Lecture 01. Arrow Pushing. Part 2


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Lecture 01. Arrow Pushing. Part 2
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Vranken, David Van
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UCI Chem 201 Organic Reaction Mechanisms I (Fall 2012) Lec 01. Organic Reaction Mechanism -- Arrow Pushing -- Part 2 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.
but what about the 2nd part of our 1st lecture in chemistry 201 and this is electron hero pushing and right now I'm going to give you 7 rules for mechanistic hero pushing when you draw narrow pushing mechanism from organic reaction how do you know that you correctly broken down into individual mechanistic steps the elementary and added the correct Kerberos so it's good to start off with only 1 in 4 of
the Act of all of us but that all of this seems like a simple drawl correct Lewis structures as 1 of the 1st things that you learn when you take General Chemistry on the Net as an undergraduate this has several components to it and you know that you're drawing correctly structures in using them correctly the 1st part of this role seems pretty simple tremendous obeyed the architectural Sony just remind you of what they are terrible says the upturn will says that for 2nd row Adams not all Adams just Adams in the 2nd row hydrogen by transition metals not sulfur not Foster's to these Adams right here in my little many Periodic Table lithium at beryllium were not going to worry about the war on carbon nitrogen oxygen and Florida for the 2nd round Adams we cannot have more than 8 electrons on their structure so why is this important but you do an example of how the optimal comes into play the predicts that you want to have a electrons when 2nd rower so if you ask yourself Why is
this method can I'm so reactive it is because of a positive charge it's because it lacks the electron boron is about as
reactive as a metal cast iron to most species in solution and it has no choice but it desperately wants to have an octave electrons likewise withdrawal Carboni mile this is another type of Cobble Caroline that you won't read generally see there's nothing wrong with having firebombs to this carbon atoms In this cargo you mind and that may be surprising to me .period resonance structure for this Carboni mine and that is to many bonds here's a resident structure this this Carboni miners villages methane posted extra Proton attached that extra Proton is sharing a pair of electrons in 1 of those for bonds so there's nothing wrong with fibers to carbon as long so don't violate the architect solo baby architectural and don't violate that rule don't exceed electrical carbon and if you have less than 8 electrons on carbon that carbon atoms going to be reactive OK so 2nd part of this will let me know give you another I'm sort of half a point to know whom you when your baby after all quite often in organic chemistry organic structures are drawn out as molecular formula like that because it's easier to take this onto a keyboard but when you translate this into a correctly structure if you do so incorrectly that suppose I I draw this out as a loose structure and I do like this this this typewritten version molecular formula version for Oceana mind cannot possibly be this where I only have 4 electrons into bonds to the central carbon atoms that can't be right that's so desperate
so desperately far away from the architect will so if you start off with this incorrect structure of Racine I get no hope of getting the correct mechanism so start up with correctly structures in Albania activity the carbon atom is very far from having comes in the 2nd part of this 1st school draw correct Lewis structures of of of the of the all of the of the
so is so party this fall is drawl every substituent on every atom except for recorded so returned to this structure for Oceana mind the correct structure for a seat in mind I could draw like this for a draw every single hydrogen atoms but 1 thing that happens very quickly is that organic has become very good at adding to the number instantly you should know that there should be for bonds to every carbon atoms if you want the carbon atoms neutral so organic chemistry quickly stopped drawing in the carbon atoms symbols see and they start drawing the substituent hydrogen because you should be very good at recognizing how many hydrogen is about this carbon that only has 1 by an army hydrogen-the bonds to this carbon which already has 4 bonds so when job correctly structured you always have to draw the the the Adams attached Every nitrogen every oxygen but for comment it's assumed that you are instantaneous that adding up to 4 and filling in mentally the hydrogen is attached the number 1 problem that people run into an era pushing mechanisms the number 1 mistake is not seeing the hydrogen atoms that there so throughout this course and to outsource more organic and you're going to write cases where you need to pull off this hydrogen disposition that is not drawn for you and so you need to practice with that until you you're instantaneous and knowing where the hydrogen atoms are so if you're not that good already than practice until are look at the 2nd and the
