Lecture 06. Alkenes, Part 1
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Starvation responseVancomycinChemistryMan pagePotenz <Homöopathie>Carcinoma in situCalcium hydroxideBohriumMashingElfAmpicillinMagnetometerPan (magazine)Chemical reactionChemical structureExplosionFireRecreational drug useScreening (medicine)WaterSolubilitySurface scienceIon channelProcess (computing)EsterInsektengiftSodiumNervengiftPowdered milkSetzen <Verfahrenstechnik>Stream gaugeStereoselectivityGranule (cell biology)WasseraktivitätStuffingDerivative (chemistry)IngredientController (control theory)ChemistryElectronic cigaretteCoalToxinSeleniteGrowth mediumFoodBottling linePilot experimentNanoparticleContainment buildingToxinComputer animation
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VancomycinDielectric spectroscopyHausmannitHydroxybuttersäure <gamma->AlkeneMan pageGraukäseSeltenerdmineralienBis (band)Chemical reactionChemical structureOrganochlorideMoleculeOrganische ChemiePhosphorusWhitewaterFood additiveAreaMethanisierungChemical compoundTiermodellBromideProcess (computing)ChlorideDoppelbindungFunctional groupIsomerSodiumOptische AktivitätSubstrat <Chemie>WalkingReactivity (chemistry)AlkylationInitiation (chemistry)Transformation <Genetik>IonenbindungSet (abstract data type)StuffingAlcoholChemistryElectronic cigaretteAlkeneDeterrence (legal)AlkoxideMixing (process engineering)PyridineSchwefelblüteThionylchloridAlkaneLactitolPhosphorous acidComputer animationLecture/Conference
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VancomycinMagnetometerMan pageProlineAlkaneDielectric spectroscopyAlkeneOmega-3 fatty acidBohriumHydroxybuttersäure <gamma->Methylmalonyl-CoA mutaseZeitverschiebungInsulinAtomic absorption spectroscopyDigital elevation modelSample (material)Modul <Membranverfahren>Dominican RepublicChemical reactionChemical structureMoleculeSpectroscopyHydrogenCarbon (fiber)MatchChemical compoundAgeingAzo couplingBase (chemistry)Process (computing)CobaltoxideDoppelbindungDreifachbindungEmission spectrumColourantHexaneKatalaseKlinisches ExperimentMolecularityPipetteSchweflige SäureSubstrat <Chemie>ZellglasReactivity (chemistry)Penning trapMan pageAmrinoneIonenbindungChemical formulaOxygenierungProtonationPressurePropionaldehydStuffingChemical propertyAlcoholHydro TasmaniaButyraldehydeMultiprotein complexAlkeneAlkoxideCarbonSchwefelblüteVerdampfungswärmeAlkaneSetzen <Verfahrenstechnik>Lone pairWine tasting descriptorsComputer animation
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Man pageSample (material)VancomycinHydroxybuttersäure <gamma->LaxativeMashingLymphangioleiomyomatosisBohriumSolutionKnotZigarettenschachtelAlkeneAtomChemical structureMoleculePolymerHydrogenCarbon (fiber)Chemical compoundEthaneBromideChlorineChlorideCobaltoxideCyclopropaneDoppelbindungEmission spectrumFluorineFunctional groupHalogenHalideIodideTool steelPosttranslational modificationPenning trapIonenbindungChemical formulaOxygenierungSet (abstract data type)StickstoffatomChemistryChemical reactionGesundheitsstörungSeparation processAgeingPH indicatorWursthülleMan pageContainment buildingGum arabicPropionaldehydBiodieselComputer animation
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Calcium hydroxideKnotNitrosamineVancomycinMan pageArginineBohriumAlkeneS-Adenosyl methionineZigarettenschachtelIsomerMagnetometerMonoamine oxidaseMashingTau proteinGraukäseLipideFatty acid synthaseHydroxybuttersäure <gamma->Chemical reactionChemical structureLipideMoleculePhysical chemistryAcidHydrogenZigarettenschachtelCarbon (fiber)GeneChemical compoundCarbonateDoppelbindungFoodFunctional groupElectrical mobilityIsomerSea levelIsotopenmarkierungSense DistrictChain (unit)CarboxylierungSetzen <Verfahrenstechnik>Penning trapSilicon Integrated SystemsLactitolSingulettzustandSystemic therapyOxygenierungActive siteSubstituentStuffingChemical propertyIce frontDe-iceMeatWine tasting descriptorsIceMultiprotein complexAlkaneChemistryBiochemistryAlkeneFatBleitetraethylButeneCarboxylateGermanic peoplesCarcinoma in situInternationale Union für Reine und Angewandte ChemieComputer animation
