Lecture 26. Electrophilic Aromatic Substitution, Part 3

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Lecture 26. Electrophilic Aromatic Substitution, Part 3
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This is the second 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. This video is part of a 26-lecture undergraduate-level course titled "Organic Chemistry" taught at UC Irvine by Professor David Van Vranken. Index of Topics: 00:10- Removing Toxic Chemicals with POPs 00:43- Molecular Structures of POPs 04:02- Summary of EAS Substituent Effects: Know This Summary 07:41- 18.9: Over-Activated Anilines and Phenols 11:56- 18.11: EAS on Disubstituted Benzene Rings 15:58- 18.11: EAS on Disubsituted Benzene Rings-no substitution between meta-substituents 18:26- 18.13: Benzylic Bromination 21:48- 18.13: Benzylic Bromination- chalk board 25:11- 18.14B: Reduction of Acyl Side Chains 30:40- 18.14B: Reduction of Acyl Side Chains, example 2 33:52- 18.14C: Reduction of NO2 to NH2 39:28- 18.15: Mulit-step Synthesis
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I just saw reference to a news article in Google about some new kind of compound actually a polymer that can be used to remove toxic chemicals and not as a source of environmental cleanup but from the air that you've read an article refers to something called Pops that's clearly an academic and so I wanted to find out more about what is this parts business sense and what does it have to do with with cleaning up the air that you've read this this is work was low by Sunday and win it at Northwestern University the
basis for this idea pops it's based on a cool reaction that you've never seen before and that the cobalt catalyzed cyclo trying realization on the Nunavut learned about an equal ways to make benzene rings we spend their time in the cafeteria-style about ways to substitute benzene rings in that benzene is very cheap he typically by benzene and then add substituent Stewart but here's a reaction we take out kinds and and you can ignore these green gas lines for the moment here and when you throw on a cobalt catalyst in this if it you've chosen the right cobalt catalysts of the Cobol Adams will grab the all kinds and start forming carbon-carbon lost so-called animal grab to all kinds maker carbon-carbon bond here and then will maneuver over and make a new carbon-carbon bond here and it'll grab another Elkind and make a new carbon-carbon bond there and if you designed kinds very cleverly and this is what the shtick here that designed and very cleverly you have an extra Alpine on the other end now that 1 can engage in this cycle trying position reactions and if there's another outline on this end of this other substrates that can now engage in cycle dramatization reactions and if overrun this piece you you've got 3 more kinds dangling off that can engage in 3 Morrell kinds in this cycle dramatization react so you end up with these benzene rings this service rigid spaces and that the ends of those you have sites for a polarization you get this massive polymeric network composed of these regions benzene rings and has lots of space inside it can't possibly factory closely so if you take these kinds of monomers there's a monomer with 2 outlines and just ignore that function before now and years of monomer that for all kinds it's shaped like a tax treaty drawn on its sort of because it's based on this sp 3 hybridized center and if you apply this cobalt catalyzed colonization reaction making benzene rings all the benzene rings are highlighted in red and with this group did is that they incorporated these 2 alcohol would ease in a protected form in the idolized office group that's chemistry or seeing him 51 seats and it left behind to oxygen is ready to be reappointed metal ladder and in particular copper and zinc metal atoms so that means this is very porous polymer now has metal atoms and copper is exceptional and binding to means so you're breathing in some sort of toxic vapor on that as bad stuff this will help absorb those papers in the cooperative's specifically will latch onto a median them out of the air very quickly so for example VX nerve gas has a mean groups on and wouldn't it be nice to have some polymer that selectively binds to those kinds of means look as Missouri cool way to make benzene rings using transitional catalysis finally gets closer to to the kinds of reactions that are being developed now and in the field of organic synthesis so let's switch back to chattering teams .period immigration history textbook and we'll talk about on the I
will talk about electrical like aromatic substitution
begin we left off with those we work that 1 of the ideas that I introduced to you during our last lecture was that if you do elective Ilic aromatic substitution on us on a benzene ring they already have the substrate there like this are a group of year I think that our group will now control where the 2nd addition of a function will go troops at a very activating and speed up electability aromatic substitution tends to to be also appeared directors they tend to cause the next substituent added or 1 pair positions by annually at a residence effect with long periods but help your groups can also do that and then if you look at the group's the deactivating which tend not to have a lone pairs that have elected negative Adams those tends to slow down electrical like aromatic substitution and also lead the slowdown in particularly slow additional author 1 pair of positions and so it leaves you with matters substitution those matter directors so I showed you this charge and I expect you to know this Charter not will seem just a little while awhile why you really need to memorize this chart there's some things in here that like this that the position of halogen that's a deactivated but it's still worth a pair and you just need to memorize there is no simple principles you could use to have
