Lecture 23. Aromaticity

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Lecture 23. Aromaticity
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This is the second quarter of the organic chemistry series. Topics covered include: Fundamental concepts relating to carbon compounds with emphasis on structural theory and the nature of chemical bonding, stereochemistry, reaction mechanisms, and spectroscopic, physical, and chemical properties of the principal classes of carbon compounds. This video is part of a 26-lecture undergraduate-level course titled "Organic Chemistry" taught at UC Irvine by Professor David Van Vranken. Index of Topics: 00:11- Lake Elsinore toddler bitten by rattlesnake 00:54- Antivenom 05:00- 16.13: Drawing Bridged Bicyclic Products of Diels-Alder Reactions (corrected slide) 06:25- 17.7: Huckel's Rule-Recognizing Anti-aromatic Compounds 12:43- 17.7: Recognizing Anti-aromatic Compounds 18:13- 17.8C: How Do I Know if an atom is planar? 19:05- 17.8C: Aromatic Ions 26:29- 17.8C: How Do I Know if an atom is planar, revisited 29:56- 17.8D: Aromatic Heterocycles-Which lone pairs do I count? 38:45- 17.8B: Other Aromatic Compounds
Digital elevation model Bohrium Biofouling Seafloor spreading Man page Vancomycin Magnetometer Lake Optische Analyse Enol Insulin Cycloalkane Schlangengift Lambic Lymphangioleiomyomatosis
Monoclonal antibodies Ionenbindung Recreational drug use Lamb and mutton Bohrium Ice sheet Substitutionsreaktion Binding energy Affinity chromatography Grading (tumors) Humus Calcium hydroxide Man page Antigen Enzyme Magnetometer Cell (biology) Protein Insulin Cycloalkane Schlangengift Toxin Conjugated system Setzen <Verfahrenstechnik> Substituent Stickstoffatom Doppelbindung Diene Walking Carbon (fiber) Antibodies (film) Cadmium sulfide Chemical reaction Erdrutsch Alkene Wine tasting descriptors Fat Alkane Systemic therapy Vancomycin Refrigerator Enzyme Optische Analyse Azo coupling Antibody Dielectric spectroscopy Mixing (process engineering) Nitrosamine
Ionenbindung Kohlenstoff-14 Bohrium Ice sheet Set (abstract data type) Hydro Tasmania Wursthülle Aromaticity Man page Reactivity (chemistry) Atomic orbital Aromatase Electron Enol Stratotyp Faserplatte Benzene Tool steel Nana (manga) Conjugated system Process (computing) Chemical formula Arginine Doppelbindung Kreide <Gestein> Chemical property Protonation Ice front Chemical reaction Stockfish Systemic therapy Paste (rheology) Synthetic oil Vancomycin Functional group Chemical compound Nickel Benzene Pipette
Pentane Proline Bohrium Set (abstract data type) Atomic orbital Molecule Electron Octane Stratotyp Benzene Elimination reaction Organic food Hexane Medroxyprogesterone Doppelbindung Chemical property Katalase Chemical reaction Alcohol Knot Death Food additive Lone pair Systemic therapy Emission spectrum Vancomycin Medicalization Atomic orbital Orders of magnitude (radiation) Chemical compound Penning trap Medical history Thermoforming Calculus (medicine) Pipette Ionenbindung Kohlenstoff-14 Species Lamb and mutton Atomic orbital Action potential Aromaticity Man page Ring strain Beta sheet Conjugated system Body weight Setzen <Verfahrenstechnik> Atom probe Mixture Carbon (fiber) Maskierung <Chemie> Protonation Water Hydrate Functional group Iron Chemical structure Base (chemistry) ISO-Komplex-Heilweise Pharmacy Atom Ammonia
Insulin shock therapy Resonance (chemistry) Diethylstilbestrol Guanine Cytosin Set (abstract data type) Calcium hydroxide Atomic orbital Molecule Enzyme Electron Walking Protein Benzene Methylmalonyl-CoA mutase Periodate Nucleic acid Substituent Nucleobase Surface science Doppelbindung Octane rating Mashing Sulfur Chemical reaction Knot Growth medium Electronic cigarette Wine tasting descriptors Systemic therapy Lone pair Vancomycin Collecting Acid Hydroxybuttersäure <gamma-> Alu element Zunderbeständigkeit Herzog August Library Cobaltoxide Thermoforming Calculus (medicine) Pipette Ionenbindung Biosynthesis Residue (chemistry) Graukäse Sodium hydride Bearing (mechanical) Ethanolamine Atomic orbital Substitutionsreaktion Plant breeding Ion transporter Wursthülle Aromaticity Man page Puff pastry Magnetometer Enol Common land Amino acid Tool steel Ausgangsgestein Active site International Nonproprietary Name Atom Side chain Histidine Molecularity Stickstoffatom Nitrogen fixation Carbon (fiber) Adamantane Hybridisierung <Chemie> Spawn (biology) Water Cigar Base (chemistry) Atom Ammonia
Ionenbindung Resonance (chemistry) Atomic orbital Aromaticity Quartz Calcium hydroxide Man page Molecule Ionisationsenergie Electron Magnetometer Phenylalanine Naphthalin Amino acid Benzene Active site Tryptophan Side chain Biochemistry Molecularity Annulation Stickstoffatom Doppelbindung Octane rating Singulettzustand Carbon (fiber) Man page Chemical reaction Systemic therapy Vancomycin Tyrosin Optische Analyse Cobaltoxide Base (chemistry) Benzene
