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Lec. 11. Eliminations (Pt. II) & Lec. 12. Addition to Pi Star (π*)


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Title Lec. 11. Eliminations (Pt. II) & Lec. 12. Addition to Pi Star (π*)
Title of Series Chem 201: Organic Reaction Mechanisms I
Part Number 15
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 10.5446/19213
Publisher University of California Irvine (UCI)
Release Date 2012
Language English

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Subject Area Chemistry
Abstract UCI Chem 201 Organic Reaction Mechanisms I (Fall 2012) Lec 11 and Lec 12. Organic Reaction Mechanism -- Eliminations (Part 2) & Addition to Pi Star (π*) 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.
OK so were still on lecture at number 11 I think you're
talking about eliminations lecture 11 continued to just have a little bit left to talk about the very important stuff to talk about lecture 11 months I tried to convince you that is super important to see and the carrier plane a relationship between bonds in organic chemistry and that's why I will push you to draw things using perfect shares with perfect axial substituent imperfect withdrawals stations because those confirmations correctly drawn allow you to see interfere planar relationships so it's this kind of a deep airplane relationship that makes these types of Riyadh throughout the lithium reagents unstable you cannot have made out Kotsay groups because these kinds of nucleophilic bonds will never make it to some carbon dealers similar electrified how they're going to donated the antibody marble and that this leading group which would be of Cox's so you can use this reaction so for example this is the way you remove which rock group but try chloral Ethel site try coral and boxy comedy of this is the truck protecting group on the the way each trigger release and removal could you typically use ink so hypothetically you could use magnesium Resources Inc is more ominous of Mauritania on metal to you so like a green yard reagent like magnesium zinc doing oxidative addition to make a coral metal Our outfield species so you can imagine the zinc while doing a reduction basically in order to make nucleophilic carbon zinc bond and when you do
that this is now set out to push out the leading group on which you now be this carbonate in iron
and of course that the carboxyl late so intimately you do these reactions in water so zinc reacts slowly with the water but very quickly without fully lights I all the steps involved here eventually found this will release carbon-dioxide to give you a free and so you can take advantage of these types of arms nucleophilic carbon metal bonds pushing all Allcock groups of with this kind of protection scheme truck I might have gone yet try try call roadbed Foxy Kerviel because the track Bloomberg the people of the world and the so
we talked about silicon carbon bonds being nucleophilic enough if it's silicon to push out Alcock seen leaving groups debate Baidoa leaving groups innovator restored about carbon metal bonds current magnesium bonds convincing Bonafini nucleophilic enough especially in what do we need to do to make up carbon-carbon bond nucleophilic enough to push out leaving this 2 things I needed you 1st of all we need to make the leading group better 2nd always somehow need to make this Bonsell nucleophilic and so weak that it's capable of pushing out leaving and the way you do that and you use good leading groups like this and you need a weekend
this bond in 1 good way to weaken that bond is if you next door put a super strong donor like this Beckham donated to this indeed binding orbital for the bond
and that will weaken this bond and make it more nucleophilic donation from the oxygen lone pair can make that bond nucleophilic enough where he can now push out the leading group by donating into that sickness and particularly for a goodly like tussling so we call these Grobe fragmentation it's where fragmenting carbon-carbon bonds upon the conceded the product of this reaction is going into a Aqaba somewhere and an old friend and plus some sort of a leading now takes a very very special arrangement of bonds here in order to make this work bonding orbitals bonds have to be perfectly aligned with the antibody models for this to work so I was going to take a look at some systems where where this
where you can see grope fragmentation action so I'm going to draw to all of this
is called a Dekalim ring system when you have 2 six-member brings in it's saturated and I'm going to show you how this is a stereo specific reaction of stereo chemistry matters how confirmation matters and how the alignment on how anti-terror plenary arrangements matter social to different consequences you make this Alcock side by deep-rooted alcohol with TV Utah oxides the actual starting materials the alcohol and they treat retreat that with potassium to detoxified ,comma and then when you do that you end up with a Grobe fragmentation that cleaves the bond in the middle of these 2 rings and going to draw a very funny shape to carbonyl groups and get the idea which still room to draw the carbon Hill in center the city of growth fragmentation cynical and dropped out of the the
barrel pushing for that so these these electrons are donating into into binding moral for the CC bond weakening in the making making the central CC
