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Lecture 02. Molecular Orbital Theory (Pt. 1)


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Title Lecture 02. Molecular Orbital Theory (Pt. 1)
Title of Series Chem 201: Organic Reaction Mechanisms I
Part Number 3
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 10.5446/19220
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 02. Organic Reaction Mechanism -- Molecular Orbital Theory -- Part 1 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 the class is going to be taped for the rest of the quarter I think John factories in charge of the
video if you do not want the back of your head videoed for he reasoned then moved to the back of the class farms so as you know as I mentioned in discussions section small yesterday I totally honor you for going up and from the class presenting problems so you can imagine how terrified I have myself on video of it will probably eventually be unused to focus so well OK so I want to
start off by continuing where we left off we're starting on our next lecture on molecular orbitals and remember lecture 1 it was more than a one-hour lecture we
talked about the fundamental idea behind aero pushing represents the interaction of field orbitals landfill orbitals 1087 rules for mechanistic Aero pushing it we are going to agree to follow as the craft as class when we do problems sets when we do exams on those of the times and you really have to pay attention to those rules and so because there'll pushing represents the interaction of the little orbitals with unfilled orbitals we have to make sure we all are on the same page report Oracle's so today we're going to talk about warbles and I want to start off with a simple problem for you to solve was just imagine that we have 2 particles that are both positively charged on the atomic scale and into making meaningful let's make these 2 protons ready to form a bond and we all understand what electrostatics does we understand who owns law if you are an electron with a negative charge what's the ideal position for
you occupied relative to these 2 . positive charges electron has a negative charge I think we have this idea I have this notion that I want I want to put that negatively charged electron right there with all of
my being I want but that electronic but if you do that you have violated the Heisenberg uncertainty principle you can't specify the location of an electron you have to put that electrons all over the place and that's what results in bonded so we have to simple outcomes to them what is we need orbitals we need some sort of mathematical description of the probability of finding electron smeared all over the place around those 2 hydrogen atoms nuclei so there's a 2nd problem here whenever we put electrons and orbitals we put them into it at times we put an electron pairs and because we're putting an electron pairs we need some way to show but those electrons will avoid each other and so as a result of that we need phasing we need face those or but also to show that there is a way for the electrons to get out of the way and so it's going to draw the canonical types of orbitals that we will use in this class and there's really only 2 types I'm underrepresented as like this is just a simple little balls and facing either hatched facing 4 or unhatched facing like this will also use P orbitals and will represent them with this kind of lame representation like this they don't look exactly like that but this is good enough to make at various orientations with the X or Y or easy Accies so these appear orbitals and to know the importance of phasing out on it here and just under 5 separated the 2 the 2 different as rules you have to imagine them on top of each other with different
facing OK so facing allows us to think about the idea of having 2 electrons from the same place in space but avoiding each other and so that OK so we're
going to talk about 3 types of orbitals today on and exposed supposed to be reviewed for you supposedly these are ideas that that you've already seen before and so the intention is to 2 of the 4 2 2 2 2 2 2 2 2 2 and so forth we like to review atomic orbitals this is the stuff that you know is a S P D and f orbitals bolted to the structure of Adams then to talk about combining those things into Hi-Bred atomic orbitals that S P 2 as conferring that's the stuff like that so you should be familiar with that and then finally we're going to talk about combining those things to make molecular orbitals the focus will switch lot of atomic orbitals hopefully we can add some new insight and hopefully you can take these ideas that I'm sure you heard at some point in time when you take those ideas in you we apply them to react no ,comma then hopefully you'll be able to do some more stuff that OK so splinter of atomic orbitals in you think about it things we continue to
work with the people who had so there's 4 types of canonical atomic orbitals that we use in chemistry commonly there potentially other shapes and other formulations but leaders are the ones that you should be familiar with from freshman chemistry and from sought more organic chemistry from General Chemistry inorganic Internet S P now fortunately we can rationalize everything in this class with just S and P were now there will be examples of Oregon metallic chemistry a transitional chemistry where we will need to put Indiana portals but we will be able explain everything in this class just by focusing on S & P in a way that makes our life incredibly simple but what you'll learn is just handling these 2 types of orbitals and the way they interact is going to be immensely complex and yet immensely powerful OK so we're just going to focus on its the in this
