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Lec. 06. Carbocation Stabilization by Vicinal Sigma Bonds.

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you where we left off on Friday on which means that it's gonna look like I just
used my clothes on the camera here so when continue where we left off and that's talking about anyone reactions were you lionized some leading group to give macabre cat iron and we use that Hammond pastor was on a regular basis to justify how fast as and 1 reactions when leading groups popped out to give cobble can hands if we you invoke the human partially we can simply look at the stability of the Carbol gather and saw how fast is it to take something like this and other leading group believe forces take something like Justin how little he lied and have the leading group leave from there that's kind of what we're really asking and that's not a well-drawn so what we need to do is we need to think about Wilhelm nucleophilic Ardys pipe bombs how able or are they to donate into the NDP orbitals how nucleophilic got or how able or are they to donate into the starting into binding work and all we need to do is draw out the energies of these different pipelines these canonical warbles for SEC bond and ask ourselves what happens if we replace a carbon atom a high bond with the lecture on negative ads what happens if I replaces Adam at the end here with the more it doesn't matter which Adams what happens over replaced 1 of these 2 Adams with a more electoral negative ads you should predict that the energies of all the orbitals associated with this Adams should drop down if I put something more Elektra negative so
carbon nitrogen pylon should be less nucleophilic should be lower in energy and less nucleophilic Tennessee C 5 R and
similarly of a carbon Neil bond should be even less nucleophilic so immediately you have a prediction and your prediction is that there should be in terms of stability that this should be the most stable and the carbon meal substitute couple can and should be the least stable because the steel pipe bond is the least nucleophilic and likewise the ionization out of elite group Alpha to Aqaba neon should be slower than the comparable on Powell chloride a leading group ionization and so that's just a basic understanding of electoral negativity and I want to draw the series of Part substituted cargo can alliance and try to compare those out I want to put some numbers on how much
stabilization we expect From draw out a series of cargo
canines and I'll compare them all to a methyl cat iron which is absolutely awful awful hard to think about it so there's a pH we use is an abbreviation for phenols you you can draw benzene ring there if you want I'm often going to drop pH instead of entering there's a simple can iron here's a probe Cargill cat and that's with the triple bond we called Papa Joe will compare all of these 2 just a simple plain on substituted nothing to stabilize its methyl Cat Island and then last all replace this with and another cat it's not pylons associated with it but unfortunately it's got this and plus there so that nitro groups and nitro substitute Carlos can and it's very easy nowadays using at
initial calculations the semiempirical calculations to calculate and compare the stability of the scorebook
headlines it's all give you some stabilization energies and these were calculated at the P M 3 level theory doesn't matter to you the point is this is a gas phase calculation you draw this new ask what's the energy of this new gas phase and compare those energies and out what I want to do will give you relative energy is the absolute energies at important what's important is the relative energies all arbitrarily assigned the metal can iron ,comma relative energy at of 0 and so relative to just a simple mathematical can a Bengal cat iron is 56 kcal per mole stabilized so would be negative energy lowering energy all destroyed is because I'm talking about stabilization of people these numbers positive How many times more stable is the methyl is Isabel can I'm car Lotfi
I don't I can't divide up by 1 . 2 I'm not good enough with
that but it's a lot right up until group of Denzel pattern is very stable and how can I is pretty close these rolling K cows from all which means you can convert them into factors of 10 simply by dividing by 1 point for each 1 . 4 K Kallstrom all corresponds to a factor of 10 stabilization and found they'll get over Europe apart Bill it's not quite as good that make that ceased that triple bond about what really short so we can remember that that the the pipe bombs very short this very stable pie bonds not very nucleophilic so all of these are massively more stable the effect of having a pie system next door but not all pie systems are created equal it's obviously bad to have this electronic nitrogen but with a formal positive charge here this is actually 31 K held formal hiring energy young get stabilization with other cat I'm with a nitro group you get destabilization so it again not because I'm calling the
stabilization energies instead of putting minuses here and work assignments OK what
happens if you put Koble Caroline's insolvent you can mimic the effect on with semiempirical calculations it's not exactly the same as measuring number in water election but that this there's ways to mimic the effects of water solvation on these and the point is they're not quite as stabilized anymore when you put can in water because water intrinsically as a stabilizing effect we get 23 K calls from all of stabilization energy that this calculated at this level of theory for eventual cobble Carolina and when you look at and how well compared to bonds or what you find is there not that different so in the gas phase if you ever happened to be running reactions in the gas phase or in hexane units which is very non polar
environment like that then you should expect bans to be better at stabilizing Koble now but if you run
reactions insolvent like normal organic chemistry in organic chemistry by organic chemist and these are pretty much the same in terms of stabilization Allen Denzel and then we get down the pro-pot all that was worse than both at we expect and of course these all relative to to metal can and again and nothing much to savor the Nitro substituted cover again and that's pathetic I don't have a leading groups leave when next and drove group because if you wanna calculate how much to proposed cobble cat eyes are on their way unstable OK I wanna make a point to you because oftentimes you're going to see numbers there were calculated to gas these calculations it's not trivial actually to do good of solvated calculations so in the gas phase and the so this has to do with