I saw this rather horrific story on the news last nite some dad was like to use skidded arrives and so there is no rattlesnake jumped out of nowhere in bit the child on the finger on I can't imagine ouster air they both were can't imagine how scared that little child was going to be a snake so far into the future of fortunately that this child is doing all right but they took them into a specialist at Loma Linda University come through and they were able to inject 20 2 vials of a anti-venom but in order to stop the action of the snake venom and so it's good talk about this in the event of a business here what's going on with the anti-venom of they're giving too the people in the hospital
so if you go for a walk in the woods and get by snake 40 EUR what's your prognosis was so this is a Southern Pacific rattlesnake that's the most common rattlesnake that you find in the Lake Elsinore region and and or if they take the win with a rattlesnake bite probably going to give you this commercial and even produced commercially don't they don't make it there in the hospital and so let's talk about this particular venom called Kroll ,comma if you look at the prescribing information adjust the title of the box says "quotation mark to lady I Polly Real immune fat from old-line and what that tells you it is that it's an antigen binding fragment that is produced from monoclonal antibodies that come from sheet that's what old-line means music comes from sheep blood so what they do is they typically collect venom from many snakes and then they use that ran on to immunize she's unionized she'd combined with something called .period adjuvant typically to get immune system going and a couple weeks later you get another boost in the immune system freaks out and is totally ready and starts cranking out tons and tons of into bodies to all the different things that you find in snake venom in this particular snake venom and there are lots of nasty things and snake venom snake venom their designs to to mess with the cardiovascular system at least these types of snakes so they contain of enzymes and proteins that degrade tissue the break down proteins that life's blood cells and that prevents clotting US economic what a bad mix of toxins this year's so you inject this English she she'd immune system produces all these different hinted bodies to all these different bad things that you find inside of the snake venom and then you come along and you to collect blood from the she doesn't kill the sheep right you can go give blood and it doesn't kill you on and then they isolate the into bodies these affinity chromatography to isolate all the antibodies in the blood jump online and so what do with all these antibodies the last thing in the world you want to do is take a sheep into body and injected a new human being CDs part right here on the antibody called the antigen binding fragments fine specifically although snake toxins but this part right here doesn't help you it's just a little balls helped your immune system home in on this and say Hey that's not human I'm going to attack so what they have to do to prepare this for a human being is to chop off this constant fragment down here and these enzymes do that an enzyme that derive from Pathein called from the pious called and that pattern comes along includes a single Amit bond on John here just a single carbon nitrogen bond it's extremely specific and so the enzyme tapping Cleaves up these alarms they throw away the bottom part don't need that and Stoppard's look a lot like the antigen binding fragments from your antibodies you're immune system can tell the difference for all intents and purposes so what they're doing is there collecting these antigen binding fragments that bind all these different snake venom components aren't they put it into a violent those things in the refrigerator waiting for somebody to get bitten by a snake so it's a simple use of an enzyme to clean very specifically in bonds here on the arms of of immunoglobulin bodies the Saigon Is this venom from what I'm not an expert on how effective is that you can't even get I'm not an expert on interventions but after reading a couple of these stories it's very effective if you can get to the hospital very quickly you're in good shape if you're stuck out in the woods on on a six-day hike that's a problem itself and this is 1 of the nastiest taxes know you notice they had to use a lot of it in whatever they said 22 while aren't even on the the kids doing fine so you're a lot larger than it kids to would be a lot harder to achieve again at a
mistake on 1 of my slides during the last lecture on the deals all the reaction and I was pointing out this nomenclature for X overseas and what I said was from the substituent down here that's on the same side as the AL Cambridge's referred to his Endo but then I had a typographical error me just a mistake so and I said we're substitutes on the same side and I again said Al teenagers said canes that should be Cambridge there not Al Qaeda bridge right they can both be on the same side of the aisle Cambridge so this is the AL Cambridgeshire and that's XO right out Kane so please replace the letter there with the letter on the bottom and and if you're not exactly sure look at the book because I just had the same word twice and that's because I was copying and pasting too much OK so we moved on from Chapter 16 Chapter 16 was a lot of dying means and conjugation and done and when we moved under Chapter 17 to talk about Eramet cities and 1 of the main points about city is that you learn all these different reactions of double bonds lots and lots of different reactions of double bonds and what's going on
