Lecture 24: Aromatic Substitution with Carbocation as Electrophiles

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Lecture 24: Aromatic Substitution with Carbocation as Electrophiles
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UCI Chem 51B: Organic Chemistry (Winter 2015) Instructor: Susan King, Ph.D. 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. Index of Topics: 00:48 - Bromination of Benzene 04:46 - Nitration of Benzene 10:46 - Sulfonation of Benzene 15:07 - Friedel-Crafts Alkylation 32:06 - Friedel-Crafts Acylation 38:27 - Substituent Effects in Electrophilic Aromatic Substitution 41:14 - Ring Activating 43:59 - Ring Deactivating
Pilot experiment Reaction mechanism Storage tank Bromine Base (chemistry) Chemical reaction Aromaticity
Activation energy Left-wing politics Reaction mechanism Nitrogen fixation Trace element Fire Electron Colourant Schweflige Säure Benzene Elimination reaction Phase (waves) Stickstoffatom Bromide Octane rating Walking Carbon (fiber) Chemical reaction Water Hydrogen Acid Computer animation Covalent bond Chemical structure Bromine Cobaltoxide
Ionenbindung Resonance (chemistry) Titration Aromaticity Molecule Schweflige Säure Benzene Elektronentransfer Elimination reaction Conjugated system Area Schwefeltrioxid Phase (waves) Stickstoffatom Walking Protonation Addition reaction Chemical reaction Joint (geology) Water Hydrogen Gesundheitsstörung Computer animation Covalent bond Chemical structure Cobaltoxide Base (chemistry) Gene duplication
Biosynthesis Bromide Concentrate Alkylation Asset Chemical reaction Electronic cigarette Water Acid Computer animation Schweflige Säure Benzene Verdünner
Ionenbindung Halide Resonance (chemistry) Steel Aluminium Chemical plant Chloride Finings Bromoethane Chlorine Lead Electron Octane Ausgangsgestein Dessert Benzene Verwitterung Halogen Mineral Periodate Alkane Phase (waves) Bromide Walking Carbon (fiber) Chemical reaction CHARGE syndrome Electronic cigarette Lone pair Hydrogen Acid Iodide Computer animation Bromine Thermoforming Biomolecular structure
Curry Chain (unit) Hydride Reaction mechanism Burn Aluminium Rearrangement reaction Chloride Carbon (fiber) Katalase Chemical reaction River source Alcohol Chlorine Hydrogen Computer animation Freies Elektron Benzene Thermoforming Hope, Arkansas Calculus (medicine)
Sense District Ionenbindung Reaction mechanism Lamb and mutton Resonance (chemistry) Chloride Wursthülle Quartz Chlorine Fluoride Nitroverbindungen Schweflige Säure Benzene Ausgangsgestein Elimination reaction Nitrobenzol Setzen <Verfahrenstechnik> Substituent Phase (waves) Alkylation Carbon (fiber) Suppository Solution River source Hydrogen Acid Computer animation Resin Chemical compound Covalent bond Chemical structure Brown adipose tissue Cobaltoxide
Lone pair Substituent Activation energy Computer animation Sunscreen Substitutionsreaktion Benzene Carbon (fiber) Chemical reaction
Substituent Gum arabic Activation energy Stickstoffatom Resonance (chemistry) Vancomycin CHARGE syndrome Aromaticity Hydrogen Computer animation Electron Tidal race Initiation (chemistry) Covalent bond Chemical structure Ausgangsgestein Active site Cobaltoxide Medical history
part of it gets started and I find that this is going nowhere standard behind so Solomon do less great today I would be more efficient nights I go too fast for tank questions requiring it started anybody's far right finally talking about nomination you guys cannot like winding down quickly so we can get started on retirement recommendation last time pilot to fill a charismatic substitution with bromine we got through most of the mechanism and now we want to talk about the very last at which alone is going to be regenerated in aromatic ring and this is always going to be an 1 reaction it will be very similar for every single and mechanism in this chapter of only difference will be what we actually use them for the base to do the 1
reaction and so on and on and really what you do is you don't what we're going to take any 1 of the residents structures that we just threw for the car intermediates and we don't worry eliminate the hydrogen spawned the same carbon that the bromine is bonded to their we're going to use the AA-minus To do this and you can see we re-establish the aromatic Wrangler eliminating a hydrogen that state adds to the curb Academy where does the the AA-minus come from out of it comes from this right here when this happens we get at the B R A 4 and that's an equilibrium With the efficacy the R 3 plus the arbitrariness so soon when we make the we do these Lewis acid-base reactions that it at their reversible just like Bronstad acid-base reactions so that bromide can come on and off that from on that fire so commanding come off and so reduce fear minus for their elimination of questions on that mechanism anybody yes "quotation mark OK I let's do it around can be added on here but centered on here I recommend drawing the 1st went over again but you could drop from this 1 and what it would look like a lot fancier and just continue with the greenery yet conical but it's more complicated than a little easier from the last resident structural heart from the present structure not not as obvious not as intuitive lewd talk a little bit the energy diagram Britain that looks a lot like the energy diagram foreigners and 1 reaction anyone reactions we have a large energy of activation This is the rate determining step because we are disrupting their intensity stopping to but we're not doing it for long because some in in the 2nd step of the reaction were going to we had this residence stabilize cover in the 2nd step we re-establish which seen that's a very very fast reaction here very fast 2nd step are right and that leads us right into nitrogen and and I like I said then that mechanism that we did for Croatian and this is going to be very similar the only thing that's going to be different is how we make the electrified in the very beginning the rest and it's gonna
