Lecture 15. Addition of E+ to C=C


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Lecture 15. Addition of E+ to C=C
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Vranken, David Van
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UCI Chem 201 Organic Reaction Mechanisms I (Fall 2012) Lec 15. Organic Reaction Mechanism -- Addition of Electrophilic to C=C 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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OK let's let's jump back into electrical ignition I similarly we're
talking about using Al-Qaeda's nucleophile files lawyers is the topic of and were talking about the kinds of reactions that you should have already covered at some point but back in your undergraduate organic chemistry courses for additional allergens in a hydro halogen acids things like that so we left off talking about the reaction of up with things like bromine and chlorine and we talked about them the way we're going to push heroes for investors initially some PRI complexation there's initially formation of an actual complex in which in which bromine and chlorine is literally coordinated the pie bond but you haven't formally signal Bonjour and we said we're not going to draw that was said we're not going to draw these pie complexes with allergens and sort of sticking 2 to double bonds were simply going to draw like this and pretend there is no national park complex formation and we had this weird said of arrows to show that bromide is getting pushed out as a leading group but at the same time that the double bonds attacking this bromine heart long prison Brom you're coming back to make sure there's no cargo can I make is formed and that's what leads to the psychic bemoaning that you take
most dolphins on this and is under typical conditions and you throw in iodine is a reagent you won't get any of this product and so why is that why
is it that this reaction works with chlorine and bromine it turns out that did Friday nite and bonds a week bromine bromine bonds a week chlorine chlorine bombs are relatively weak there is a strong demand anemic driving force in order to generate a died bromide alright at the Diet bromide product here or to generated I chloride but because the bond dissociation energy for a carbon benign and bond is only about 51 K calls per mole this is just barely and fell quickly favorable and if I really write this as an equation is another word that this is only 2 K Kallstrom more favorable and topically the entropic costs counteracts that overall in terms of delta G under typical conditions you can't get i'd nation toward equilibrium actually favors the starting material side arms
you're not going to see very many cases where people and iodine but a simple double bonds the special conditions obviously could use potentially English actor liaise principal dumping excess iodine and helped
drive that equilibrium on but it's not going to be a good situation so you can taking on advantage of this all show you an alternation procedure that's based on this instability and so why is it that onto another you but I dined with cycle hexane what's important computing .period point is that it's not that there's no reaction that would be a mistake if we said there's no reaction there is reaction you do I make the double bond it's that the equilibrium is poor so in other words it's not that you're not forming as iodide is that when you do it kicks side I'm right back out exactly the same mechanism you drew for forming it undergoes a reverse this is an equilibrium problems so I don't draw this out the equilibrium here of favors the starting materials side because of because of entropy OK so if
you take any kind of a dial and you don't want to dial and I'm going to give you a very specific example here
the substituent on and on system don't matter on just given you a literature example of people that you don't need to know the mechanism for this sort of for this replacement reaction but there's a reaction called the appellate action will cover that only at the phosphorus retake phosgene traditional fasting is typical at acknowledging that bromine and chlorine and I don't and you can replace the villages with allergens this is much better than using acid like H R for HBO are the special combination of conditions on allows you to replace hydroxyl groups with allergens but in this procedure you don't get the halogen In place which is you get a double bond and so what's happening here for year undergoing something called an appellate reaction me try redraw the
starting material here and again will talk about this ,comma later I think it's called the appellants of
Apple will begin the idea and so essentially you get the equivalent of replacement of those 8 0 wages on with iodine and of course as I mentioned before those are unstable guidelines the leading group the lone pairs on iodine adjudication at pushing the other 1 out and so that goes right back to the whole offense so it spits out iodine as a byproduct in the reaction OK so on Brohman Asian chlorination of double bonds this summer dynamically favorable nation is kinetically a good reaction which is in Immokalee unfavorable OK so you don't always have to add to the scene of halogen that acts as the electrified was the nuclear file so here's a reaction it's