class and I want super important statement to make it to
the end of this year in the than middle of past this and that is that he orbitals are hiring Energy Minister warbles I think every 1 of you knows this already but what you don't knows just how powerful that it's absolutely and start off by graphically representing the fact that he orbitals are hiring energy than s orbitals and I'm going to start by using a construct that we're going to use many times in this class called a molecular orbital or orbital energy diagram I'm going to have some mystical water lacks here and I'll call that he sometimes alright eased with the subscript like Andover molecular orbitals medial described here orbital and I'm going to show you some atomic orbital slots graphically represent the fact that P orbitals are higher energy Minister warbles and I want to focus on appeal orbitals on a carbon atoms because this is organic chemistry we care most about carbon usually everything that I talk about is going to be carbon roles nitrogen oxygen and sometimes things from slightly lower levels so this is your orbital Kennedy there's 3 types of pure the orthogonal to each other and if I draw the shapes out for those orbitals and I'm going to draw little subscript here on that piece to tell me that I'm talking about a pure and you'll see why that's important that I specified that in just a moment so we will try to represent those people orbitals this would be a pure aligned with the Y axis and there's 2 other orthogonal types appeal rules that can coexist in space on a carbon atom he said the other types of atomic orbitals there would be 1 on the x-axis and I'm showing 1 of 2 arbitrary combinations here and then finally there's 1 sticking straight out at you that would look something like this not try to draw the hatched part going in back of the plane of the board against those appeal the important point is that these away hiring energy than S orbital on carbon companies subscript their vastly higher energy if you were an electron in canopy orbital give me much more energetic and likely to attack the things an electron in Minnesota that's the importance of energy and that's what you care about you care about which electrons are likely to attack other things it's the most energetic once conversely if I were a pair of electrons and wanted to put myself somewhere I would want to go into the ArcelorMittal because it's lower in energy electrons always want to go to war bottles that are lower in energy that makes sense the more stable at a more stable place for them so that's what stroll
little comparison there here just to let you make some room here and all dropped 2 different times let's think about these 2 Cat irons
momentarily and try to imagine which of these 2 can finance is more reactive I just gave you enough information into this question you probably have an idea for which of these types is more reactive or maybe you don't but I just told you essence and into this question so that tutoring can science and waited to days into this question as we finish this up by drawing the fact there's an NDP orbital on cotton centered on carbon here and here there's an NDP located on nitrogen let draw it's empty it would love to have a pair of electrons there and what we need to do is think about the effect of electron negativity and the energy of atomic orbitals and all orbitals associated with that nitrogen atom so the effect of electro negativity is that all of these energy levels or brought in by were an electron I would much rather be on 1 of the few orbitals on nitrogen than on 1 of the people of rules on carbon the effect of electoral negativity is that these people were bills will be lower in energy effect elected negativity on the that they will be lower in energy on nitrogen and that makes sense when the sketch out the periodic table for you just in miniature form as we march across the periodic table from boron the carbon to nitrogen dioxide in the flooring things become more lecturer negative because there are more protons in the nucleus there is 1 more Proton in the nucleus of carbon there yet 1 more Proton in the nucleus of nitrogen and there's 1 more Proton in the nucleus of oxygen both protons of a positive charge in you on electron you would enjoy those positive charges more so this makes total sense that as we go the more and more elected negative
Adams that we should expect that all the orbital energies to decrease if they are involved with that nitrogen so that's a powerful