on the In Chapter 10 yuan more reactions of pie bonds in all kinds in Chapter 11 but for some reason the double bond the benzene are resistant To the typical reagents that you know bromine doesn't add across a double bonds of benzene rings HBO artisan out across a double bonds advancing England's became Hydro board the double bonds of benzene rings and so it's it it seems like it's pretty important for us to be able to recognize when double bonds have this property of Eramet city when as a double bond part of an aromatic ring system we need to know that we know which double bonds have low reactivity to what's typical lecture region reagents so in my mind to give you a just 1 moment you're going to give you India my act together .period it it is amazing how quickly they have now all mixed up all of my little sheets that I had at here you have to just pardon me but you can stare at the chalk board behind me while I'm sitting here trying to sort through this city just to note that we have extra office hours next week next week as the last week of lectures in this class on but of course what that means to use you got 1 week left to study for the final exam which is on Monday of final exams week so please make this last week count on as we're going through that kind of material the focus I want to talk about Erickson's city and how to recognize the aromatic ring systems are when they're there in front of you and um OK so I'll I'll just do the best to sort through my disarray of notes here but 1 introduce you to some of that's not the issue here sorry about that that's not what I wanted to give you here's what I wanted to show you it's time to try to give you the ability to recognize aromatic community aromatic compounds so probably you have your notes in front of you know where they go OK so let's talk about this how recognizing aromatic compound this process this property of Eramet to city that that causes double bonds to be on reacted the causes protons in unanimous the shifted way downfield parts per million that super particular to benzene rings in the proton on so it's important to recognize city and we're going to use a set of 3 rules in order to decide whether something is aromatic not adhere those 3 roles and the 1st of those rules is kind of a mathematical rule but I have to explain how we do this accounting for this mathematical is called vocals rule and it's very simple Maddox for and plus 2 where n is a whole number that allows you to calculate how many electrons should you be counting up when you try to add up the electrons in a potentially aromatic ring system and because and all the whole number like 1 Will 0 1 2 3 or 4 when you do the math that means it's telling us that it that call aromatic ring systems have either too electrons 6 electrons 10 electrons on etc. and in practice he typically don't get things with more than about 14 electrons it takes a lot of synthetic work to try to design systems that have more than that many electrons but but we still give you the mathematical formula in case you want calculated out to infinity so let's take the the the canonical aromatic compound that benzene on 1 when I think of emeritus the benzene is always the 1st thing that I think of and if I count the electrons here this pie bonds it's too for a 6 electrons but there's a special requirement for those electrons that I'm adding that 1st of all they must be in a planar cycling career so if I look at these these pipe bombs in benzene data in a planar psychic grave benzene is plainer benzene is cycling and they're all connected to each other and conjugated and if I come over here and I look at this this past 6 carbon chain that is not connected here there's no bond here this is not aromatic because it's not psychic so does have the 6 electrons it satisfies that locals warrantless tool but it's not psychics obviously that can't be an aromatic ring in fact this is just a really reactive trying on and in the final on the point here is that the pipe bonds and and or P warbles you can have 2 electrons in a P word they have to all overlap with each other and so when I come over here and I look at this compound on cycle Hector trying this C H 2 group prevents this stock ended this double bond fear From and interacting with the descended this double bond over here so those 2 wins or not in conjugation they're not part of a continuous conjugated cycling career and I'll show you this business about orbitals none of these actually had an example of electrons in a the world OK so that would be an example of an aromatic ring system on and so was going extend that idea someone a compliment that by telling you about something that would be the opposite of aromatase city and that would be interior to city so what would be an example of something that is in the aromatic and I think I'm messing this up against women
just give you the ability to write on
