it's with
water urine alcohol in so just by comparison for managing for a moment I wrote let's let me pick a particular alcohol will pick ethanol as an alcohol and so nailed we would get butane and really thought the magnesium bromide of course this would be the same with the carboxyl Aghazadeh just about anything that you would normally think about as even mildly acidic alright well going
.period reagents are 1 of a broader family of Board of organic metallic reagents another family member of the family that reacted very very similarly Our Donna lithium reagents and so we rode green yard reagents sort of generic layers of RMG acts that would be a generic way of writing of green yard reagent can writer again lithium reagents generically as online organic lithium reagents formed by reacting alkyl or Harrell halides again were talking iodide bromides chloride with lithium metal I write a balanced equation safer Bromo benzene and lithium takes to lift the arms and that makes sense if you think about it right were carrying out of 2 electron process here and lithium has 1 electrons to bring magnesium has 2 electrons and solid balanced equation the comes that we get gentle lithium class lithium bromide and again organic chemists are awfully awfully bad about writing products of reactions put the lithium bromide unit in parentheses because I might not bring right it so typically a writing this synthetic reaction and I imagine generating an hour down lithium compound and reacting it with an organic compound or give you an example of what I might write so I might take global Benzinger might take Rabin's unify wanted treat it with lithium metal now or galaxy every reagents can be generated in Anita conservator coordinate but they also form clusters and so they actually can be generated in other solvents including hydrocarbons and I'm just going to skip the solvent here because it's much less important than integrin yard reaction let's say as my partners since I gave you with long before I'll take an elder applied the elder hide I've chosen is clear about the high that's the trivial name or 2 to dine Mathilde now would be the idea packed name and again I'll imagine doing some type of a police work of others like eight-story yelled last year to indicate
I haven't specified the acid it could be a quiz states CLE could be a quiz sulfuric acid 1 that I personally like to use in my own
laboratory is a Prius ammonium chloride which is a very mild acid and very good for work cups of reactions like this anyway after a workout the product now has a new carbon-carbon bond like so and of course because we've generated hysteria said the molecule we generated as a mixture of 2 Indian tumors we've generated 2 different tumors in equal amounts which generated the ransom worried
in part in part because you're textbook mentions various different Oregon a metallic reagents at this point I wanna
follow along in part because I want to remind you of what I think are really really useful line items and part because I wanted tie into this concept of PKA I'd like to at this point I talk about a satellite of Fireman's Messier have a question the and I think would be the last you might think you would have no way make light of the ovation what's that the question was why doesn't the magnesium bond to be overweight she doesn't well there's no way Oh you're saying in that reaction because the ethanol has now given up its Proton to react with the Butte Bureau parts so the Proton has come off of the ethanol onto the carbon of the butane leaving an NFL oxide an iron which combines with the MG br plus component and it did so we had in the case of ethanol we had the TRO MGB are in the case of water we had H 0 mg the DR so we had a very analogous reaction another question I great questions in that 2nd equation are we supposed to have to lithium so this is very typical of how organic chemist will writer reaction so typically you would see that 1 might not particularly as you became more used to writing reactions it might be implicit but indeed you would have to meet with the INS so you can easily envision writing lithium parenthesis To equivalent served for 2 lithium and again this is very much part of the shorthand of writing organic reactions particularly when focused on synthesis good
questions are great question whether Donald lithium reagents not be created if you had only 1 lithium will now unimagined you would what would happen with the you'd have 1 Buell the other 1 Buell bromide 1 mole of lithium you'd get half a mobile I hope you lithium now here is
where the fun comes in and like that said it at a low temperature and used it quickly I would have a reaction of 1 mole of you with the of one-half mold of duel with you but if I let it sit tried to put it in a bottle and I now had better again or lithium reagents setting for a long time with more Buell bromide I would get the 2 elimination of war because the region is strongly basic to give bewteen and butane war I would end up having s into displacement to give octane were evolved great questions so yes I would definitely used to perform alright well at this point I want to talk about the satellite and and certify all along with the textbook but also because the the manic glee in the city so as I said Assemblyman Valentines in general are especially acidic while they're still very very weak acids PKA of about 25 they're strong enough acid said very very strong bases can pull off the proton so for example if I treat an alkaline with soda bed I get the sodium a satellite and no sorry and so little more electric positive there the car but then lithium lithium has an Electra negativity of 1 sodium of . 9 by the point you get to again 0 sodium reagents they're pretty pretty ironic and the violence so I generally think of these as I and they are great candidates to a N H is sold bed and affirmed