ideas so you can guess from this that this MDP your role is more reactive moral lecture filet the NTP that I drew on that cargo can I just basically is based on a lectern negativity and we represent that with their orbital energy diagram of a very powerful idea to extend OK so let's talk about hybrids atomic orbitals were done talking about just plain and simple atomic orbitals SPD and let's talk about what happened as we mixed together different atomic orbitals 1st of all in the name of of the work the focus so I'm going to give you a rule for mixing orbitals for thinking a lot about the way that warbles mixed together it's best to think of them as mixing 2 at a time and the role is pretty simple .period it is it was In the Tektronix toward also you get 4 balls out I take 2 orbital dynamics and together and there's 2 different ways that they can combine together and this is a result of that phasing idea there's 2 different facing combinations for every orbital when you mix them together there's 2 possible ways that they can interact based on the reasons for start off by drawing out there not just an atomic orbital energy diagram once again I'm basically repeating what I showed you before and that this sort of arbitrary axis is used to really bother me when I was a graduate student at why don't the drawing unit on that the units are actually in electron volts if you'd like you can convert those indicate how come all the way to do you any good the only thing Energies Inc a Kallstrom all are good for our converting into number ratios tend to want 30 to 1 0 0 2 to something that's the only thing K calendar he's a good boy and were never going to do that with orbitals never going to divide into ratios this orbitals 99 cent more populated than the other ones so don't worry about the fact that there's no energies on its axis again measured in electron volts typically but you don't need to worry about that from the start off by drawing up the warbles on this could be on a 2nd row Adam and it could be carbon nitrogen oxygen doesn't matter analyzes baubles that matter are the 2 s orbitals than that
to the world that someone else orbital that way down below the level before that's never going to be involved in binding don't worry about that so I'm going to start too soon abbreviated like I did over
here which is writing P and S but you have to remember that the 2 estimate 2 periodicals that are important for a 2nd row elements like carbon or nitrogen oxygen so if I represent these orbitals only once again draw out on these canonical orbital shapes and the phasing is arbitrary here someone is aligned with the x-axis we recall that the piece of X Orbital Science y axes 1 is aligned with z axis coming straight out of the board that would be the peace of the world etc. and yes orbital we would draw sort this sphere I'm actually twiddle has a deal core that has the opposite facing combat I never represented in court by distrust and that's good enough for us which to arbitrary freezing contributions to that but I want do when I think about the fact that in order to get ready for bonding we can think about this in a different way we did exactly that same carbon atom this is part bit and we can think about a different set of 4 or by mixing models together and we're going to call this hybridization when we make rules on just a single atom were not forming bonds I'm just talking about a single carbon atom I'm a different way of thinking about this carbon atoms for example and what what I can do is I can think about just invent little games like what would happen if I mixed this to its orbital With this Tupi warble that I take a low-energy orbital elected to us a little and I mix it with a high energy or elected to pure on average I get to warbles out because I'm export rules and they ought to be somewhere right in between and that's exactly the picture that we get so let's imagine that I take this orbital here the PY warble and I mix that together with the the on the call at the PX with that looks like an exact I take the PX over I mix that with the 2 as horrible what I should expect as these other toward will stay the same energy I'm not talking about mixing those but I should get to know orbitals out and they should be halfway in between the high energy and a low energies all try to draw my new orbital energy lines here and here's my 2 hybrid atomic orbitals it's just a different way to think about this carbon I'm not changing the carbon atoms in anyway and so when I get out of this or 2 non-binding models it if I draw them that way to new orbitals that are ready to form bonds and the hybridization of those orbitals not S it's not it's 50 percent s and 50 per cent and we represent that with this
SPD sort of symbolism here so carbon atoms which normally has arms for electrons ready for bonding so now I would have 1 electron in each of these orbitals and 1 electron in each of these people were ready for bonding and so you know this to be the hybridization offer something
like an Al kind those 2 bond sticking out at the sides of the studies but what are the results of these hybridized orbitals these sp hybridized baubles and then of course you have room for pipe bonds on the major drug use in sort of a bluish color and then we have room for PY bonds if we wanted to form an kind like this that's with the P word rules would do talk about that the construction injustice at the point is that we can take the the atomic orbitals and we can think about hybridizing them with each other so it's good to look at another hybridization combination there's other ways that we can hybridize the reason I hope you're familiar with these sorts of all they take on 1 of these orbital I mix it with those others will be left with 1 of the few articles but I still have 3 other orbitals left and now these orbitals of a 2 of these P orbitals was 1 of the Sorrels but 3 more orbitals and now it that extra orbital mixed in the energy the average energy ought to go up and these are sp to hybridize orbitals likened all these with the little non-binding of symbolism there will talk more about that in just a bit and hopefully you know that whenever you have triggered a low-carbon he's the orbitals they're forming those bonds they had this hybridization associated in the test to finally I'm going to try to move to the other Borgelt of last possible hybridization combination and it's and and
