Lecture 5: E1 Mechanism & Double Elimination

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Lecture 5: E1 Mechanism & Double Elimination
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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: 01:12 - Alkene Model 04:19 - Rate Law and Mechanism of the E1 Reaction 06:13 - Energy Diagram for an E1 Reaction 09:01 - Important points on E1 Reaction 11:27 - Examples of E1 Reactions 18:30 - Competition between SN1 and E1 23:25 - Kinetic Isotope Effect 27:53 - Double Elimination 37:27 - Elimination Reaction Handout 42:35 - Animations
Übergangszustand Ionenbindung Activation energy Skarn Surface finishing Set (abstract data type) Wursthülle Atomic number Alkene Ethanol Molecule Ballistic trauma Common land Beta sheet Mixture Vitalism Setzen <Verfahrenstechnik> Substituent Bromide Octane rating Concentrate Alkylation Walking Tuberculosis Carbon (fiber) Wine tasting descriptors Electronic cigarette Hydrogen Song of Songs Computer animation Tiermodell Azo coupling Covalent bond Acetone
Übergangszustand Isotopieeffekt Ionenbindung Ice sheet Gene Soil conservation Wursthülle Optische Aktivität Alpha particle Ethanol Deterrence (legal) Solvent Hyperpolarisierung Human body temperature Colourant Cryogenics Elektronentransfer Elimination reaction Sea level Mixture Periodate Chemical reactor Setzen <Verfahrenstechnik> Substituent Octane rating Alkylation Singulettzustand Walking Hydrogen bond Asset Calcium hydroxide Carbon (fiber) Food additive Electronic cigarette Wine tasting descriptors Systemic therapy Hydrogen Gesundheitsstörung Computer animation Reaction rate constant Functional group Azo coupling Covalent bond Chemical compound Base (chemistry) Deuterium
Alkyne Sense District Ionenbindung Recreational drug use Substitutionsreaktion Süßstoff Wursthülle Chemistry Portable Document Format Restriction enzyme Anomalie <Medizin> Molecule Electric arc furnace Solvent Electron Sodium hydroxide Tidal race Shear strength Elimination reaction Periodate Vitalism Area Octane rating Walking Hydrogen bond Rearrangement reaction Constitutive equation Carbon (fiber) Elephantiasis Hydroxide Systemic therapy Hydrogen Computer animation Tiermodell Functional group Electrical mobility Covalent bond Base (chemistry) Biomolecular structure
Übergangszustand Ionenbindung Hydrogen Computer animation Functional group Tool steel Carbon (fiber) Elimination reaction Hybridisierung <Chemie> Death Wine tasting descriptors
Setzen <Verfahrenstechnik> Übergangszustand Hydrogen Computer animation Carbon (fiber) Base (chemistry) Cobaltoxide Soil conservation Stuffing
Organochloride Computer animation Electron Functional group Hybridisierung <Chemie> Conjugated system
Computer animation
OK so we are going to have hopefully finish after 8 today for a little behind right and so we'll figure out something to get ourselves caught up at some point in the quarter ,comma words are not talking about the you want reactions I wanna continue and talk about that he wanted only compare 1 s and 1 the 2 U.S. and 2 and I will make decisions about what reactions that take place so I have 3 things to show you what happened last Friday as I had all 3 things loaded on the computer at the same time ready to go on and that's because needed a class so I don't have that although there was do things 1 at a time and I'm breaking apart the lecture into smaller pieces so I don't think have any more problems concentrators on now that can't figure out what's going on under any questions before we get started I want to show you 2 things before we start I said a couple of things that maybe noticed maybe didn't notice but I said that when you have no consumers now became it's kind of it's falling apart hysterical doesn't stay good for very long and so you have 2 black carbon series hydrogen is that it doesn't matter what Adamaitis so but they 2 carbons that are part of the double bond on the 4 atoms are all in the same place they so we want to make sure we draw them that way but if I tried to move 1 of these out of the plane like this 1 for example of what I do is a twist bond break it any always falls off except now they're right here the class not falling off is that bond rates OK when you try to twist 1 of those that is out of the plane you get these 2 durables are no longer parallel to each other so they're not overlap and you actually applied once again it's sticking right now because I think that everybody and that's why it's doing so that's point number 1 so the 2 cognizant a part of the dump carbon-carbon double bonds and and arms the 1st add just the 1st and then the other thing is is that I said don't try France Alpena six-member range if you try to do with your models models but these ones have kind a flexible bonds and so I have 6 carbons here you can see very well well-developed upward appears you can check it out your way out so I I have a I have this is mine and trance how keen so there's my hydrogen a one-sided hydrogen on the other hand I'm going to try to join the 2 wins here and you'll see that some very strange things will happen here 1st of all the only