that balance my equation and as I said organic chemists are usually very bad about this ammonia thank you thanks very much ammonia is the other by-products of reaction and now we see yourselves very much in the situation of a Bronstad acid
Bronstad based reaction so we have PTA of about 25 and the content of about 30 he ain't and so a difference of PKA means that equation lies way way way to the right tend to the 13th equilibrium constant through their about basic whether 1 mole of sodium analyzed 1 mole of an al-Qaida and I get essentially fall satellite and an outright right a balanced equation all right a synthetic equation year in which I say take pro plying I treated with soda in N H 2 which you can make by dissolving sodium metal in ammonia with a little bit of a liar and it reacts to give sodium and and for the heck of it again I'm just trying to give us a range of carbonyl compounds for the heck of it I'll take to Butte known and then since I mentioned that I like Gateway as ammonium chloride as a source of acid were worked out I'll just demonstrating what I would do in my own laboratory which is to use a police ammonium chloride and the product of this reaction is this it is the alkaline with the alcohol this is of course precisely In other words you textbook points out very nicely that you're going to add new nucleophile from both the front face and the back face of the carbon and so we have won an anti-American which the awaits is pointing back and the outline is pointing out we have another inning anti-American which it's entered from the back face and now the all-ages pointing out and the alltime is in the back and we will get equal amounts of these both of the and of the US although this chapter is focusing primarily on carbonyl compounds it's also beginning to introduce ideas of organic synthesis and carbon-carbon bond forming reactions and so your chapter reminds you of that you've already seen certain carbon electrify
also for example you've already seen upon oxides so there are lots and lots of types of Elektra files you can generate Europe compounds with that you can can react you're a satellites and other carbon nuclear files with and I'll just point out 1 example here that brings out a couple of additional police cell Bureau lithium is commercially available to comment source of a highly basic organic metallic reagent that can be used not only as a
nucleophile but also as a very strong base and so euro lithium it is a great reagents for pulling off moderately acidic protons for example protons from outlines and also protons former means like Daiei sepulchral Amin which you'll see later anyway you lithium would react with our alkaline remember a peak the Alpine is about 25 PKE of future of butane is about 50 and so would react against in a acid-base reaction to give nailed and now lithium agent and so we can use this as well as a way of making an alliance and I'll just give you 1 example of this as well as a way of making carbon-carbon bonds so just to give you some diversity in your Europe chemicals in the molecules that you see outtakes safe analysts said Elaine and we could envision treating it with butyl lithium you'll often see you will lithium written as in and means normal normal just a fancy way of saying it's the regular it's the 1 you lithium rather than say the lithium seeing the 2 position of butane which is called sector you left or being on a tertiary butyl group which is called review lithium and as a stronger base anyway let's envision using the common reagent and viewable lithium treating our panelists settling with that's going to give us our lithiated fennel settling our our organic lithium compounds and just to demonstrate the point of other reactivity we can picture the reaction save with an epoxy side and then again in a police workout Page Gremio class and the product of this reaction is an alcohol just as we've been generating and all of the reactions I shown thus far but what's interesting about this is now the alcohol instead of being connected directly to the carbon that had been or directly to the carbon where the nucleophile attack it's said it's 1 over you can think of this as Aurora and the alkaline lithium .period reacting with the Parkside is so we're going to draw electrons flowing from the carbon with the embossed into the carbon oxygen bond pushing electrons onto oxygen an opening up our bringing but but but but but but but but but
Our it has so what we've done at this point is this we've really overviews of basic of fundamental reaction of carbonyl groups and we've introduced these compounds these reagents that make for a very very strong nuclear files hydride nuclear files like lithium aluminum hydride in particular to a lesser extent less reactive sodium hydride and in various organic metallic reagents like green yard reagents and that Oregon Elysium reagents at this point I want to