I should say last possible these are kind of extremes on but if we if we understand these extremes and can understand things between and finally the
last possible combination is to take these murals and mixed in with these last few of to add even more P character and so this is supposed to be on the same access and hopefully you know that this is as 3 hybridized 3 parts P character 1 part as character that's the recipe now he's a little non-binding bauble combinations of those would look something like this this is supposed to be a territory carbon atoms was 4 sp not as Orioles ready for what's the really important point here the really important point is that when every see orbitals the higher energy them more nucleophilic if I were an electron in a higher energy orbital I would be more nucleophilic if you're adding to an empty orbital and it's lowered energy you're more Elektra hybridization tell you about chemical reactivity they tell you about where to start your arrows we need to narrow pushing it tells you where to end users of so last important point me keep this forwards with at the same level as to do with the strict
correlation between or hybridization geometry of
the new this we could do this and Adam geometry correlates with privatization and it's it's may be correlated is from a port in weights With hybridization so if I take a nitrogen atoms if I were super small and I could reduce myself to the atomic level and I could grab onto these bonds on colonial armies and stretch them upward so that this were a planar molecule what would happen if the hybridization would have changed in response to the geometry if I placed this mean into some molecule that constraint it so it had to be player that lone pair would become screaming not in terms of nuclear Felicity because by changing
the geometry I would be changing from an S P 3 hybridized orbital to 1 it's
purely hybridized and I just told you what the differences between something that's S P 3 versus something that's paid sp free orbitals lower energy BP orbitals when you try to draw all these on a single diagram so that you can see what's going on so finance orbital down here and appear orbital appear S P 3 orbital are lower in energy and pure bills are hiring energy as pure rules amid weighing between NSP to orbitals are up here and you may look at this diagram this pathetic diagrams that energy difference is so small the energy difference it would appear that the 3 hybridize electrons over there and a pair of P hybridize electrons is massive the difference is massive in terms of nuclear Felicity cannot put some quantitative numbers on that just a little bit but you need to appreciate his differences in reactivity just by changing the geometry it's not sufficient to say that the longer nitrogen we have to go beyond that privatization OK so hybridization is super important understanding the hybridization of every Adam and every molecule is essential to it of 1st of 2 of the OK this is a command for you it's a commands that you must do this every time you see a molecule I want you to deconstruct that into atomic orbitals I'm going to start with a very simple examples so we can see how that works Celtic Hydro Sianna gas must try to think about the atomic orbitals about a picture of bonding that's based on hybrid atomic orbitals only think about what kinds of hybrid ,comma orbitals would make a bond between nitrogen and carbon a signal Bondra pipe so the way I think about that has just draw the 3 Adams here without the bonds must try to draw some hybrid atomic orbitals associated with that OK what's the hybridization of the carbon atoms here today as the hybridized and you know that because this is a linear molecule I told you that geometry correlates With hybridization its landing here that means there's toupee orbitals that never mixed in trying to draw 1 pure orbital it's on the Y axis and another 1 coming out at us this is supposed to be aligned with the z axis coming out of the water but I'm not very good at drawing what's the hybridization of the nitrogen atoms get testy also did so again I'll try to draw 1 of the few articles coming out of the board and I'm going to label is P orbital on carbon pure carbon open little subscript see there just so that I don't forget that that sort of pure carbon atoms and as we just said a few on a carbon atom is not the same as if your role on nitrogen atoms Bureau in the on nitrogen atoms are lower in energy and that's how you get those bonds 2 of the 3 bonds Europe-wide bonds that result from the mixing of those people OK last for a drawing of a hybrid atomic orbitals and I'll change this line near to blue just so I can more easily see it then I'll remember that there's an SPT orbital as B to orbital sticking out the side hybridized in this way there's a tiny most back and for the nitrogen atom there's another as Worrell it's sticking out of bits and these 2 are combining together To make that carbon nitrogen signal bond and there's a little support on the back and sticking out look at the 3 orbitals now McGowan label these This is my S P 2 hybrid atomic orbitals all colors as 2 now say that it's on carbon and this when you open a little label line is key to on nitrogen and those 2 hybrid atomic orbitals get together to make a signal bond the blue signal bonded Lewis structure will be theirs alone .period orbital that sticking out here let me draw that and that's sticking in another sp toward with its logo on the back end and I can face it this way if I want me not phase park and call at another