all related to Hilo hydrogen formation where you former cycling kill only a minor like this for ammonia mine here you don't always have to have
bromine actors union the apology do these reactions in water hopefully you know this already water will come in attack the ammonia mind and sillier than OH-group indeed to the bromide I mean it doesn't have to be you know group so here's an example where if you have a nucleophile that's poised to nearby like this ,comma along pair and form I don't unicycle guide only an intermediate on you can get oxygen atoms to act as nuclear files but we want these reactions and so this would be an example reform initially a three-member revived only an intermediate I-9 here but before 9 miners and come back in an attack this snapped shut to make a five-member rings and I'm not going to show the whole mechanism for that but this turned out to be scarier selected there's student equal faces to decide only minor became
formalized only 1 1 face of the other faced 1 phase of the other face reversible 8 but then eventually this will cycle eyes preferably to make this ring systems stereo selectively the peso on
what's this is let's talk about another disturbing type of electrical condition that relates to this idea that there's this other business .period complex that I haven't been showing you or that we don't draw when we draw pushing mechanisms on and I don't think I have such and such a problem thinking about this pie complex on the drawdown in case you forgot this from the last lecture I don't want us to draw this do Arab pushing but I just want you to remember that 1 Electra polls come close to double bonds on date they can form complexes and those complexes uniform forming them has the transition state disrupting them as a transition state but because we can't push heroes with the state of tight bombs I would prefer that we don't draw them but I don't want you to forget those types of of date of bonds now it's come to and what seems like a simple reaction but maybe is not as simple as we think and that is the addition of of acids across double bonds hydrochloric acid hydrobromic acid at even Hydro me hands on and I'm going to remind you of an empirical rule but but for these types of conditions called on so Marconnet colossal is really just an empirical on I prefer that you understood the underlying mechanistic basis for this rule that allows you to predict the Regio chemistry buffer Ajax additions and so the idea is that whenever you add on a lecture files across double bonds but you end up getting the product but the federal Adam nucleophile and draw the H that initially got added
seated a chair of circle it's you can see the age that was part of the the fun part
of our electoral so Marconnet cultural says that the Harrell Adam the nucleophilic heroin ends up attached to them or substituted position soldiers right this year on war substituted cotton an agent up added to the less so I hope you remember that rule but I have a more pay and better than that I would prefer that you understood why this rule works the rule works because when you initially probe make this this pie bond with either HBO are or HCL or some sort of acid source if you would prefer to probe made so that you get the more stable Koble cabinets the was supposed to be the basis for this and that is the basis for this will you probably made so that you leave behind the more stable Koble can find and then the nuclear comes in attacks and I will show you that pushing mechanism that's the idea behind Mark ,comma but let me show you some on the results of some of some isotopic reaction studies were instead of adding HBR HCL you had the deuterium analog and then allows you did to track where are where the Proton is going and in particular the scariest chemistry and Sony store up by drawing the substrate and although this this sort of Cissell of substrate I'm never going to different directions and contracting types of reactions the strike tracking a reaction on it in this direction we're heading of deuterium bromide instead of HBO and so the deuterium is going to add to 1 side and the bromine is going to add other so far as ephemeral group that stabilizes the Carbol can iron out
prediction should be that it the deuterium ads from for example the bottom face you'll get a cargo Caroline next to the phenyl ring Villanova Denzel
,comma can I'm here and the brown like an attack from either face of that kind kind that would be a expectations did you approach made the double bond to leave a stabilized bins allocable can and then there's 2 faces to the comic and bromide doesn't care which face a adding to but if always not of good cargo Caroline stabilizing group and here's something that it may seem a little bit bothersome Saudis imagine 1 R is equal to methyl if you probably made from the bottom side he it's equally probable separately from top-to-bottom I'm just going to draw the product of "quotation mark meeting on the bottom it turns out the due date mostly indeed edition if you're postulating that there's some free car here rotation around this bond then something's wrong
here write something has to be wrong here let me give you another piece of information so others write down that the observation is