here OK so that Indiana to city is the opposite of Eramet aromatic compounds a stable there's a thermodynamic driving force for organic compounds to want to form aromatic ring systems those confer stability and conversely it is the red intimately unfavorable for systems to foreign interior matter compounds what makes a compound in the aromatic and again there's going to be 3 sets of rules that I'm going to apply and there are almost identical to the rules for deciding Eramet history and the only differences instead of foreign plus 2 electrons it's 4 and electrons so whenever I see the more electrons like 2 pipe bombs in a cycle career or 8 electrons in a cycling correct or 12 electrons etc. that tells me that that's probably going to be a very difficult compound isolates probably that compound is going be filled with self-loathing and tried to self-destruct or react in some way so everything else is the same if I see for electrons electrons in a plenary cycling Caray all conjugated in together and they're all in overlapping pylons and p word also the conjugated on the net tells me there's going to be problems so the money taken example and whenever I think of Indira Maddock here's the prototype McGowan a black pen for this on so I can see how this 2nd draw this more clearly cycle beta dining is the canonical interior matter compound you cannot just make cycle cycle beauty dying and put it in a flask it's not stable yes questions US 16 earlier thank 16 electrons thanks for asking that yet and I guess I'm not so good at math here with her for what she did to those larger numbers it's very typical of sorry about that math mistake there OK so of course the problem here is that got to double bonds pipe bonds in a psychic array and I had the electrons here and this is definitely in the aromatic and that's why nobody has ever made this on its own chemists have managed to track cycle beauty dining little cage-like molecules so it can't escape that's 1 way to stabilize the problem is but when you when you try to make cycle beauty dying it's not like we don't have reactions elimination reactions that can make that is that it starts to react like this residents the hates being idiomatic medics so much you can imagine if I take the electrons in this bond here and I give 1 electron tubes each carbon I'll draw residents structure that to die radical and that's a better picture for Cycle beauty dying that each electron missing for kids that other thing away from me I do not want to acknowledge the existence of that of the electron I don't wanna have applied bond I don't want to have conjugation and so it acts like this this is what this is how much cycle Budin Darlene hates being of an interior Mattock molecules now there other apparent in the aromatic molecules that have been synthesized but somehow managed to avoid being interior manner so for example and chemists have made cycle octave territory cycle octane rang with 4 double bonds and it looks kind of aromatic it looks kind of like a benzene ring the problem is that it's got electrons so there's 2 electrons in each pie bond to electrons here 2 electrons here to electrons here and 2 electrons on top here that the electrons and the way that this avoids being interior Maddox is it bends into this boat like sheep that prevents the double bonds from being in conjugation how clever about molecule that it figured out that it can bend into this kind of shape so that the pie bonds were literally orthogonal to each other so I did in fact cycle architectural scene with 4 double bonds is not interior Maddox simply because it's not playing and if you tried to somehow flatten it to make it plain it would freak out and probably start director could I radical or deals all the reactions would find some way to not be forced to react and and turn into a stable molecules OK so try to recognize aromatic compounds because they don't do edition of the reagents that you're familiar with bromine HBR are war ation on hydration and they have special properties in an unmarked spectrum and don't expect that you'll be able to make American bonds because you won't be able to synthesize those they'll find some way to themselves out of being trapped that they won't be OK so well OK let's talk about this issue of plenary how do you know if anatomist cleaner and I'll show you why this is important in a moment not every aromatic compound has only carbon atoms in their sometimes you have to count lone pairs as part of your foreign was to calculation or your foreign calculations and we have to decide how we're going to calculate that we had to decide which pairs of electrons were going to count and I wanna start off by a by addressing this issue of how did know whether a pair of electrons is an appeal orbital or not and you little and I'm going to start up by looking at ammonia and I think all of you know the dead weight but because somebody had a set of notes that I can look at it contributed contract aromatic clients OK perfect thank you but then I'll get to this all come back to this issue in a 2nd again how did know if something is plain before we look at this issue of lone pairs how did know whether whether an I plane so let me start operate by taking a look at a series of ions and went on so for most of these compounds here there's very little opportunity for these 2 to bend out of plenary pretty much forced to be playing here