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Lecture 05. Carbocations


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on a start up by thinking about a very simple reaction the substitution reaction here and like you to
think about what kinds of mechanisms you want to draw this reaction maker born on nitrogen bond so maybe things get something out on your piece of paper must get something out on my piece of paper here on the
unwarranted try try to draw molecular orbital interaction diagram that corresponds with the mechanisms that drunk and I'm not showing what happens to the HCl here there's a loss of HCl that's not important some missteps of the orbitals in these 2 components 1 of them is the nuclear file and 1 of them is an electrified and what my herald pushing says it directly and 1 step this 0 pushing brings me to the product done case closed here is the problem with that according to Meyer pushing I'm taking 1 of the lowest energy orbitals a signal bonds down here in energy and I'm using it to tap to attack 1 of the highest energy orbitals a Issigonis store but all we talked about the
relative energies of these field and empty orbitals we said this is story signal mortals are lower energy than
lone pairs based on that the right thing for me to have done would have been to drove along Paris here used to attack use that is my nuclear and the right thing for me to do is to completely avoid breaking this born chlorine behind because that requires me to dump energy electrons into this super high-energy orbital did but there's an NDP orbital right here that's where the interacting sulfite correctly interact the lone pair with the NDP orbital albeit all this interaction energy out and be a highly favorable reaction that's the reaction that I should draw a music and color to draw the right arrow pushing because that would look like this implies that I'll get an intermediate at least 1 intermediate in this reaction that's the correct 1st step and you could have predicted by knowing nothing more than the energies of those 6 canonical frontier orbitals is no pipe bombs in structures that Alpine style
so you already know how to answer this question just by knowing something about the relative energies of canonical from 2 other us so that the
area is it would simply make another action you have to have a base here to pull off the upset of the Borens form complex just for Maddux weapons book yesterday yes there's so that what is the root of this reaction would generate an initial intermediate and energy of a base president no then you can pull off the hydrogen can lose the quantum into correctly dropped the charges on this year end up this year with the structure and then I could go on and do other stuff so the point is even if this is the final product you don't have to get there in 1 step when you look at the relative
energies of sigma bonds ridges along long period the better nucleophile P warbles the better electrified on all this
was going to take a look said that some armed types of NDP orbitals and compare them all of the I'm trying to keep this as simple as possible by taking the substituent age that's not really practical you'll be interested in much more in much more complex types of the substrates with
NDP were but if he you consider the interaction of some nuclear file with the interview on this
if we do the era pushing you'd want to do something like this and what I want to do is I want to compare the reactivity of this MDP orbital With other NDP orbitals as I might the same march across the periodic table but so I've got a car being a mile on over here so it's a cargo can iron but it's it's it doesn't have enough to recall this type of complicated and occur union Lyon a nite treating my on and IOC senior mine and the floor in my hand and so let's try tormented measuring the rate at which these things react with nuclear files that I keep the nuclear file the same in each case and I can imagine adding to some MDP orbital and we don't always draw these things here when we do we're pushing mechanisms were not always going to draw that entered the level of distraught on the
carbon case here and you can just imagine them being there for these other atoms so if you measure the
rate the rate of reaction of these types of appliances what you'll find is on fall react at equal weights I'm not sure that matches with your intuition but if you measured the rate at which these things that have water attacked them you'd find that they all have rate constants for the reaction of about 10 the from of how can it be that they all would react the same rates and
here's my prediction the virus
sketch out the energies of Sigma star that's crummy pies I energy there's no pie orbitals there and then get down to the speedy orbitals and compare them if I think about the pure belong carbon and then replaced carbon over there was something that's more like a negative like nitrogen versus something with oxygen as I replaced carbon with more electric negative Adams in the same I should expect that this oral the NTP overloaded drop in energy you kind of know not only the flooring more elected negative I wanted that Astor Wines that they all had at the same rates they're all adding a diffusion controlled no no reaction connect can work faster than the 2 reactants diffusing toward each other and solution it's not that the Floridian hunting is more reactive but right this is already so reacted every single collision resulted a successful reaction we can get more reactive than that
and at a faster rate were not going to get anywhere by making these comparisons is really the point that I have to make were really going to spend our time here