calculations which had a rationalization this be true this is even when all else is equal to larger ions are more stable so what I'm telling you is if you compare this cargo cat I just approval can like this With a longer can find what you'll find is that the larger Caroline more stable slipping draw this can we find some way rationalize the wines that if you did some calculations for the stabilization energy of this primary gobble cat Ives's this 1 that this 1 would look more stable and more carbon atoms you add to this change the more stable it would seem and this is 1 of the things about calculations that you don't
see it a similar effect in solution the way to think about this at least 1 would think about this is that both of these
have any dividing warble associated with that empty without cargo cat and there's an empty word over and how we think about what stabilizing that while the CH bonds at a stabilizing that I might look at this CC bonds it can overlap with that and and it can donate into that anti-war bill Sigma CCE can donate into NTP rely on carbon that's a stabilizing effect is always stabilizing to have billboard roles in directing them toward rules that always leads to net stabilization and so I look over here I've got a C bond that can also overlap with that NDP warble but there's another CDC bond right here that's on the Periplaneta this way and so I can highlight that money drawn this this CEC bonding mortal here and if I think about this bond right here is donating in the Sigma star that should raise the energy of having this bonds due a nucleophilic attack will weaken this bond and make it a better nuclear files and you can continue this onto the entire chain every single interaction between Phil orbitals and will help to stabilize this so when you look at gas leaks calculations be careful because anything bigger will see more stable because there's more bonding orbitals interacting with bonding orbitals even if when you put it in the solution this actually isn't really different instability so be careful analysis of the effects of those calculations OK so at school and make 1 final comparison had been talking about long pairs in our last lecture donating in the cargo guidelines so I've just finished talking up I systems double bonds triple bonds
donating into and stabilizing cobble cat come back and look at Cigna bodies and were not done with singer bonds another kind of this is 1 of
my favorite cargo Caroline's not because it's really interesting but because it's easy to draw so you'll find that I often dropped cobbled Caroline's and sought more organic chemistry in this class not because they're they're super great just very easy to draw the Carbol can I mean it's a realistic cobbled cannot on the it's not hard to make tertiary coral can and solutions 1 point that I want to make is that TV will cobble parents are more stable and is now on Denzel cat and so why
is it I what's the nucleophile it's donating into that and Sony
remind you what donating into that anti-war In a TV or cargo can know what's stabilizing this TV will provoke can iron with the donation of these skilled orbitals the Ch there's a canonical frontier molecular orbital associated with this there is a single word at all the city of and there's electrons in the bond and they are overlapping in space with this NTP orbital and this 1 isn't well I'm 1 of these 3 hydrogen will be well aligned there's no way you can spin this methyl group and I have at least 1 of those Of those bonds aligned with his endured and there's 3 of them back here at the bonds they can align back here and there but there's always going to be some group this TV tertiary characters and there's always going to be something that's aligned to donated them and it is true that these bonds are very nucleophilic but the close in space and it's hard for them not to overlap in space with that word so that's why the
cobble kind and are more stable than just a simple Alois Denzel so if I compare that with this this
isn't as good that Al-Qaeda and is not a stable Nunavut now of course this is not a typical Koble can usually there's extra substituent on there at that point as soon as you put 1 extra methyl group the substituted I'm becomes more stable which is the Raul Alcala and with only 3 gardens not as good as a team Beutel couple can OK I want to come back and deal with an issue that related to this effect of electronic activity so signal bonds and donated to cobble that I was given no you typically don't draw ch groups attacking things and a good start off by thinking about this and and what I want to think about is the ionization of this leading Group and what's available to help push out that how fast is for the chloride tube to pop out in these 2 cases and so the question that we want to resolve this if we draw this out to buy if I try to draw the so what are the mechanistic possibilities here so 1 mechanistic possibility that I have Is this bond I just told you that bonds the nearby nearby bonds can donate into into bonding orbitals let's to this carbon nitrogen bond it's got a pair of electrons associate with the canonical frontier orbital you can imagine that maybe this bond could bend over and push out that Leading Group think that's not hard to imagine if I did that because of the way I do this 0 pushing I have to draw my products like this what I'm saying here Is that I'm making a pie bar and I'm ionizing offer Leading Group and I'm leaving this nitrogen without 1 bond if I use that bombs to attack and then taking the electrons away from nitrogen I have to draw those as the products that's the same thing I would have to draw offer it as a resident structure for the TV will cobble can there's another way to
think about this may be true that is it may be the lone pairs on nitrogen could donate in order to give us some sort of a bonding interaction here