Peter Worrell on nitrogen and I need to do the same as thank you everybody who who got upset that USB hybridize that's what we said before the beginning of the people be happy here this is the these sp hybridized we said Cardenas sp high-rise nitrogen is sp hybridized so these are asking warbles on 1992 due to do the same thing carbon atoms and on another bond going back here for me to another as he
walked along carbon sticking out on the back and then finally that makes a bond with hydrogen and I can only have the 1 as orbital to contribute we don't need to worry at all there is no way to do hybridization without with a hydrogen as it's only got 1 or can hybridize with it with its own atomic force it's the combination of this 1 as oral and SQL on that makes them on someone mice soul intensely interested in the hybridization of these individual out why am I so intensely interested in the hybridization this bond why am I so intensely interested in the hybridization this lone pair what I'm trying to do is I'm trying to gage how much P character there is in that bond in that moment and you should be asking yourself this every single time this is the fundamental question you need to ask for every single structure you dropped for every single bond for every single loan appear how much peak character and this remind you of why I'm always asking myself how much the character there is no it's because fewer rules are high on energy and the more character you have the more nucleophilic you are I'm always asking myself how much the character there is every single 1 in every single moment because I care how nucleophilic this bond is I care how nucleophilic that long periods relative to other markets that would put some numbers on this I keep
telling you it's important to think about P. character on the The Tonight on how important it is to think about the the girl it would have to be
a I think this is the thing to do so the fundamental idea is that the more P character the more reactive ,comma start by Libya nitrogen long pairs because it's easy to rank the reactivity based on PKR acidity someone a draw little table here and in my table I want to compare lone pairs on nitrogen so if I had somehow killer mean with carbon bonded to an to group there's a on there but I have some sort of mean the longer nitrogen as 2 other violence to it that's not the same kind of a finally I compared that to that to the hydro Sianna gasoline data to an organic my child I would end up with something that looks like this so there's 3 different nitrogen on pears are all lone pairs the all on nitrogen but they're different the start off by ranking the hybridization with the hybridization of this a loan from the top nitrogen it's sp 3 about the 2nd 1 the immediate for period the automated old and finally get down to the Nitro and we're ready said that sp hybridized now wants the percentage of peak character in his top Case sp 3 75 per cent of the character as the 2 what's the percentage of people character about about two-thirds or 67 per cent and finally there the 50 percent Lisa poultry differences 75 cents 66 cents What's the difference there right how big of a difference could make maybe you already know something about the relative basis any of these I can go to a a table and look up the converse of basic city acidity what you find out as well our call sign is a relative value will 1 that NSP 3 or hybridized nitrogen longer is 100 thousand times more basic than NSP to hybridize nitrogen on we know you put 1 dollar in front of me and 100 thousand dollars I would have no problem seeing the difference between the 2 piles of money it would be totally trivial and yet why is it so hard to see the difference between these 2 the difference is just as great a 100 thousand times in reactivity so when I'd come over to his other born here and racism
4 and then I dropped these 2 molecules which of these is
more nucleophilic the the answer should be instantaneous this 1 is more nucleophilic is about 100 thousand times more nucleophilic impurities nitrogen but they're not all the same and that's because this is sp 3 hybridized and this is speed to hybridize the longer they're totally different now might come down to 1 sp hybridized OK this is like a difference of what I'm not good math 8 per cent versus 17 per cent of big of a difference good that make it How many zeros that doesn't matter how many zeros like drew freely it's 15 zeros and for 10 to the minus 50 years huge difference in reactivity This is the effective P character what looks to you like small differences in peace character translate into phenomenal difference in an orbital energy and this is why if you from the very beginning of sup organic chemistry were not paying attention to be character I don't know how you made sense of the subject we probably told you this at the beginning of the book is the beginning of the 1st quarter and then they forgot to emphasize how important this is so I'm going to ask you to pay attention the hybridization from now until the end of your career organic chemist at the base of let's make sure