that under most conditions you get a mysterious Pacific anti-addiction but is not 100 per cent empty but it's mostly empty the addition of the D & B R so news of another observation charges relying here to take some sort of an Al-Qaeda and yet HCL to this and this in particular was done in nitro methane so I'm not going to file claim that these kinetic results are the same under every set of conditions on nature missing is very poor hydrogen-bonding but it's very polar the end of the unwanted draw the product out for you it undergoes my on off editions agency held find different carbons and the chlorine is attached to them more
substituted carbon that's exactly what you expect and if you were to drop some sort of a mechanism redraw their bond
there you draw some I would draw something like this rate that makes total sense mecarbil can iron stabilize tertiary couple Caroline and the chloride comes in attacks that from the opposite face and and as with most reactions that may crumble Caroline's its formation of the couple Caroline it's the rate determining slow steps it's easy to attack a tertiary Koble can find but if this reaction is faster or slower because of that 1st step but somebody some crazy person when and measured the rate dependence and here's what they found managers rate equals here but the rate depends on the concentration of the olefin 10 times than you from product 10 times faster what makes sense 10 times more old often form the product and times were faster but it also
depends on the acid here on the HCl concentration 10 times more HCl it turns out reactions 100 times faster now that does not
make sense there's a 2nd order dependence on the concentration of HCL and if this is the mechanism then that's not the rate equations right mind my equation here says that I have 10 times more my my mechanism says the I 10 times more hydrochloric acid then NYT article like 10 times faster inform this 10 times why would be 100 times faster something is wrong with this mechanism we instantly know this mechanism can be correct you need to have some sort of an explanation for why this thing might be the dependence of along with 2nd order dependence on the HCl concentration so I'm in order to write out a mechanism for this you have to have 2 molecules of HCl in here I'm going to drawl of a kind of picture that most consistent with
what's going on in this reaction mechanism and I'm going to have 1 of these and trying to draw the sort of -dash high volunteer here member 1 of the things we set about
Proton transfers the idea mechanism for proton transfer starts off with a hydrogen bond that's what I did show and if you want to show what's going on here and follow that I did mechanism then you need to draw some hydrogen bond or something we can't push heroes with and and have bonded to the hydrogen so if you want to have some sort of an explanation here for what's going on you need to draw something that has to each seals in it and you can have this chloride still bonded to an age doesn't matter now that's the kind of mechanism that will explain second-order dependence it but if you cut the concentration of HCl by a factor of 10 it hurt you both ways in pursuit will because there's less nuclear volunteer hurt you because there's less Proton and the top face this is probably a better description in nature from a thing of what's going on in this mechanism OK but when we draw
mechanisms so I made all this hullabaloo about the actual mechanisms unlike you to continue to draw the simple mechanism OK but Sunday
when reasonable then Rankin said that not just OK just remember that in the ready to fling it out when you're talking over coffee farm but drawl euro pushing like this but never forget this this sort of picture of pie complexation that we solved with halogen and even for each CEO OK so let me bring you back and to a series of substrates and let's talk about reactivity you're going to see a very similar pattern on the reactivity but when we look at various types of substitutions ,comma on office to handle the substitution patterns on this affect the rate at which you any checks is very similar to the kind apparently Soffer edition of halogen sling bromine and chlorine 2 and seal to so good start by
asking what would happen if I put a single substituent on here single CH 3 the C bonds on this matter but should draw was was ch
bonds those ch bonded donating into the supply system and making it more nucleophilic or if you if you like on the server software level picture you could say Well it stabilizes the Carbol can and and by Hammons past whatever the bottom line is just a single Napolitano ch is accelerates rates Ajax edition so if you look at the relative rates for edition of and I don't even know on what acid ice-free don't have that I don't know which acid this is for the THC Ella HBO so that when you're adding HCl reached bureaucracies double bonds on its attended the 7th faster 10 million times faster to have that methyl group on the double bond you may makes you may look at and think Wow we have a double bond the end molten that Seoul reactive while that reactive so he put 2 methyl groups all depends on how you put the 2 methyl groups and it
doesn't matter whether this sister trams I put a 2nd novel group known as saying sigh but on the other side this is about the same rate is about 60 per cent faster