another 2 very different types of interactions so worried that stabilizers that makes ionization faster Armed or fast this is called a master this class of compounds where there's a nitrogen beaded to alleviate plight the mustard diners so fast to the point where they're using chemical warfare and to kill cancer cells ,comma it's not this it's not the signal bond it's the lone pairs it's not the sort donating it's the lone pairs that are donating In other words you don't break the 1st carbon nitrogen bond which you do Jamaica 2nd carbon nitrogen but that's the way we think about it so it's not that all signal bonds are equally nucleophilic signal bonds attached to elect a negative ads are very nucleophilic and that's what you'll find me give you another set of of ionization reactions and some rates and will try to rationalize why summary faster and why summer smaller he is the sole but we had talked about this reaction of the foxy methyl chloride Montoya hours of methyl group this turned out to be very fast it's much much faster to ionize is leading to about here vastly faster than if he is having had a primary Alcalde fluoride and
it is true that you'll have some electoral negative ad I'm
attached to the coral kind but that's not what's important here the important point is that this lone pair can easily push out that Leading Group and when I look over here what's available there's no loan guarantees carbon atom here which is the CHT will the only thing we really however ch bonds and some CC box and finally if we compare just a simple alkyl chloride weather-related system where we moved the oxygen atom 1 farther away what we find is that American is much greater than others change that a greater we find that this is
less reactive it's slower time is up the court when we have an oxygen beta sold matters where we put
that oxygen atom over there the lone pairs can help but here the oxygen lone pairs unlike nitrogen the oxygen on pairs aren't nearly as nucleophilic you don't get this affected the lone pairs all you get is this crummy electro negativity effect here where oxygen is a lecturer negative and you can imagine what that's going to do to the Carbol Kanye stability OK so why is it that this bond is not very neither the lone pairs can article looking for the bond on bonds to elect a negative Adams unless nucleophilic so you hear this CC bond could do a little bit to help push out to help donated them to buy more world but the seal bondage is nowhere near as nucleophilic and so you see a much slower effect focus oxygen cans can help ionizer leading groups but it really depends oxygen atom has to be right next door that leading so that the lone pairs can push it out OK so that's the end of this this initial lecture on Koble Collins found on ionization reactions to generate cobbled parents and I want
come back to this idea and really focus on another it sort of looks nice to think about this idea of a C C
bonds donating intervening orbital or ch bonds donating endangered by moral and pushing up believe Europe and I wanna talk about some really good signal bonds that can really really soup up the rates of ionization and that's the entire next lecture what is that she said
this is the 1st this is not the other way and I
wanna remind you of this relationship that we have got a name that is what I mean when I say this in all this is a personal relationship between 2 bonds between 2 groups in this is referred to as a general relationship so you can see there is promise this is sort of like a 3 bond on this sort of organization and this is the 2 bond that's you commonly use that language in the tug of proton NMR coupling constants have 3 bond listen all coupling into Banja ultimately officials thought about this arrangement of leading groups and signal bonds and
where some surprisingly stable Koble cat that can result from that region and in order to get us ready to think about
that I want to become very good at drawing a specific type of by cycling system with a Norborne ring system looks like they're straw cycle hexane and all 1 Covered Bridge attached to it and there's a very common classical way to draw this that looks like a coat hanger and more I just want to tell you don't draw like this others right no don't do that because when you do that were missing a very special relationship and that's the point of this lectures special relationships between bonds instead I want you to use your best share drawing technique for drawing all grown up Norborne owing system suspect is drawing cheers in all I was an undergraduate I suspend count that I don't know how much time is spent ridiculous just practicing drawing cheers on paper over and over and over again in the bathroom Nixon this window in the shower was leading there's some special relationships that were trying to gage when we draw chairs what I'm trying to do every single time I draw a chair than trying to emphasize parallel bonds this bond is exactly parallel to this 1 and exactly the same way like that I've drawn the chair correctly that parallel relationship should come through here's another pair of parallel bonds little point out to you these bonds in front of a parallel the ones in back the bond there and it's not just this relationship it's the fact that if I correctly drawn Equatorial substituent but it is empty parrot playing to those 2 bonds in the ring perfectly parallel perfectly the same length and perfectly willing to ante Periplaneta those bonds in the same way In these relationships have to come out when you correctly drawing cheers so I'd like you to drink when you draw Norborne all ring system is drawn in a way that allows us to take advantage of your ability to represent 90 Periplaneta relationships Texas good start off with the silent on for how to draw all I would like you to draw born ordering systems so we can see
these anti-terror planar on relationships between bonds photo to answered often
notice that a chair as is a six-member meringue but in the normal range system is composed of vibrant member rings what I'd like you to do that I'd like to start by drawing a chair and then remove 1 of the carbon atoms specifically that Straw bond across here like this what's there we go and I have a five-member grave maybe you could adjust to on this very lightly let's practice again and I will be so upset when I when I can I ignore the ,comma Adam on the side now the the important point is I want to be a little more perfectly axial bonds and enjoy axial substitutions and I don't have another year's agreed upon when I draw axle substituent on a chair they should be perfectly straight up and down not angle to the side not leaning over perfectly straight up and down and all 3 of those axial bonds have to be parallel erroneous anti-terror planar relationships amid all that bonds on the bottom straight down straight down the straight down enough of drummers correctly that means this plant here is a deeper pleaded that 1 and what that means is that this bond can perfectly donate into the antibody were little for the axial 1 next to it and those are the relationships that we want to see if we care about the directions of