sort of broaden out thinking and start to talk not just about the Townsend NL the Heinz but more broadly about the reactivity although at the carboxyl economists in the family and to just put this into context I mean carboxyl like existed but essentially all compounds in which we have carbon in the Plus 3 oxidation state I will get to meet several questions in just a moment Esther is being another member of his family offensive chlorides so I'm going to paint in a very broad brush and later on we're going to get to any anymore specific understanding called the reactivity of this family but right now I'm gonna with a very broad brush all included in the family and misidentified rides the union maybe maybe chose to ratify the Indian members of the family all talk about my plot people were really discussed their reactions with down metallic reagents I saw several questions I think there was 1 here 1 their best year if you on great question question was when the lithium attacks the epoxy side does attacks from the top or the bottom does it occur with inversion of Styria chemistry and indeed it does although there is no 1 chemistry at the center that we formed here you can imagine what say having 2 different substituent here like the hydrogen in a deuterium and we would get inversion of Styria chemistry typically apart sides attacked by nuclear files by basic nuclear files at the less directly hindered carbon so for example if I had the but the apart side with the methyl groups called propylene oxide this 1 is trivially called ethylene oxide if I had the epoxy side with a methyl group on 1 side proper lithium where the alkaline would attack the carbon that didn't have the methyl group on this that makes sense to you know the question I saw 1 young white that same question and I like you the wider we like to use Urals stuff great questions so all all all of our hydrocarbons ultimately come from petroleum and so 1 of the ways in which Beutel lithium is made it is by 1st cracking heating petroleum very hot to get smaller fragments and 1 of the fragments that's easily isolated is Beauty and the bewteen can then be taken on to various types of products including Beutel bromide for example so so this is 1 of the reasons that that you always used you can buy the trouble lithium but you can buy great big bottles of butyl lithium metal was another common ones so you like does the chemistry rely all I love that question all or almost all of organic chemistry ultimately goes back to petroleum some of the chemicals that we use a simpler building blocks come from other sources like carbohydrates and then you know modern not ancient plant sources but the almost all over organic chemistry comes back to petroleum so the seeds that you're sitting and have a plastic that maybe Polly Ida anodes polypropylene or something and a covering that's a synthetic fabrics like nylon all of those have come from petroleum and so I look at petroleum as much as I hate to pay 4 dollars and 30 cents at the pump women think about the amount of the stuff you're getting you're getting a gallon of gasoline this is too valuable to be burning up because there's so many things that you can make from it you get get you get get a gallon of anything you can get a pounces 7 pounds of anything for 4 box I can't get a gallon of beer for 4 but and yet we go ahead we burn so yes petroleum is incredibly valuable to organic chemists and 1 of my my dear colleagues favorite question 1 that I will be asking you what an exam because it's it's still too open-ended and far too ridiculously complex for you at this point in your sophistication is to go ahead and do it right a synthesis of a steroid but cholesterol or test tossed around you've seen in your current chapters sums steroids starting with petroleum so that would be 1 of her favorite questions are right but I want go government 2 I wanna go now to the reactions all of esters and all of the various members of the carboxyl like acid family and I thought your text books presentation particularly in the reductions section may have been a little bit confusing because there are a lot of subtleties and when I think about a subject I like to think about it in terms of sort of the general rule and then exceptions to it and there a ton of little exceptions in your textbook has picked 1 and we're going to the talking about lithium aluminum hydride with means of more with our will talk about that later but right now I want a paper plate with a very broad brought a sort of general reaction of lithium aluminum hydride due the strong nucleophile the support nuclear files hydride sources particularly lithium
aluminum hydride just reduces the crap out of everything al-Khalifa and reagents like methyl lithium just had To everything as much as they can do it all for green yard reagents with certain exceptions so again a very broad-brush view from 30 thousand feet but we're gonna take a specific reaction were gonna take metal