on but the problem is that if I think about how this ch is donating when this siege donates it's going to make it more nucleophilic here and more basic about carbon right if you draw the Carbol can I knew generate by propagating here would be next door did this but the problem is the ch is not activating the same carbon and that's why you don't get a significant increase when the 2 methyl groups on a different position on the view come over you put a bends position on nearby having a benzene ring right next to this carbon your rates of Ajax edition have become significantly faster
so this is now a benzene ring of benzene ring makes that 100 times faster than just a simple alkyl group like Neville so you sort of know that cobble Caroline's
form more quickly I wondered when the band's elected and neither of these is good and I'm going to draw DCH is on here is what I have to Alco wrote this goes back the idea that a tertiary cobbled canon is more stable than a beans with cobble can and it's should it's related this is now a thousand times faster to have these 2 methyl groups on the same carbon is the benzene ring and it's attended 5th faster than the 2 novels or are on the same so again if you want to understand why this is true anyone as sort of comeback the principles that you learned on sought more organic chemistry draw the cobbled cat I knew would generating you can see the reality good cobble can I'm in matters were those novels
on the double bond so if you ever want to do selective additions to double bonds of got some big substrate molecule was 5 double bonds in their you can get significant selected
just based on the substitution pattern of your double bond on and of course if you put a 2nd methyl group on here but it doesn't really have that much of a difference in terms of rates these are pretty similar to each other but in the 2nd half of it doesn't buy you a lot so sewer Ajax edition on not all the sort of start with this pie complexation under difficult conditions you don't have to draw that just a regular hero pushing mechanisms that can a couple kinds and will be able to explain a lot it would be OK so let's switch off of protons has electrified in here and in
the world and we're going to start by looking approximations with
but proxy acids so I'm going to try to draw up double bond substrates as best as I can edge on here so we're looking at the edge of some sort of an old friend and got off on this particular finished is trans substituted so he configuration we come in with a proxy assets so proxy acid is not like a regular carboxyl gas and immediatly you can see that there is an old bond in there a week old bond that is some sort of 0 0 bond cleavage in this reaction I can think of that many reactions and peroxides with a peroxide blond doesn't break OK so when you look at reactions approximation reactions the stereo
specific Sony followup oxides those reactions stereo specifically use proxy acids or proxy type substrates so if the
2 are groups the opportunity to each other in the starting material they end up 80 to each other in the product and I hope that that's not that's not new information OK here's what we're going to do further given that 1 of the most common reagents very cheap it's medical proxy Menzella gasoline basis relatively pure form until they found that in very rare cases the stuff can go off seemed jars of CPB being with blue flames shooting up the top you don't wanna see that on so now they ship is only 35 per cent pure other 65 per cent on is just the carboxyl aghast so the radio buys not pure got this acid in their whenever you do these reactions importer remember the conditions are acidic unless you've pretty purify MCP so when we draw only that we're going to draw a transition state for this company and once again I'm trying to draw on all the John How would I envision the transition state for delivery of a single oxygen atoms and it's going to look really bizarre and weird fears the transition state looks something like this and so were members struggled to figure how don't draw this with an narrow pushing mechanisms and you draw partial bonds for the bonds at a breaking it was so there is a set of bonds that are involved in the transition state the MCP PBA comes in and delivers not the oxygen that's closest to the carbon that stays on there it's the oxygen it that start off with the agent gets delivered and you can tell that some nucleophile is going to come in and break that oxygen oxygen binding
decisions and will show you a way to draw this that doesn't drive insane because if you tried just too many heroes in 1 step will drive you crazy wanna start by
looking at the of the rates for up oxidation they're not exactly like this reaction so when these types of reactions we tend to draw cargo Caroline intermediates there's no Koble Caroline intermediate and up oxidation reactions there is no cargo can and so we should expect this order the release the quantitative order of reactivity won't be exactly the same but there will be similarities 4 of the people of the world for so long and for reasons I don't on the following note for reasons I don't understand I do this in the opposite water with the most reactive often 1st some initially relative rates for up