warbles lentils I'm going to come over here and draw the axial bonds I'm over here on my five-member brain here's 1
and now over here I'm going to draw the other axial bond and notice how clever I was not to draw this carbon atom directly below this 1 because if you you do that you're screwed right if you drew this carbon atom directly below that when these overlapping lines and no human on the planet can tell what you're doing so you have to practice at another drug these to axial bonds with the same might elect elected is join us together and there is mine or watering system ready for me to emphasize in the period planar relationships
again why should you care so much about crime ,comma about drawing things using share-based
confirmations and I'm just going to give this to you as an example I was please advise this is actually a try cycle compound there's a bridge on the system right here when draw that Bridgend I'm making this and bolster indicated it's coming out toward you and we were try to assess the ability of of his oxygen specifically the lone pairs on oxygen to come in an attack and displays that bromide it does not look very good managers just has not seen very good but let's try to reassess this and draw this using an armchair based confirmation so why straight be so particular about drawing a fine ever trained that will five-member
agreements based on United Rosenkavalier that's based on a chair recycle hexagons that I draw like this
it's very easy to use other chairs together if used correctly drawn your 1st year it's very easy to use cheering still other things correctly drawn and so the advantage of me drawing a warning based on a chair is that it's very easy for me to use other chairs on the Hill there we go that's the 6 firing system I can see NatSteel methyl group at this really junction there is right there sticking up and all that extra muscle groups there we go and I can see the Norborne ordering system over here majority the bonds here in line or warning ring system there it is and now when I draw this bromide bromide is picking up here the major sticking out toward the and it's sticking on the same side as this bridge that's coming out and all the important part is I don't all the hydroxyl group going down there's an age that axial pointing out there's no way to pointing down here is the age bond hears the old and now it's totally obvious to me that this side of the the easiest bond forming reaction in the world you could not stop this oxygen from attacking that remind that this guy with a base there's a bond there you go maybe even without base that will end up cycle unstoppably and you need to be able to do this without some fancy computer ,comma program that that defines the minimum energy for you want to be able to draw structures based on diamond lattices and based on cycle Hexham chairs I expect you to practice I collecting chairs and I expect you to draw warning not like this I don't want to see you go like this I want to see you drop like this or here confuse on other
check on other six-member chairs and I'm going to give you problems where you need to see those relationships focus was talk about why the North morning ring system is special it's
going to help us to see the importance of bond alignment and proximity the fact that whenever I use the word solve lawlessness that means I'm doing SN 1 reactions and the solvent as the nuclear file so if I say sold Wallace's you might think about doing Anderson 1 reaction is ethanol then ethanol a nucleophile more typically the resilience of studies in the 1960's and sole Wallace's reactions most of those done in a gasses are where acetate is the nuclear file I'm going to start up by comparing 2 different Norborne all ring systems are on nor morning starting materials in 1 of these I'm going to have the leading group sticking down here and in this particular study was a softening the wasn't a tosser Lake Louise's toluene armed with some sort of Bromo benzene sulfur native I remember correctly so they compared to different isomers this particular position is called the 2 positions of the nor warning ring system so I guess you could have called this the 2 position Azizabad but by impact this is called the number 2 position OK so it's good and compare this with a dire staring in which I angle this instead of pointing downward or or upward so the merchandise Gary Myers of each other there's an age at an element of so we can see the relationship there appears to different dies during to Norborne Areas soulfully and they're not equally reactive sometimes elected darkened bonds they're closer to me ,comma I want to really emphasizing space what's closing what's far away maybe that's a little too long OK so here's my 2 airing of years might to Norborne all we have a name for this particular isomer because nor morning ring systems are so common we call this the Endo isomer if you say all that said Andover true nor mornings soulfully derivative anybody any chemist will know what you're talking about a recall this particular isomer the XL dies during the XL license so and itself and you simply need to remember that begin think about ionizing this Inesita as the solvent to produce all of Wallace's where the sole actors access the nuclear power is actually in this case it was a buffered the and potassium acetate so it's it's probably acetate that's attacking the cargo so
that is you've got a leading to at least 2 general cargo can and acetate comes back into attack if we look at the the reactivity