bends here to exemplify .period Morgan unimagined treating it with lithium aluminum hydride and deliberately writing this is a synthetic reaction will talk about what's happening in a moment and then in a it's worked up with others right generically each real plus a new might do this reaction save th UHF and I'll be the person the right a balanced equation or at least that I will write a balanced equation but I will at least right might organic products of the reaction here organic chemists is typically focus on the big stuff but I'm gonna write this product Denzel alcohol and the other organic product methyl alcohol methanol and collectively then these 2 constitute the organic products of reaction and what this ends up illustrating is a new property that we haven't yet seen the called in addition elimination reactions but then we're going to see that this additional elimination reactions goes through an intermediate called then Zelda and to a certain extent maybe with the exception of here if I touch to any of the compounds that I'm a racist and treated them with lithium aluminum hydride you would get a similar reaction of them alright so as I said this is a big mouth all and I'd like to bake a big mouth falls into bite-size pieces so let's think and sort broad mechanistic terms here all right and that I think about all right now Robinson away from home alright our methyl benzoate weight and I will at least for the moment and try to be a good person can write a good mechanism in which I write lone pairs of electrons
and try to keep track of my charges and to keep things simple that right rather than writing out all of lithium
aluminum hydride I'm going to write hydride justice this abstract Schoonover hydride and I have and the 1st thing that hydride does is is a good nucleophile oppose nucleophile we've talked about the reactivity in general of carbon groups the Carbondale group is an elector filed electrons flow from the nuclear file To me electoral files and onto the oxygen and I'll try to be a good person and right all of my lone pairs all 3 long pairs of electrons around the oxygen and and 2 1 his other oxygen now this is not a stable species this is is not something that you can isolate its intermediate and strong going to remind us of the fact that it's an intermediate by drawing it in the black could we have a special name for this intermediate because we've gone from a friend in all carbon a carbon with 3 things around them to attack for he'd roll carbon carbon with things around there and get a call at detector he drawled intermediates but but the but and as I said the Tatra he'd roll intermediate he is in stable the territory here only intermediate can break down electrons flow back down from the oxygen they push now my thoughts are high and now we get a new carbon at this point we've gotten bends out the highly intermediate that I mentioned in thoughts outside and With its 3 pairs of electrons on it the
reaction doesn't stop at this point as serious art less selective
fell like an elder another words out hides or more lecture felt like can ask if we can write residents structures for Astor's or a resonance structure in which the Mattox the group donates electrons into the carbon yellow and makes it less electrical held up hides on the other hand have less going for them and so we have more nuclear file and you can't just stop at this point it's going to further get reduced and so here's around the here's our age minus again and again I'll try to be a good person put in quotes and electrons flow From our hydride onto the oxygen nailed to give rise to an topside and iron but and at this point that's what I'll sit around in your class that haven't drawn the counter I answer anything until you do a workout and Aldus right this says workout meaning ending some ambassador adding some water output this again in their search 30 thousand could view of state plus and the product of this reaction these bands allows the whole but and the other product of the reaction is will also coordinate our math oxide so the other product of our reaction is all around
but that parenthesis here are so I want to show you some generalities I want to show you some analogies into this and so at this point all right essentially the
same reaction with just a slight difference on itself before we could have been thinking about lithium aluminum hydride I said let's consider lithium aluminum hydride at this point let's consider methyl lithium and alternate seeing as there I'll take metal bands away that aren't treated 1st commitment to lithium In all right (left parenthesis to equivalents on to either try to remind us that we're using the full amount events and then secondly will treat this with some 8 weeks asset and the product of this reaction now instead of adding it to hide rides instead of adding into hydrogen we've added in 2 metals it's essentially the exact same thing but and so now we've got alcohol as a product in which we've added in 2 methyl groups the reaction is going to go just like any other 1 we went by Zelda hiding here the reaction is going to go by way of the key called the seat ofa known but just as in the case of the other ones we can't stop at the key tone with wonderful moment methyl with the tone is more reactive than the Astor and so as it now is sitting around it immediately react as well and so that's our sort of view at 30 thousand feet of the reaction of these very very strong nuclear files with members of the carboxyl like acid family as I said there are some exceptions some differences but we can kind of catch this general spirit of this on the following equation and so gonna write this I don't always like the way you textbook represents things particularly with a lot of abstract