bond weaker and more nucleophilic and those can push out the toss away leading group and that's what leads to that fragmentation of the middle bond if they take an alternative and this maybe is not so obvious but if I take an alternative Dyess Deromer where the hydroxy group at the bridgehead and the Proton and the bridge forests into each other on the same face of the molecule in this case got the tussling going down so now I fragment this then over 90 per cent yield you get a different product and sort of steered the ring around the
important point is you get assists double bond you don't get a transdermal what you get assists double bond that's important points have moved to the Adams around a little bit but
happened gives you the and the bottom 1 gives you this such I draw these doubts that we can understand why you get these different these differences and this these are examples of stereo specifically actions you start off with this isomer you get the isomer product with this alternative sterilizing and you get busy prior to destroy these out as as of introducing chair conformation so we can see the relationships that lead to those different products from Haskanita best share drawing skills here so we can see these these really important anti-terror cleaner relationships so I'm going to draw
the agent the Bridger going up in this is the 1st of starting material and none of the that Allcock citing I'm pointing down those
of both axial substituent if you them correctly they should be perfectly parallel an anti-terror planar to each other and finality that toss elite group it's going up with the wedge it means of the 2 groups here there's an age and there's a tussle at the toss leaders on top of that through the ages pointing out under I'm age there just so we can see that there's another substitute at that center so this system is set up so that these long pairs there's long there's been all over this things are set up to donate into the antibody model for this bond the loan terms on oxygen donating to and weaken that bond and Nancy bond is perfectly because of the rigidity of his restraint system is held always antique airplane air to that toss Alexi Leading Group C bonds so the system is perfectly set up for this growth fragmentation of In terms of so again this bond is perfectly parallel to the 1 in it's auntie to that 1 that's into paraplegic and you need to see those relationships now when I drop the product I'm simply going to draw the same 2 rings and then I'll erase the bond in the middle you know you can just drop the Middlebourne very lightly if you can if you're writing in Cambodia which just erase the bond it's not there anymore in the product the CEO bond is here but now it's a double bond and the product and the 1 thing I need to do so in order to correctly drove the product is to see that there was an on the relationship between these 2 protons here between the CH bond that's each this year bond was empty to the 1 on top here in the story it will do indeed to that in the product and that's how I know for a fact that I'm going to get a transdermal bond here like that I still had energy range in age and if you didn't see those protons and
their relationship it might be hard for you to see why you get a transdermal 1 and only a transformation on the front that could drop them on the system :colon system the 2 chairs
and this is the new just after practice writing system :colon systems you know how to use the chairs together will start by dramas Equatorial substituent here instead drawing another chair in a regular chair conformation I'm going drop 2 bombs going straight down that's how you draw assist Declan system where the ring fusion insist and so now I can complete this by drawing another chair here like that so that's called assist Deco ring system and if I look at the rink fusion now as I do appear this this hydrogen this ch still axial this CHS to be in the top of this all has to be in the topics as well although that is an equatorial substituent relative to this 1st rank and there's my old minus intermediate that I get when I do fruit to which he
oxide and now when I look at the orientation of the toss locks substituent fish to substituent at this position here present and there's an H and
there they are the H is on the top face the task leaders going kind in that they just coming more toward you the toss ladies going farther away from the remake bond the same length as the other CC bonds it there was an essential OK so strongly around these or rolled out again here's a non-binding along pair it's donating again into indeed bonding orbital for this ECU bond it's weakening that's easy bond that's the effect that nucleophilic along donated next door to C C bonds so these electrons are donating into the into for this CEC bond it weakens it makes it more nucleophilic and more nucleophilic bond is now pushing out the leading group by donating
interesting story and again I want to look at the relationship between those 2 hydrogen atoms so when I draw the product everything the same
except I'm going to leave the raise money bond there and going erases melodic you wanted you could draw on that is very lightly or something that if you're using a pair of using a pencil it's easy to embrace it was the 2nd so what I sold this 6 6 ring system we called Jacqueline when it's got all single bonds and that's called Dekalim sometimes used as a solvent high boiling solvent this particular 1 we call trans Jacqueline because it has the trains are infusion 1 up 1 down at the injunction physical system :colon was 6 6 rings system that has assists substituent at the reinvention focus so let me draw out the stocks again it's still stored of Equatorial here on the course