look very much the same so make collective filed but let's try that we have nitrogen acid and sulfuric acid concentrated nature Gassett concentrated sulfuric acid is what we use for this reaction so this is what nature Castle looks like In the recent war and the sulfuric acid and he is To properly the oxygen because we're going to lose "quotation mark the fix we're going to try to make the oxygen is on the right hand side I like the fact that I hear a lot of cooking Kissinger you're changing colors which I should be doing right now now and then traces the that'll be here all right not the obvious oxygen to you might think of all the oxygen as the other oxygen on the left is the 1 that should be probed but it actually is the 1 on the right is where losing that group as water and so what's going to happen here is that we're going to have the electrons on oxygen here for new double bonds between the oxygen and nitrogen and they were going to kick off this leaving group as water and that's why we are the sulfuric acid so this is our suited up Lecter file it's called Nitro meanwhile and that's going to be electrified file In the 2nd phase of this reaction the benzene is going to attack the electrified so here we
have benzene attacking nature of the violence and so any 1 of those pie was of the benzene can attack on just choose this 1 here within a grab attacked the nitrogen and many kick electrons up on top oxygen an altered the nature group right here I'm going to drive out the 1st time since even looks like an understand abbreviated as NOT I always put the hydrogen on the same added that the new Elektra file has come in on that's the hydrogen were going to eliminate on the other side of that double bond that we attacked with that will get a positive charge and our and we definitely have resonance stabilization we should you should always be able to dry off 3 residents structures within a positive charge the around 3 different spots in the benzene ring so like I said Nauman abbreviated as an 0 2 here and then we can go here and and anyone make sure that you chapter to make sure the joint free residents structures there will be you will be getting points for every resident structure that you show on the final exam but be careful don't draw too many of the draw extra resonance structures there wrong you get those cancel out once the right so I had people dropped 12 Resona structures so we don't feel we we can pick out the right answer and the advances so you want to make sure that you're really certain and sometimes people will duplicate residents structures just make sure when you have 3 residents structures when you draw your car intermediate and then it with every regenerate the aromatic ranked I'm going to redraw the first one we got some possible different groups bases to news here we could use water we could use the conjugate base of sulfuric acid those would be the 2 likely possibilities here also sees a conjugate basis sulfuric acid better and this is our 1 elimination were going to grab this hydrogen ever going and making new double bonds here to re-establish so as you can see Step 2 instead of 3 these are very similar to accept all we're doing is changing the electrified changing the basic we use to regenerate areas and aromatic rings so really the 1st phase of this reaction is the only thing that's different alright right so that titration that's a
great way to put an eye to agree upon on a benzene ring we also have sold the nation and I'm abbreviate this 1 even more Scottish actually show you how to make the electrify the seconds apart in the 3rd column relief for you to try on their own so here's solve the nation we have 2 different conditions concentrated sulfuric acid fuming sulfuric acid which is on sulfuric acid that contains all sulfur trioxide also in there so depending on which 1 year starting with let's see what that looks like a review starting with concentrated sulfuric acid and this is what it would look like we're going to get a proton transfer here from 1 sulfuric acid molecule to the and then just like that I never gonna lose water so very similar to the previous 1 Regan Owens water here water's going and that gives us some there's a souped-up electrified if you use fuming sulfuric acid which is what I usually use what I'm doing this reaction so let's put a little note there I use this 1 you start off with the sulfur trioxide Indonesia's programming so if you use then if you start with the 1st 1 this is what it would look like fan would just an approach made here can grab that Proton break the hydrogen oxygen bond that's the sum of hairs on the oxygen and that gives you go the same thing just like the peso that's how you make electrified and instead to 3 benzene attacks in the new regenerate aromatic ring on additional look just like the previous ones that's really good practice for you I write so an interesting thing about aromatics