sense because from my way of thinking it's easier to start at the concrete and then worked at the abstraction for computer I think it's very good to like start with an abstraction and you know we
can spit out all the examples but we just looked the 2 examples are now going to write the abstraction and I'll say many members of the carboxyl family but but but but but but but but but but but but but but but but but and I'm gonna write again this sort of abstraction all in you -minus about God so some type of strongly basic nucleophile that encompasses all of the reagents that we've been talking about it's also strongly the basic nucleophile that includes for example lithium aluminum hydride or LIE Ravenel lithium reagents are mg acts in other words all of these species have in common is that they have a bond between our medal relatively electoral positive metal and a highly Elektra negative species hydride or I'm sorry are a more electoral negative species hydride were with him were carbon so basically the generalities of this type of reaction are that in general we get an hour )right parenthesis access here just to avoid confusion when you have access in general who's going to observe the addition of 2 equivalent of Europe nucleophile returned as a witness in you plus the miners so that would sort of be the biggest biggest abstract Sharon and I guess I'll try to be good news
people electrons in checks Albright a balanced long period alright so what we want we've looked at here what we've looked that here is an addition elimination reactions and we've seen this general principle that when you have something like a meth Oxy group on a member of the carboxyl like acid family the reaction doesn't stop things go on now too many students the 1st time they see an
additional elimination reaction they find it confusing and here's why they find it confusing here's our let's there as the changes we've just added a nucleophile too at a new willingness but a former Arteta here intermediate neutral intermediate isn't stable it breaks down it takes out the are group in other words electrons flow like so to push out our own group that serves as a leading group but the In the 1st time people see this having already been through 51 billion warrants and arson to display was at 51 beer 51 Angela you to display 51 a and seen a nascent to displacement reaction people start to think about this and say Wow what's going on here we don't save and all our group like a mad thought group leave in an arson to displacement reactions but this is a little bit different here less basically leaving group is OK but at the end of this century displacement reactions you've got a crowd 5 things around carbon you don't have a stable intermediate that leaving group was perfectly happy attached to the carbon and yet something's coming in and pushing it out it's going over this high-energy barrier this transition state to make that Adam we and so that I Adam that leaves hostile really really want to the electoral another words a good leaving group in nascent to displacement reactions has go ahead and have a very stabilized and iron or conversely because stability of the Anaheim and means of acidity of the conjugate base conversely as strongly acidic conjugate base so in this case it's a little different because there's nothing bad about that renewable intermediate we haven't had to clear out anyone in here it's easy to get to this point but now I can happily kick out the OR group and wanted to get in return is a carbon-oxygen which is very strong and so there's no problem in getting your Tedra he'd roll intermediate together it's not pentavalent there's nothing bad about it but it's very good to go downhill and the breakdown a kick out leaving group and get back in your pipe bomb so what I always like to think about here he is in an arson to displacement reaction you've gotta have a good leaving group but in the case of this reaction addition elimination reaction a less basic leaving group is OK and by comparison but I'd say maybe less than 5 people today is good for a leading group in arson to displacement of were made even 2 elimination Fox a questions at this point doesn't work like
a substitution indeed this is a substitution reaction so the very 1st step of our methyl lithium plus methyl benzoate await reaction was to substitute the Mets Oxy group for methyl group and get a seat ofa known and then of course we couldn't stop at his seat ofa known because it's even more reactive than methyl bends away so another equivalent of methyl lithium ads but indeed it is a substitution reaction on like an ass into substitution reaction here you can have a leaving group that a little bit less acidic like alcohol or no ,comma side are you added a water