on thinking about cobbled cat not these cats and let me just make up a more definite point for you were going to spend a lot of time thinking about cargo can finds that arise through N 1 ionization reactions in other words were some leading group leaves In order to generate a couple can iron and then in the 2nd set some nucleophile will add to that the that's a classical and that's in 1 reaction and what we are not going to think about is the ionization if I compare the rates To give nite trainee alliance we're not going to think about ionization to give Oxy alliance and we're not going to think about personal way we've just seen horrible for me to think about ionization fluorine mind in fact none of these processes where these things simply leave to give empty rules those unknown that's not to say period leading groups in here but usually something will migrate over and pushed that have out never have an
interview of going there 2nd internal lesson to type reaction OK so we're only going to spend our time talking about these
kinds of empty on carbon that's going to be the rest of our lecture for data for today and some of our lecture on Monday just talk about this idea of making travel patterns your bills on cards are important because were interested in making carbon-carbon bonds actually edition of your on Warner also this look in more detail at a reaction that I expect you to be familiar with some of the undergoing drug reaction coordinate diagram to remind ourselves of some characteristics and governance and 1 reaction if you have some sort of a nucleophile in the presence of some sort of carbon atom with a leading group you can think about this ionizing a former carbon cat that is definitely high in energy that no longer satisfies the architect will cover can I'm just angry they want more electrons and then usually there's some sort of a nucleophile that attacks to make a product more stable and if the product more stable he would be running the reactions so they wouldn't make any sense and I'm going to draw that sort of a nucleophile attacking here and we would still have our X minus and on the phone line floating around on the Internet that the classical reaction coordinate diagrams ,comma let me make a point about this Koble can and so this is a two-step reaction the goes through a high energy cargo Cat and
explained what implications that let me just remind you that there's 2 types of cargo Qatar and
here's 1 type of cargo paradigm that I mentioned to you before you can have too many bonds to carbon and as long as they don't violate the act at that is structurally OK there's nothing intrinsically wrong with this species this is what type of cargo can I recall that a Carboni mine and I can't think of any case and where we're going to talk about her alliance this quarter so when I say cargo kind here the other type of cargo Qatar here's what I need I mean a carbon atom with an NDP were so when I say couple can I and what I really mean
is this type of problem and this is called the car you mines
hobby I'm sorry about that from being mind so when I say cobbled Kenai and you can just assume that I'm talking about Herminia minds for the rest of course you know there's this other type called Carboni in my house that's not confuse those OK so because the couple can find its explain way here there's implications to that that's about let's suppose I go through a lot of work to do an asymmetric reduction to make his alcohol and then I want substitute that alcohol With some sort of other groups Hey I can do this in a CD gasses of C stands for and hospital group the world of and so I'm really interested in is the stereo chemistry that
common run by again wanted to agree not reactions and then some metal catalyze nickel
reaction so could stereo chemistry do expect substitution process it has a lot to do with what you think the mechanism so it could be innocent to reduction in fact incendiary reactions of faster when they're apply systems nearby but Sorensen 1 reactions so really if you say that this reaction is going to be scarier specific and give you the bromine going back then you must have decided it's 7 1 s and 2 where is if you think you're going to get a mixture over a scenic mixture then you've decided that exists in 1 and the reason it is receiving mixture they think it is because this is playing and because the nucleophile cannot either the top face the bottom face so you already knew that I hope you already knew that puzzle kind playing and the nuclear file can add from either face that's the implication of that plan there area so generally because the nucleophile I'm sorry I'm covering itself were done considering this example generally we use nuclear files that are more nucleophilic in the leading group if we didn't then it probably will be some manically favorable he is leading groups in our very nucleophilic and because of that this barrier going to the products is lower in energy in the barrier going back to the starting materials because we use leading groups operating nuclear power so this is generally true that this is lower in energy than its initial transition still just a general properties of typical lesson 1 reactions to the synthetic useful you know what you go through the trouble of making that cargo and they're just about any nuclear file that you put in is going to attack very
very quickly the rate of the reaction is dependent on how fast things can and a couple
can I'm thinking can handle cargo can quickly the rate of the reaction is dependent on how best to form the Cobble can so this is very bizarre aspect to this reaction that the nuclear force structure usually doesn't affect the overall rate of the reaction it doesn't matter whether I'm attacking the couple with methanol or ethanol to achieve Bunal they all react fast the slow step here is making the couple can I'm not attacking was some sort of an alcohol is another interesting factoids about Anderson 1 reaction that allows you mechanistic way to provide