not double bond in the product so carbon United draw that really centered correctly so there is the carbon Hill you get as the longer on oxygen kick around when he drove the
CHT was pointing up it's still pointing out that started off this started off center the siege over here so it's also that ch is going to states a system that worsened and so that's why you get persist double bond OK so long fragmentation 0 wait for me to test whether you see these deep airplane relationship so of course on the problems and don't ask you all kinds of group fragmentation and no I'm not going to join in the right confirmation for your body to do that and yes I love to put these kinds of problems on exams because it's a test of whether you're practicing drawing cheers and seniority .period plane relationships OK so that's it for eliminations sold practicing interfere planar relationships is about all I can say so we're going to major which about
to probably the 2nd major farm theme of organic chemistry we talked a
lot about cobble can chemistry that switch over to carbonyl additions it was the 1st thing it would be the people of the 2 of them and so let me just started getting situated here about what we've been talking about so far In this class we've been talking about the addition of some sort of filled orbital which could be lone pairs pipe onto a single bonds donating into empty orbitals we started off mecarbil can find and keep your schools of the most reactive things you can attack those are the lowest energy orbitals empty or religion and electrons into and so then we talked about sigma store but also ominous and to reactions elimination actions and now we're going to talk about things attacking pipelines things attacking piled donating the piste work so we taxi Siegel bonds and held sort completed a world tour through things that you can attack and won a start by comparing pipelines because all pipe bombs or not he will most certainly band and on the the Internet and all of the we believe
that the selectors set up by contrasting 2 different reactions and will ponder on on the relative facility we expect these 2 reactions to have when you set them up to the date some sort about the lithium and too lazy Robbie lithium salt or ester lithium it's the same idea the until the manager and the reaction of the lithium with carbon Hill it's not a bad reaction I hope you all know that reaction from some earlier version organic chemistry what about this pushing is exactly the same thing they can persist kind heroes I just finished telling you how glorious priced or is it being attacked but that was lower in energy and so I don't know about
you but I don't feel so good about this bottom reaction that I feel really good about the top reaction feel so good about the bottom reaction I I think you know that that these kinds of
editions of nuclear vows the Cardinals especially about the Lithuanians ingredient those always fast but no cases 1 no windows aren't on when this kind of additional action is not fast you can have it 2 simple CC not not substituting don't just simple Al-Qaeda under certain conditions now tell you those conditions when is this fast because intrinsically it's generally not something you worry about it's fast here yeah very nucleophilic so it's not fast with at the lithium that the primary alkyl within the same way the Beutel within his primary if you look at the product of this reaction if you start off with a primary alkalinity and at the lithium and whether a symbol of and get another primary al-Khalifa just thermodynamic later you haven't done a whole lot for this system you just cost you something interbreeding bring these on all of these next to all of those debated Robert price and you didn't get anything out you started with high morale within you end up with 1 on there is a trade-off bomb that's that's worth a lot actually company candidates ,comma even if it's slightly authority namely favorable you really need Abbas supra nucleophilic al-Khalifa will talk more about the secondary and tertiary more nucleophilic than primary al-Khalifa without a way to make it fast is used but most of the substitute often on the planet and that would be at the nine-year rarely going to bubble ethylene gas and Yuri actions so that if Europe polymer chemistry might do that you can make it advanced by putting in super-secret additives that have nucleophilic alone on try Appleby those can poke their
electrons in the lithium it makes this with ,comma bond more nucleophilic will talk more about that than by making use all its present in very high concentrations it's the same idea resists the
oxygen monitoring very nucleophilic but it's as if it's the solid there's a lot and those controlled their electrons in the lithium and make the kind combined more nucleophilic so that's what it takes in order to get you to add calculations this simple CCW double bonds it takes all 6 to ordinary stock generally you don't worry about how the lithium's on attacking simple offense so it's kind of get this disorder reminders this special stuff right if you don't see those special circumstances don't worry about about Opula lithium's on reacting with simple sensible wants to give you 1 example of this seems I would say synthetically useful to me now you can use entropy to help make this work so 1 is say saying so it's not
fair for me to say you can never see al-Khalifa yams which are about as nucleophilic as we can imagine I'm adding to simple double bonds there's a