guessed that now when we left off I showed you the special rules for Friedel crafts reactions as feel cracks reactions of all these exceptions you have to memorize and so it is called upon carbon-carbon bond that's undeniably cool but the problem with real grass reactions is that a silly alliance are nowhere near as reactive as naturally my answer or those other electricals we showed you gobble kinds nowhere near as reactive as these are the kinds of arms of Elektra files that I should you so anything below this line here and the draw the line anything below this line in the functional below this line deactivates the benzene ring so much that you can no longer do Friedel crafts reactions with a silly amines and cargo cannot so and that that line there just happens to correspond to this this line between Meta directors in mortal peril directors which just happens to be so we've got this simple rule that any benzene ring as amended director on it is simply to deactivated 2 to work with real Craxi's deletions or calculations and anything above the line we can do it on but then there's this additional problems and I don't want to go into the details of this but that is that if you had amino groups and benzene rings With 2 alkyl groups or ages on the mean that's till activated it's still activated to working in real crafts reactions basal Asians inoculations so you can do other types of of electrical like aromatic substitution the Nazis C bond formation so those are all those exceptions or somebody exceptions with Friedel crafts calculations and installation problems horrible exception OK so let's continue to talk about exceptions where some more the exceptions that we have to remember that that's going to make it difficult and and let's focus again on this over activated ended that charts the top end of the chart with things are just too active and get too hard to control and must talk about it and phenols and start up by talking about finals without lone-parent oxygen if you have a hydroxyl group 1 of benzene ring that released donates into this benzene ring activates b that benzene ran to the point where once you once you add a single chlorine atom and it is true that foreign Adams is it slightly deactivated but this ring is still so
activated that you cannot stop a 2nd chlorination so it adds again and you still cannot stop another coronations with ads again even if you had only 1 equivalent of steel to chlorine you'll still get try substituted products coming out this just
can't stop this year because ugly mixture so you can't stop over chlorination arm when you're using this super active recipe with chlorine and ferric chloride but there's a simple thing that you can do To what that will allow you to get Monaco substituted products and that is to leave out the Feerick he lied catalyst to leave out the ferrochrome hide at the Bureau 3 were to leave out the ferric chloride at the 3 if you have
all you want to add just 1 allergens can invariably you only want to and nobody wants to add 3 allergens if you just want to add 1 halogen leave out the FEB R 3 that simple that now you and you're still going to get a mixture of water when parent that's OK create a mixture of water and parents we didn't have all those extra allergens on here so it's those hydroxyl groups active in benzene ring so much the region on Over Over halogen nation unless we leave out that ferric chloride affair catalyst OK so hydroxy groups are very very activating amino groups more activating the hydroxyl and it turns out there is nothing you can do if you got a die out Filomeno group for Justin NH 2 groups taking off the benzene ring there's nothing you can do
you're going to get over ruminations these cases so in this case it's all do the case which to methyl groups there it if you've got a diabolical amino group you're going to get but every single or so in Paris substitution brominated it doesn't matter whether you include the fared remind you may think of others the Fairgrove now that I cannot it'll still remaining in the and the scanner lands at the very top of our activated benzene rings list and you just can't stop over on activation so that that makes so again there's all these exceptions
and you have to memorize these exceptions I expect you to know those exceptions for electrical automatic substitution expect you to know that if you want broom anything all that you have to go on leave out that very catalyst and just go straight bromine that's how activating the hydroxy movies yes with energy can model brominated and we used to do than the 51 last and I don't know if we do that were so in other words if you had any image and you were going to cover immense In an amazing an infinite detail Holik scored a city of Aqaba real group on there and you can model Veronica and again these the I'm not sure if they still do that in the 51 Ladson 51 Elsie but you may do so here you could monolog romantic and what's particular about that is that the carbonyl group is electron withdrawing any longer spend a lot of time donating in the car video instead of into the benzene but you don't know how to make immediate cannot hide idolizes back off wait till can 51 will will show you that and they will be asking you about this hammered case in 10 51 and 51 see they're going to check to see if you remembered this over halogen nation of him OK so that's the more exceptions in more