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MagnetometerVancomycinDigital elevation modelAlkeneLipideMan pageFatty acid synthaseBohriumEnolCalcium hydroxideOctane ratingMorse-PotenzialMixtureInsulinMonoamine oxidaseLysergic acid diethylamideAspirinChemical reactionChemical structureISO-Komplex-HeilweiseLipideMoleculeÖlOrganische ChemiePharmacyPolymerAcidDeath by burningCell membraneFatMineralElimination reactionStorage tankOxideCarbon (fiber)PhosphateSulfatePotassiumCommon landAzo couplingBase (chemistry)LeadBromideCarboxylateProcess (computing)CobaltoxideDoppelbindungCell (biology)FoodFunctional groupGlycerinHalogenIodideKohlenstoff-14MethylgruppePaste (rheology)PhenobarbitalReaction mechanismSchweflige SäureSecretionBenzeneChain (unit)AlkylationDehydration reactionSoybean oilAdipose tissueMan pageCheminformaticsChemical formulaOmega-6-FettsäurenSystemic therapyOxygenierungProtonationBreed standardActive siteStuffingCorn oilDerivative (chemistry)AlcoholOceanic basinWine tasting descriptorsBeta sheetElectronic cigaretteAlkeneEtherAlkoxideMethoxygruppePhosphorsäureesterSynthetic oilPhenyl groupHyperpolarisierungRiver sourceComputer animationLecture/Conference
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Chemical reactionAlkeneLecture/Conference
Transcript: English(auto-generated)
00:09
So I saw this little news report from a station in Baton Rouge, Louisiana. Let me fix this screen.
00:22
And the news report was talking about it was, they were interviewing some pest control person about how they deal with fire ant problems. It's a problem you don't have here in California yet. It's coming. I spent a lot of time growing up in Texas, Louisiana. And I can tell you fire ants are really nasty.
00:42
What caught my attention is that this pest control person was talking about, and I'm sorry you can't see this very well. I've lost my other laser pointer. But he's talking about some special powder-like substance. And more importantly, he was talking about, and maybe I can use the mouse to come over here
01:01
and try to point here. But he was talking about some granular product that is water activated. And somehow or another, that just turns me on because it sounds like, wow, maybe there's some chemical reaction between rainwater. Yes? Oh, yeah, thank you for asking that, but I'll try
01:21
to turn it up until we get to feedback stage. But somehow the idea that there might be water. Here, let me keep going and see if I can get a little. The idea that water might somehow be chemically reacting with some pesticide, and maybe, who knows, doing SN1 reactions or some other type
01:43
of substitution process. That just sounds intrinsically cool. There's not a lot of pesticides or drugs that are designed to react chemically. So I did some searching around to try to figure out what they were talking about. I had to Google a few terms. But what I came upon was this, oh, I am missing the file here.
02:05
So there is some pesticide by a green light. And let me see if I can go back. I apologize for this. I should have gone with the PDF version from the beginning.
02:21
So there is some pesticide here. You can see the cover of that. That contains something that is called water-activated granules. And if you look, of course, you always look down to the active ingredients. It contains .1 percent bifenthrin. Oh, and immediately my heart sank because I know
02:40
that this is going to be a chrysanthemate derivative and nothing new. You wouldn't know from the name, but there's a whole class of insecticides that end in the letters thrin, permethrin. They all contain this three-membered ring and an ester. And they're based on a natural insecticide that's found in chrysanthemum flowers.
03:01
Those pretty yellow flowers have a natural insecticide that's a selective neurotoxin towards arthropods. So maybe if you ingested this entire bottle, it could affect you, but it's super-duper potent against insects and crustaceans and things like that.