special place in the home at the for somebody showed that you can take a alcohol and you can get al-Khalifa aims to add to this the double bond so what did they do this to equivalents of isopropyl with him so they're starting with the secondary help you with the him in so I think that many of you have used Beutel lithium before it's not there ,comma I would doubt that any of various face approval if united he said the lithium it's easier to get your hands on somebody example here of 1 of those tricks that I should you switching to a secondary out and of course it's fast for
al-Khalifa to deport me the alcohol so you're going to have it in this solution lithium side and there's a 2nd equivalent of isopropyl lithium and there and of course
lithium wants a electrons not just too so it shouldn't be surprising to you that's the oxygen lone pairs will be be donating into lithium atoms have to conserve my charges if I if I use a long-gone oxygen to attack with the 5 3 bombs designed to put a positive charges and about to bonds to lithium I need to put a negative charge on there and by drawing this this Louis structure correctly it reminds me that this this will be a tear this negative charge and lithium soaks up the nuclear felicity of all the bonds to lithium the negative charge a tells me all those bonds are with nucleophilic and in particular this bond right here is more nucleophilic that's what negative charge tells me that's why it's so important when I say let Cooper at Talladega and listening for a sound and so on when this is coordinated nominates floating on a solution but when it is coordinated this despondent souped-up nuclear Felicity and now find Adams away is that is that all fringes dangling there waiting to be attacked and that's the best kind of transition state the number of collisions between this bond that and that CC double-bond to the collide so much more frequently when the 5 Adams away that's what makes this reaction work so normally you can't add I don't want you to believe that you can normally add calculations dolphins but you see all this stuff that's built into the system that's what makes it happen of course there's nothing else in the reaction mixture that can react but much anything else would react faster than the CC doubled OK so this ultimately on swings around and forms a key late but that's not really important for the reaction but all draw so that oxygen lone pair of draw there just swings
around but took on that wasn't for the important thing is that that sort of intramolecular area effect the fact that this brings in this very nucleophilic double bonds helps to collide many
many times more frequently that's the effect entropy OK so it wouldn't take a look on stereo chemistry and we're going to start off with the problem was basic issue 1 can think of and that its trajectories tradition of various groups of the art of the fact that the people this will the most he also
won a start out by saying something that I think is totally obvious net is Kerviel groups a
polarized oxygen is a lecturer negative more Elektra negative and carbon that bond is polar and if I drop that resonance structure in reminds us of why carbonyl groups are more bombs are more but a lecture filler concedes he had in fact won make a point of efforts and come back over here so why the park ,comma losing more electoral filet policy more reactive but I mean more reactive words nuclear files they just simple CC double bonds why is it so the 1st reason has to do that with this polarization so readers to reasons and they're not the same reason reason number 1 is a kilometer effect relative to this so if I compare all the charges on these 2 types of pie systems there is a substantial amount of partial positive charge on that carbon atoms is also partial negative on oxygen so from the strictures strictly economic point of view of my nucleophile has any partial negative charge and they always do the good ones do united expected to attack faster here at the Colonial Affair totally separate from that is reason number 2 if I sketch out the energies of the molecular orbitals the canonical waddles here for some sort of nucleophilic filled with little begin the like algae lithium bond or some long period doesn't matter and I compare Thai star orbitals for example for a CC double-bond What happens if I replaced a carbon atom In easy double-blind with the more lecture negative ad I should expect the energies of that orbital to drop and if I go all the way down to oxygen which is even more election and nature and I expect price started the lowering energy if you weren't a pair of electrons when she wanted donated lower energy orbital more than the higher energy or of course you would so there's 2 completely different reasons why carbon a somewhat more reactive than CCW bonds 1 issuers charge and on issue is the energies of the frontier orbitals losses of 2 completely different issues you can you can guess to make the relative proportions the contributions of these 2 residents structures by looking at dipole moments so Ahmadzai moment and I'm not sure what kind of technique they used to measure this dipole moment is measure is defined as as as a separation between 2 charges so far a distance times charge differential but charges and if you measure the dipole moment for acetone lives 227 thereby units had no idea
what the heck at by its whatever it some charred unit times distancing shows what you can put that allows you to do is allow you to say that there is the