evidence that it is going to innocent 1 reaction and that is if I add extra leading group here I can slow down the rate of the reaction In other words if
I add I have a bromide leading European ahead 10 times more bromide it makes it 10 times more likely that this will go backwards of the shifting the shape of this free energy diagram by adding more and more X minus the diagram that I drew up for you here isn't everything as it 1 more but I can change the shape of this by going by crossing out the standards the diagram and having things not as 1 molar concentration so if you add extra X minus you can slow down the rate if this is going through this into action and it's interesting sorry that Anderson 1 reaction it's innocent to reaction adding actually even group won't slow down the reaction of all recalled as the common ion effect this idea that you can
test to see whether it's really hasn't won by throwing in some extra leaving Group as an but this let's take a look at the kind of leaving
groups I'm going to show you throughout the rest of the quarter when we talk about us and 1 reactions there's all kinds I'm going to start up by talked about charged leading groups that are common and 1 and help you are going to rank the and quantify them in terms of how good they are as leading groups were going to start off with 1 of the best leaving groups may nitrogen gas is 1 of the best leading groups which reflate is 2nd to that and as far as stable things that you can put into a bottle potentially trip played is about the best thing with imagine that a trifle Roman things sold so instead of uneasily with Amabel trip late has a trifle room and that really stabilizers that an iron worker Tripoli Cassidy super-duper acidic this is 1 of the best leading groups got and it is substantially better than either toss a late or Meza late which are also
sultanate's proselytizer toluene instead of trying Apple Meza Lake has a methyl instead of four-month-old and late is about 10 the 4th
better as a living if you really want your reactions to be 10 thousand times faster would that be great if you could get your Ph.D. 10 thousand times faster here's a recipe created in that just a note for you your side reactions will also be 10 thousand times faster that's the problem so these are better than he realized toss easily better than alive by a factor of about a thousand and there is and I think you learned about this kind of stuff is a your introductory organic chemistry courses and that is that iodide is better than bromide is better than chloride by somewhat and these are much better on the Esther leaving groups and alright parent nitrobenzene away to get these weird abbreviation is what I mean I knew of a bends wait so carboxyl league-leading group and this particular when they tried to make it a little better by putting an electron withdrawing group but it's still not very good he typically don't try to displace esters to the reactions it's not that you can't but hey light is a much better leaving group vastly better output by attended by million so if you really wanna make a good leader can now call you make investors make on that he lied to the floor or just as easily could make on the toss literally the late Soviet charged and ironically groups and you can see this huge range of reactivity 13 orders of magnitude we just don't want among this list here are from the best to the worst personality look at them ,comma neutral leading
groups that start off charged with a positive charge but then when they leave they they leave is neutral molecules that are very common in Essen 1 reactions and we're going to
see them over and over so this would be 1 of the most common leading groups that would be either water on alcohol so by Croat mate and eat this can walk away with the electrons and generated cobbled cat I would give you a neutral alcohol methanol as a leading this case is not going to the relative orders here if I have Esther I can make it as direct as leading group this is the basis for her own law hard amount of peptide synthesis chemistry the idea is that you probably is carbon meal and now that very easily allows this to walk away as a carboxyl gasoline leaving neutral and you always permit the carbon Hill you'll probably this carboxyl oxygen
you prove the Cardinals to make that of Italy so another thing you were going to frequently see throughout this
quarter to make carboxyl it's better leading to this is to convert this into a not Sonia mine and not by adding a proton but batting from silo Silicon loves oxygen silicon oxygen bonded functions very easy to Silo leading agents like him strictly in order to silently harbor your oxygen so that this can leave to generate a silo Esther and then an extremely important class of Leading Group mechanistic leader arrives in different ways Is this fast only a minor somehow transfer of phosphorus atoms on the here and this phony this turns out to be a fantastically leaving we mentioned the stability extraordinary stability thermodynamic of phosphorus oxygen bar it's never going to leave this way and the electron wave articulated with phosphorus electrons are always going to go here and I can draw is making a double bond or I can just leave the
electrons on oxygen those are both equally acceptable