of the analyzer I don't think it should be a surprise to you that you get this you get the XL acetate is the product but you don't really know the mechanism for this reaction just from the fact that you got inversion of configuration you get 100 per cent clean version of configuration and a license another would you start with the leading group down you end up with the nucleophile up there's been an inversion of the center City take the XLI summer you get exactly the same problem you get 100 per cent clean retention of configuration so what's going on there so 1st of all it's very easy to conclude that that and this is not an arson to reaction all you have to do is run under conditions where you decrease the concentration of the nuclear file and you find that the rates not changing 10 times less nucleophile the destined to honor the 10 times faster but he changed conditions and bet a lot in a way that allows you to reduce the conservation nuclear power is no difference in the rate step monotonous into action but more and this is what I is advice that with 1 any aren't you married this product is receiving if I start with a single and aunt era this suddenly you have a Rossini mixture for your product when I come over and look at this XL isomer moreover we find that it undergoes this substitution 350 times faster focus which tried to rationalize these facts this was completely inexplicable in the early 1960's ,comma and there were fierce arguments about why these things should be true I'm
going I'm going to notice something that's important with no warning about that makes it so
special right off the bat and this is why I want you to be careful about what you perfect non-alignment and yet so I said Let me draw out this this Exxon all type derivative again and I want to emphasize this relationship between the leading group and in particular this axial bomb clearly highlight the leading group there it is and here's this bond here is perfectly axial and it is perfectly aligned with the antibody morbid with the Sigma story antibody word that I dropping antibody here it the into binding orbital that Sigma star for this carbon Leading Group bond that's the empty orbital there if you put electrons into 20 antibody orbital you break the
bonds In this bond right here this carbon-carbon bond right here is aligned to
donate into that is overlapping in space you cannot not have it it you can't help but overlap with this into binding water at all times there is no option here in terms of flexibility the structure is 100 per cent of the time deleting it into money and weakening his mind and soul that explains why this is so much faster when you look at where this NOI summer you don't have this place and it may well look to you because of my crummy drawing it may look to you like that bond is perfectly overlapping but it's not and I wish I had a three-dimensional model to show you that's not overlap in space and OK so you get this perfect bond alignment that really weakens this XO license and as a consequence it's very fast to ionize out this leaving group and so when I drove
off this cargo Caroline intermediate MacDraw that
empty orbital here I'll always like to draw the Adams the attached on my on my car broke out I had to tell the readily see what stabilizing and here's the cargo can I'm intermediate now in my nucleophile comes in it can add to the more accessible face result in this particular example I gave you acetate is a nucleophile and it can come in an attack on this NTP orbital like that but there's an end to Bonnie orbital that is overlapping in space with the bottom will with this keyword that bond right there it's the it's the fact that this is donating from the side that makes it harder for the acetate to attack from the bottom the transition state for an attack on the top where you got a partial bond here is the same type of transitions that you drew for the leading group leading from the top of the transition
state for leaving 4 of the leading group is lower energy
when it's XL then you should conclude the same for nucleophilic attack as well as we do with the important point is if I want to draw some sort of any interaction some sort of a resident structure of the where I where I had this bond donating and NTP orbital 1 images shifted over 1 of shippers over and have bonded to them and the way I'm going to depict them as unwanted draw start with the other type of chair there's almost 2 types of cheers you can draw I would draw the suits at the same level as drive me and saying that it's not the same level but not much better whatever that's good enough OK so there's like by Member rings and so now I'm willing to adopt Sweden keeper ion that carbon atom right there and I'm going
to draw the diatonic carbon and ideas so I can really see it and now I've moved this despondent over so it's
now attached to the dungeon ,comma now the couple get over on this side and the ability and doable now that I take the electrons away from this carbon atoms I should leave an NTP were there and there's my plus George that's why you get receiving product this is the structure of the hormonal cannot be a resident structures there's a 50 per cent of a bond right here and there's 50 per cent of onto dotted carbon the true structure of the normal on Ocalan has this sort of bridging interactions there's no happy way for us to draw this with this to bonding interaction or I'll struggle to draw this don't really know a good way to draw this nobody's ever figured out a way to draw the student to Norborne O'Connor you get this carbon atoms ticking down here it's in back here the carbon atoms in front of the doctor now 1 and somehow or
another you have to draw partial bonds to these 2 carbon atoms here's a partial bond there here's a partial images looks ugly
right moreover you can't use these that bonds for aerial pushing so I would urge you not to draw the normal I like this even know that's a pretty good representation of the structure so we're going to drop your opponent can I like this because with regular bonds weakened euro pushing on now what I want to urge you not to do because I want to urge you not to on not to think of this as a step-wise process where this bond while many of the money change that little admonishing you not to do that but it's not that this is very quickly migrating between the 2 it's not just this is very fast because if you think of this as a chemical reaction with this bond comes over and forms of on-demand comes back like a windshield wiper that means there is that there's an energy barrier on the
transition state there is no transition state this is not a chemical reaction this carbon atom here simultaneously