equivalent of pasta minus . to 3 charges on acetone and that a number you should keep in mind essentially what it's telling you is if you think about the contributions of these 2 residents structures it's like 75 25 the 25 per cent of a positive charge on the carbonyl crime accident so that 1 reason and 1 of 2 different reasons why nuclear files were so adept acetone so keep that charges you in mind acetone and extrapolated to other types of Cardinal Miguel wanna look at it so that's the charge issue let's come back and look at the issue of this piste or were brought from what should we expect it to be this fall when
it found this will get a chance to talk about the effects of Elektra negative Adams Maloney energies of orbitals but on the shape of the world and we haven't
spent any time talking about this so this is going to be kind of news that the it was found that it was time for the people who work to with the government these are the frontier orbitals we care about the highest occupied molecular were little look at the home of the little things that seemed stunned by Starr and so elected negative Adams distort the shape of the water levels and I'll show you how well it does that for a cardiologist and so I'm going to fall back on determines let me explain that term because of find myself using it over and
over and all seems sort of mysterious I'm going to use the term from molecular orbital theory maybe at some point in time you learn about something
called linear combinations of the tonic warned that basically said take to pay your bills you mix it together you get a pilot molecular orbital about the data fifty-fifty mixture of 50 per cent of 1 pie or appealable in another pure and you can make Taiwan 5 warbles out of that so coefficients uses these things from linear combinations of atomic orbitals was a coefficient is a 50 percent pianist Adam plus 75 per cent as character from another hour tools of the coefficients the 50 per cent in the 75 per cent so coefficients this is because of the cost of the war but it was it was reported that the company will I tell you about the relative size of Hi and price on each had held draw these out in just 1 moment in the majority concluded so want to draw a diagram here and diagram and the energies would be dealing a lot with energy 7 talking endlessly about the energies of unfilled orbitals and fill laurels and now I want to talk about the shape Of these orbitals so take a simple Kerviel groups acetone somehow the it doesn't matter what I I expect unconnected to 2 different pictures of the orbitals here so we start off by drawing and I don't care that there is a double bond there will all drawing more than 1 minute to minute or 2 pictures of acetone and I'm trying to draw this kind of energy on I don't know if you can tell me and kind of distorting it because I want to see sort of side on this and priced Oregon survived a picked up I Iowa Werdel as arising from a
contribution of 2 orbitals mixing together when rules makes together in Phase I get up I bond that's where electrons want to be they want to
be a bond and here's what I would see if I looked at those 2 On P. orbitals and I'm running out of room to draw here so you may have heard of these by the so here the code of the contribution from the Thai orbital on the carbon atom sorry fuel and there's another P on oxygen that combines with 10 Automated People and in what would find it and I and I apologize you can change a drawing appropriately adding that 2 big here we go and all phase that what I would find is something that if you think about it is totally into it and that is that if you look at the bonding orbital the coefficient the size of the par-5 orbital is bigger and more Elektra negative no 1 is that if I were a pair of electrons I will want to spend my time closer to the electron negative on fears more protons in the nucleus of oxygen that makes total sense that's totally intuitive to me that if I were a pair of electrons and wanna spend more time with the oxygen so that's the shape of a pylon orbital on carbon Hill it's distorted to be bigger on oxygen here's what's not obvious I don't think it's obvious if you look at prices that are now when you combine orbitals together 2 different bureaus together to make bombs to make binding combination we change the phasing in all phases 1 downward and what's not so obvious is now in the hands of I'm mortal electrons don't want to be on the electronic and it's the opposite of everything you think about bonding for the piste whether it's the opposite the phasing in opposite and the coefficient sizes Oropeza and there's powerful powerful implications to
this drawing the implications of this the implications are if you some sort of a nucleophile trying to head into Aqaba Neil and the draw
ice .period clarified that pair of electrons and trying to donated normal no don't donate here it's still don't even know the handiwork I'm going to want to try overlap with my field laudable somehow with this picture and what's the area that I can overlap with want overlap where the the coefficients big with the order looks big but phasing is important to correct facing Leitzel bonding combination incorrect facing leads to an island in the binding of configurations so I will just imagine if you will a nucleophile communion but may coming right here but suppose I make the phasing hatched what's going to suck here's my nucleophile can be like a long period of time because of this and demanding ,comma another former bond like that the government up with an
empty box need to make freezing match so if I just happened to some extent as arbitrary or like they chose