oxidation with medical row peroxide and sewer and has the more the try substituted opens the most reactive
you know there's no cargo can intermediate try substituted opens are more reactive and I substituted which are more reactive than mine was substituted so MCP electrified I'll try substituted all forms of more active Why is this more reactive well the siege bonds here that the donating in the party system and making it more reactive than the more neighboring bond you have mixed up I system the more they're going up the energy of the home OK if the benzene ring or a doesn't have to be a benzene ring any sort of price system that I put next door that can donate into that double bond will increase of the Homo energy that double bond and so that's that makes that more reactive than just
a simple substituted often but come back here to just a simple internal out
again there's no cobbled Caroline intermediates in the approximation reactions on and of course this is vast I don't have a number for a criminal offense but it wouldn't be but it was good just simple ethylene is 50 times slower this just give you a sense for the importance of having these bonds nearby BCH bonds alkyl bonds simple limit has nothing on here can donate into that price system activated for being too that's not a very reactive office and we can deactivate and orphans so in other words let's try to what can I do to this 1 to make it less reactive what I could do they could put an accepted here a pie accepted like a carbonyl group some awards
instead of reacting like that like this some simple styrene derivative soon and guess it is now even less reactive and ethylene itself so in other words if you have a
substrate that hasn't been alone and just regular helpings you will have no problem selectively epoxy Eisenhower regular help keen and leave the EU known alone you know they're not very active and not for yes because the carbon electron withdrawing emulating draw this out in terms of our before I go on because I don't want this to be made in anyway so if usually when I'm drawing operating mechanisms and drawing an diagrams them diagrams just something to fall back on if you're looking to explain things as I explained the reactivity of some sort up ICC double bond traders got a
pair of electrons CCW ones of a pair of electrons by hiring energy that is the more nucleophilic the lower energy that is the last nucleophilic fuel is
so far I have some orbital next door so let's suppose I have some molecules and conjugate on Carbondale well what I'm saying really is that if there's a Khalil next door and there's is empty a pie stars CEO then instead of my double bonds attacking the nuclear file they're going to be attacking the carbon and if I draw that new die if I draw this new molecular waddle out that shows what happens when I makes these orbitals together you can graphically see what's the effect of the carbon but that's sort of the graphical depictions that allows us to see the energetic consequences of having the double bond attacking the instead of attacking your electrified that Celeste nucleophilic solo home over the the home over this overall system now I'm not sure how I would describe Soviet this long pie see
double 1 cc doubled so now the home of this system on ends up lower energy is just a little less
nuclear fuel and you don't have to draw the Senno diagram to explain hopefully when you push heroes you just as you can see the carbon he'll there and had an intuition that the carbon Hill is kind of sucking the life out of that often making it less nucleophilic focused on how are we going going to push heroes for this but for this very complex reaction here you would think that would be and here's the way I would like you to do it and I'm going to redraw the proxy acid like this here's a picture of a proxy acid and I'm going to draw hovering right above the dull Vonnegut's epoxy guys and I don't want you to just start drawing euros billion and up with 15 thousand euros on there enter look so strange in crazy that you don't know what's going on in proxy acids there is an internal hydrogen bonding proxy acids have an internal hydrogen bond that means is going to talk is vibrating back-and-forth between these 2 oxygen atoms and so I'm going to start this mechanism by simply drawing the age transferred over there's a fast vibration there with age goes back and forth and some simply going to transfer the proton there and as soon as I do that now it becomes much easier test saying How I can deliver a single oxygen atom In a concerted reaction now that I've broken that off now it's much easier for me to see Hong going to deliver 1 oxygen atom the thing that's going to look crazy to you as my elective filet oxygen in this particular structure now has a negative
charge and that's going to throw you off so legal and draw this initial h and trained the proton transfer OK so
if don't worry about 0 minus here that's still the elective Oleg oxygen worry about but think about the fact that there's this pathetically weak oxygen option bond is going to break so I have a nucleophile that's my molten salt is mostly weird for you to think that apology by Wolf and can attack and break that oxygen oxygen bond so you may not like that all minus there but look at this leading group now become much better as a leading group that is with positive charge and how satisfying this me and this is like nomination are coronation at this point you got this leading Group believes but you don't want to leave a cargo can I here in fact to redraw this 2nd obey the three-year-old when the draw different residents structure on it my residence