03:21
So this is the structure of that active ingredient. And there's an ester in here which, in theory, could hydrolyze in the rain or in water. But that's not the way this works. Actually, the way this works is kind of clever. I think this is how it works. So what's notable about this particular version of this chrysanthemum ester that's a neurotoxin to insects is
03:44
that it's very greasy and has almost no water solubility. And if we go back and we read what this pesticide control person was very excited about, he was excited about the fact that whenever it rains, the ant piles get soaked, and all the ants come to the surface so that they don't drown.
04:02
And so they're all hanging out on the surface of their ant pile. And so what he does is he comes along and he spreads this powder on top, and it just sits there and sits there and sits there, and the ants are way down deep under the ground and ignore that stuff. But as soon as it rains, the ants all climb to the surface. And here are these particles.
04:21
And as it's raining, the rainwater is washing off this outer coating that's water soluble, and it's leaving behind this waxy bifenthrin that all these ants who have just come to the surface find and think is food, then they ingest it and start dying. So while it's not the chemical effect that I thought it was, like I thought maybe there would be a chemical reaction
04:42
with water, it is sort of a kind of a cool idea. So I'm not sure if this guy appreciates how cool all this stuff is. Gee, insect neurotoxins, this happens to target a sodium activated ion channel in neurons. That's very cool as well. But next time you're smelling a chrysanthemum flower,
05:03
you're probably getting a whiff of some of those kinds of compounds. Okay, so let's, let me make a point about Monday. Monday is national holiday, and it's a university holiday, Martin Luther King Day. And I just want to remind you of this quote
05:22
from Ben Franklin, drive thy business, or it will drive thee. You have an opportunity to choose what you do with your Monday, your university holiday. I hope you'll do something to honor Martin Luther King but I would urge you to find some way to set aside some time to spend on organic chemistry.
05:42
It's very rare that you get the gift of extra time to get ahead in this class, try to use that time to get ahead. Okay, and also because we don't have discussion sections on Monday, if you're in a Monday discussion section, try to attend one of the other discussion sections throughout the week. There will be four days worth of discussion sections.
06:02
You'll be able to find one that you can squeeze into. Okay, Chris asked me to make a point about this, an issue that's going to become pervasive throughout organic chemistry. And so I'm just going to draw this out. I want to remind you that we're going to start doing something in this class and in this book
06:22
where you do lots and lots of reactions in a single process. So I want to give you an example. This is typical of the kinds of examples, kinds of questions I'll be asking more and more throughout the quarter where I ask you to take some starting material and then somehow convert it into a product.
06:41
And it will never be, well, almost never be one step. It's going to be multiple steps. And so how do you depict transformations that require more than one chemical step? Ah, thank you. There we go. So how do you depict transformations that involve more than one chemical step?
07:02
And so here's an example of a question. How do you convert this alcohol into this thiamethoxide? There is no one-step way to do this. Now, the key problem here is that you need to figure out how to convert that alcohol into a leaving group. And you have all kinds of reagents
07:20
that can convert alcohols into leaving groups. Thionyl chloride and pyridine, tosyl chloride and pyridine to make tosylate leaving groups. PBR3, no pyridine, just PBR3 will make an alkyl bromide out of that. You can pick any one you want. I'm going to pick PBR3 because it's easy. But then the second part of this is we have to,
07:44
we have to add in some nucleophile, like a methane thiolate anion. It's like a methoxide. It's just that there's a sulfur atom there. I'll just write sodium because, so there's sodium plus, thiamethoxide minus. Now, this is immediately wrong.
08:03
It's wrong. And it's wrong because if I don't enumerate the steps with numbers, it implies I'm mixing everything together at the same time. If you don't add numbers to these reagents and steps, it means you're simply dumping everything together in the same flask.
08:20
And if you dump any kind of nucleophile in with phosphorous tribromide, it will react faster with the phosphorous tribromide than the alcohol will. And the way to make this correct is to enumerate the steps by writing the number one. And the book uses brackets. I usually use parentheses and writing the number two.