Silvana gas is this is a reversible reaction can be driven in either direction OK so in here here would be the equilibrium and you can imagine that since water is a product here if you if you don't have to to lose if you add water so you dilute the asset it's going to go to the left faces increased the concentration of water applies equal to the left if you only use concentrated sulfuric acid and then you have a little water it's going to drive in reaction to the right so this is actually very useful and synthesis also use example we we get to the end of the chapter that that forward and reverse is actually very useful and so it for the former direction concentrated fuming sulfuric that's the way to do it for reversed direction you a heated up again water or dilute sulphuric acid very useful and were going to be doing as putting this all-female group wanted direct incoming substituent sought to block a position where I normally substituent would go and then once we have our groups on there that we can take a right back off again so actually very very useful I write questions so
far anybody you're going to talk about Friedel crafts no real grasses alkylation and there's real crafts installation will talk about alkylation 1st in this reaction we have from our CEO of this can be primary secondary or tertiary a L C L 3 that is a Lewis acid catalyst for brominated we used Expedia . 3 try bromide that's also Lewis acid catalysts so that a common thing to do and in an electrical current substitution and what you do is you incorporate an art group onto the benzene ring so the big deal here is going to be making the unelected file will do making electrify limited to an abbreviated
Step 2 and 3 OK so on it as an end in this it's going to be work remind you of Chapter 9 where we had a different mechanism weather was primary secondary or tertiary so if it is passed secondary words tertiary tertiary alkyl halide uniform across the continent so that hopefully is insane well not just an idea of moved from Chapter 9 and then you can imagine if its primary primary were not for primary copycat so let me give you an example of what this would look like yeah yeah but she's Cherpitel chloride it doesn't have to be chloride by the way it is a L C L 3 but it can be a bromide Warren iodide so they don't have to match the halogen stew not have to match so this is a L C L 3 and this is going to do what Lewis acids like to do which is accepted pair of electrons of forms from something especially something with a long hair very favorable it so this is going to be a steel plants and entails sealed 3 miners were changing charges after we after the woman had sex with that accepts a pair of electrons OK and there was going to happen is that so we're going to break the bond the carving and exploring To make tertiary care now we have a L C foreign and you're going you can imagine that this is a L C O 4 it's going to do the same thing that on tribal dear those chlorine can come on and off the aluminum solidity using Chloe chloride ions in the very last step of this reaction OK so that's what happens if it's secondary or tertiary and make copycat I'm not if it is primary don't former primary ,comma Academy so Oregon were going to keep this attached to a ALC operate are absolutely give you an example here use at all Ethyl chloride now you know will use ethyl bromide so you can see that it doesn't matter if we change the halogen so long period remained attacked the aluminum luminous have because it has an fulfilled its octane ruled that the electrons now and so rather than having a true believer that's going to be are electrified so the electrify was gonna change fast are electrified also E-Plus for abbreviation for electrified and on this 1 this is going to be our electrified so also you there are pushing for a on the 2nd part of this reaction so you can see how it's different between the 2 so enough secondary or
tertiary it's gonna look like this benzene is going to attack the tertiary Carver :colon don't forget a positive charge there we're going foreign aid complicated residents stabilize Kerber Catherine but I always put the hydrogen on the same carbon where the incoming group just came a lead the other hydrogen is often discussed might include here because that's the hydrogen I'm going to be eliminating 1 I do on the final phase of this reaction so there's that plus and 2 more resonant structures its primary let's see without outside they get used to be this could the iodide this could be chloride and we have a positive charge on bromine and so what we're going to have is that the fear is going to come from the pipeline just like in the previous example but in attack carbon and in this whole group is going to leave and see how we bypassed forming of primary purpose yeah Ghanem put the hydrogen on the same carbon there's going to be a plus 2 more what on the test you will need to draw those