reason I can do that is the molecules are flexible look what happens To say may see a problem with that and that's not really even OK so that's what it would look like this the hydrogen is jutting straight into the ring the case it since geometrically impossible the smallest thing that can happen as that trans I think is a in my correct on that date so you have we added 2 more carbons we would be able to accommodate a trance but not in the six-member and itself you don't believe me can come and take a look at this and you'll feel that will see that everything about this molecules very strange impact so most the things I want to show you before we got started let's keep going with the E 1 reaction far-right so we should the mechanism we make a Aqaba can and then in the beta hydrogen comes in and eliminates on debate with the vase comes eliminates the beta hydrogen to make knocking so you can see that we got something very similar going on here just a little bit different the 1st step is exactly the same as we would see em in arson and someone reaction here the only difference here is that this was an innocent 1 of this guy right here with common tactic of pattern but instead it's removing beta hydrogen and so that's what's happening in the 2nd step of the 2nd set was the only 1 it's different in the E 1 when comparing and wanted you 1 so these 2 reactions are very heavily in competition because we know with the with that the rate determined steps In Sn want you want is for the macabre Carroll the 2nd step is very unwell of activation solicitude rates are very competitive so we hope we were definitely going to get mixtures so if you will get an example here we have and if we have you should actively In ethanol at room temperature was troubled products this is our answer 1 product you recognize that Chapter 7 will also going get anyone father so if you look at the energy diagram for the structural it's very much the same as energy diagram for an answer 1 reaction so we combine around light in ethanol we make a cover can now looks exactly the same as innocent 1 doesn't since then so then the 2nd step which is the 1 that has a very low energy of activation is the only thing that's different and so for that step on was struggles struck transition state here so leaving the police dispersed at this rate determining step we start off with the mutual here we end up mutual ,comma we end up with a positive carbon so will the Soviet partial positive and the bromide I'm starts off neutral the the burly starts of mutual ends up as a bromide so this would be the year and so we have a partial negative there and then in the next step they on the basis of his in a removal beta hydrogen so that has a more complicated looking transition state let's let's give it a shot here so where were going to be making any at a new high volunteers so that bond is forming we are breaking the bond between the carbon and hydrogen are based here we have a choice we have a choice of either ethanol or we have a choice of bromide ion so I'm going to just go ahead and use ethanol because that's what I have drawn down here in the products we have ethanol comment that's going start to grab the speed of hydrogen song showing that Bonn partially formed also and Indiana drawn part the positive charge partial positive partial negative charges of the look we have a we started off with positive carbon we end up with neutral so this right here should be partial Poseidon and then we started off with an ethanol mutual ethanol mandate we have from needed ethanol right down here so that would be partial passes so that's what the transition state looks like questions about the energy diagram anybody on mechanisms more important points when the outgoing contains more than 1 type of BIG Naoki with the greatest number of alkyl substituent AP a double bond will be favored so this is sets roll right the same as the 2 just as with the S
1 reactionary 1 reaction corresponds to stability of the corresponding Kerber Katerine so tertiary is going to be fastest followed by secondary followed by primary followed by Mathilde and I would definitely say that primary NFL no reaction the reaction preparing level the cover Foreign Affairs Deputy 1 reaction is planners of the beta edition can be removed from either side so we don't have that worries some in tight carry Fleener thing we have with the 2 we don't have to worry about that at all so that wants a lot simpler so the result is we get CNN plus entire limitation so that means that we're always going to be able to get pulses Cintron also introns even if there is even if there's only 1 on being a hydrogen will be elegance system transfers that rotate throws going to get the ball system trams show major product will still be the multiple groups on opposite sides of the double bond because it is the more stable after that's right for that so let's look at a couple of examples here the far-right so we have found secondary kill mind and we have a weak nucleophile we face don't wait ethanol I'm just going to draw the army we will we will get the substitution product also but