because they are so small that the ring sizes so small there's no opportunity for these 2 band out of pulmonary like this I collected Tektronix on kind of the the largest ringside all talk about here a seven-member ring and so let's talk about some water options here I obviously can't have a double bond here on this last carbon atom the top carbon atoms of this three-member agreed and so what I'm going to do is I'm going to put a positive charge here if I had a upcoming electrons are innocent DPU orbital and I'm going to struggle with all that NTP orbital there there's 0 electrons someone I have all the electrons in disarray this array of conjugated double bonds and will find on visitors to electrons and because there's 2 electrons here that's aromatic that's foreign us to wear equal 0 so this would be a much more stabilized cobbled can find than you would expect and if truly is aromatic and we ought to be a withdrawal bunch of residents structures where we localize the pie electrons all over the ring malicious practice that just to make sure that it has this property you of the localization like benzene and trying to draw an arrow here where shift that double bond but start to draw some of these residents structures were a shift and I have to draw this a little bigger here where shift that double bond around that I take the electrons away from this carbon and move them here now my cat I'm is over here and I can go another resident structure 1 of those electrons To here and take the electrons away from this this other bottom carbon and so this has this property of the localization just like a benzene ring but as foreign plus 2 electrons it's plain error in fact I don't think there could be anything but again so this very strange-looking even with all that strain on cycle pro Pini and my hands are stable and remain in the laboratory on the it's not like you can put it in a flask but they have been made and you can get spectral those kinds of species OK so what we need to do to a five-member ordering in order to make that aromatic if I put a Koble cat I'm here like they did with this cycle pro Pini on on if I put a couple and they're only have electrons have definitely do not want to do that what I'd really like that here is is electrons 5 and 6 so what I really want to have for this to have this property history is I wanted
to be a cop online at the center and so I really like for these electrons to be an appealing quarterback and I'll address that I was just getting to that is that years P 3 it's enough I added my electrons I've got a planar array and I have to for 6 electrons Bush's dad that up to 2 1 2 at 6 electrons that is an aromatic an I that carbon iron is amazingly easy to make it's very hard to make program finds it hard to pluck protons off of carbon atoms but in this system because this gets to the aromatic it's very easy to make that by deep-rooted meeting part focus now it's come back to the last the seven-member ring and it takes practice to learn how to draw 700 rings that will come with experience so now if I would have 6 or foreign plus 2 electrons in the system do I want to have a cobbled Caroline here or a carbon and I there yeah we 1 0 electrons we've already got 6 electrons we don't want any more so we don't want to have a car banner near here we want to have a cargo carrier that would be a stable aromatic so if I had a ball electrons there's 0 in its pure baloney try to draw the P word all here and I'm not going to draw all the different residents structures there's lots on but if I had my electrons to inspire bonds to his pipe bombs to inspire bond there's 0 electrons and AT P orbital that the 6 electron system and that can time would be aromatic and exceptionally stable so what are the implications here implications for you with respect to these aromatic on Ireland's that if you're confronted with cycle Brendan Donnelly it is so easy to pull this Proton that you can use regular basis like Alcock side basis and no other simple helping allows you to do that by you could just take that and pull that Proton not because the product here should have used a red hero there because the product is aromatic the product years aromatic and heavily stabilized relative to other types some of organic molecules but so you can use Elcock siderable protons of hexane for cycle pentane or even if you had just 1 double bond in this room instead of 2 you could use Allcock said proving that Societe exceptionally acidic somewhere on the order of 30 for orders of magnitude more acidic than regular outings this back over here and look at the seven-member ordering and how it's different and I'm talking about the probe programming this but what I've done as I put an alcohol on here that's been impregnated if you just touch a proton onto that I'll call to put a potential Leading Group misleading will fly off and again the reason why this is so fast the reason why that is so exceptionally fast is because it generates an aromatic kind so reactions that generate aromatic ions whether it's the probe nation or or ionization those reactions are amazingly fast and the situation would be totally different now is if I did this just to be clear here if I only had 1 double bond In this rain that's no longer fast there's no base signed the simple based that the Juneau over will have heard of it became 51 series they could ever pull this Proton off so I'm just gonna put a gas line here because this is insane there's no way you could pull a protocol that's not going to be here in Seattle look for systems that have the potential to be aromatic those reactions will be exceptionally fast if they generate an aromatic by the ,comma iron for for Anaheim and let me just sort of remind you that this is fast and this is fast and this other 1 is just there's no way inconceivable so G agreed to become aromatic and you get to enjoy all that stability OK so I Drew