on and in this case and make good oxygen CIA of people only focus of older common leading groups they were going to see throughout this quarter look for them look for reactions that will generate these kinds of intermediates because immediately leaving this it's ready to take on case only bring you back to classical dance In a classical introductory concept it really messed you up in your introductory chemistry course in organic chemistry some of the state's some to variations on the Hammond pastureland and I'm going to state that for you now suffers Necedah with and then all sketching out since you're talking about the of To that's 1 statement of the Hammond highly and built a maker and we're talking about elementary reactions highly and authoring elementary reactions involving great products like transition states highly ex-soldier Mike elementary reactions we're going way down the hill in
elementary reactions that with 1 transition state and it
involved Earth the involved early transition states that look very much like the starting material so each artist's sketches out for you so you can see graphically what does this mean was all this stuff about early and late transition state me I'm going to start up by drawing a reaction quarter diagram again so I keep wanting to put Delta there this just free energy belittles superscript means standards that were just pretending everything is 1 molar concentration that's not an important distinction for this and so what you have to imagine is if you start off with some substrate here this is called Mom chloride this used to make the vaccine methyl ether protecting groups on alcohol chemical substitutes chlorine this
interaction doesn't involve the alkyl doing anything to reaction involves this
lone pair attacking and making them come out and so this chlorine is going to move farther and farther and farther and farther away but by the time he reached the transition state energy peak that chlorine is almost all the way gone you're almost at the point where the chlorine so far away you wouldn't even call it a partial bomb and other words the transition said the transition state for this reaction the high energy .period looks a lot like the product of this elementary reactions the Canuck product In the transition state the chlorine is sold far away so here is the transition state ultra sketch set out for you and all exaggerated there's a partial negative charge personal positive charge so that's what we mean by product like transition state that he can even tell that there any bonding interactions
and we call that a late transition state because his client gets farther and farther and farther and farther and
farther and farther away there's this reaction coordinate you could make the reaction Corbin the common chlorine barn door the distance between those 2 sets an example of a late transition state that I wanted to sketch out a reaction with an early transition state I can take exactly the same Cat Island there an air of ex-soldier make reaction and then if I have some nuclear in here that can attack this like an alcohol I can imagine this coming in attacking them the expectation is for you don't have to get very close you know you just sort of some words Gooch over here and the kind of close to this and you've already got some binding interactions that antibody waterless so hungry for energy further electrons the anywhere in the vicinity make this my
partial bond if that
is that all gets anywhere in the city that interview you already could be moved over the area and you're ready to form formalize so this is an example of an early transition state of the transition state looks almost like the Carvel cannot stand and finally when I get to the product here at least half of this step there's a bond here ready to be needed by some sort of basic you have it in the reaction mixture OK so the power of of the arm of the human actually is that we really want to say something about rates were always going to be worried which is fast which is slow which Europe pushing mechanism is likely with Europe anachronism is unlikely when I talk about
whether Europe pushing mechanism looks correct or not correct I'm usually talk about whether I think it's faster or slower than some
alternative and that means we're interested in transition state transition states determine rates for reaction not product stability not starting material stability but transition states that it is very hard to think about transition state but they haven't passed through that allows us to do something that really simplify their lives it's so hard to think about structures where the virtual bonding and dashed line and partial charges and so the haven't parcel it allows us to instead of focusing on his transition states allows us to to focus on the cat I'm interested we can predict the rates of less than 1 reactions ignoring the transition state and only looking at the castle can instability that's the power of the and partially we're very good
at looking at Cobble cat eyes deciding whether they're very stable more practice at that and the reason why this works and you have to always keep this in mind it's because the Carbol cat I am looks like the transition and that's why they haven't actually works the big mistake you will make his starting to apply this to other reactions all I see what he's saying they're telling me that stable products always mean faster reaction now stable products correlate with fast reactions only when you're going uphill and energy the other
half of the time the Cobble can instability has nothing to