right rather than right plus 2 who care so I'm just trying to save a little time and space here and then on to ways to show the final step were going to do it from here you can use a CEO minus we got it also got bromide ion you can use bromide going on To do this final elimination like that you can do and how the book doesn't which is this warehouse showing how the desert a L C L 3 -minus moved any trace acknowledged only stew still discoloration here In the book they have the Erika and this is important not from the chlorine comes from this aluminum chlorine bond so you can have a view that also the the 2nd error would look exactly the same soldiers but agreed here the secondary look exactly the same but really important that you don't have to have this comes from the lone parents for anything they have come from the lone parents chloride ions that's OK but you don't our bromide but if you're doing it this way then the has to come from this aluminum scoring once all those are part of fine choices for you questions that we've learned a lot of ways to make arbitrary you you don't have to use this way macabre parents pretty much any of the ways we talked about making a corporate parent can work for this reaction so let's take a look at the next so we
learned to Abkhazia recognized both of these wastes by culminating in our country and we can make a perfect yeah chapter was destroyed now interpretation OK so that they can give you is that gives you a carpet Catherine like that this propaganda and does not care where it came from it will work equally well as the ALC of 3 examples that's another way to do it we can also improve made alcohol that was what chapter that was checked in line sevilla back so the Carter campaign doesn't care how it how it was forms it's going to benzene ring is the Benson doesn't care how the car accountants form and it's going to still do the same thing about how the copycat I was formed and it also doesn't matter how the cargo carriers form with respect to what we know that cover carriers like to do that they like to rearrange so when they rearrange so this is going to go to this this is another way to make that Kerber Caroline and we have watch out for rearrangements that's can also go to the same place doesn't really matter how you make but we do always anytime before Mikhalkov
accounted for by any means and we have to watch out for rearrangements so for example if you do this reaction with the straight chain hopeful chloride for example you actually get to products you get straight chain is actually the minor product believe the on should have formed a straight chain that is 35 per cent and then we get rearranged so that protocol rearranges too and I isopropyl and that's actually major problem product alright so how how are we rearranging their productivity we on making a primary covered cat that's the burning question I'm so let's let said that some of the hottest looks mechanism for cover cargo-carrying rearrangement well is that for secondary and tertiary really straightforward let's try that for secondary and tertiary of this is just a review of chapter chapter not least 1st started talking about rearrangements so this will be a good review for Our rights of the chloride ion attacks a L C L 3 that's certainly 1 way to do that so we former Lewis acid-base addict and then the chloride is going to lead so negative charge aluminum positive charge on chlorine and so that's going to leave were going to form a secondary fervor can iron and flashing lights to be going off in your head like something telling you that while I'm forming a secondary Curry Canaanite I watch out for rearrangements and this 1 has a really nice 1 2 hydride shift that will convert that secondary Kerber clattering into a tertiary so that's what it would look like if you were Starting with a secondary Alltel here like that's what the rearranged would look like if instead of starting with the primary and we were going to rearrange but we don't want to make a primary Courbet can find out what's going to happen is we're going to have a really do 1 you hydride shift at the same time as the ALC L 3 is leaving so these 2 things happen simultaneously so we data rearranged product without actually ever forming Lewis acid-base aspect I mean without informing a primary curvature so this here were going to attack aluminum just like that we former Lewis acid-base added that movement he thinks that I would have to drop out of high margins so we have that we have C H 2 ALC Alfred negative charge on aluminum positive charge of chlorine and what can happen is that this hydrogen can migrate at the same time that is leaving so here's what it would look like hero comes from the carbon hydrogen bombs moves over here simultaneously on this group is leaving so we just formed a more stable secondary coverage time without actually making a primary curvature as you can see from the results of the experiment that we get that this is our major problem How so more stable secondary curbing that From our rights tax-free don't grab some calculation let's talk about the past installation this will work with us