bonded to those 2 it's not just quickly moving back and forth OK so let's talk about this idea of world is adjusting the 1 to share for I don't know or want to shift faster slow we've heard of cargo can I'm 1 2 shifts this is this is a basic stuff in stock more organic chemistry so let's talk about 1 2 shifts so they can try to distinguish this resonance interaction from from a stepwise 1 due out till shift that has the transition state it says the toluene sultanate on this cycle hexane derivative and if you draw this out with this tussling leaving you'll get a pretty crummy Koble Carolina secondary cargo Caroline here's my secondary cargo that's awful but fortunately this thing can go downhill and energy it's simply move this moves this carbon-carbon bond over and that's called a 1 2 shift so there was an eight-year limit on age sales like to see the things that are attached to my complicated and so the process of migrating over gives you a tertiary cover that I'm that's the modern favorable so both medical groups and I it overruled art can migrate to give you want to share calculate relations tend to be faster than me just say this week Indiana right out there 1 to kill migrations to cobble had inspired do you very
fast ,comma give you a calculated energy barrier if you take just as very simple TV substituted cargo cat I'm like this and you think about the rate for this methyl group to migrate over the calculated that the transition state energy for that it looks like this there's a methyl groups in the transition state there's a methyl groups that simultaneously bonded to those 2 carbons but you carbon that equaled charge this is a transition state for that 1 to migration and is very low and energy so that the transition state energy years 5 kcal per mole In can 202 undertake mechanisms to learn more about what is any type of
alcohol transition state energy means this is very fast the have for this is on the order of about on it's less
than 10 seconds I don't know it's on the 2nd long timescales very quickly moving back and forth if you're trying to do some reaction where you want to trap 1 Carbol Karin before local worlds shipped on that sometimes a problem that's very often a problem you probably learned offer free or crafts reaction that it's hard to track the the tertiary Koble Caroline before those should start taking place so 1 2 migrations a fast even those in theory this would be a very fast 1 to migration it's not very easy nowadays to do transition state calculations using electronic structure calculations and they tell you that this is not on the transition state this is actually a stable entity with partial binding not a transitional transition state energy barriers were stable molecules are energy and this is the truth structure of the novel it's not a vast migration and
it's a slow 1 focus on other types of ships because you'll frequently in the older literature see C alkyl
ships flying all around and mechanisms and over used of the canyon have won 3 shifts 1 4 shifts into yes we can but they are a very very rare let me give you an example of and I'm going to try to draw a stop sign here a member during an the fighting do this to me is drawer stops on the way I know how to draw a stop sign eight-member during their life member during it's not so good San never practiced over Oregon running member brings only practiced drawing cheers the consumer society that is the focus was thought to substituent every I'm going to draw a methyl groups on 1 side of the same and way
over on the other side of the ring among other a leading group and when you allow this sort when you keep this
up enough for this it takes about 45 degrees in a polar solvent that's the kind attempted takes further put on a reasonable timescale for this tussle a two-part ballot the product that you get out of this reaction is still an eight-member during still has another on there but the tussle is gone and there's now a double bond right next to where that methyl group was initially it doesn't look so we're going to realize full what that means is you have to lose this H. Adams on this side you can get to that of the struggle I guess it's possible the methyl groups and the other side and still be stuck trying to explain what happened the Adams the other features that were next to them what's happening here is 8 eight-member brings are very crowded 8 numbered rings are the hottest rings to make organic synthesis because of something called Trans angular interactions you cannot start bumping of Adams across the Member during musical trends and interactions with the trying to make them they kill you and your reaction rates for cycles Asian and for the particular Koble Carolina due generated when you up that tussle group that possibly Group unit of Cobble can has this empty orbital sticking toward the other side of the range felony charge emphasize which bonds are closer to assume I have that sometimes I like to darken bonds that are closer to us help us see spatial relationships so you have this P orbital and here's the state-owned and right there with its electrons in signal box and that is not a very nucleophilic bond we all know that but it's right there always is physically overlapping in
space I didn't do this justice minister steric interaction in the starting material where this age is already close that CAT Fund is already close to the antibody model for the toss
late so it is not hard for this age Adamson across it's overlapping in space but that in word to jump across sold in other words you can get longer range I outfielder hydride ships but they're very rare so McGowan redraw this this product here and here's the tertiary cargo can that you get as a result and then there an a genome over here the gets plucked off on the other side by the acetate this is done in a seedy gasses the gives you this resulting elimination reactions so you can get longer range shifts they are very rare and requires super special molecular
shapes to allow those 2 could use which to the army might see so that