08:41
Then it's absolutely clear that what you mean is I'm going to take the alcohol. I'm going to treat it with phosphorous tribromide to make the alkyl bromide. And then I'm going to purify the alkyl bromide. And then I'm going to use my pure alkyl bromide and throw it into a completely different reaction. So more and more, we're going to be doing reactions
09:03
where I simply enumerate the steps because I don't want to draw every structure and every intermediate. And if you don't enumerate steps, if you simply write all of the reactions and reagents over one arrow or with one reaction arrow, that's just not right. So pay careful attention to this idea of enumeration
09:21
of steps because it means something completely different if you take the numbers out, the numbers one and two. Okay, so let's get on with our new chapter here. We've got a bright, shiny new chapter that we can spend our time on. And I just feel like I am emerging from the woods
09:41
into the bright sunshine, finally getting away from this hell of chapter seven, eight, and nine, and this SN1 and SN2 and E1, E2 business. That stuff is just awful. I feel like I'm hearing some buzzing and feedback. I don't know if I can. Whoa, that was a mistake.
10:02
Okay, so we're going to start about talking about alkenes. And I want to introduce this area by telling you two specific things about alkenes that differ from single bonds. So the first has to do with the reactivity of single bonds.
10:26
And I'm feeling like I left off a piece of paper here, but let me just go with this. So I want you to, let me try to do this in the same order. Does somebody have printed notes here that I can look at? Because I'm missing one of my pages.
10:41
Okay, let me first talk about the configurational stability of single bonds. And because I lost my piece of paper to write on, I'm simply going to show you what I have here on my written-on notes. Okay, so there's a key point, a key distinction
11:01
between double bonds and single bonds. And that is you can rotate about single bonds like this. And you haven't really noticed us doing this, but every time we've drawn some sort of a structure like this, I see every single one of those bonds as rotatable in that simple alkane. And that becomes very important when you have to think
11:21
about reactions where two ends of a molecule have to bend around and get close to each other so they can react. So we haven't talked a lot about intramolecular reactions so far, but we're going to as the quarter progresses. And so when I see a substrate that looks like this with some alkoxide at one end of a molecule and some alkyl chloride at the other end of a molecule,
11:42
I recognize that this great nucleophile isn't going to do anything unless it can get close to the alkyl chloride. Nothing will happen if those two can't get close to each other. And so I would rely on the fact that unless, that if I do rotate about these central bonds here,
12:00
this is not a chemical reaction. I don't really need to draw this as a chemical arrow, but that's an initial requirement in order to get this close enough so that it can do some sort of an SN2. And so bond rotation allows these groups to get close enough so that you can end up with an intramolecular displacement reaction. Kind of like an SN2, but it's intramolecular.
12:23
Okay, so bond rotation. You take it for granted, and you've probably taken it for granted throughout this, the whole book so far. And starting in this chapter, because we're talking about alkenes, you can no longer take that for granted. The problem is, let's take exactly the same molecule, except that we're going to put a double bond right in the middle.
12:41
And the configuration of that double bond matters. So I've drawn a particular isomer. We'll talk about this nomenclature shortly. This is called the trans isomer. And with this trans isomer, you cannot, with this double bond here, you cannot freely rotate about that CC pi bond, about that double bond. It's locked in that configuration
13:01
with those two groups sticking far apart from each other. And if you can't bring this O minus close to the chloride, it will never cyclize. So double bonds matter. They're locked in a particular configuration. We'll talk about that, where the groups are on the same side or their opposite side of the double bond.
13:20
And that's going to dictate some of our chemistry. And so if you haven't been thinking about bond rotations occurring previously, you have to think about that now. Okay, so that's one important distinction between simple alkane single bonds and double bonds, the idea that CC double bonds can lock configurations. Let's go ahead and talk about a difference in reactivity.
13:41
How does a CC single bond differ in, yeah? Well, the bottom one can't. Yeah, so I've got, let me write, I drew dashed arrows
14:03
to indicate that that's sort of fictional. I'll just write no. And if it doesn't rotate, then no. So that's what the intention. These other things can't happen. It cannot start off trans and then suddenly be what we'll call cis. So I'll introduce that terminology later. Okay, yeah, so the bottom stuff can't happen.
14:24
Okay, so what's the key difference in reactivity? And this kind of, in a way, I'm going to sum up this entire chapter for you. So here's something that you haven't seen. Let me draw out an alkene, or alkene for you here. And there's nothing special about this alkene.