sections of let's stop talking about the exceptions and start talking about on some powerful tools to help you further figure out how to selectively add substituent to benzene rings now I talked about this case what happens if you have a substituent on benzene ring you need to know which groups the auto Perry directors media which proved many directors that you can make a prediction where the 2nd substituent undergo what happens if you have to lose substituent son of benzene ring How do you predict where the 3rd since the joint is going to go which of these groups delayed pay attention to when we look at around and we have a very very simple and powerful role to help us predict on which groups who will control the Regio chemistry and also has the strongest activating group the on the benzene ring controls the Regio chemistry controls this issue of
Oracle Pera verses net so if I take this cop example here I've got but I think this is called crease all Despair Metal fund all year about got 2 groups there How do I know whether the prominently in here is that 1 of these examples where I'm going to
brominated and I see the hydroxyl groups I'm smart enough not to add that ferric chloride tablets because I don't want over brominated I just want to brominated once and so which of these 2 groups control 3 geochemistry according to the rule I I gave you I go to the highest group on this list and it's over here hydroxy group so in other words the hydroxy group controls 3 geochemistry not the methyl groups and hydroxy groups are also pair directors it is right that here the direct also pair ignore alcohol it's not as high as hydroxy in our in our listed so the product of
this is going to have a halogen wherever the hydroxy group makes the halogen and so I'm going to put that I can't put it here the pair opposition is already a methyl group there so really the only product should get out of this in high yield is going to be that amount rumination product or so to the hydroxyl it's the hydroxy group that controls regional chemistry but it would go down this next example you have got a carboxyl and substituent now and again I have a methyl substituent on and so when I knew what I think about where their 3rd substitution is going to occur I have to decide what whether it's the carboxyl a gasoline or the methyl group that's going to control the real chemistry and someone I come over here and I look at my list well Carbondale
groups down here ,comma oxalic acid key tones Aldo hammered any carbonyl compounds but higher than that are out there groups like methyl and that is once again that in war tho Perry director I need to know that so when I look at the 2 groups the methyl group is controlling the radio chemistry and the pair group the
group Paratore metal is already substituted and so in this case the the new substituent the sulfide gas and substitute is going to occur or tho on or peer-to-peer is blocked tho To the methyl groups so that use that lots of pretty simple it requires that you had memorize this list you straight have to memorize that list of activating deactivating and appeared directed so you know that let them know how to use it so that's that's the simple idea funny just circle again the groups that are controlling the Regio chemistry this is the group that controls the regional chemistry here it's also pared directing and down here it's the methyl group which is controlling the regional chemistry and that's also pared director if you have too many directing substituent it's the most activating or maybe least deactivating medicines obstetric units from the highest Rubin list for peso and their problems in many many problems in the back of the chapter that we should work that will give you practice with that problems in the on-line sampling work that will be practice with that so fractious that work all those problems and keep working but the user and observation that's based in hysterics is really overblown as a
as a source of control in organic chemistry is residents effects are much more important in organic chemistry from what simple loosely referred to as electronic effects involved molecular orbitals explanations but here's a very simple steric effectiveness and the idea is simple if you have 2 groups that are amended to each other like this if you have a choice for example here in this group is in mortal peril director so both of these are equally activating so this could be the north of Harare director it's going to direct the new substitutes to go or so for
Paris and this methyl groups just so happens because of its positioning will direct to the same positions so now I have 3 positions and released positions here this position here is different from these 2 here position to and 2 or both identical there's a symmetry element in this molecule you couldn't tell if I substituted at the top position to where the bottom position to and signed aside and simple rule is that if there is a choice you don't substitute between medicine stituents right here in between its 2 strictly hinted it will be faster the
substituted not between those 2 methyl groups so here even know there's all these positions where you could substitute you only get 1 product as the major product and in good yield you'll get very little of the product where you substitute between these 2 methyl groups even
Oracle perils predict and that this middle positions activated so 1 product to have the carbonyl group down here and the other product at the carbonyl group over Europe other position to but that's the