chlorides and will work with acid and around and there is a mechanism for bold I'm only going to use this time I will only test on this type what is this type type use acid chloride as is so good and I sure as your group not nodding hiring all right so what is and what isn't a solution well if it means of we're incorporate bringing out a carbon onto the benzene ring this whole entire group right here that's been bonded to the benzene ring is called over much more about that in 51 are Axelsen's and not going use in hiring and I can show you the mechanism for making the and hydride around the activated Electric filed souped-up electrified so I'm just going use the acid chloride alright so what's going to happen is a glorious green attacked the ALC offering this is not strictly correct but this is the way Rigano learners if I was teaching is to you in 51 C I will a different way that is good enough so it looks like that if you're curious about the of the exactly 100 per cent correct way to do this you can come ask me after class but I will not be tested on are exceeded imagine what's going to happen this whole group is going to leave just like we've been doing were going to break the carving chlorine font to form a very strange-looking compounds that doesn't look very stable and that's exactly by design it isn't very stable which is why benzene is happy to attack very very leptophilic you can draw like bats but it it is residents stabilized so it has a resonance structure that we can draw here where we have positive charge on oxygen suppositories can be carbon the positive charge can be on oxygen and this is called in a silly minor so you can see it found that the reader comes from the sheep assault consistent Group and now you can imagine that the next thing that's going to happen is that benzene ring is attack that and you can have it attacked either 1 of those residents structures your choice of I'm going to use the 1st resident structure because that's the way students usually show it and that's perfectly fine here so benzene is going to attack this very very very Elektra fell like a silly mine can when legislative I'll put the Acer group right here I will put the hydrogen on that same Adam and I will put the positive charge on the other side of the double bond that I just attacked with all are you can use the 2nd structure this is what Europe pushing would look like this is actually better resin structure because all items have an architect but again I don't really care which will use it use Al-Amin attack carbon and even a push electrons up on oxygen that will lead you to the same exactly that you got the other Arab pushing away but you're going to get back closer to residents structure and they no we're going to have fluoride ion commandeered elimination this is our final Phase III 1 within a ground that hydrogen within a former New carbon-carbon bond and it will look like this is so Group Incorporated onto the benzene ring so we just on it brominated we've done I tration done nation we don't across alkylation the oppressed installation 1 of those is going be on the on the final guarantee and cars on the final you will draw resident structures crystal beginning points for them question so so far pretty straightforward some new mechanisms to learn now going to get a little more complicated because what happens if we're not starting with benzene would have starting with that of benzene ring that already has a group on whereas the new group and ago we develop predict that in plan that I know why OK so clearly give you an example here you will be
impressed with this is good old and it's so reactive that you don't even need concentrated Itar-Tass and concentrated sulfuric acid like example we did this game this is rapid at room temperature daily and you to products on the amount of each the nitro group can go on and win the pair position and the Niger group goes on in the awful position so we get to them for a film parent only 4th appear only no matter that example number 1 if we compare it this if we have a nitro group on the benzene ring already we have to use fuming in nitrate cast which is more powerful we also have to use some concentrated sulfuric acid and 100 degrees centigrade so we have to keep that to get that to go on Iran you'll be very surprised if you haven't read the chapter yet VAT in this case we get mad only no worse so no parent that only so you can see the head of a group that's already on the ground that make it easier or harder 2 put on unamused substituent it it can also direct to where the news institutions are going to go all so phenol is more reactive and nitrobenzene is less reactive so that's not something you can actually have to memorize because I'm mean explain all of it and you will understand why that is the case so it will be 1 less thing that you need to memorize preserving understand why that's the case because it's all gonna make sense when we get through this section are as wantonly doing is we're going to be
dividing up the groups that are already on the benzene ring into ring activating ring deactivating and in the 3rd column category allergens and each of those has their own the those has their own army