and acid yes I'm not exactly following the meeting all you mean you mean in the 2nd step would we yes if we do so in the work up with acid we would prefer that India and 1 1 more question was the OK what do you mean great question What do you mean by leaving group has less than 5 PKK in an arson to displacement reaction chloride bromide iodide a wonderful leaving groups speaking of the conjugate effort respectively about negative 6 whatever did number use about negative 6 4 HCl for the conjugate acid about negative 8 or thereabouts for HBO are about negative 10 4 8 and you can go a little bit less good leaving group I can write had equation I can give you an example of a case where instead of having a very strong acid counter for the conjugate acid in arson to displacement you could go slightly From negative you negative 6 4 chloride into the positive range I can't give you an example as low as the fight with the PKK beyond that Monessen to displacement it pretty much isn't going to occur unless like in the case of an epoxy side you have rings strain P K of the conjugate acid a park site is 17 for an alcohol but you've got that roughly 30 kcal per mole rings strain associated with the IOC surrendering making it popped open so that's the rare case in an arson to displacement like reaction where you can actually have what's essentially Alcock side as leaving room for the spring-loaded however in the case of an additional elimination reactions absolutely no problem taking out meth Oxy group at that group PKA of the conjugate acid 70 great questions are right at this point I want to move on to the final final point that I want to make in today's lecture and to bring us to some ideas of synthesis and showing you how powerful organic metallic reagents are in carbon-carbon bond RIA forming reactions but also the process by which organic chemists think about using these reagents and using reagents in general to build up molecules and so I'm going to give you a little bit of a contrived example here but it's very much like the type of thinking that people use as they become more sophisticated so the example I'm gonna give us is to set of particular compound I've chosen it as as an example to illustrate a point but he needs something very much like it could say be a useful Insect Fair moment that you might want to make for a track procedure companies Beatles so we're going to try to develop a synthesis of at for all the compounds containing go for carbon atoms serve fewer but but but but but but but but but there's nothing magical about 4 carbon atoms but many if you look at commercially
available compound in general most of them are small and you can buy a whole range of different compounds and more begin more complex compounds often are not is available so you can buy many compounds containing 4 carbon atoms were
3 carbon atoms or 2 the 1 course you can buy .period the containing 5 but for purposes of this example we're going to say for of them were going to do with this is illustrates the way economists then the process of retro synthetic analysis then we can call this the process of thinking backward about Paris synthesize something In the reason retro synthetic analysis is so powerful the reason that the process of thinking backwards is so powerful is it's so easy to get caught up in detail was when you try to look at things from a forward point of view that it's very hard to see how to get there from here From compounds containing 4 carbon perfume were all well we're using organic metallic reagents to using dental lithium do I use a grainy argue I do I use a III and faster do I use an acid chloride I used on Bureau lithium as a base to I use methyl
lithium so retro synthetic analysis is kind of like thinking your way through a chess game we're gonna start with big pictures and then work their way to the details so let me show you how I would think about this particular example when you'll encounter on this week's discussion problems several examples very similar to those that involve processes of thinking backward at various levels of
sophistication alright so let me draw out my compound so it is like to 1 2 3 4 5 6 7 8 so here's my target molecules now when I 1st think about this I could look at this and say how well OK he said for carvings and we just learned about edition of organic metallic reagents to Astor's so I can envision adding taking some master would have to be at a methyl ester of pro-bono because that's for carbon I couldn't use anymore and I could envision forming this bond by adding in Ural the and maybe again from the point of view of viewed from 5 thousand feet of 30 thousand feet from Kenneth Bacon abstractions of some metal whether to bring lithium doesn't doesn't matter and again I can't think Well here we had some metal and that kind of captures the strategy but we've got a problem here the problem is how are we get selected just said you can't really add 1 equivalent of a graveyard reagent Werner down lithium compound to an asteroid won't stop at 52 was at your question however so when we take this same idea and see if we can think back backward all so we know all see here I'm trying to do it all at once so much time of myself going here it's a lot better than saying were going to think forward but many think a little bit backwards we know all that and alcohol can be formed by a key Tony and organic metallic reagent so we can imagine something use this arrow here this this big open narrow means retro synthetic means of thinking backwards their organic chemist love arrows Kerberos equilibrium arrows residents arrows this is a reticence that it down so I can envision going ahead and going back through this key Tony and I could envision but did I do that right now if I could envision this she told To Hexham knowledge ended a bureau metal reagent and that work I could add new lithium review
magnesium bromide to chew Haxtun alone and that would be OK to make that alcohol but then I'd need