same thing that's the same product is industry so Samples based on steroids and help make that kind of obvious that it's a little more hindered between the methyl groups but you wouldn't have known that that would be useful enough to actually really dissuade groups to go in between OK so again if there's a choice don't get between the 2 medicines stituent and that's another thing that you have to look out for and it will help you to do since this season to answer questions on the back of the chapter in the Sapling problems OK let me show you a useful reaction in covered all this radical chemistry back in Chapter 15 was all kinds of radical substitution stuff I and lighting seems to efforts has just made me see that status that's driving me insane you go back to PC here again the media half of the
week and you hear some credits on the PC and and try turning this thing off his Union
Miniere all sort this out the man
in the office is going to kill us it is the you you this seems to be a
doctor can problems so
commuters check out what we've got here may not have this lecture on my I don't know to fix fixes .period himself we may have to make a choice here between charcoal or OK charter schools located in that I'd like to be able to do that and I apologize for the dot area area and a lot of success in getting given 1 more chance here just to see if we can make this work Seattle last time I talked him 51 B it was shocked and people in the back complained that they didn't I and I write with the big shock the complained they couldn't see the by writing and thought I wrote itself OK let's see if we have any chance here not spasm its passes out again and go right to the chocolate always been to so far so good grocer fingers you at the gate so pinned all that radical stuff and you're never gonna see radicals against that the the I'm considering giving it a couple times again good a talk and started new rising back I'll try to make an attempt to make sure that we can see what's going on became 1 of remind you of Chapter 15 stuff we learn all this stuff in section 15 . 1 0 about little rumination and in cases like this when we treated Alameda with NBS and heat for peroxide you don't use br 2 1 year because of alleged roaming across the double bonds muses-and Romo sits in his compound the problem with this is you get a radical where the analysis radical where the group can substitute on both ends of that our radical and see almost always got these hideous mixtures when you do a little rumination and who wants a mixture and there's also on top of that the security you generate news union extended it's not such a big deal but nobody likes to get mixtures of compounds as products in inorganic chemistry and so I'll show you now is if we do the same reaction and instead of doing it on this kind of analysis of straight we simply switched to offense Billick substrate it does the same stuff so many redraw that a substrate here and all I'm going to do is make this part of the benzene ring and I do the same conditions and pro-Milosevic sentiment and light but this time I don't get mixtures of products you'll get selected brominated of 1 of the 2 ages there'd been benzoate positions and that makes this way useful whereas overlooked rumination is not useful I would say we're useless would be a better description of the look of brominated yet as Super symmetrical substrates for rumination begin you clean up product mixture so that I can replace 1 of the 2 agencies with this same actually learning Chapter 15 1 isn't important because that's a leading group we can go from something that no functional groups here relate to something that is the leading group at that position on the U.S. and 2 reactions elimination reactions so that's very powerful this idea that we can do that we can add leading groups wherever you want to have most of the because there's no easily brominated will double bonds and benzene when you don't have to worry about using and Romo's 6 extended so in other words we can take this same kind and you can have other substitute on the benzene of ring they don't get affected in reaction of to his distraction hearings this summer and because we don't have brominated will double bonds were you and your 2 across you can use br to in this reaction if you want in fact more typical and the book shows and other types of waste is already it's simply keep the reaction so hot that you generate small amounts of radicals so you can do a little experimentation with the R which you can do Ben Stiller rumination with molecular bromine and it works just fine and become a powerful letters we can add a leading group anywhere that we want to have a leading group so on you should know that reaction and be ready to use their reaction from because again that's very powerful that leading group look I'm going to show you 2 more useful transformations of side-chain so really what we're talking about now is what is useful things you can do once you've added aside chained to a bed in the morning and we turned it into a useful functional groups and let me show you too powerful reductions of criminal groups when there is an air over 1 1 side is the very efficient reduction reactions socially away to take the carbonyl group attached to a benzene ring and burn them down to a C H 2 groups so here's 1 version of that reaction but but but but but this is called location a reduction and don't need to know the name of his reaction it's not important this is of a reagent called hydrazine there's an an bond H 2 N in H 2 and you have to do this under strongly basic conditions of sodium hydroxide and there's a 3rd thing for you remember and that is you have to keep these reactions these are not mild reaction conditions someone directed Big Delta under so hydrazine