do with words not it's the other half of the time the product's stability has nothing to do with the rate of reaction the other half of the time it's the starting material that matters and in every single case the general rule that always applies is it's the transition state energies and so I just want to find a way to dodge the fact the transition states requires to draw and hard to think about this it's going to happen ultimately to you to drop 3 sorts of species here I'm draw this reaction out in more detail but dropped the starting materials here for this ionization reaction that struck the transition state where the partial bond and then I draw the Carbol can product in that 1st steps so they can pass tells us that this Olivier fastest and 1 reaction because these lone parents are donating into the P
word and making them more stable Carvel and this is a
fastest someone 1 reaction and I can tell that because it makes the stable carbon can now I could just have easily applied all that thinking Oh it's long periods that are making this a fastest in reaction I could just have easily applied that to the transition state Ryan got this sort of this isn't quite in assessing star orbital is not quite an empty pure village somewhere in between what is this is that a key orbital but there's something interacting it looks sort of like a pardon chlorine sing Star on DP we don't know the sums sort donation what you'll find is as we go through this course you will find yourself using these kinds of donation arguments more and more not on the Carbol kind intermediates you're going to find yourself applying these types of orbital interaction arguments to the starting materials everything we said about the Carbol can we could just have easily applied To the transition state and this could just have easily applied their thinking to explain why this is so fast we could just as easily applied their thinking to the starting materials we could just as easily have said this is the fastest and 1 reaction because the lone pairs are donating in Sigma starting in body orbital and when you donate electrons into an antibody marble you break the bond that's why it's called into this session 1 reaction is fast and we could afford it that simply by looking at the starting material and not the crackle and talked about the field work rules interacting with them OK so fast that someone reactions that's going to be the general we have good good donor orbitals nearby so let's take some examples of some very fast as anyone 1 reactions but they don't call it as 1 reactions in the introductory Oregon costs for long periods are fantastic donors here's a great 1
nitrogen on pairs are very nucleophilic of I put that next to something with the leading group this is about the best S 1
reaction I can imagine and you might not at all that it hasn't 1 reaction but when we 1st introduced you to Essen 1 reactions in some organic chemistry this is what we should have shown the hats fast lone pairs of nitrogen pushing things out it makes a lot of cargo carried by United a different resident structure so was another example of what you should expect to be the fastest among the action after towers are intrinsically unstable anytime I see to Harrow Adams with lone pairs attached to an 3 three-set center what I'm thinking is there pushing each other out each 1 is trying to push the other 1 out and the 2nd I tickle this other 1 with a proton it's gone 5 so whenever you see acetaldehyde and now also you need to be start
start to think about taking out a leader of 1 of the other
doesn't always have to be alone there nearby you probably know that a Lilic substrates a very fast to push out leaving groups and that's not you could argue all that because it is a stable cover that know that's not exactly what I it's because this pipe bomb is donating the sickness doll the weakening of that's why that's fast enough to talk about the Carolina did not talk about the transition state it's the same sort of thing and then finally we get to this and now it's not quite so obvious what's donating Anderson must start we know that this is leaving something is weakening this bond and in this case it's all these
ch is a nearby that are donating not good donors
Sigma ch that bond is not very nucleophilic but there are electrons and their bond and they are overlapping in space with this empty Sigma stalwart electorate that down here using the star for oxygen and that's why TV will cobble Tarrance form so quickly it's because the CH bonded donated into that of that and and it's not as quick as shallow and it's not as well depending on the substitution and it's not as quick as either these these ways to form ammonium ions or toxic review took itself as 1 reactions the good ones and owner warbles right nearby that's when Hassan 1 starts to look really good so take a look at shapes of cargo can I answer and how they relate in a dramatic way to stability of but the people let me go and
redraw hybridization diagram for you and what I'm going to do is I'm going to try to sketch out the energies of empty molecular orbitals in our mind you need to have Sorrels a really low in energy into pure gold a very high in energy and just at a conceptual level but suppose these were filled understand I think conceptually if he these were both killed which 1 of these orbitals is each year to take away the electrons from and even the pig it's easier to take those away these are really happy it's very hard to grab electron stood to make an anti-liberal that has lots this character you to not want to leave as character orbitals empty because electrons will want to go into those orders they don't want to be empty they want to be filled it's the high-energy will want him to do so legally sketch out cement durables here for you and 1 drawn to puerile typically there empty because some people will have to cobble path and so what would happen if we compared to this type of and 20 S P 3 hybridized orbital into an empty sp to hybridize were all the more as character that we examine the harder it is for that too exist without electrons and so what I think about all the stable coral Caroline's I'm used to seeing they usually look like this that's a typical Korbel can Island but the TV cobble cannot govern