structure look like this of sorry you when know you hate it when I I'm in a draw another resident structure this village
like this and now maybe it's even easier to see what's going on so here's another resident structure we could draw were now it's even more satisfying to see that Leading Group Lee so the same narrow pushing with this resonant structure all my double bond acts nuclear file it breaks that week week oxygen oxygen bond or give the electrons there and now hydraulic on perilous online as I can see how it can simultaneously common attack in cargo can find before it gets a chance to form and that's how you get sort of simultaneous bonding and so you can see now readily from either of these on I'm worried about this mechanism here cause I violated the 3 rule I told you I want know that likely to draw this resonant structure and so now you can see how you get up oxide and how you're leaving group is going to be on carboxyl again acid so by the end of the reaction even if you start with Purim CPA with no
products acid you're generating carboxyl as the reaction proceeds so unless you have some sort of based on like
bicarbonate is common on you're going to end up with acid in your reaction conditions OK so I'm not going to make that more reactive how could you make MCP more reactive only minutes it's a part the so this is a long known observation only on probably before we had a clear understanding of what's happening with proxy assets so below balls and this case will draw a stereo chemistry here when you up oxidizer locale calls with proxy
acids like medical Roper Occidental Gassett you end up with Sinop oxidation seemed the hydroxyl group and that's
important for stereo selective synthesis on this particular day she about 20 standing empty and the reason why this is true I'll draw this this is called the hand best transition state for I'm going to draw this on this a local call another would you have I think about what the effect of an OH group it could be that this oxygen lone-parent up to oxygen longer is 1 of those 2 is somehow hydrogen bonding with pH or it could be the a H on the alcohol is somehow hydrogen bonding with 1 of the oxygen in the and it's this effect here that causes you to attack or prefer to attack from the same face as
the outcome it turns out that what makes this react selectively from the top face Is that when CPB
hydrogen bonds to the proxy acid reagent you can imagine what will happen if you put any partial part anymore partial positive charge on that oxygen that is the leading group at the same time the Jamaican this more Delta plus the also making this more Delta minus on buying by by having the hydrogen spent any time bonded to that of the oxygen and it for this can act as a nucleophile an attack bonds here will make the system more nucleophilic it'll make the electrify region were leptophilic you get an acceleration from that affect the hydrogen bond makes the Electra Elektra and makes the nucleophile more nucleophilic so the transition state or call this that both of these transition states that I-shy drew a transition state somewhere on these recall the hand best
transition state we deliver this oxygen here but to the to the double bond so as you might expect other hydrogen-bonding groups like the
minds of many Jews can also and this effect of directing of oxidation from the same phase will see the same thing sort of influence OK so it's so that switch away from approximation that's all about approximation must turned to another classical reaction of double bonds acting as nuclear files also a concerted reactions like approximation so if you add a Boraine reagents that doesn't matter where warriors these go was reasonably good Regio selective aerial discussed that in just a little bit too but would you say is the opposite of
Ma ,comma competitions that's not bromine that's a boring at the worn sold the product B R 2 is not wrong OK so when you add
h adds to the most substituted carbon and they had a Adam adds to the least substituted carbons and so we call this tumor ,comma competition from here I don't wanna really dwell on that mark on a coffee sort of nomenclature I just wanna go straight to talking about the transition state of mind .period madam analyst simple way to introduce this summer just going to and understand going to start off straight with with those that the complex picture here to draw boring molecules and this is
not perfect so boring is cleaner but Boraine just like HBO are just like B R 2 just like
transition metals can complex with bonds so I hope that's kind of obviously Boeing would desperately love to have an extra pair of electrons on the 2nd row adamant wanted electrons so mix warnings in with pipe bombs you can end up seeing some sort of a pie complex forming the problem with this pie complex even tho it's it's a real intermediate this we can't push heroes with that pipeline so when I ask you to show me narrow pushing mechanism you don't have to show this pie complex the daughter transition state for this Hydro Mauritian reaction in the transition state has just ignore my debut bond years -dash interaction and imagine what would happen if I had this double bond