Endy P orbitals with cargo can finance the this sort of Kobe where the long hair was an appeal like orbital and how you decide the hybridization of that how do you decide whether on electrons are an appeal like orbital because only if the electrons are appeal orbital do you add them up as part of your foreign plus 2 calculations so let me just remind you on that will use nitrogen not carbon is as far as our example here I think all of you know that that simple means are pyramidal ammonia adopts a pyramidal geometry that's the lowest energy hybridization for this are up for this nitrogen out so In this sort of a scheme here on these long pairs exist in this S P 3 like water and that has differential sizes on each end of the but also 1 1 end the orbital is being the other end of the war small I'm so there would be an S P 3 former hybridization it if you would shrink yourself down to the molecular scale and grab are groups and bend until they were playing here you could force this nitrogen atom to adopt NSP to hybridize geometry means each of these bonds had sp to hybridization but the electrons in the long pair there in appeal like orbital an appeal like orbital has the same size on the top and the bottom and that would be a requirement for us to add this to add this tools so let's see how that comes into play how do you decide in this In this five-member ordering system here what I'm doing is I'm drawing a John this is really just the molecule parole discussed substituent Somalis Aijaz substitutes sommeliers and so the question is is cool aromatic does this five-member during on without nitrogen Adam and his loan period that aromatic Viscount that lone-parent my foreign plus 2 well being if that lone pair can contribute to intercity but it will contribute to to cities there's 2 possible hybridization is for this most demeans don't exist in a planar form but when I give this lone pair the opportunity to participate in an aromatic ring system in this forum posturing system it will really hybridized so flat in this case it is more stable because it gets to be aromatic and that's not normal for a means most means don't do that by being flat these electrons get to participate in a P word so there's my pure little there and when it's when those electrons in API orbital we have equal hybridization there on the top and the bottom face for equal air just the appealable has equal size in the top and bottom phase and that allows it to effectively overlapped with pipelines which have electron density on the top and the bottom face so and so you'll you'll count lone pairs in this pointless tool if they can exist in like like water and making a big deal about this because there will be cases where a lone pairs cannot exist in these people like collectibles and to you'd expect those to have less aromatic resonance energy OK so take a look at some systems that have nitrogen some rains that have nitrogen or oxygen on and try to
decide should we count the lone pairs and I'm going to give you a simple will tell you I say a simple maybe it's very wordy but once you use it a few times it becomes very user-friendly so I'm sorry for maybe the rule is not so doesn't sound simple so there's a whole set of heterosexuals federal cycle means there's ahead Aladdin rain usually oxygen and nitrogen and lower row at around 6 sulfur in the rain sofas for Henry Adams I would decide which of these pairs of electrons to Addie to my foreign policy tool to decide whether these are aromatic green interior and here's our simple rules now we decided to give the Federal Adam is not part of a double bond if it's not part of a double bond then you can count on 1 lone pair Towards the foreign plus 2 no it's a whole string of logic there's let's practice using them so they had a and is not part of a double bond look at it well that nitrogen is part of a double bond that means I shouldn't count that long I only count lone pairs if they're attached to Adams that are not part of a double bond many wooden cross this out no I don't count that it's put the nite part of a double want to know how many electrons do I have to count that just the double bonds left over that has 6 electrons the Mets aromatic so I think you you'll be as good as I am at 4 again figuring out which of these federal Adams are part of a double bond OK so state is next on Hatteras cycle this is called fury OK if they had a Adam is not part of a double bond will that oxygen is not part of double there's only single monsters oxygen OK if they had rotten is not