NTP or what you're not used to seeing this cobbled patterns that event and when
seen that we did start off by saying that cobbled parents tend to be playing that's because the this and what you not seen this stuff that goes like this you may have seen this far less frequently this couple can I'm speaking off the side of a double bond and I've never heard of or seen anything that looks like this ever I don't care what how little leading group you put on there it didn't go through that here you may substitute leading group at the end of an al-Qaida but it didn't go to describe began to do not want to have an empty warble was all that scary focus will seek a look at some examples and I'll start off with this S P 2 hybridize ,comma cat I'm so we can be clear about what about what I'm saying
but I'm telling you there's lots of reactions that can substitute finally lights you can have
conjugate addition elimination reactions metal catalyzed reactions there's all kinds of reactions and for substituting bromine was some sort of a nucleophile and none of them went through this there are no reactions we substitute finally realize that that involve the bromide just popping off to the sky skyline the important point is I'm not telling you can't make vinyl cat lines and is telling you can make them like this so unidirectional I don't do that so there are some reactions to go through 1 candle give you some sort of up at an example of the known intermediate so this is an example of a vinyl cat so I'm telling you is that this reaction like this intermediate it didn't involve loss of some sort of a meeting of generate cash like that there's son was generated it took advantage of entropy and the fact that it was very hard for this and media hand and to get away from the outcome that so likely this is flopping around its bouncing in Alpine over and over that increased the chances that the anti-war but all the empty pious store owners would interact and increase the chances that that would attack and want you attack this cannot be attacked by by some so it's not there's all kinds of examples regenerate vinyl and you just don't generate in U.S. and 1 we generate them by adding things out ,comma and that's how you generate the Protestants examined the
importance of shape here because what you can see is some kind of working the angles here I start from the Tigers
120 degree angles to me and changing the hybridization in the sheet so the ideal cobbled that I want to be plainer and so what happens if I somehow constraining the system so it can't adopt this ideal playing shape I can make it very very hard to ionizing Anderson 1 process some members by drawing and Adam mantle system on my want you guys to practice drawing cheers it's going to be important in this class and there's nothing that's going to help you other religious practice of drawing lots of cheers and so many draw drawn from madam mental system simply by having someone you had some action groups to a cycle accident here you go so I can imagine that if I have a bromine atom on here you know maybe I can ionizing still make a planar Koble can but these groups on the Carbol Caroline who they would have infinite flexibility in how much they want in how much room they can leave when when this thing starts to go playing so it's think about this process and what I wanna do is compare this with some other polycyclic carbon compounds where maybe it's not so easy to complain and I don't think that this I'm going to draw 2 2 2 was called by cycle close to 2 2 octane this to bridge it's here and it's not the name is not important but I may refer to this later so in in you pack nomenclature we call as a bias cycle to to acting ring system to province to province to province you haven't registered
with the nomenclature ,comma so maybe it's not totally obvious to you but it's harder for this
carbon to prior to go planar when it's constrained like this it's harder for this carbon to move down right in the center of the 3 carbon atoms years that can adopt a plan structure and I can make is even harder by drawing out Norborne systems so novel got only a 1 carbon-rich here that makes it really hard for this carbon to move up and the plane as the leading group meeting and if you look at the relative rates of S 1 reactions here only yeah if you look at the relative rates I don't know what the absolute rate constants are here I can tell you in a relative sense how fast the bromides Lee or give us a relative rate of 1 this 1 is a thousand times slower and then when I when I had just the 1 Covered Bridge here it's really hard for that carbon to move up so the the planar now it's time I don't hold on at to company's 0 0 1 2 99 0 in his career it said it doesn't matter it doesn't matter who and this is really lot it's really hard when I keep something from adopting a planar structure it is really hard for this resulting couple can be plane and that just shows you how expensive it is to empty out of the world you look up there is trying to make us and in the orbital but it's that as character in it and it's not plainer that becomes really really expensive very expensive OK so let's not talk about some of the donors lone pairs a fantastic I wish I could have a alone .period owner next to these 2 donating the antibody Mooreville helped push up the leading group but some