a way to make this ski town in all well OK we could make that Quito we've only learned reactions that form carbon-carbon bonds to make alcohols at this point in this course so I can imagine making that he told by oxidation of the corresponding alcohol Of 3 hacks and all and again right now I'm not gonna worry which reagent to use whether I use chromium trioxide whether I use potassium comedy whatever but now I look and I say all right and I can think backwards again nailed to the point of operable metal reagents and proper and at the strategic level we have now broken this molecule of part reviews the process of thinking backwards to figure out how we can put this molecule together and now having completed are at present Vedic analysis now we're ready to go forward and worry from the strategy attended tactics of OK
what reagent do we choose how do we do our details and so the last thing I'll do in solving this hypothetical problems is to show you the synthesis that I've worked out so I would start with proper
nouns have completed the requirement with each of my 3 components of 4 carbon serve fewer livestock with rope and all pro-bono it's commercially available at fits the requirement while added just for the fun of it all use probable magnesium chloride I could use portable lithium I could use proper magnesium bromide problem magnesium died and carry out my work up the date with 8 I could use a quiz sulfuric acid I could use a quiz ammonium chloride occupied the lazy and writing each 3 0 plus over the arrow but I'm going to go to the sacrament get some chemicals and I'm going to ask them for some 8 CIA the product of that reaction your workout reaction also I now and ready to oxidize my 3 hacks and all you learn lots of reactions last quarter for oxidation they taught you potassium dichromate In sulfuric acid and water sometimes called Jones reagent there are many many reagents based on chromium 6 sodium dichromate chromium trioxide there are lots of safer alternatives including alternatives based on voyage but we're going to use
reactions that you know so we're going to use potassium dichromate then at that point we have our hex and hour to Hexham known question absolutely we years chromium trioxide as an oxidizing agent lots to choose a back from my niece and I represent Vedic analysis not having
to worry about getting the right yet and now having going in choosing our reagents and choosing our taxes are arrived tactics finally to complete our said this is I'm gonna take you know lithium and I'll donate wears worked up and again I'll use HCL I've it below the arrow here written above the error there doesn't really matter chemist read it the same way have launched hold I have proposed a rational and selective synthesis of our target molecule 4 for as as are in all and this all art of recognizing something in the molecule and seeing where it comes from is going to grow and grow and the cost right
now we've seen in alcohol and we said all I know how to make an alcohol I can make an alcohol by adding in 2 carbon nuclear files I can make out halls by adding in carbon nucleophile later on we're going to see all sorts of other
families of Carbondale ,comma found by I will see on Thursday will start off with a 10 minute Quayle
Chemische Bindung
Elektron <Legierung>
Fülle <Speise>
Zulauf <Verfahrenstechnik>
Bukett <Wein>
Aktives Zentrum
Setzen <Verfahrenstechnik>
Gangart <Erzlagerstätte>
Barrel <alpha, beta->
Klinischer Tod
Spezies <Chemie>
Krebs <Medizin>
Organischer Halbleiter
Chemische Struktur
Sammler <Technik>
Systemische Therapie <Pharmakologie>
Biologisches Lebensmittel
Eliminierungsreaktion <alpha->
Chemische Eigenschaft
Funktionelle Gruppe
Aktivierung <Physiologie>
Valenz <Chemie>
Organische Verbindungen
Kleine Eiszeit
Chemische Forschung
Chemische Forschung
Chemische Verbindungen
Proteinkinase A
Schweflige Säure
Einsames Elektronenpaar
Primärer Sektor
Bleifreies Benzin
Chemischer Prozess


Formale Metadaten

Titel Lecture 03. Reactions of Organometallic Reagents.
Serientitel Chemistry 51C: Organic Chemistry (Spring 2012)
Teil 03
Anzahl der Teile 19
Autor Nowick, James
Lizenz CC-Namensnennung 3.0 Unported:
Sie dürfen das Werk bzw. den Inhalt zu jedem legalen Zweck nutzen, verändern und in unveränderter oder veränderter Form vervielfältigen, verbreiten und öffentlich zugänglich machen, sofern Sie den Namen des Autors/Rechteinhabers in der von ihm festgelegten Weise nennen.
DOI 10.5446/19424
Herausgeber University of California Irvine (UCI)
Erscheinungsjahr 2012
Sprache Englisch

Inhaltliche Metadaten

Fachgebiet Chemie
Abstract UCI Chem 51C Organic Chemistry (Spring 2012) Lec 03. Organic Chemistry -- Reactions of Organometallic Reagents -- Instructor: James S. Nowick, Ph.D. 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. Organic Chemistry 51C is part of OpenChem. Index of Topics: -1:36 Ketone/Aldehyde Reduction -5:56 Grignard Reagents -12:31 Polarity of Grignard Reagent -16:01 Basicity of Grignard Reagent -19:22 Grignard Reagents and Water/Alcohol -21:32 Organolithium Reagent -25:50 Acetylide Anions -34:07 Making Acetylide Anion -38:29 Reactivity of the Carboxylic Acid Family -44:56 Addition-Elimination Reaction -48:12 Examples of Carboxylic Acid Reduction -53:29 Multiple Additions onto Carboxylic Acids -59:50 Leaving Groups -1:08:27 Synthesizing Example -1:16:54 More Examples of Synthesizing

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