I'm just going to do elimination here alright so this leading Group is gonna leave N Crusaders macabre Catherine they advice if I eliminate from that car Academy and then I get this product In the 1st draw positive charge here that would be the product I get if it eliminates from that particular confirmation but of course we know that this can rotate this bond can rotate rotates a single bond and so on if that rotates now we have this here up in this direction and that have Ethel here notice now I have a hydrogen below the cover conservation opposite side and we can also eliminate from that when meet all distraught Arab pushing for that 1 here H over as we haven't drawn too much of that from this and what you can see it this she was going to grab that being hydrogen remake a double bond here are leaving group is already left so that's all we need to drop henin attention to this product Of those 2 products which 1 is the major Top Bottom focus groups on the opposite side right focus groups on opposite sides therefore especially major this is our major product now and in end of course let's not forget about we will get substitution and were but right now we're just talking about elimination soldiers right that here we will get substitution in addition to other elimination for this particular reaction what if we take that same Qalqilya light and we do it the 2 alright so this 1 here is the 1 this once 2 conditions here we but as we got a problem here because it has to be intact .period This is our already drawn in tight carry so let's eliminate here if the if the beta hydrogen in the leading group are already in Thai curry clear you don't have to put it into a new and projection just directly draw the product so here's the arrow pushing for that this is the only product that you get here it is not the only stable product and is not the most stable product that's the only product you can get because of the constraint of the entire currently the elimination so we must be in tight Perry plane so we really don't have a choice of the other product in order for us to jobless product we would have to have a same Gary Player transition state Gary plane elimination were not going to happen all right so that's kind of a complicated example who has questions on that when in a very yes of at the top 1 but when me demonically what is this change color here In the field of Philip purple OK so here that the Alpha hydrogen that's the offer ,comma bonded to the winning group and this is here the beta carbon so that's the hydrogen bonded to the leading group on the Altha hydrogen we did not eliminate this would be the alkyl hydrogen system that will make the itself hydrogen and we are eliminating the beta effect see that more questions over here well I'm not saying OK so if I ask for the major product would only draw this 1 hears someone say have to drop all from saying that you always get the opportunity of having involved with anyone not with the 2 far-right OK but some competition between us and 1 on anyone and I will talk about competition
between all 4 reactions so bold as to 181 reactions here ,comma intermediate the cargo-carrying bites both favored by the use supported with and polar products solvents so everyone is usually favored over anyone especially at low temperatures so we said have that same we have that same thing that would turn higher temperature favors elimination that's both for anyone and you too the ratio of at gene which is you want to substitution is greater when the team formed contains more than 2 alkyl substituent AP a double bond or is exceptionally stable so here's an example right here let me draw all 3 products and what you'll want to do is on your own go through and show how you get these products a case you recognize that as a substitution product In this is an example where I'm actually drawing all possible products not just the major now we're keeping the temperature low that's room-temperature were running this reaction at room temperature were keeping the temperature low so they can help us here so we normally would be thinking to ourselves well and looks like substitution will be the major let's see what we actually get here we get some 38 per cent substitution at 7 1 we get yet so 62 per cent elimination so that is gonna contradicts what I just said right this 1 would be minor because it's a little less substituted this 1 would be major because it's substituted and the reason that elimination is the major product is because this out can we just formed has 1 2 3 4 are groups attached so it's exceptionally stable so that's what I mean by the ratio about his substitution is greater when the keen for contains more than 2 Sosa's substituent at the double bond or is exceptionally stable so try substituted Tetra substituted elimination is going to be a major part meeting will increase the percentage of 81 years you can see that on the next page but even in spite of doing that you're always going to get mixtures you're always going to get substitution elimination so wants elimination Oli you're going to use a strong base and and eat your