3rd part of our rule to use correct Lewis structures In that Mexico is so draw every charge draw every charge so when I take a simple structure like this this is try metal meaning an oxide it an oxidant and some reactions were used in the Kornblum reaction there needs to be charges on the structure and if I don't follow those charges that the charges that are necessary for a correctly with structure that I'm going to miss some of the potential reactivity of this molecules so once I dropped the charges on a train methyl Amin an outsider Indiana on Sunday recognizes that oxygen is probably the nucleophilic Parker this molecule now I have to be careful not to avoid the 1st part of our role wages drop correct Lewis structures every single part of my body wants to take 1 of the lone pairs of donated down to that nitrogen because it's blessed but don't do that and just say right off the bat that you can see that's going to violate the archetypal so don't do like this I'm just leave it with these charges a plus and the minus the separate instruction :colon on because it gives you an indication of the kind reactivity should expect from the molecule the
last part of our withdrawing lone
pairs of electrons trawl every lone pair of electrons 95 per cent of every organic reaction mechanism out there starts off with a narrow coming from a lone pair almost all the cases and if you don't trust them you may forget those things are important so I don't remember to draw alone years this is a molecule called TB utilizing a although the charges but I don't remember to draw the lone-parent Carbon Maine this that that's the nucleophilic end of the Molitor is likewise if take a typical mechanism here is an example of a reaction between all and molecular bromine directions involves carbon bromine bond formation it starts off with word looks like it starts off with from Yukon bromine bonds but the reason why this double bond assault reactive is because their lone pairs on this oxygen and the donating his piste are making nucleophilic sold direction starts off
with a loan on that oxygen and if you didn't draw it you might forget that that's why the carbon criminal bond also reacted focus draw correct Lewis structures there's a flip side to this about drawing correct Lewis structures and that is what it is all good Lewis structure frequently were going to draw structures that aren't Lewis structures and I'll show you when you confront those so there's 2
types of bonds that you join chemical structures that you have to watch out for hydrogen bonds indeed bond socially examples of both do not use Kerberos with these types of bonds so the main is for those 2 types of bonds when you drop chemical reactions all need to Kerberos as a way to represent the making or breaking of hydrogen bonds are dated bonds so as to give you an example Tulsa up by showing a regular error pushing mechanism is carbon I'm bond and when correctly drawn if you itemize that iodine animal you should get 2 different clients out of this that I really am taking electrons from carbon I should end up with the Carbol Qatar and there's only 6 electrons and if I really am getting this pair of electrons so we'd iodide that I should pick up a negative charge initially in response thereto electrons 1 long Diamond belong carbon but I take that that cartons electron away that's why in the minus on needed the plaster
book is what would happen if I tried to do this kind of error pushing with a hydrogen bond new start by drawing the hydrogen bond and typically that's represented
with -dash lines in biology and chemistry so there's a hydrogen bond between some sort of an alcohol or water in the Carbondale this could be the backbone of the protein that I try to use this kind of Errol pushing to represent on the breaking of this hydrogen-bond I'm going to be forced to draw structure that leaves me with a positive charge of this protons and a negative charge on his oxygen and that can't possibly be correct this started off this oxygen atom here started off with 2 electron answer to lone pairs and it still is too long there's it's going to be a neutral oxygen not this minus Johnson enforced and upward so what's the correct way to represent the cleavage of this hydrogen bond the correct way to simply omit the Kerberos control curvier I think that the reader or the viewer can tell that you just broken the hydrogen bond you don't need to draw the Cordero to show people that so distraught the steps and leave out the Kerberos there on the woolly due to strong conclusion could signal example of another type of bond and that's dated bonds in organic metallic complexes typically also in some some organic structures here is an example of dated bonds so here's a nickel try Carbonell driven off asking complexes it has for bonds here this is not a Lewis structure if you're a little structure after charges on for example oxygen on nickel on these are examples of data upon state of meaning donor if to show that the fasting can dissociate like this and drop the products it's going to be the same situation or be forced nickel in neutral for it now has to be nickel pattern and that's not true dissociation of phosphate does not generate a nickel cash tender were regular bottom I cleaned it would force the of the native trout and phosphorus and that's not right .period so what's the correct way to deal with this cleavage but they don't want don't show the Kerberos to show the reaction so once again leave out this curve there people can see that you broke Annabel phosphorus bombs people can see that so the leader the Kirby not forced to all those incorrect charges that OK so number
1 in general draw correct Lewis structures that hydrogen bonds not dated bonds drive the lone pairs store every hiding out among everything except the carbon and put charges in 2000 structures so will number to
Fairbury Kerberos should start with either a bond alone there every Kerberos should start from 1 of those 2 places and the reason why they start from 1 of those 2 places is that's the 2 different ways that we represent fuel orbitals more specifically
field frontier orbitals every borrower and every long pair in an organic molecule is a representation filled canonical work so initially examples of how to use it