we understand these differences which of these oxygen and is more nuclear was more I guess what I'm asking is facing which of these oxygen atoms would you expect to be more basic than that of the Tony yeah the the oxygen From the food and they both have to lone pairs but the long prayers ready to hybridize alone pairs ticking off this oxygen recipe 3 hybridized now the important point is we look at a peak at a table and the difference is not tender that it this time it's not always tend to be here it's only a thousand times more basic pattern can when you're pushing heroes if you know the 1 longer is a thousand times more reactive than another what kind of settles the issue it doesn't have to be 100 thousand times even a thousand times more reactive is useful to you in terms of thinking about reactivity this is incredibly powerful stuff
mm 1 sort of flying ointment hear 1 word of caution in applying this very simple idea that hybridization is important and key character correlates with basis city and nuclear Felicity more P characters means more nucleophilic and more bases this
is the 2 oxygen atoms you're gonna closing the locks in on top and a carboxyl oxygen on the bottom to top and bottom which oxygen and is more basic the topic we mentioned this yesterday in discussion section the that is more basic I don't know of a single example ever in the field of recorded organic chemistry where the bottom oxygen atom acts as a nucleophile where the proton now why is that the only way to understand that is like truly understanding the structure geometry this molecule in order to understand the geometry modernization we need to remember that there's residents and resonance is going to influence our picture because it tells us about the hybridization the true structure this molecule really has partial double character between his carboxyl oxygen in the carbonyl oxygen once we draw resonant structure because we realize that the lone pairs appear or not really as and this long pair that had drawn at the bottom it's not as P 3 you can't think about the hybridization of these Adams until you've drawn the resident structure and this and that and thing that is the point of this so you have to incorporate residents book bore you assign the hybridization that something so really this is more like a speed in this extreme residents structure and this is more like S P 2 and if you draw all the charges it's even less likely would ever ever in your life make the mistake of trying to prove makers oxygen the bottom who who would not nobody nobody would make that mistake so you have to think about residence before you try to assign hybridization and as soon as you draw the residents structure it absolutely clear that this is the more reactive said electrons on top of oxygen there's no cases where the the carboxyl oxygen on the bottom is more reactive OK so we've talked about farm atomic orbitals will talk about hybrid atomic orbitals we talked about the supreme importance of P character the characters the orbitals higher energy more P. character means more nucleophilic but wouldn't talk about mixing hybrid orbitals in order to generate molecular orbitals so again the intent was that this is supposed to be review and I'm stunned I went back and I looked at the soft more organic chemistry text that I teach of all stuff is in there but somehow it
just gets lost and dropped all of these important concepts that lost .period you get to the chapters beyond Chapter 1 OK so um and and was going to build up this picture that of starting with a carbon atom has atomic
orbitals on it's only going to pick the the atomic orbitals on cars there is to as orbital it's shaped something like this on the monopoly worry about the phasing there this a shape part of the world this in the center I'm not even going to draw that because all make the picture too confusing inside you're going to draw the the picture of a 2 x orbital the story of PX worked their there's appear orbital encounter overlay on top looks little bit confusing the actual overall shape of of appeal but was it fits inside a sphere on so can draw draws the support of all shapes the so badly distorted never know what a real pure looks like so we take to atomic orbitals lots suppose carbon atoms and we wanted to go to get ready for bonding what we think about is the mixing of the P orbital here with the US orbital here to it to its orbital into pure gold and we think about the idea that they can hybridize so just into center but now not drawing up the energy diagrams and and destroying pictorial the way I think about this yeah unanswerable 1 appealable can get together to make 2 different on sp type orbitals so here's 1 of the 2 sq work also amended this particular 1 phasing combination and I can imagine this interacting with another time to make a bond so this is my hybrid orbital here not draw that interacting with a hydrogen atom and I'll make sure the phasing combination matters if I want to represent the formation of a bond have to make sure that the phasing the arbitrary facing either hashed unmatched matches the phasing this award if they don't match the means and the intent behind the opposite of a bomb and when I make these 2 orbitals together the nite of the high makes this arm in 1 as orbital on hydrogen with this hybridize sp too although on carbon sorry as were 1 card I get a new job and that's a signal and has a shape that looks something like this we try to get this