reaction and were we're going to find out especially when we get into Chapter 9 is that Hassan 1 human reactions are complicated the even more complicated than were showing here because they do cover tenants like to rearrange and so we're going actually other products that we wouldn't expect so if you wanna get elimination you have a tertiary out here like you just what you want to do anything you want eliminated using a strong base it will be a much cleaner reaction Our rights OK some worry about asset 1 versus the 1 verse us into verses each shoe was see summary sheets whats dues but let's wait and will finish this chapter and I will go to the summary sheets because I wanted to have everything loaded but a course in life I do that the things that Impressionism was just finish this chapter and they will summarize everything will go to the Web site look at all that the summary sheets of paper so there's 2 things we need to talk about what its Connecticut isotope effect and 1 is double elimination so those are all things that were really talking about here at the end of the chapter are I to so when we've been talking about mechanism 1 of the things that we do is do we do kinetics to help us figure out what the mechanism is and that's what we've talked about so far as we want a reaction we change 1 reagent was see the fact has enraged the change the other Regency defected has array there is also some other there's also some other tricks that helped me decide on what would type what is the actual mechanism for reaction 1 of them is to use a kinetic isotope effect and this effect compares redirection of a compound containing hydrogen with the rate of reaction for compound which 1 or more hydrogen have been replaced with deuterium which is an isotope of hydrogen it turns out that deuterium and hydrogen they are isotopes of each other and they behave similarly but they carbon deuterium bond is slightly OK so that Kerr-McGee deuterium bodies is all it's a really small number it's only 1 . 2 K Cal's from all stronger than a carbon hydrogen bonds but if you are breaking a carbon hydrogen bond in a rate determining Stephanie replace that hydrogen with the deterrent it will slow the reaction down and that is called the Connecticut isotope effect I'm so and kinetic isotope effect in invited do it is you you take a reactor reactions that has all hydrogen and you running a new measure of rights and then you take a reaction where you've replaced some key hydrogen is that interested in and with deuterium and then you measure the rate and then you just to to you calculate determines at affects you take the rate constant for the hydrogen containing reacted and divided by the reconnaissance for the deuterium and Natchitoches La isotope effects in these numbers are usually have about in the range of space 17 on something like that would be common so just that 1 1 . 2 K Kallstrom slows the reaction down 79 times slower so it's a really you have to know definitely a noticeable effect so let's see how we would do that there's an example here where we have a reaction and it we want and what we're doing is we're just looking at elimination here were not limited looking at the substitution we will definitely get substitution but we're looking at the elimination and you know you saying yourself well OK I see a strong base their but I also have a potent solvent so could I possibly be getting any like the 1 in there too in addition to the 2 could I possibly yield is about about this year I'm saying you want question whether this reaction is going by and the 2 the once-a-year underreaction with high hydrogen and where use he here to favor elimination because we will also get substitution here so these are both heated up pretty high so he added to favor elimination all right and so if we did that we measure rate we did KDH here then would have the same reaction and we measure the rate this would be kg now we what we find out is that kph over key deed it is 7 . 1 which means that we are breaking up carbon hydrogen bond in the rate determining step that's all that tells us so breaking away carbon hydrogen bonds the rate determining step so what does that mean the mechanism the it it yours anyone it has to be a need to write because in any 1 the rate determined suffers from a macabre cotton has nothing to do with the the hydrogen the hydrogen is removed in 2nd very fast fast steps so that tells you exactly what we would thought was that that was the to on the 1 alright so we have a Brahmin discussion like that we will get to it today really doing next week but you might want to try it on your own over the weekend far-right