the advantage to this summer's when the high-grade migrates over it leaves you with the tertiary Koble cannot handle any state that another way the reason why the CAG is so nucleophilic is that there's a lot of other bonds the into pure pointed to weakening and if this were if this were opposite a secondary that siege might not be it would be a nucleophilic so will it be the same hydride migration I don't like your prediction should be that it should be slower so maybe he did time at temperature you get it so you might get a mixture in a case of double bond on this Ives's double bond on the other side OK so any and all but the thing that I want to point out to you is that when you at work I'm going to give you a bunch of problem the problem that had to deal with Norborne and I told you don't bother drawing like this we can push heroes with this 1 out tell you is going push
heroes if you'd like to make it easier I will allow you to pretend with Europe
pushing the Norborne all systems are migrating flies process so when you don't mechanisms involving Norborne all Catalans like this I will allow you to do this like this but I want you to know that that's not really stepwise these are actually residents structures of each other I will allow you to draw it as a step-wise process back-and-forth but I like you to remember that stepwise just agreed that you're going to remember a side that's that that this is the direction of President's structures focus with talk about it that's just enough time to mention another type of bond and I don't have time to fully today to impress upon you how nucleophilic his bond is gone but I'll try to be so we just finished about it's an example of the effects of perfect bond alignment in proximity so instead of talking about bonds that perfectly aligned I want to talk about bonds that are very nucleophilic I want to start by making the comparison of hybridization different hybridization bonds with different hybridization and how that affects nuclear Felicity something we've already talked about but I want you to know I compare these types of some molecular structures and see how bond angle correlates with hybridization so what's the hybridization and alley on an alkaline discovers forming a signal bonds on each on opposite sides with the the hybridization of the hybrid withdrawals that the carbon to that sp hybridized about over here if you haven't helped the university toner that's all actually this limited-run angle here the sp sp 2 and finally get detector he draw carbon when we would heard that this P-3 hybridized that I look at the bond angles here what's the bond angle right here that's not an error pushing 280 about the bond angle for Al-Qaeda told 120 How about in a perfect methane molecules I can remember the . 5 it's gonna leave 109 OK how much P character is there in this case that's 50 % p character how much be character in this case it's not 67 66 doesn't make any difference whether you 66 and 67 and finally addressed 375 per cent character what's happening to the nuclear Felicity the signal bonds the president has the bonds are becoming more nucleophilic not the apply bonds that the single-minded becoming more nucleophilic as we increase the peak after sundown Monday dropped something maybe that's not quite so familiar and unusual cycle propane what's the bond angle and cycle prepared all depends on what Bonanno I'm talking about about Bonds in the center of the the CEC bonds but I'm also got the CH bonds and
a pick you look at a simple cycle propane reigning world what you would see that the bonds that ring have to
be about 60 degrees I'm sure there's some sort of geometry math class you could take the teachers back out there and equilateral triangle the bond angles 60 degrees but what's interesting is that in order to attain that bonding it has to use a weird combinations of orbital to achieve 60 degree bonding for the C bonds in the rain that's the CCC bond angle but in contrast the agency age bond angles this is shorter than you're used to than anything you're used to the H H bond angles are larger than what you're used to foreign territory told type carbon those 120 degrees tribunal if you know the bond angles you know something about privatization bond angle correlates with privatization and so what you would find this if you look at the
per cent p character for something that has a 60 degree bond angle it turns out that it's
about 83 per cent p character holy cow that's a huge amount of P character in their peak character correlates with nuclear Felicity gold bonds ought to be very very very nucleophilic and look at the CAT bonds the bonds at speaking outside of the ring what you find is that they only had about 66 per cent peak area it's like an S P 2 hybridize bond it's like SCH pond on his stuck on an outing associate Montana cycle prepared so the expectation is that you have anything that's electron deficient next to these bonds that they can donate into and stabilize for pushover leading groups and let me go and show you the idealized arrangement for a cycle propane next to Mom I'm
going to go in stock so when we come back on Wednesday we going to talk about what it means for cargo
Caroline's when the next cycle propane ranks of super nucleophilic
Pipette
Zusatzstoff
Geröll
Katalase
Organischer Halbleiter
Eisenherstellung
Reaktionsführung
Chemische Bindung
Elektronegativität
Besprechung/Interview
Chemische Forschung
Biogasanlage
Reaktionsführung
Kohlenstoffatom
Computeranimation
Azokupplung
Substitutionsreaktion
Pipette
Chloride
Stahl
Chemische Bindung
Elektronegativität
Kohlenstofffaser
Base
Stickstoff
Substitutionsreaktion
Gensonde
Katalase
Phenol
Eisenherstellung
Distickstoff
Methylgruppe
Benzolring
Nitroverbindungen
Dreifachbindung
Katalase
Metallatom
Eisenherstellung
Wasserstand
Methylgruppe
Besprechung/Interview
Lactitol
Konkrement <Innere Medizin>
Pipette
Destillateur
Sonnenschutzmittel
Katalase
Chemische Bindung
Nitroverbindungen
Dreifachbindung
Systemische Therapie <Pharmakologie>
Geröll
Wasserstand
Reaktionsführung
Chemische Bindung
Hexane
Vorlesung/Konferenz
Wasser
Konkrement <Innere Medizin>
Geröll
Katalase
Metallatom
Reaktionsführung
Organischer Stoff
Konkrement <Innere Medizin>
Katalase
Besprechung/Interview
Kohlenstoffatom
Konkrement <Innere Medizin>
Leckage
Katalase
Chemische Bindung
Kohlenstofffaser
Kettenlänge <Makromolekül>
Coordinating European Council for the Development of Performance Tests for Transportation Fuels, Lubricants and Other Fluids
Systemische Therapie <Pharmakologie>
Dreifachbindung
Konkrement <Innere Medizin>
Lösung
Doppelbindung
Katalase
Organischer Stoff
Bukett <Wein>
Chemische Bindung
Ausgangsgestein
SINGER
Lösung
Hydrierung
Elektron <Legierung>
High throughput screening