to face the nuclear file according to my depiction what I want to do as I want to come in like this I don't want to come in over here because of all the overlapping with this and into binding interaction with the oxygen I want to steer away from that and I don't want come in from the back again because now the interacting with these other on cash flow the ideal trajectory is that come in from an angle so they can skip the antibody interactions with these 2 will result is right here that's bad that starters leave to intervene in combination and this is a good interaction and so what's the preferred angle here protests this was known on the preferred for attack was figured out long before people understood and
that the molecular orbital origins and this trajectory people will the
Jack Dunnett his famous Swiss crystallography who work closely with the chemist Hollansburg Tandberg made lots and lots of organic compounds lots of 910 member ring compounds and would go get crystal structures of these and and Birdie tended to make compounds that can all kinds of of Adams strain enough where items were just uncomfortably close to each other some of them look like this and maybe I'm not doing a good job here but this would be an example of way to design a compound where Adams adjust uncomfortably close to each other to get in each other's face and what was done it's noted because all we had were crystal structures to look at crystal structure after crystal structure after crystal structure as when he looked at the distances between the nitrogen in the car heels in these compounds we he noted was that In crystal structures where the nitrogen the cardinal carbon were close to each other with the Cardinals were no longer he noted that there was a distortion in the car toward capturing geometries and he 1 these out replied I was the angle this N. C O angle here and what he was able to show is that the closer and closer to the nitrogen carbon battle bonding distance the closes that reached to 109 degrees and this is now referred to as the brigade on that single you'll recognize this as the angle between bonds in methane
or any territory legal structures so nucleophile don't want to come in and attack carbon meals from the back and or directly from the top and they preferred to come
in from there is much to the bonding angle they prefer to come in from an angle of 109 degrees that's the burden its angle if you want to analyze trajectories the lead stereo selective additions you have to recognize that all nuclear powers have a preference to attack on renewal .period general give preference to attack pies start from 109 degrees I don't like this so that's the burden angles OK so let's see how that plays out and analyzing stereo selective additions and and president and we believe that was the 1st time in the office of the
governor of 1 of the people at the foot of the summit show you how to predict stereo selected additions and I start up by giving you an example of mysterious selective edition was just imagine taking a nucleophile and adding it to this ,comma ,comma Neil where there's a sterigenics center at right next door that doesn't have to be next door but that's where you'll see the biggest effects the focus of the scarier center next door that stereo center is going to influence which face the carbonyl you add to this is a problem the 1st with the People
1st started to deal with in the 1950's so I lithium aluminum hydride that donates 100 0 groups it's going to form a new ch bond but the carbon he'll you'll don't get
equal edition from both faces so some of the hydride groups add is after work up from the front face and some of the Hydra group said from the back of a city the the and it's about a three-to-one mixture inside 1 . 5 . 6 K Kallstrom from all different in transition state energies so to the 1 would be .period 48 hours for more so this is three-to-one 1 pockets so there's something that's distinguishing on the
facial selectively Don cramming the CLA was the 1st to come over the rule that explained almost all the conditions that were known as
the minutes say almost all additional say over 80 per cent of the examples out there so when he when he did as he tried analyzed so there's a sterigenics center here would Cram said is just orient yourself like this you can view down his bond now way if you imagine looking down their bonded and when projection you could imagine how these 3 different groups disclosed on different sides of the cardinal might influence 1 trajectory versus the other and so the Crandall said the the Crown model said assumed that if you draw Newman projection that the medium-size groups that would be methyl in this case it is sticking on 1 side while but the important part of his role was to say assumed that the big group in this case the fennel is taking away from the carbon so soon that the big groups funnels with downward away from the car and I leave you with 2 other groups of medium and small way and according to crams model that medium group in this small group would now distinguish edition from 1 phase of the other but if you put the big group gone away from the top of the hill that now you would expect the nuclear file to attack on the same faces a small group because there would be less of a skeleton interaction and that explained most of the cases 80 per cent of the cases but obviously if it can explain all the cases that there's something wrong with the rules of the world doesn't work in every case cancel GM role is now known to be incorrect this is not the ideal trajectory the ideal confirmation in the transition state please let's talk about the transition states now to think about them so you can correctly predict on which faces preferred 4 additional funds here's would years