activity in their own directing effects so and there's ring activating a group that makes it easier to introduce new substitutes is reactivating reactivating substitutes are electron donating this is the order of brain activation but these guys are made they make benzene electrons and in this reaction in Electra Philip aromatic substitution the benzene is the nuclear file so anything you can do to make it more electron rich is going to make it more reactive and so these guys here I would say the use following at 2 0 are a strongly activating and are in a RRA Armenian just another benzene ring attached these would be weekly activating and these are all going to be better than if just straight benzene no substitutions all and they want all the strongly activated almost all of these have in common except for the weekly activating what would you say I heard it all pairs became the 1st pairs on him and the fact that are in a R don't have long Paris's that's 1 of the factors is making no weekly activating to be strongly activating you have to have a lone pairs OK so that's what they all have in common so all have hair accepts the weekly activities so that's regimental look for 4 activated Ranger rings that have constituents that have pairs there's ring deactivating good that makes it harder to introduce a 2nd substituent is ringed deactivating ring deactivating substituent or electron withdrawing and I would say that all of these guys here Our strongly deactivating and over here to tone down goddamn ancestors carboxyl gasses because of preceded difference here between but this year is a carbon you are right here there's a problem you might here what's the difference yet this is the 1 this is the group that's actually bonded to the Benzinger whereas here the Carbondale itself is actually bonded to the benzene ring of 1 of these of all have in common so now it's looking for this I know well
I mean major struck native about good good idea no 1 major books like so let me give you a hint look at the charge on the nitrogen look up and look at the charge on the nitrogen so these the ones they're the most deactivated have a full positive charge on Aden bonded directly to the aromatic race the rest of these guys have partial passes 1st of positive person positive partial positive partial positive so all right have partial positive or full positive on the bonded directly to the aromatic rings that's what's making them deactivated and you write about Elektrowatt during the ah Elektrowatt withdrawing that positive charges elected the fact its division and it pulls electrons towards itself Pyrex sobering to talk about those rules for reactivating constituents rules for rain deactivating substituent we will start with the real 1 referring
activating reactivated substituent starting coming since its ruins into the Oracle propositions they affordable parent directing I've repeatedly on the order here and activation of the reasoning is an electron donated stabilizes the problem catatonic intermediate only when it is auto parrot to the site of substitution so what we're going to do is we're going to show up thought have also attacked provincial matter attack Arab initial and when we do this we are going to be able to show why the substituent are going to be going into the worth of position so what only use for this 1 is just the Nitro if I have this on Tennessee would certainly want to but you certainly want to show how you that other women have years this double 1 coming intact nitrogen kick electrons oxygen if I have not had tack let's show without looks like same double one's going to tap except I would have put the nite group in a different position if I have to prepare an attack van on the nature of truth is going to go here now I have to use this double want "quotation mark same idea tho so now let's put this sounds nature group in the auto position positive charge goes on the other side in a straw in a double bonds but again that hydrogen there's a one-word eliminates re-establishes its history and its there so I don't accidentally put a double bond there when I'm drawing resident structures if it's going to go into the matter position this is what it looks like now the positive charges here In these other double bonds stay exactly where they work it it's going into the pair opposition here's 1 another to here's my high on agenda here's my positive charge right here just like that and now we wanted do is won a draw resident structures for all these annual notice I had skeletons drawn here to save you some time and notices in the author attacked and appear exactly as she had for residents structures when we do matter we we don't get we don't get 4 are right so let's let's go ahead and move electrons around here so the positive charges can go here the positive charge and can also go go here no agenda other than With a double bond here don't belong here positive charge here and you can see that I gotta be careful not to put a double bond hearing sight repairs here's what that won't here does for me it allows me to kick electrons right here to rent make an extra resonance structure member that the higher and intermediate we've interfered with their electricity that's a high-energy intermediate we've made and I knew I present structure and that what is actually especially stable resonant structure I will talk about why that is but you probably figured out by looking at right now why that's the best part will continue on Wednesday