cobbled can eyes kind of framework for thinking about donors different types of donor orbitals so so what we'll do is we'll end up spending some time thinking about and if I draw some sort of ammo diagram here will think about the ability of Cobble can irons like that and all sketches of the 2 men DP were real cotton to interact with various types of donor warbles and which ones would I expect to be more stabilizing and so the best don't orbitals will be non-binding lone pairs lone pairs on nitrogen lumbers on oxygen and those are the things that are going to donated the Carbol plans when their next door and make them more stable substituent right here and here's my substituent if this is the hydroxyl the
longer the dot that's can be a very high-energy don't there's another substitute I could replace
for the doctor they could have some sort of vinyl group here so prize not quite as good as the lone pair that's still pretty good and then the least nucleophilic donor I could have next door to the cargo can and will be at the DoD is equal to some sort of a C H bond here that ch Bonnie there that far can can potentially be a nucleophile and can donate Endicott have so you got its own body discusses higher energy don't donors will donate better and so the best couple can will have donors next door let's put some numbers on how big of an effect that is depending on a long time all employers are not created equal just try to quantify How much relative stabilization we get by
having nitrogen lone pairs verses oxygen lone pairs versus other
types of loans next to a couple of times 1 nite you know there's a really great they're very nucleophilic means a basic because of that is so I wanted was a wonder compared this horrible cat I'm really it's in many ion and disjointed as a carnival contact residents but if I if I draw the structure with a high bond :colon and this is really a prorated ,comma beyond its disguising it as a hydroxyl stabilize cargo all of these have long pairs on them and then find out compare these 2 something looks kind of offensive to me they just a plain naked methyl couple there's nothing next door that can stabilize that there is no longer on hydrogen and there's no signal bonds speaking of hydrogen condone into that interview it's totally unstabilized when you look at the stabilization energy we can compare all of these to a simple methyl can has nothing next door that can donate into this this as no stabilization energy associated with Trailfinders that flooring substituted Koble on his 6 kcal per mole stabilized relative to a metal cobble path 6 Gatehouse from stabilized now you know as well as I do that flooring
elected negative so yes flooring is elected negative and trying to suck electrons out of this and getting nowhere but the
lone pairs on fluorine I'm donating into paradigm in its Internet beneficial effect fluorine stabilizes Koble cat eyes the 2nd row Adam and you can make the same kind of inspired by doing that donation of course hydroxyl lone pairs are better substantially how many times more stable as a fluorine Koble can and then a method of lines of so 1 . 4 cows from all of the 10 times more stable Sunday times 1 . 4 to 3 Portabello it's about 10 the 4th more stable catches Unit 1 . 4 K Gazprom or just by having this Florian longer nearby money a hydroxyl and I'm I'm not good enough at McAfee 101 . 4 is going to that but it's a lot the
hydroxyl substituted cover can in some way more stable than a flooring subsidies couple and the
morning when we get over here to nitrogen it's now 20 was at 29 K Kallstrom or more stable I can't convert that of the I'm not good divided by 1 . 4 scholarly like 10 to the 20th the sums so vastly more stable so these energies in key cows from all you can convert those into numerical ratios of stability OK so 1 lasts 1 last sort of little snippet of information about lone pairs there isn't a type of cargo you could consider this to be a cargo that I know I can draw resonance structure for this that looks like this called sillier minor you've
seen it before and electrical like aromatic substitution we
need feel crass isolationists and I might look really weird to you at the time we were drawing those out but that's not really weird at all it's about a stabilizer TV will cobble cat you know looks weird and that this weird triple bond and and you might think Oh my God positive charge an oxygen that jury can this has this structure tells you that every single 2nd rower Adam has filled up electron that's fantastic you'll never get to that with the T-bill couple can I'm so the long there's a good donors and they can stabilize that's about as good as computer program but they were going to continue on every got a little bit of
stuff to finish up with several times when we come back on Monday
,comma would continue to push heroes but somewhere underneath all that Arab watching there's all this cool ability to use molecular orbitals to explain why you here
Computer animation


Formal Metadata

Title Lecture 05. Carbocations
Title of Series Chem 201: Organic Reaction Mechanisms I
Part Number 7
Number of Parts 26
Author Vranken, David Van
License CC Attribution - ShareAlike 3.0 Unported:
You are free to use, adapt and copy, distribute and transmit the work or content in adapted or unchanged form for any legal and non-commercial purpose as long as the work is attributed to the author in the manner specified by the author or licensor and the work or content is shared also in adapted form only under the conditions of this license.
DOI 10.5446/19224
Publisher University of California Irvine (UCI)
Release Date 2012
Language English

Content Metadata

Subject Area Chemistry
Abstract UCI Chem 201 Organic Reaction Mechanisms I (Fall 2012) Lec 05. Organic Reaction Mechanism -- Carbocations 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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