right never I wanted to give you extra information often but subscripts on my orbitals to give you extra information that's not just a signal bond it's a sigma bond between a carbon and hydrogen atoms and that's different from a single bond on nitrogen and hydrogen atoms orbitals on nitrogen a lower energy unless nucleophilic CAT bonds are more energy and more nucleophilic so this is an act of molecular orbital and you should already be familiar with this nomenclature double and triple bonds recall pie bonds single bonds we call signal bonds company should be familiar with that kind of idea someone return to this the way we started our class we started our class by talking about Errol pushing and idea that we're going you 0 pushing to help described 1 part other powerful equation for thinking about reactivity but of the I 1 of the things that people in the industry world so remember I start out by telling you that any time till things get closer and closer together if we wanted to think about the interaction between those the energy we get either forming a bond or starkly bumping into each other we have this equation that we used to think about the energetic consequences and this and this and and this and this year thank you for I was the we said that this equation obligates us whenever we have 2 things interacting with each other obligates us to add together all the charges so off I had some sort of an Amin interacting with some sort of an electorate like organic compounds like Bromo methane as these get closer and closer together if I wanna calculate how good or bad it is for these things to get closer and closer I have to think about the charges between the Proton and the bromine the Proton carbon the program the age but the thing about the injury those the charges on the nitrogen interacting with the Proton that you have to add that up for every single atom in your system if you wanna get a full accounting for the overall
charge effects of these things come closer together we have to think about the non-binding interactions hysteric interactions that don't form bonds the bonding of this age into that age the bombing of this nitrogen and adding in addition to thinking about
the formation of a new bond we have to think about all pumping interactions and good and we held them together as these get closer and closer together and and finally this is our aero pushing we agreed that lastly Errol pushing wasn't going to represents wasn't going to review charge was going to represent the interaction of this field orbital this S P 3 hybridize or nitrogen was some sort of immunity bonding moral that we usually don't draw with Lewis structures I want to get down to the nitty-gritty of this equation because I didn't tell you the form of this equation and now I'm going to have to give you an equation that may look sort of complex it's not too complex and that's the equation this is the equation that underlie 0 pushing it said What is this equation tell you that if you want to think about how good your arrow pushing his a good aerial pushing the isn't likely or unlikely without a good idea from you push heroes like this you have to think about the interaction spatially of the Order of the getting close to the overlapping in space how good is isn't agreeable and then secondly you ought to think about the difference in energy between orbitals is this high in energy and is this anti-war following energy and it is the difference between the field orbital energy and the empty warble energy that determines how much energy you get as he gets closer and closer Phyllis Tickle look at that the ominous start off by using something called a molecular orbital interactions tied to device that you should have been introduced to back in freshman chemistry and then you never use it again was like Why did we learn that I had no idea why we learned these molecular orbital interaction diagrams it's only a start off by by reviewing Victoria only the molecular models in a molecules that bind drawl and energy diagram showing the molecular orbitals of ammonia for example what it look like at the at the level of resolution that I think can again don't worry about the energy and the energy access the big point I wanna make you get all these old molecular orbitals associated with any molecule man you look at the electron occupational looks something like this there's still articles that have 2 electrons in each and above that there's empty orbitals not all mixed together it is and always these empty orbitals you call them and molecular orbitals and those who want to the empty worlds are always higher energy in the field work a fundamental fact if I measure the energy difference between filled an empty it's there's always some sort of an energy difference associated with the focus on going to learn about how to think about the interaction of 1
molecule here that as energy levels with another molecule that has its own molecular orbitals that different upon in and how to think about the differences in energy and those warbles but some of them from the instead of thinking about an actual chemical reaction what I wanted it was only draw pictures of some sort of a species and when ask you what you think is the geometry of the species