correctly so as a hydroxide in iron and there's 3 long years on there and if you show that attacking acetaldehyde and the correct way to depict that his start with a lone pair and then have that attack a carbon atom no break this carbon-oxygen bonds starting next year from you the pipeline between carbon and oxygen so each year on year starts with either abound alone that's a correct use of long years here's another example of correct Aero pushing it well to promote made this carbon-carbon double bond and hydration reaction start off with Hydro me my aunt and start my 1st hero from this carbon-carbon pipelines and I'm very picky about this don't start with a narrow it touches the bond make sure your wasn't touching the pipeline bond and start from the middle of the pipe I meaning you can't actually tell which of these 2 carbon atoms I'm going to prove that's a real source of frustration for many students they feel like they want to start the year over 1 of these 2 carbon atoms that's not what Arab pushing is meant to represent is meant to represent that this carbon-carbon pipeline is attacking the and is another example of correct usage there are pushing if I don't 1 to we arrangement here and alkyl shift I would start this this 1st error from the middle of this carbon-carbon bond ensured that carbon governed by moving over to this Adam nobody very careful to avoid that charge there and
Schollmeyer landing on the carbon OK so these are examples of how to push heroes the example of how not to do it now
this 2nd part of this rule and the rule is that Aeros do not start on charges do not allow your heroes to start on charges so is an example suppose you hydroxide which is a nucleophile and the Kerviel group that you push Cheerios starting with the charge no predicts the correct intermediate as a product for that elementary reactions steps but you shouldn't do this this is the wrong way to push heroes charges don't form bonds electrons form bonds specifically the interaction of Phil orbitals without the laurels creates new bonds so electrons don't foreign bonds so charges don't seem electrons from behind just emphasize why this is so bad you lucky here in 50 per cent of cases appear using charged as a way to do euro pushing starting from running on charges will predict the incorrect resulted 50 per cent of cases since taking example principles I have Borel I drive this is a reaction is covered in every organic chemistry course at the undergraduate level next door high-grade reduction of carbon heels if I start my hero from this born on In order to attack this Kerviel are you really going to make a fist Vontobel and violate the got that's what they're pushing says it worked for you will be with hydroxide will ultimately fail you over here so remember never start heroes who charged them with electron start with lone parents were start with bonds those are the 2 choices but the 2nd set of caveat that we have His air heroes should not
start 1 announced the problem is I'm going to mislead you by saying things like all that bromide pops listen to what I'm saying I'm saying that bromide parts of gold bromide if you don't like that
you're not representing anything that's related to fill orbitals under locals you decided you 0 to represent the trajectory that bromine at the correctly joint mechanism should have the electron starting from the current bromine bond and you've been misled by the fact that I said the booming pops off another example I'm going to say probably made that double bond let's take a proton a double bond my description suggests that you should try to depict that then maybe you might want to try to depict the hydrogen that protons popping onto 1 of those 2 carbon atoms and that's a misuse of errors that's incorrect the criteria pushing mechanism should have the CEC double-bond attacking not desk it's not meant to help pushing is not represent not meant to represent the trajectories of hydrogen atoms it should be this easy .period bond acting as the base and obstructing the Proton so that's the correct euro pushing for that make it OK so make every arrow started on a Bonda alone
there because those are representations of field also you book a rule number 3 of whom over 3 is to
make every Kerberos and on either an atom or bond and the reason is end these are representations are best representations are not good but that the best we've got these representations and unfilled orbitals and this is 1 of the hottest parts of mechanistic hero pushing every single Cordero that you draw is meant to represent the direction filled orbital on for locals but unfilled rules are not part of Lewis structures honey nowhere There is an unfilled orbitals stakes some examples of a barrel pushing mechanisms where are the unfilled orbitals in here so when he and his every single place that you have a bond there is also an antibody binding or if I have a signal bond here than there's a stigma story and declining modeled on the back side of that so when I draw this Cerro pushing mechanism might break this HCl bond there must be some END bonding orbital than donating into some I use a lone pair here to attack that Proton that's attached to chlorine if I'm breaking the bond that I'm donating into a Sigma store were built between each the CIA everywhere there's a
bond there is also a need to binding canonical order it so