there's 4 different factoids that you need to know In order to understand how to analyze its unsolicited offer
factory Number 1 and this is really came from Crane so this is what trend that right people who some of the most but the and what kind of right and which which was almost a revolution for for him to be recent cases was he said stop looking at the products start drawing up Newman projections that look like this with an oxygen atom years nucleophile here and some group there in small you can look at the products as much as you want and you will never be able to predict by looking at the products what's the favored correctional attack the products don't tell you what what the transition states look like when you add strong nuclear powers like al-Khalifa hands or lithium
aluminum hydride the transition state early they look like Kerviel worlds not like text so that is a revolution 2nd trapdoor
that helps you to predict things but the this was it then the big group that Alpha to the Kerviel doesn't want to be opposite the Carbonell group wants to be on the old as far away as possible from the nuclear bomb somebody would draw out to different Newman projections and this is the way you should always analyze stairs selective additions so what arm the correct way analyze this visit the big wants to be on the opposite face 190 degrees from the Carbondale not down here the big group wants to be on
opposite face there's 2 different ways that the big group can be on opposite faces of the carbon 1 would be if it was swung over on this side someone would be if it swung
over on the left and the other would be if it was 1 of the light so these are the 2 conformations the reactor confirmation that put the big group this fall on the completely opposite phase of the cardinal from where the nuclear file is coming so that's the number 2 number 3 but you don't attack at 90 degree angles directly away from the curb appeal you attack at the burning down its angle if you don't come in directly opposite the the group Yukon Manitoba done it's and straw that trajectory and so in other words the nuclear file is going to come in and start forming a bond with this 109 degree angle there's 109 degrees that any kind of a lot of lines going on
the see the idea and that means the nuclear file is going to come in if the big groups over there the nuclear wants to come in at 190 109
degree angle those of the 2 competing transition states and now it becomes very easy to distinguish these because of I feel in this medium and small related to those cases that I should above now I've totally distinguished the good from the bad transition states so if you are a nucleophile would you rather be eclipsing almost directly on top of the small group where would you rather be coming directly on top of the meeting and medium but it's a small 1 and it's almost totally eclipsing with this word the bumping into each other as bad as you can possibly imagine and so this is the preferred transition state can adjust to little explosion lines
hears you could see them knocking into each other so this is the bad transition state this is
a good transition state and so the last part of the analysis you want to minimize eclipsing interactions and so if I ask you and I will ask you to predict the stairs selectively every single time I want you to draw 2 different reactions don't just roll 1 draw to draw the good ones and the bad 1 label 1 is good labor 1 is bad by using the term you want crappy great cannot whatever but dropped to Newman projections OK so that's how you analyze stairs selected additions as 1 last factoid and that's not obvious 1 sign of marker at the weekend and this is kind of like Rule
number 5 of them at the foot of the local but with so a polar group when you're out of position that
acts like the big group with it for the the and the talk about why so in other words if you have an all-party group Major Ralph opposition here nucleophile Wednesday opposite from the Alcock secret even cuts he might not be as big as an apple the important point is that it's poorly treat polar groups like the foxy quarrel treat those like the big groups so in this case the preferred trajectory of attack and I don't have a
Yukon all the other human projection yourself but in this case on this would be the better Newman projection that's the preferred trajectories and the least preferred trajectory would be if the nuclear tax the opposite side OK let me try to explain
why that's true if not I'm going to draw this out so that you can see in pure-play interrelationships as I'm coming in with my nucleophile dead into this carbonyl group if I have this polar group here it could be something like lower my foxy the important point is my nuclear both coming in with its field if you can maximize overlap between his polar bond carbon fluorine carbon-oxygen if there is an empty orbital here the nuclear file wants to interact with them in lowers the transition state energy it's not a Astaire interaction it's the interaction between filled and unfilled laurels yesterday morning into this laudable if you can also donate this envelope super important that's the preferred transitions focus let out a project stairs selective additions ,comma give you 1 last type of stairs selective edition will come back ,comma and lots of problems we were practicing history
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