double-elimination this is going to something that we're going to be using for Chapter 11 so women talking about al-Khalayleh 1 of rehab outfields Xylia life and they can undergo 2 consecutive elimination actually to get products that contain 2 with 2 double wall and so on here we had we would have to have excess hydroxide this is going to be in the champ army let's see what we have going on here so the 1st detailed I'm religious liberty on on the left-hand side these are both identical out there he lied in each side of this molecule OK so that her 1st you but we have excess hydroxide so let's now would decide in which hydrogen were going to eliminate for a 2nd too so let's take a look at this this is our furnaces are carbon-varying leaving group this is Bader and this is fatal so we can eliminate 1 of these 2 hydrogen or we can eliminate this hydrogen right here we think the places so that the 1 right that's if we eliminate and hydrogen will get them were substituted team will get try substitute because as 1 of our group 1 of our group than those that are prepared if we eliminate on this side will have a conjugated team which one's going to be better conjugation sorry eliminate this hydrogen right here so 2nd to so we have to keep making all these decisions so now that we will we draw that we get this spot double bond is conjugated with about double bond on the left engine so that's what we're going to get right so that the product so conjugated can't you don't want to hear it means alternating double 1 single bond double bonds therefore are more stable even no less to tutor With some say that I to new bonds all right here this is not carbon hydrogen off except just a 2nd for more stable even tho the last substituted so hydrogen right there the now if Tualatin during the same carbon which is cultural daylight or adjacent carbons then we get alkaline instead we get a carbon-carbon triple bond that forms so let's take a look at that so this would be on this all which means on adjacent carbons and this is chairman of drug that could be out of time that we get here and we're many users reaction at all while in Chapter 11 reduces its time in Chapter 11 so this is a book that is is 1 of the army I like to call famous regions that we're using a lot all year long so this is really common here and noticed that the bases I want to point out the base we actually need a stronger base for this reaction OK so let's go to the mechanism you'll see why we need a stronger base here so another aged to here managed to minors very strong base rabin eliminated hydrogen so coming gravesite agenda movies electrons over kickoff are leaving now therefore step we could've easily with sodium hydroxide the 2nd step is a little bit harder to do with sodium hydroxide why's is that what we need to wages dropped the 2nd step for you maybe they'll help you see the answer to that question so what we need to do here areas eliminate this hydrogen move electrons here shake off leaving so sodium hydroxide works for this 1st step it's not strong enough space for the 2nd step by step why do we need a stronger base for the 2nd step the company yes it has Morris character that that's a stronger bond S the 2 carbon hydrogen bonded stronger so we need a stronger base for that 2nd step so that's that's labeled 2nd elimination it as more difficult harder more difficult therefore you need a stronger base and the reason why is that we haven't asked you and carbon hydrogen bond or breaking here they were breaking up on the rate determined step for that that 2nd step ,comma so why and as the 2 carbon hydrogen bond is stronger Bob rights questions on double-elimination so when energy right now is that go to our class to Web site let's see how weird this has been a nicely cooperate with me which granted we want you sweeteners like wrong today Our soon now you see what I wanted to have this all
moaning but you know what you gotta do what you gotta do it OK so I added some new items on announced soon noticed from 3 mobility of patients I had submitted answer substitutions shall last quarter were made over elimination this is still the same philosophy on this is still the same this is new substitution verses elimination this is news substitution verses elimination flow chart I don't usually use a flow chart of some people find it really helpful so let's take a look at the summary of elimination reactions 1st OK here we are and that's the PDF America right on about that application 1 just point out things OK so Tuesday at mechanism 1st step will make the cover Canseco 2nd this step will later be hydrogen compare that with the it's you that's 1 step right into it .period player here and that we make the opening so that a two-step reaction so the 1 2 steps like the S & S A 1 and A E 2 2 steps like the other 1 step like the other to fanatics first-order rate depends only on the constitutional killing aligned and lead to a 2nd order with we aware the Constitution the base and the outfield here like matter stereo chemistry no special steric chemistry and required for the test for the EU was on for the each Ubaidah hydrogen filling a group must be a typo player entitled player in a six-member bringing Tyco planners Transkei axial will have to have that for us to get reaction most able out favored will stay blocking the favor sometimes you can get the most stable locking because of restrictions here on the stereo chemistry a crisis undereducated the most stable but if you can dutifully morning period again solid facts requires an ionizing solvent polar this is just like and to ride