Bukett <Wein>
Organspende
Chemische Bindung
Methylgruppe
Monomolekulare Reaktion
Sekundärstruktur
Orbital
Chloride
Phenobarbital
Tube
Elektron <Legierung>
Aktivität <Konzentration>
Kohlenstofffaser
Besprechung/Interview
Orbital
Elektrolytische Dissoziation
Stickstoff
Azokupplung
Chemische Struktur
Chemische Bindung
Methylgruppe
Altbier
Substituent
Senf <Lebensmittel>
Zelle
Single electron transfer
Methylchlorid
Einsames Elektronenpaar
Reaktionsführung
Oktanzahl
Krebs <Medizin>
Kohlenstofffaser
Setzen <Verfahrenstechnik>
Biogasanlage
Stickstoff
Chemische Verbindungen
Bukett <Wein>
Chemische Bindung
Blitzschlagsyndrom
Methylgruppe
Fluoride
Einsames Elektronenpaar
Chemische Bindung
Elektronegativität
CHT R. Beitlich GmbH
Vorlesung/Konferenz
Chlororganische Verbindungen
Systemische Therapie <Pharmakologie>
Kohlenstoffatom
Sauerstoffverbindungen
Konservendose
Reaktionsführung
Einsames Elektronenpaar
Chemische Bindung
Elektronegativität
Besprechung/Interview
Vorlesung/Konferenz
Rhamnose
Initiator <Chemie>
Ausgangsgestein
Beta-Faltblatt
Stickstoff
Sauerstoffverbindungen
Oktanzahl
Chemische Bindung
Azokupplung
Chemische Bindung
Besprechung/Interview
Organischer Halbleiter
Dampfschlepper
Katalase
Molekülbibliothek
Chemische Bindung
Hexane
Vorlesung/Konferenz
Gletscherzunge
Systemische Therapie <Pharmakologie>
Substituent
Substitutionsreaktion
Chemische Bindung
Antikörper
Besprechung/Interview
Chemieanlage
Natriumglutamat <Natrium-L-glutamat>
Substrat <Boden>
Substituent
Systemische Therapie <Pharmakologie>
Kohlenstoffatom
Alaune
Rauschgift
Chemische Bindung
Wasser
Systemische Therapie <Pharmakologie>
Kohlenstoffatom
Periodate
Hexagonaler Kristall
Einsames Elektronenpaar
Besprechung/Interview
Systemische Therapie <Pharmakologie>
Chemische Verbindungen
Sauerstoffverbindungen
Hydroxylgruppe
Reaktionsführung
Feuer
Zellkontakt
Base
Magma
Altern
Chemische Struktur
Leukozytenultrafiltrat
Chemische Bindung
Methylgruppe
Bromide
Systemische Therapie <Pharmakologie>
Sauerstoffverbindungen
Acetate
Kaliumacetat
Reaktionsführung
Methyliodid
Reaktivität
Besprechung/Interview
Toluol
Werkstoffkunde
Gasphase
Ethanol
Isomer
Altern
Oxoglutarsäure <2->
Chemische Bindung
Pharmazie
Alignment <Biochemie>
Benzolring
Lactitol
Pelosol
Sulfur
Bodenschutz
Acetate
Oktanzahl
Reaktionsführung
Mischen
Versetzung <Kristallographie>
Besprechung/Interview
Krankheit
Gangart <Erzlagerstätte>
Konzentrat
Lactitol
Isomer
Braunes Fettgewebe
Diclofenac
Derivatisierung
Elektron <Legierung>
Chemische Bindung
Kohlenstofffaser
Antikörper
Setzen <Verfahrenstechnik>
Orbital
Adenosin
Chemische Struktur
Tiermodell
Chemische Bindung
Besprechung/Interview
Alignment <Biochemie>
Wasser
Torsionssteifigkeit
Alaune
Eisfläche
Acetate
d-Orbital
Übergangszustand
Chemische Bindung
Setzen <Verfahrenstechnik>
Orbital
Chemische Struktur
Wasserstand
Chemische Bindung
Kohlenstofffaser
Setzen <Verfahrenstechnik>
Vorlesung/Konferenz
Kohlenstoffatom
Azokupplung
Chemische Struktur
Elektron <Legierung>
Chemische Bindung
Kohlenstofffaser
Vorlesung/Konferenz
Gletscherzunge
Kohlenstoffatom
Chemische Struktur
Aktivierungsenergie
Chemische Reaktion
Übergangszustand
Chemische Bindung
Kohlenstoffatom
Chemischer Prozess
Altern
Stockfisch
Derivatisierung
Fülle <Speise>
Organischer Stoff
Mesomerie
Übergangszustand
Besprechung/Interview
Hexane
Base
Zellmigration
Chemischer Prozess
Toluol
Katalase
Alkohol
CHARGE-Assoziation
Aktivierungsenergie
Oktanzahl
Übergangszustand
Kohlenstofffaser
Methylgruppe
Besprechung/Interview
Konkrement <Innere Medizin>
Chemische Struktur
Falle <Kohlenwasserstofflagerstätte>
Reaktionsführung
Übergangszustand
Sekundärstruktur
Besprechung/Interview
Setzen <Verfahrenstechnik>
Molekül
Zellmigration
Konkrement <Innere Medizin>
Stratotyp
Methylgruppe
Phthise
Terminations-Codon
d-Orbital
Tiermodell
Elektron <Legierung>
Reaktionsführung
Oktanzahl
Antikörper
Besprechung/Interview
Organischer Halbleiter
Doppelbindung
Altern
Geröll
Katalase
CHARGE-Assoziation
Sterische Hinderung
Chemische Bindung
Methylgruppe
Alkoholgehalt
Biosynthese
Acetate
Altern
Exon-Exon-Junction-Complex
Besprechung/Interview
Genom
Nucleolus
Hydride
Flüssigkeitsfilm
Eliminierungsreaktion
Gasphase
Tamoxifen
Körpertemperatur
Mischen
Chemische Bindung
Sekundärstruktur
Methionin
Zellmigration
Hydride
Doppelbindung
Methanisierung
Molekülstruktur
Chemische Struktur
Chemische Bindung
Kohlenstofffaser
Alignment <Biochemie>
Setzen <Verfahrenstechnik>
Molekül
Hybridisierung <Chemie>
Coordinating European Council for the Development of Performance Tests for Transportation Fuels, Lubricants and Other Fluids
Systemische Therapie <Pharmakologie>
Chemischer Prozess
Propionaldehyd
Altern
Molekülstruktur
Chemische Bindung
Kohlenstofffaser
Besprechung/Interview
Setzen <Verfahrenstechnik>
Alkoholgehalt
Vorlesung/Konferenz
Wasserstoffbrückenbindung
Tropfbewässerung
Stockfisch
Destillateur
Katalase
Chemische Bindung
Querprofil
Besprechung/Interview
Teich
Gold
Hybridisierung <Chemie>
Elektrolytische Dissoziation
Propionaldehyd
Propionaldehyd

Metadaten

Formale Metadaten

Titel Lec. 06. Carbocation Stabilization by Vicinal Sigma Bonds.
Serientitel Chem 201: Organic Reaction Mechanisms I
Teil 8
Anzahl der Teile 26
Autor Vranken, David Van
Lizenz CC-Namensnennung - Weitergabe unter gleichen Bedingungen 3.0 Unported:
Sie dürfen das Werk bzw. den Inhalt zu jedem legalen und nicht-kommerziellen Zweck nutzen, verändern und in unveränderter oder veränderter Form vervielfältigen, verbreiten und öffentlich zugänglich machen, sofern Sie den Namen des Autors/Rechteinhabers in der von ihm festgelegten Weise nennen und das Werk bzw. diesen Inhalt auch in veränderter Form nur unter den Bedingungen dieser Lizenz weitergeben.
DOI 10.5446/19216
Herausgeber University of California Irvine (UCI)
Erscheinungsjahr 2012
Sprache Englisch

Inhaltliche Metadaten

Fachgebiet Chemie
Abstract UCI Chem 201 Organic Reaction Mechanisms I (Fall 2012) Lec 06. Organic Reaction Mechanism -- Carbocation Stabilization bt Vicinal Sigma Bonds Instructor: David Van Vranken, Ph.D. Description: Advanced treatment of basic mechanistic principles of modern organic chemistry. Topics include molecular orbital theory, orbital symmetry control of organic reactions, aromaticity, carbonium ion chemistry, free radical chemistry, the chemistry of carbenes and carbanions, photochemistry, electrophilic substitutions, aromatic chemistry.

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