part of a double bond you count 1 lone pair Towards the foreign press tools so that too long here I'm going across 1 of the out I'm only going to count 1 of them so how many electrons in the system 6 2 4 6 years to win this lone pair and then to in each bonds that a total of 6 electrons that aromatic it's tried to Tom to apply to this Hatteras cycle here that residue nitrogen is but next to each other so if I look at this again my role as if they had a is not part of a double boiler walls neither of those nitrogen is part of a double bond then I get to count 1 lone pair Towards the foreign press 2 so I count both of those lone pairs both of those nitrogen not part of a double bond and so on account of these electrons here that would be a electron and that would be interior matter if you could somehow synthesizer molecule that pattern of bonding that molecule would be very reactive it would try to find some way to distort out of plenary or would try to find some way to you what they would try to find some way to react and so wouldn't have double bonds in an arrangement that molecule would be extremely unhappy OK so here's a five-member during this is the side chain of the amino acid histidine it's called and it is old and so let's lets users little accounting system here if it had a lot of it is not part of a double bond will this nitrogen at Amon Carter here is part of an old 1 so I don't count that lone pair it's the nitrogen is part of a double bond but it looks at the bottom nitrogen and our rules as if they had a lot of it is not part of a double bond you count 1 lone pair towards for implicit we count that's so now counterpart electrons wished to win this pie bond to in this pie bond and to another lone pair that 6 electrons the side chain of histidine amid is always aromatic tune aromatic ring so every protein your body is filled his histidine is a common amino acid it's filled with aromatic rings on the surface of the proteins and the inside OK here's the on 1 of the bases of DNA and RNA this is adenine and sold now others 2 2 sets of rings here and I can draw different resonance structures whenever you got a double bond between 2 different brings a fuse together you double counted double bond you can look at each ring independently and counts that double bond toward the trains let's take each of these rings independently I think you can see that the rain over here on the left-hand side is emitters all we already did that 1 right but supplier rule if the lone pair is not part of a double bond well this lone pairs part of a double bond I'm going to count them and I come over here and this nitrogen atoms was part of a double bond means I'm not going to count that I know about this nitrogen animal rate well that's part of a double bond they can't count that so the only long per account is the on the nitrogen that's not part of a double bond so now when I start often 1st count up this five-member ring here and I edit those electrons fish stew in lone pair 2 in pipe and 2 in the pie bond this rainy here 6 electrons and that's aromatics now I come over here to the six-member during I don't count any of those long periods and there's a loan nitrogen but that's not the amino substitute that's not inside the ring that's not part of this razor don't even worry about the substituent so I have to 4 6 electrons this means that both the reins Of the DNA-based on aromatic and you draw the same conclusions on about guanine cytosine depending on which residents structure you draw for those of you could consider the other DNA bases to have either partial or full to cities OK so let's just come back to White as this will work that the reason why this rule works and it's very empirical you don't gain any insight about the geometry of the molecule simply by deciding whether anatomist part of a double bond on all those old electrons that we were counting is part of that rule will exist in P like orbitals so when we were counting lone pairs in our In our foreign policy tool that because they were able to adopt geometries that were flat so that the lone pair could be P like orbital so it could interact effectively and that measure might try to draw the scene here but with pipe bombs that have electron density top and bottom What about the electron lone pairs that we crossed out in every case where we crossed out alone pair won a header Adam was part of a double bond like hearing period Dean what that means is that lone pair existed NSP to like orbitals sticking out of the side of the aromatic ring so when you didn't count the electrons they're not sticking up and down and pure pluralist sticking off to the side of of the aromatic ring or the benzene ring her period in on the implications are these long pairs that are involved in Eramet they're busy don't try to mess with those because you'll disrupted electricity so what you would find is the lone pairs like this were simply not reactive it's very difficult to probe make them you couldn't prove that In fact if you try to prove made few struggle to me purity by throwing a powerful acid it properly done ,comma even so don't try to mess with their lone pair because it's doing something that's trying to make the system systematic