by by ending my heroine and Adam I'm showing them breaking the bond and adding 20 bombing work so is the next type of place that where you don't actually have a bond that's breaking if you're not breaking the bond so suppose I added Koble Kanye and this this methyl cargo can iron they use alone pair I can also add Adams not and on and on his Adams because they're breaking the bond you're not breaking any bonds but I'm heading to an empty pews there's an NDP orbital here that's not part of a correctly drawn to a structure and that's an empty word alone it's fair to add to that and we don't sometimes withdraw those in sometimes all sketch out some sort of a world ruled that might look like this sometimes with some phasing in there whether I'd rather than NTP oral or not there is a need to cure situated on a carbon atoms in here is another example of and in my arrows on Don Adams and bonds there's an elimination reactions as part of the U 1 elimination reactions there a cargo Catalan at
1 of those 2 carbon atoms on it in the middle of the structure so by correctly draw
their operation mechanism when I'm going to show is that I'm adding to this hydrogen atom in breaking this signal bond between carbon and hydrogen if there's a bond that means there's an antibody were the antibody marble it's not drawn is singing star age card and so on the back side of this and now these electrons when I had to endure all and that's adding to an NDP were all situated on products which I haven't tried true that go up and down well with the NTP work so these are examples of correct pushing where you can see that all the zeroes in on either Adams it is on this case they can on bonds and I can use that as a as well as a 2nd way to represent the fact that this ends up forming a pipe bomb so there's 2 different ways to represent this you can make this double bonds went down for the 2nd bonded carbon apply bonds or you can make these the electrons had that NTP workable and both of those are acceptable commonly used in organic chemistry focus once again the important caveat is that heroes do not end on charges charges don't form bonds electrons formed on
desperately wants to make your negative charges that have positive charges this is a major driving force in organic chemistry and tried to dissuade you don't you 0 pushing to represent the direction of charges and that's not to say the charges are too important in bond forming events that were not using our heroes to represent the direction charges for care will number 4 is not really driven by some fundamentals of quantum mechanics for any fundamental rule a lot nature I'm going to give you a rule that the safety device to prevent you from going out of control and we have something in this class
called the three-year war In relates to curb euros so as long as you're taking can 201 I expect you to abide by this three-year rule so the idea is to you're not allowed
to draw any more than 3 Kerberos in elementary reactions that Sony leading example how of abuse this this rule so can elimination reaction we take this alkyl chloride beta coral cycle we treat this with a strong base like sodium the bauxite and this and that doing elimination reactions and there's 2 possible products that we can draw for elimination reactions 1 would be the conjugated know and the other would be that the beta gamma unsaturated non conjugated you know this is the major product you see none of this plan conjugated known here why is it must have something to do with the colony there's clearly a proton has being removed and I draw this mechanism and I draw something like this I might start off over here with the sodium oxygen bond that ends up being broken in the end I make sodium chloride and now I have to do something with these electrons MHC bond when I break apart now I swing them down pop off the chloride will then I'm not explaining why didn't get elimination here there's also protons down there the reason why this prime-time hits extracted is because those electrons can do make into the company when I do that I have to break this carbon-oxygen bond and then in the 2nd step longer oxygen swing back down and then create some sort of any related pops out the chloride and Hardaway represent this there's no legally drawn on here they destroy a 2nd behind you then use those to week over ultimately that was
something that was wrong at every single level of detail and the problem is that I advise the problem is that I have not broken this down and elementary reaction steps that's the number 1 problem but a true that I wasn't breaking discounted elementary action steps as they have all these crazy arose so this is simple
in this class don't have more than 3 Kerberos because if you do so when your 1st starting off offered agenda In reaction narrow pushing and her drawing up which mechanisms that you have more than 3 heroes like this kind of weird scheme right here on the probably not breaking things down and elementary reactions sold in what happens there will be cases where you just
want to agree maybe you did this because you feel like you had enough space on the page to draw mechanism that doesn't make it OK to draw long mechanism to let 1 suggestion that can be used by experts for drawing nearer pushing mechanisms and you're not an
expert yeah maybe by the end of this class you'll be an expert so what do we do if we want to abbreviate things we think are obvious this is not the right way this is fundamentally incorrect implies is also concerned so the correct way would be 1st to draw areas for the 1st step to draw arrows for Step 1 and then draw a series of stacked reaction arose not Kerberos the reaction arrows on balloon example of works such as opposed don't have enough space to draw a correct opening mechanism you did not come back to this simple hydration reaction that we did we considered earlier so Zabaleta hydration reaction which amending water across this CEO pie bond and I want to give people some idea of what the mechanism is for this reaction it's not one-step reaction this is an acid catalyzed reaction what I can do that I want to give people an idea of what's going on as a control their operation for the 1st step that probe nation this carbon to an ox only a minor appropriated carbon Hill and then to show that there's 2 more steps in the mechanism can abbreviated like this this gives all the