it's a couple can iron ore is it credible candidate would assist look like I think that stabilized and I think you can tell that stabilized but how you think the stabilization is like like an aloe cast iron there's a sort of a little at resonance if so that would be the positive charges distributed on both these governor but the alternative way of thinking about this is maybe the lone pairs donated to that and maybe really looks like this linear molecule it might be best represented like this and what kinds of told you have at your disposal to answer a question like that they are exactly the same tool that used to think about this reaction between 2 molecules and the differences here we're talking about 2 kinds of nuclear files a pipe on diverse as a lone pairs that are attached to the same nite now it's just the same story here and talk about a nuclear into different molecules and you're I'm talking about 2 different kinds of nuclear files that are on the same matter someone to start off by drawing a molecular orbital interaction diagrams and they will immediately answer that question from 10 years with a molecular orbital interaction diagrams about some nucleophile that still orbital about some electric welding and durable so I'm going to start up a representing a case where the lone-parent nitrogen is interacting sorry the pie bond nitrogen the double bonds interacting so that that bond between carbon and nitrogen the pie bond if it's donating the Carbol can I and I need to draw that is my nucleophilic filled with gold and on the other Adam the carbon atom of that some handiwork of this and the Carbol cast iron worker and the carbon and I have to think about the interaction of these 2 articles when I'm mix to orbitals together when they donate electrons from that carbon I into the cobbled guidelines this donated that I have to get to know orbitals out here is the warbles in my product when I mix to warbles I get to orbitals when I mix of field orbital with an anti-war bill 1 I don't eat these electrons in I'm going to get to orbitals back out so here's what the warbles would look like in my product no 1 is going to be lower in energy In 1 is going to be higher in energy use and if I tried diagram I'm going to try to draw this sort of edge on you can see what I'm talking about Mom I'm going to have some empty orbital here on the carbon atoms that's an endurable and P. carbon and then there's this pie bond and I don't know how good a job I can do to represent despite volunteer here but I'll try to smear some electron density and make that my pie bond issue on this is that the pipeline between the other carbon nitrogen so what happens when those 2 orbitals overlap what happens this pride bond between carbonation donated her book and they're all get to know orbitals out and this 1 is going to have high symmetry the new wardrobe that I get out and this is isn't there in the correct phase in combination with the topic is hatched in the top attached but there's also an interface in combination to the way those 2 can combines and when I makes the other facing combination of getting into bonding model we represent that with stock that's just as destabilizing as the new bond in combination with stabilized coal generates some new piled on it if I think about that interaction and Melanie that and I'm going to try to quickly drop this diagram because we're running out of time here but the contrast that with an alternative scenario and that's the lone pair interacting and I'm going to try to draw my my diagram with the same access I didn't label it over here and I'm trying to try to make sure I grow my IP orbital at exactly the same energy because that's not different the Carbol Caroline is the same but instead of thinking about the pie behind interacting with that orbital I'm going to think about the lone pair on nitrogen interacting and what I am really need to do this think about the idea the non-binding long Perez on nitrogen P to hybridized non-binding wonders of nitrogen are higher in energy supply with calls and this is something that we will talk about shortly all tell you how we know that you are in our next lecture and if this is higher energy military drive while flying across here just to show you that I'm trying to draw this is non-binding long from nitrogen being higher energy if this is hired energy than the difference between these 2 is smaller and it's the difference between those 2 is smaller I've lost my equation here that equation that I showed you it's the difference in energy is smaller the overall interaction energies bigger In other words you want more nucleophilic things at a higher energy and it these are closer and energy in the energy differences smaller the overall interaction energy drop is bigger you get more interaction energy out when these 2 were smaller so this is dealt even between our analysts like more interaction energy out piece of interaction I get
more interaction energy out and when these are far apart you kind of knew that what I'm telling you there's will this less nucleophilic of course it's
harder to donated the land your this is more nucleophilic of course it's better to donated to that anti-worker hit more overall bonding energy what that tells you the answer is it's the nitrogen lone pair that should want to donate into that cat I and this should be a better representation of that
structure because nitrogen on pairs are more nucleophilic pocket so I went over and I kind of get
back together on Friday and I'll tell you about how did I know that this nitrogen non-binding lone pair with the more nucleophilic enough I thought
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