in contrast the lone pairs here other sticking out to the side of an aromatic ring no problem reacting with those and you know that already puritanism base you've already done reactions were you use purity as a base so of all kinds you can do all kinds of reactions with these lone pairs that are not part of the aromatic foreign close to so no problem reacting 2 with the parent period Dean where this crossed out lone-parent histidine if you look inside the active site of enzymes 1 of the most common lone pairs used in catalysis is this lone parents taking off to the side of the histidine side if you look at every single bond that is produced in every single protein in your body every single and bond is created because this long bear on the bottom of this saddening ring a single adding a single lone pair inside the ribosome is responsible for the synthesis of every single protein every single and bond in the human body so long pairs stick off to the side of the completely wrong or completely reactive wears lone pairs that are part of aromatic systems are not reacted at all OK so I think you can see from mean that you confuse benzene rings together and have much larger aromatic ring systems so I'm going to give you an example of of some
fused systems here she conceded that year that there's more than 1 way to account for this foreign plus to rule has more than 1 way to do the addition there so this is a molecule called naphthalene if you go to the the hardware store and buy mothballs but turns out the crystal and Nathalie despite solid balls of crystal and naphthalene and for whatever reasons and moths some defined that repulsive and will tend to stay out of your closets so and there's multiple resonance structures that I can draw for this is if I can't around if I just ignored this this ring this bond in the middle of those 2 rings that signal bond just pretend it's not there I can count around the outside edges of this flat molecule if I count around the outside edges of the flat molecule what I would find that there's too 4 6 8 10 electrons that satisfies our foreign plus Chulanont that aromatic there's another way I could have done the accounting for this but slightly different another way to describe this as I could have drawn a resonant structure for naphthalene in which I put a double bond in the middle there's a different way I can shift around those electrons and so remember what I said is that there is a double bond at the ring fusion you can count that double bond for both bands for both rings so in other words the other where could the countered this is I could have said In this reign over here on the left-hand side there's 2 4 6 electrons and that's aromatic and then I look over here this ring on the other side and there's force double get accounted double bond again and that's a matter so I can count that middle that double bond in the center twice and I reached the same conclusion either way and that is that all of the carvings in this ring system are part of an aromatic rings I will reach a different conclusion so you confuse these things in all kinds of different ways but let me give you another example of another aromatic rings very common that's refused this time it's approval for infused onto a benzene rings this is the side chain of the amino acid tryptophan canceled a straight trip here there's a long Peronist nitrogen so again in this rank system on both ratings of both of these rings in this this is called an indoor oldest despite psychic ring system both of these rings aromatic this ring over here which obviously is benzene that era Maggert 6 electrons that I look at this five-member ring over here there's 2 electrons in the Nigerian 2 electrons on this side bond and into electrons over here that's also aromatic so the side chain of tryptophan is fully aromatic as is the siting of tyrosine phenylalanine you guys probably learning about those in bio 98 right now OK so am you can feel it can go endlessly you confused benzene ring after benzene ring after benzene ring on onto each other you may have heard of carbon Man 0 2 0 gravity that's basically what those molecules are there just infinite to made out of benzene rings or fused together but it's about the last parts of this chapter on interesting but they're not going to be useful to you for anything else in this quarter and they have to do with molecular orbital base of error to city and I think you want to read that I would never discourage you from reading anything about it's not the kind of thing that I can test on on your floor about those powerful concept if you take up a division classes I would love to teachers to you there but we just can't that those in with the time we got be able to recognize aromatic rings they will recognize interior Mattock brings you need to be able to know when when ionization reactions will generate aromatic analyzer Medicare find those ionization energy provisions will be fast on and be able to recognize 1 Hatteras cycles with nitrogen and oxygen for aromatic ,comma OK so be
ready when we come back on Monday were going to do chemical reactions of benzene rings when when you do a lot of them


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