information that we need to give I've broken it down into a series of 3 elementary reaction steps I should there'll pushing for the 1st step without adding incorrectly other arrows that would suggest concerted reactions so alternately later on when you start to become very good at Aero pushing and you don't feel like you need to show everything to the viewer the reader you can use
this kind of a shortcut but for now you need to draw every single step in every single intermediate in every single Caribbean there will be times when you'll desperately want to draw more than 3 Kerberos and in fact there are many mechanisms in which the correct mechanism is drawn with more than 3 Kerberos but for this course there is always a way to avoid that I'm beginning an example of a reaction that would be correctly correctly depicted with more than 3 Kerberos it is and so this would be after Kim 201 after you've taken this course how much you depicted on this reaction of electoral filet aromatic substitution with parole was some sort of a parole species for is aromatic but it's a very nucleophilic because the long pairs here on on on nitrogen are donating into the spy system has let me go and draw out there the electrical like aromatic substitution of parole with any silly online so this is a nucleophilic simply because the long hours and Ikena donating down and I can draw this teraelectronvolt double bond here and then I can use this pipeline to attack my hastily in mind this is the correct mechanism and that's the correct way to depict that I believe
that used for Kerberos to do this how can I am satisfied my three-year-old still drawn up this mechanism that I could have
done as I could have started off with a resonant structure of Peru I could use 0 pushing to depict the resonant structure and if I start with this residents structure I can use Kerberos to get to his residence structure now I don't need a violate the studio will in order to show this bond forming event now I've only got 2 heroes in my hand my mechanism where mine now using this lone pair on my resident structure approval to attack the silly mind and taking the time to draw the residents structure between your initial intermediate between this really does inform you about why pool in nucleophilic so it's a good idea
to draw resident structures way of gaining information about reactivity on and it will help you maintain this stay within the bounds of our three-year-old the strictly for this class a safety device to keep you from going out of control look at Rule number
5 the I the think there are no term molecular elementary reactions when give you an example we set the goal of all of mechanistic hero pushing is to break reactions down into a series of elementary reaction steps is a common transformation in organic industry has to take phenolic hydroxyl groups in all metal later there's many natural products and by biologically active molecules that will methyl groups and the way you typically do this in way that is using methyl iodide on and your phenolic compounds in potassium carbonate is a base Indiana supporters solvent and that's how human bone that the late phenolic groups of potassium carbonate is clearly the base and so you might have a tendency to want to depict that the mechanism if I ask you the mechanisms 1st of all for starting off wrong here by drawing a lone pair without drawing the Lewis structure that's OK which is not worry about their right now the purpose of the basis to deeper make the final and I think everybody can see that then this and species become more nucleophilic an accountant who have not signed the 10 attacks the carbon and the release the idea that I didn't violate the three-year-old this still has only 3 Kerberos 1 2 and 3 of the bureau's this is
what the problem is by drawing all these 3 heroes In a single reactions that implies that is conservative what does that mean that that implies is a
series of not a series but a set of simultaneous collisions it implies that this base had to collide with this protons at exactly the same point in time that this oxygen atom was colliding with this carbon and releasing that's what it implies it is extremely unlikely that any 2 species in organic chemistry will collide with enough energy and the proper trajectory to make-or-break bonds usually it takes hundreds of thousands of collisions for things to form a bond that just the right energy just the right angle just so trajectory the chance that any free molecules will simultaneously collide there is no chance there are no known reactions in organic chemistry that occur in the solution phase where 3 things simultaneously collide and 1 elementary reactions step generate products the problem here is I didn't break this down into a series of elementary reactions steps the true mechanism for this reaction involves initialed the proud nation announced fast and reversible the 1st step is the proud nation and that will happen millions of times before this phone oxide in finally collides with the mother lied with sufficient energy and just the right trajectory to displace the iodide so
great mechanism involves 2 steps so don't draw all elementary reaction steps that have more than 3 2 components colliding at most only 2 things can collide with just the right time and was just the right geometry and trajectory and energy to form Pontypridd bonds look at the 6th rule it