hydrazine H 2 and H 2 sodium hydroxide and you boil it and when you do that the product of this reaction is now missing on the carbon deal but it's not so much that it's missing the Carbondale it's that you now replaced the problem you'll have something to group and all drawl that that CH 2 group for use you concede it's not that there's nothing there on the stage is there and you don't need to know anything about the mechanism for this war occasional reaction but I think you can see that useful and the reason why this is useful is because you can't make that products through real crafts alkylation so I want you to recall the real grass alkylation 1 finery although lies suffer from this problem of migration so I want you to recall this problem here will actually recovered and is the 2nd the 1st talk about an alternative set of conditions suppose you can't remember hydrazine for some reason and she's completely escaping you there's an alternative set of conditions we can this is a reaction called Clemmensen reductions and involves taking is you buy this stuff called zinc mercury amalgam appears no way we represent using mercury amalgam please write like this he digs in powering the mix with mercury and malaria absorbs onto the surface so you put the mercury in parentheses it's called zinc mercury amalgam and his case it's not strongly basic conditions it strongly acidic conditions and again these conditions are not mild you have to boil your your key With zinc mercury amalgam and hydrochloric acid and sold on Delta symbol here that means you're boiling the heck out together to work and this will do the same thing as that qualification a reduction with hydrazine poisonous ICC issued about 1 of brominated within Rome was extended but that's because whites called introduces siege to groups focus so this is a way to take carbonyl groups and reduce them down to siege 2 groups and you're not going to see anything like that on other chapters it's a while maybe there's a different type of reaction with living alone might never mind here on in this in this chapter that's the only kind of reaction will take a Carmel Group and reduce it down so let me make 1 important point because you're going to do tend to get this confused in Chapter 20 of you cannot burn down the groups of esters warrants there's a different side reaction from Killian yesterday with
hydrolysis and so you're not going to be able able to ever take something like a methyl ester at the last year and convert those indices to groups by using this Keeshan reduction we may have some other other chemistry to do something like that ,comma there's but not exactly like that similar to this with esters not with on its leverage told but think the only place where this is useful and you have a tendency to want to do that now you might ask which of these 2 should I memorize which of these 2 is more useful typically the basic version is more useful the hydrazine sodium attractive because there are so many functional groups the acid sensitive you're going to find the boiling things with acid is usually going to screw up some other part of your molecules so I usually prefer this war Keeshan aversion is hydrazine sodium hydroxide if you want to have you know there's 1 thing you wanna really commit to memory the most on that would be the ones that would be most useful to this quarter OK so let me remind you why this is useful and because of this limitation in the Friedel crafts reaction remember this problem with primary outgoing realize is that they will rearrange and so really limits what you do for your reactions on the Net so this is just a continuation of what I want to do this this Clemens introduction oral history reductions if you wanted to take this benzene ring into a free-for-all craft reaction with his primary out of a lot if you wanted to make that kind of product look at this stage to appear you might see that and tried to make this as a reaction but there's a problem with this you wouldn't get any of the product data over there what you would get would-be anti-deal group substituted on and the reason is when you draw the primary cobbled Carolina 1 it this is not do anything so it's not a primary couple Caroline and will do it quickly the primary cobalt and iron intermediate that you generate enough draw when we draw that Chelsea got here will very quickly rearrange the and to give you a tertiary Koble Qatar and that's what's going to attack the benzene ring it's going to be the tertiary cargo on that attacks the benzene rings and as Israel Kraft alkylation reactions so if you want to add added the this over here you have to do it in 2 steps 1st Fieldcrest installation and then use 1 of these reductions to reduce the calming down to the siege to groups so that's the slated to do things now there is an exception to this and I said don't try to do primary out here alive and in but you can do there are 2 outgoing realize that you can do this kind of looked like their primary and the book seems to love these in the online homework seems to love these and I want you worry about the mechanism you can do with this because methyl it is not susceptible to any kind of a hydride migration there's no 1 to migration possible for a medal because a lot a 2nd carbon the other types of starting material that you'll see using fetal crafts alkylation mainly in the book nonchalance not in real life is Ethyl chloride and why is that not a problem with hydride migration relic of migration it's because of you migrate hydride from 1 side of the metal bulkhead the other you get back and have at those are the only 2 instances of things that look primarily where you