a variety of solvents OK so also the examples we did we did no to that OK let's look at effect ochre tertiary Shareef faster than secondary fashion and primary 41 42 tertiary vary for faster than primaries that better than secondary faster than primary so they have the same right there have the same effect of model that I'm competitive reactions S N 1 and rearrangements this is going to be after Chapter 9 so this is the underdeveloped secretly been hiding from you about what happens with copycat I'd still like to rearrange and so you know and and so we just kind of have been ignoring that's that's kind of the elephant in the room that we've been ignoring and we were not ignore it anymore after Chapter 9 so that it when you come back to select more sense answering arrangements are a big problem all the since long eating by suppressing dissenting but of course we know when reusable the base attended Italy's substituted product not only do you have acquired it would file the case is OK this is present only remove the beta hydrogen from the carpet padding system has no effect on the race on each 2 on the other hand needs a strong base OK so that's pretty much everything summarized fostering substitution versus elimination this basically I'm summarizes everything that we've been I'm talking about the strength of the needs of all determines the order of the reaction was order the reaction is the 2nd orders for story so I'm not going to read this to you you can go through a look at this is going to help you tremendous amount primary using undergo as actions sometimes you too if you can get find yourself a strong unhindered base a kind of tertiary allergies to undergo the E 1 each year reaction was strong racer make sure you wanted in arson 1 this is a really helpful here and I want you to take a look at it and threw it on your own and definitely secondary Oppenheimer lights are the most difficult to predict so unlike you go through that
and you're on there here's our substitution elimination flow chart we think some people really like this so it's here for you as a tool it's here for you as a tool when you're working problems leading up to the mid-term will not be with you on that none of these handouts will be with you on the OK so after you do this for a while you'll be really get easier it will be easier to predict what's going on I write questions anybody would you like to see some innovations became sponsor I guess it looks quite on alright so weary of the 2 let's go back for a solid orient ourselves here here's the made hydrogen that's the signal between the other as the 3 carbon and the Ivorian awareness changes in hybridization here once we have this reaction here is hardly being group that's a signal bonds on the basis that it can in from the bottom OK there goes right dead rabbit a hydrogen look what happens to see that in the cool OK so noticeably personal negative personal negative now that's kind of the transition state right now it's boasts more slowly here we see hybridization is changing OK that's the 2 let's look at that 1 more time and to look at the ones OK Cuomo there's a transition state someone that flashes blue that's a transition state the student 1 more time and too much fun here Casey yeah OK let's go back here alright citywide will
copies so far it's only every week she was body made the
garbage that I am but still back here there's a carbon content that's oriented stuff there's the carpet patterned on the left-hand side there is the bait hydrogen it's still a signal born here what is this little business going on right here hybrid conservation to stabilize the harbor carrying right if that sounds like another language rights is said to go back and look at that they talk about that in Chapter 7 Type a contribution so now no no no don't do that obtained OK that was too fast I actually slowed things down quite a bit with the OK so there's are based coming in their bases the solvents and remove that made a hydrogen so there's this there's the transition state when everything turns blue parcel positive on the carbon that was the cover Caryn Baird also partial positive on this oxygen here cassettes and have a positive charge when it's all done they grounds that hydrogen takes away the actually getting here let's you know what we can achieve it here let's let's do the show the copycat informing me she'll
remember that you have the last word Bahrain year-ago
so alkyl chlorides this was going to be breaking this is the is in a leave on its own review cover and this is still as the 3 hybridized there is a greater rights is not going to do anything yet OK so select groups about to leave so that so so so this right here is just the pair of electrons in that in that below and would keep going so that is so there's dotted line right here that's the hyper conjugation it's helping stabilize this score was seen will return so there was no change the hybridization there was 181 sitting here we've got 1 more minute you with suitable for each new or anyone you want again OK
gridlock far-right will stop right there and we will start Chapter 9 on Friday