may seem like a lot to keep track of the all these rules 7 more than the sum rules most of you have already been obeying the rules In the very gecko you're probably already obeying the rules and you didn't know it constantly codifying probably what you've already been doing in organic chemistry this weekend to protest at the foot of the Book of the of the of OK this is a very simple and that is the H is always attached to something and the problem is you're going to be misled because I'm going to use terms that mislead you I'm going to talk about proton transfer among to talk about hydride reduction reminded of a hydrogen atom transfer reactions folderol describing functional groups so when I say a proton I'm not talking about some free-floating age plus I'm talking about a functional groups when I say hydride I'm not talking about the species here each class I'm not talking about each minus all of them are not talking about each doctor of the species have no role whatsoever in solution phase organic chemistry the place you find species like this is maybe if you fly into the center of the sun you'll find these kinds of free species floating around that's the kind of energy it takes to create free a cluster hydride billion here is so in other words how should we draw these mechanisms that involve will look like species like so here's what you'll often see rain the literature
something like this when you want to talk about appropriation for example
this key some people will drop this agencies plus there is no such thing as a plus in any organic solution reaction but the correct way to draw this out proclamation of key is to show that the age was attached to something and if you don't know what the beach was attached to just representatives some generic Gasol talk a little bit about that in the 2nd so this would be the correct mechanistic depiction Sony offered you not to do anything like this because there is no such thing as a fluffy bottle of age plus that I can get lap so it's not that much easier to write this the Director of bonds to enable break the bond and that's the correct wages to be depicted so similarly you might find some reactions in which that might be depicted like this incorrectly there is no such nucleophilic hydride that floats around in solution that look like this there's no such thing I might talk about a hydride reduction or whatever really talking about is a hydride functional group attached to something else so here's an example of a tad hydrate illuminates species we would refer to this region is a hydride owner of the functional group it's donating is a hydride with a pair of electrons but nowhere in solution that I ever had each line is floating around free in solution and likewise might have a hydrogen atom transfer reactions so here's a key teal species with a carbon atom 7 electrons is just a single electron carbon and it's reactive and this will pick up hydrogen atoms from places reaction but it never picks up a hydrogen atom by simply joining to .period there's no such thing as a it around solution of for radicals were not going to cover article this quarter before radicals views stylized official carols that had the only focus
solely on I use terms like Proton and hydride and hydrogen atoms that doesn't mean you should ever draws free species like this at the very beginning of the reaction this starts off attached
to 2 and conjugate acid it starts off attached to something In the transition state it's attached to 2 things and in the end it's attaches oxygen it's never attached to nothing at most it's attached to 2 things so well .period drawing species like this Illinois use language like that so likewise don't simply have Proton part of like this and released free protons because that's completely incorrect the reason why this bond will break is because something had stood at Entebbe on moral and breaks the bond but solely on that done
and over with that of drawing these types of free speech because they don't exist in a typical solutions so the 2nd part of the
rule of law number 6 and you will see violations of this throughout the literature index which don't like this is the agency there so you might see my reactions like this strong were somebody wants to hide relies on acid house you wanted to hide realize this acid town you might see a depicted is sometimes in the literature there's no reagent 8 plus the given unless it is not that much harder if you wanted to show how you idolize acid house it is not that much harder to draw this catalytic agent you don't have to draw catalytic if you don't want to just simply to draw that caters attached to something and better yet show the actual reagent that because that affects the rate and speed of the reaction so that we can narrow through this don't do this kind of a depiction either in your
mechanism in reagent above a reaction so you really had a parade plus like this but "quotation mark surrounded the show that sophisticated enough to know that there is no such thing as each class as a region you can have I will come back to this acid concept of how represent acids in just a moment here but under Alaska law 7 and all of the people of the world