don't suffer from this problem in general if you see a CAT contributed to a benzene when you should make that serve to Friedel crafts insulation and then reduce the carbonyl group down to CH 2 that's the general way up to to attach siege 2 groups to benzene rings and that's the way I would recommend but it could so lots of stuff you can do with these carbon substituent chicken brominated company can reduce Don Garber meals to CH 2 groups of that's powerful stuff much talk about carbon nitrogen Bonjour nitrogen substituent on benzene rings I apologize for those of you and back problems these arranges don't do the best job of erasing usual here and so you're trying to see my riding through this piece of chalk on the board at the start about converting nitro groups which are pretty useful you can make make medicines that nitro groups on the those cause problems with toxicity when their metabolites so that if you want to make useful drugs that have nitrogen on benzene rings typically what invariably you're reducing those nitro group down and doing something else about so here's an example or so Nitro toluene to Nitro toluene and and and you it's very very simple to reduce these down to to give you something To give something that's useful to work with and it's the same condition the genes for hydrogenation and that's and palladium unheard of the right only solvents and that's why I was hesitating then so palladium on carbon is a catalyst it's the same thing you're doing with hydrogenation double bonds aren't typically we don't show the stoic geometry in fact it takes 3 equivalents of hydrogen generally I want you to write the story geometry on but for hydrogenation is you don't chemists typically do not draw out the story geometry for hydrogen so I think I can see you're going to lose to H 2 0 was at a minimum here on and then another set of each choose go on the nitrogen atoms so we don't show stood geometry for hydrogenation Ted reactions were going this is the best reactions ever everyone of feel reaction in the lab we get 100 percent yield and no by-products and all use filter your reaction to this is the way to go that will give you to other recipes for for producing amino meant troops to amino groups in this only works when they're attached to benzene rings by the way and you can do this on calculators cyclical another set of conditions I don't know what push past you I got some like so here the other set of conditions that the book shows on the bookshelves Chanin ACL on some books I can whether it's this 1 shows sealed to HCl that's actually more typical conditions Stanislaw wide on the shows teenage steel or iron powder NHC also tend powder is that and hydrochloric acid and the product of his reaction but they show in the book is the same thing that you get with hydrogenation and white as the book you all of these different recipes behind hadn't hold why does the book shows you intend to do 1 these recipes here and why you any chemistry want to do this it turns out if you have a halogen hob above here the Bulls hydrogenation conditions will clean the current halogen Bonn where's the teenage conditions do not clear the carbon halogen and you're never going to run across that in the 1051 0 series I'm not going to ask you that the book is careful not asking that so that's why people might not want to use the hydrogenation is because that maybe they don't want to lose bromine the 2nd little trick that I expect you to add that they did that here in this book and that is it if you're a stirring around an Armenian hydrochloric acid it's not mean anymore the product of this reaction is actually an ammonium salt and I want you even if the book doesn't want you expect you to draw out of it you want to give free Amin to which you have to treat this with sodium hydroxide to impregnate that the toll-free basing like likely freebies Coke this weekend it's This is what you're doing the prevailing in the and I want to show that Freemasons that if you do stand as chloride but that's managed to and running him so not just draw this one's dead 10 and hydrochloric acid on what I
want you to do a 2nd structure sodium and of and usually we just enumerated step 1 10 hydrochloric gasses step to a sodium hydroxide and OK so generally column in which can hardly I would use hydrogenation if I didn't have some some other reaction was trying to avoid that this of the way I no the by-products series of 282 of the byproduct so easy to 2 of those molecules of hydrogen combined with the oxygen into waters the 3rd equivalent of hydrogen and I don't worry about the mechanism you don't need to know that you need to know that that's a fantastic reaction it works every time again last let's talk about let's talk about the multistep synthesis you learn a lot of reactions in generating actually nothing 5 elective Ilic aromatic substitution reactions and I did not show you some fancy ways to to to dress up those side chains that you put on the reduction etc. The yeah for multistep synthesis when you do that involves elective like aromatic substitution in the main admonition that I can give you to strategize Regio control if you want 3 groups onto a benzene ring with a super particular arrangement you have to know which group you at 1st because each group was either an awful Parra director or a matter director and so you need to strategize review control so it's taken example where we want to do some sort of a synthesis let's suppose the jury asked by somebody to take benzene and injured some number of stats show reagents and steps that would allow you to put on on these kinds of groups here and you have to think about what away at 