attacked the born out if I take the electrons away from 1 of these carbons like this 1 here and I attacked the born on the Brawn will start to become more nucleophilic and start to develop a credible can I'm here at the end and that means at the same
time 1 of these ages will come back in an attack high drill ruble comeback in an attack I'm going to draw the transition state years you can see there's a four-member bringing the transition state this is the transition state furrow of fried of oration reaction it's a four-member during transition state there is no cargo Caroline intermediate and I drove oration reaction it's a concerted transition state put the double dagger there just you know that's that's not an intermediate and transition stage so the prediction is if this is true and it is residual always gets in addition and that history you don't get into addition like with ruminations on the addition of Ajax double bonds aren't so highly
drawling Errol pushing for this because that's what I'd like you do this course and I could hear oral question we're just not draw the apply
complex so this is the way I would like you to draw Errol pushing for these types of reaction just attacked the war on and at the same time the you're attacking the boron don't leave a cargo carrier Ryanair uses a to B bonds to come back in an attack 1 of the 2 carbon atoms so the pipe bomb attacks the morons and then this BH bond at the same time will sign simultaneously comeback in attack here's what's weird about this that and it's not going to necessarily bother you until the next quarter .period next quarter income 202 if you take that course you undercover Paris likely agree actions but the deal's older reaction EU
reactions signature rearrangements and 1 of the 1st thing you learn is that this is not possible but this concerted two-plus-two
reaction violates fundamental rules of orbital cemetery in here the reaction that is considered the key here is that this is his concerted but it doesn't have a particular property and this won't mean anything to you now but I'll give it to you hold onto for later this is not what we call a parasite quick-reaction but doesn't violate properties orbital cemetery because it's not parasite that there are many concerted reactions that not Paris cycle so later in camp 202 ,comma I should put excess so cells a later you're going to learn that these types of reactions are not possible as pro cycling reactions and the reason why this can be inserted is because it's not parasite click OK so it's come back in an you can
and try to think about how we think about this ,comma I
Mauritian reaction of people and unfortunately the best way to think about a high deliberation reaction is to draw it as the stepwise so let me help you think about the stepwise Highgrove oration reaction if I were to think about any sort of Elektra filet condition twin Al-Qaeda I might want to draw resonance structure maybe this will help us and you might you might offend you to draw this resonant structure could you look at that ,comma gang you think are 1 of those Collins doesn't have an architect that's a crummy resonant structure but just draw for not not not when you're there pushing but just to help you think about the real geochemistry OK so it sucks because
1 of the carbons doesn't have an architect that's a succulent fruit prison structure the knowledge all Hydro boarding region it doesn't matter what X is it can be an oxygen substituent In this
particular substrate born on does not have enacted electrons in once an architect of electrons moreover the hydraulic periodic table here boron carbon nitrogen oxygen and Florene city body Electra negativity for carbon the only 1 I know we don't know any others well maybe in a couple of others but I can figure these others out the letter negatively for 19 in history anybody notice for oxygen knowing what I do here 3 . oxygen 3 . 5 it's anybody know the election negativity for flooring sports monotonic the only thing on training about changing the size here and just changing the
number of protons and neutrons some income would come back to boron carbon is more electoral negative than born and a proton that's
the other elected negativity that I know is 2 . 2 so I look at this age the bond here when I look at the age the bond hydrogen is more lecturer negative than boron so finding nothing the charge even if I didn't understand the architect rule I would tend to want to make this carbon atom attacked the boy so if we drew this out stepwise it's not stepwise if we do it out stepwise and acknowledge that it's not stepwise here's what we would see as we come and we attack this this war on the doesn't have an architect would end up with this intermediate where there's a nucleophilic boring "quotation mark -minus In an intermediate although Barnstable or on a more nucleophilic so it makes sense that if I start to
develop this handwritten Borat character that this Hydro boring bond would come back in and attacked the couple cannot do so again this is pure fiction