for the benefit of the people and the people of avoid Proton transfers from four-member transition state very often in organic chemistry you're going to run into species that have territory the dual Adams like this this might be a species that you run into we knew idolizing cycle icing to make electing him so far to try this cycle eyes this in order to make a lacked and at some point I might want to have some sort of a up a proton transfer step occur or if I were to do the reverse animal thoughts are in line to open electing him so at some point and I want to move proton from here over to his oxygen in order to complete my mechanism and the important point is do not draw if I count up the items in this transition stages for items that means the my transition it has to be the shape of a square that requires this oxygen to attack the Proton at a 90 degree angle and that's simply implausible that energetic leaders favored the thing that you want to do in these cases I'll show you that just a little bit his have something else come along From exactly the backside and pluck off the hydrogen and then we delivered to that oxygen in 2 steps not a one-step mechanism through a four-member transition state but a two-step mechanism involved some sort of conjugate base that arises from an massive sums simply telling you that's slower than a two-step alternative it can be much worse than that there's any all at the trauma of a key town if I wanted to show how the proton ends up at the opposition that I would need to come somehow move that Proton over to two-year on cards and you cannot draw a plausible mechanism that looks like this that violates
common concept called the concept orbital symmetry and there is no parasite cycling concerted reaction that looks like that so that's implausible OK so what our choice what are the alternatives for that the alternative instead of doing these types of one-step Proton transfers to four-member transition states something that's slower versus something that simply impossible all
label this is impossible as a concerted reaction was the choice here and the choice is to 1st and foremost determine argue reactions taking place under acidic or basic conditions continue my form going on OK that was the best most of the people so 1st thing you need to do and will use this talked harmonization is an example that he wanted to avoid some four-member transitions is 1st decide whether this normalization is occurring under acidic or basic conditions it's occurring under acidic conditions instead of moving his Proton over a single step due in 2 steps 1st on the proton and then plug the proton so if you know that the conditions are acidic use a combination of so if it's acid was a combination of HA freer acids and A-minus bases don't use the symbol be a stick with these 2 symbols you have an acid base what I use those so for example here was under acidic conditions I would probably make that the 1 1st and then the 2nd step that dry probe made a double bond amuse the electrons oxygen after I broke made double bond now I can come along With my name I conjugate base of my acid and pull the proton back off 2 steps and mechanistic Wiebold will talk more about proton transfers later in this class but both of these types of reactions proton transfer reactions are very fast as opposed to a slow four-member transition state type process so if I know the route that conditions are acidic the news this combination of a simple HA an A-minus or at my conditions are basic the nation use a combination of and as as an asset and indeed as a base and you can add pluses reminders on their it as you would like depending on whether you believe in your base is neutral or not neutral so here's how I would do this type of protons with a DUI proton transfer using this combination if I knew that my conditions were basic but suppose I wanted to transfer Proton ,comma In this allied territory he drew intermediate so I somehow wanted to move Proton from his oxygen to this I means so that the image of the leading group and I know my conditions a basic I would start off with my symbol and I don't need to say whether that's Cox on arena later just a water molecule on just using this as a symbol no wonder but this intermediate so the two-step proton transfer but entirely plausible and now I use these new pro conjugate base that I generated and now I can transfer the the 2nd step that provide also this would be the correct way to depict these types of proton transfers after I 1st decide whether my conditions are acidic or basic analog president of parts that ready to push out the OK so
that's the end of our of our 7 rules for mechanistic hero pushing Sony's remind you of the rules of the coveted so will
number 1 correct Lewis structures if you don't start with correct Lewis structures your chances of drawing the correct mechanism ,comma are substantially diminished who'll will number to make arrows start with bonds long pairs bonds and long pairs of the way we represent field canonical orbitals it's the interaction of film warbles with unfilled orbitals that is the goal of Aero pushing school number 3 big arrows and on Adams or bonds and when we draw correctly structures we don't draw the the unfilled orbitals but each bond you draw there is also associated with any into binding work will number for obeyed the three-year-old This is not a fundamental rule law in organic chemistry is just a safety device to make sure that you break mechanisms down into elementary reaction steps will number 5 don't draw her molecular elementary reactions 3 things never collide simultaneously to react in an elementary reactions step will number 6 h is always attached to something so don't draw free protons each plus floating around in your solution or as reagents above a reactionary and finally will number 7 avoid proton transfer to four-member transition state use a J as a symbol for acid and show the breakage of the HA bombings or use B is a symbol for the base and NBH assassin under those conditions focus when we come
back for next lecture were going to be in a regular classroom setting ,comma and we'll talk more about the basic concepts like energy and molecular orbitals and bonding


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