1st and what do I had 2nd and water all those exceptions that I have that I have to worry about so this could talk about this whole week typically when you're given a synthesis this is you have to do you have a choice either work forward or backwards I usually start by working backward daily services where all the different ways that I could make this and some of them are some of the ways you know for how to make that well maybe 1 possibility is that we could start off with nitrobenzene and then do some sort of an alkylation reaction but you already know that doesn't work right nitro groups cemented directors nitrobenzene is to deactivated for you to do any kind of real craft calculations are slated to just forget that out really your only choice is to to somehow had some kind of a group that there is an alternative here and that is maybe my last step and I said this was reduction of 1 of these carbon Hill worlds using that Wolf kitchen a reduction or the Clemmensen reductions but may be the last time I synthesis was reduction of carbon this this has to do with me being so clever that I could see that to and I remember those Carboneau reduction reactions that I just thought maybe that was the last last Or maybe other possibility that we have here is that the last step involves 9 traineeship now that actually looks pretty promising and I looked promising because alkyl groups also pair directors we could have made this by 1st putting some sort of an alkyl group London England and then doing a 9th tration reaction as reminders of what those conditions on the creation it's nitrate gasses and sulfuric acid so of these choices to me what's looking pretty promising here but is this nitrate Asian so maybe the last step in the census boldly tration and I think we can probably figure out how to put a protocol group of benzene ring and so how would we do that How would we had a probe move to a benzene rings Well this coming back to another exception that you can directly I had local groups to benzene rings leaders right that problem for you here what was the problem that we just finished talking about was trying to do this and in 1 step but the problem that we talked about is that if you take chloral propane and you try to do real grass alkylation the land abilities hydride migrations that primary Koble Caroline would be unstable and if you made something that looked anything like a primary cat I had I'm not saying that that's what happened here but if you started to generate something that looked like a primary ,comma guarantees hydride and migrate over before industrial processes and so in that case you wouldn't have improbable groups attached to benzene ring you have isopropyl groups attacked chimpanzee right so you can't do just straight field crops to make this how do we make this well this is where those Kerviel reductions come into play but the best way to to put that seeks to directly attached to avenge the is to do 1 of these reductions and I'm going to choose the Walt Keeshan a reduction that hydrazine will reside in mind that you don't have to prove that an and bond and there's 2 other parts to this recipe sodium hydroxide and heat but if you want to do the same ,comma archery thing With HCl and it's perfectly fine to so now it's starting to look like we've got a route here then we could start benzene and Friedel cracks insulation an aluminum tried chloride and then for steps to we could use some sort of a reduction hydrazine and sodium hydroxide and man that's the molecule we have over here and 3rd step we could nitrate and there's 1 little Stokley .period here then leaving out and this is the last thing that I'll tell you in this chapter and that is in cases when you're doing synthesis problems in cases where ask you to efficiently make some product I'm going to allow you to claim that separation of author 1 pair isomers constitutes an efficient chemicals and would add that in here so in other words if you take something that looks like this new brominated this you will get a mixture of water and Paraiso maybe there's no way he could you can get around that so as 1 of chemicals that any synthesis I will like to do this right seperate worth care and then just draw whichever 1 that you want the art I admit it yeah you only got a 50 percent yield of each 1 and that's not really that officials who were just going to pretend that this overall process of making bold torso in Beira and separating out the 1 you want but let me just draw 1 of those I suppose I want the Australia just pretend that that's an efficient combination of steps so what I need to do here is acknowledge the fact that nitrogen is going to give me a mixture of 1 pair and I need to add an additional step here so what we need to do here is on the right step and I don't know how to raise his border so step 1 is going to be nitrate and no lobbyists go back a little bit here and let me do it like this .period back over here with my probable benzene and all right step along so and I drink acid and sulfuric acid and instead to just like I just told you separated or so and terror and that's the way you deal with that when you generate or so pair mixtures but you only want 1 of them I would like you to do that OK that's that's it
that's the end of what we've got to awry I 1 last thing to tell you a final exams on Monday morning at 8 AM seating chart opposed it and I'd like to be in your seats at 10 before so these are passing the exams and this weekend drive by business and when you finish this class and are going on in 251 seats drive your business and invest in your career Maryland organic chemistry so thank you it's been a great time