it's not it's not stepwise like this so remember it's not stepwise but you can totally see why you get this week geochemistry on when we try to pretend just momentarily itself was quite bore all the text was substituted 2 on simple Elkins OK so that would take a look at the real geochemistry fragile origin reactions now that mail all this big deal about on this mark on a coffin Regio chemistry but with the with the 5th and won a start by drawing out some here's 1 source of boring that you might think that you might use very commonly it's a stable region it's boring teacher complex that's the Lewis structure is very stable alternatively you might use died Boraine here's the structure of diver warning that he would die if you put Boraine some sort of like contained that boron is used desperate for another pair of electrons and it doesn't get it from the helping solvent it'll get it from another war on molecule another word Gillette is weird structure where His born starts to steal electron density from other E HP bonds hardly draw withdrawal like this Haniyeh's looks crazy but if you wanted to draw some charges during broader writing minus here minus here and plus that I don't worry about the charges that's boring and associates to give boron as soon as you put it in the solutions it's in equilibrium dissociating and it's the same with Warrington Jeff complex it's a more stable formal boring because the boron is spending most of its time hugging the lone pairs of the teacher but for either of these in solution there's an equilibrium where releasing free boring and what I want to do is a wonder drug table here where I look at various different substrates and elegant way what happens when I Hydro board a double bond with boring derived from these regions it is squirting Maureen teacher of complex but the squirt indictable Dybul rain you're really just adding this this is the real reagents doing job oration and I'm going to give you a series of different on substrates so we can see how good is the Regio selected so what I have here I have a simple terminal 1 and is more substituted with an annual gathering is less substituted and then over here I have a sterile group another with about a benzene ring that's conjugated nexus double bond sorcerer conjugation effect on top of a steric effect and then I had just 2 alkyl groups on opposite sides 1 ball here was less bulky isopropyl versus method and so what I see for Regio selection when I use boring remember our rules said that the boron is going to end up attached to the less substituted ,comma and that's basically what you see for a simple terminal helping it's 94 per cent of the products have 94 per
cent of the products of Baumann molesters subsequent ,comma it's not 100 per cent still 6 per cent of these other
review isomer were born as on a more substituted carbon that's still pretty good 21 selectivity approximately when I look at it as dialog Roper there's an extra electronic affected their it's not quite as good now it's 80 20 get a significant amount of born attachments next to the fennel and I wanna come back and try to use Terex as my basis really the the Telectronics urine are not that different regions individual carbon it's almost one-to-one the 1 side boron and the other working is not a very big region so it's not a big givers ,comma sent a huge differences some difference between ice problem the muscle Suarez boron is concerned if you want high levels of
Regio selectively you can buy cheaply reagents that have a huge spirit
bias and I'm going to drop 1 of them for called 9 B H on to draw this appears slightly at the same levels all arrays that sorry when I read it just wanted released here from my table this is called 9 median age is 9 Bora by Cyclone if I replaced the Bologna with carbon than we try to draw not doing a good job of drawing my chair but a minute or 2 axial dungeon and cheer there's 1 there is the other and so this carbons there will be no name their benign carbons a by cycle existed with 9 carbons I cycle no Maine but it's got a boron and there's was borrowed by Cyclone no but you could see me what's the deal with this it's gonna be a bond that's reactive that's fair directly injured has issued stared with his non-electronic changes at the steric change the way you typically see people use B N H 9 media is what usually refer to the test but if you want good reduce solitude you don't go get a bottle of pouring it on behalf of 1980 ,comma that's greater than 99 per cent better than 99 to 1 reduce selected its 99 to 1 in the case of that styrene In the case of just proper losses of methyl group it's again better than 99 to 1 Select Committee that's just steric effects so scared can be in this particular case the steric effects a very powerful for distinguishing and approval on Nokia run out of time here that just to last things to to cover when we come back on Wednesday on the relate to born eights and stuff
we've already covered before ,comma were pretty close to done when we come back on Wednesday of the Senate of the last things we talk about these .period intermediates and then we can start
talking about using double bonds seasonal bonds to form carbon carbon bonds and that's 90 per cent of the field of organic chemistry is that reaction


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