14:47
So far some of the most reactive reagents that you've seen are things like sulfuric acid, maybe hydroiodic acid. And you've shown all kinds of things acting as bases and nucleophiles to attack.
15:00
Here's what you've never seen. You've never seen a single bond just come along and attack a proton or attack an electrophile. You haven't seen that. And you're not going to see that. So CC, single bonds, are not reactive. They don't act as nucleophiles.
15:21
They don't act as bases. They don't, and that's sort of obvious. If you take butane, it doesn't do anything. It doesn't react with anything. You could probably use that as a solvent. But I want you to contrast that with Chapter 10. Here's what we're going to learn in Chapter 10. And we're going to do it over and over and over and over
15:40
and over, have I emphasized that enough? We're going to do this over and over and over again. We're going to take substrates that have CC double bonds in there, and I don't want to say until you're sick of it. I hope, hopefully, you'll be happy about it. We're going to use pi bonds between carbons, CC double bonds, as bases and as nucleophiles.
16:03
And so we're going to do this kind of stuff over and over and over again. So it won't always be attacking protons, but we're going to use that double bond as a nucleophile to attack things. That's this chapter. So get ready for that. Get ready to do that. What I just did, let me be clear because I want to make sure the arrow starts from the middle
16:21
of that double bond, close. So we're going to do that over and over again. Now, it's not quite as reactive as an alkoxide anion, and maybe depending on the type of electrophile can be about as reactive as an alcohol lone pair. We're going to see lots and lots of examples of this. So let's do it.
16:41
That's what our chapter's about. Okay, another little introductory idea here. We're going to characterize before we start talking about, God, I'm anxious to get started on those reactions, but I have to resist here.
17:00
They're so cool, and they're so much better than this SN2 business that, okay, we're going to talk about a way to characterize compounds based on their molecular formula and their structure. I'm going to give you a new sort of parameter that you can use to describe compounds, and this will help
17:22
you when we get to spectroscopy. When you're taking the 51LB lab, you're going to be doing all kinds of spectroscopy. Somebody's going to give you this super complex looking spectrum and a molecular formula and say, okay, what's the structure of the molecule? And you'll be going, you'll be freaking out. And so this is where this is going to help you.
17:40
So you have to hold on for a couple chapters until we start NMR, but this is really going to help you when you get to that. So we're going to introduce an idea called degrees of unsaturation. It's a property associated with molecules, and you can back it out knowing nothing more than the chemical formula. So once you know how many degrees of unsaturation there are in some molecule,
18:02
just by somebody giving you the molecular formula, you can very quickly rule out structures that don't match. And so the degree of unsaturation is basically the number of rings plus the number of pi bonds in the molecule. That's it. So a saturated alkane like hexane has no pi bonds
18:22
and has no rings, so that has zero degrees of unsaturation. So let's practice figuring out the degrees of unsaturation in these five molecules here, just by simply adding up the total number of rings plus the total number of pi bonds, so how many rings are there in this isobutylene, this 2-methylpropene?
18:41
Zero. How many double bonds or pi bonds? There's one. So this has a total degrees of unsaturation of one. That is one degree of unsaturation. There you go. You've mastered it. Okay, let's switch over to this. Oh, my God, there's an oxygen atom. Doesn't make any difference. Okay, so how many rings are there in this?
19:02
There's one ring. How many pi bonds? There's zero. So here's another molecule that also has one degree of unsaturation. Okay, let's come over here. Oh, there's a triple bond. There's no rings in there. I can see there's no rings in this. This is called acetonitrile, common solvent.
19:22
But now if I count the number of pi bonds, that triple bond has two pi bonds. So I have to add the number two here. There's two pi bonds in that triple bond. Each triple bond is composed of one sigma bond and two pi bonds. So this has two degrees of unsaturation. Okay, let's get to more complex structures.
19:42
How many rings here up above? I see one ring. How many pi bonds? There's two pi bonds. That has three degrees of unsaturation. What you'll find is that typically the more degrees of unsaturation in your molecule, the fewer hydrogen atoms in the molecular formula.
20:00
Okay, here's pyridine. It's a solvent we've talked about. I see one ring in there, quite plainly, one ring. And then how many pi bonds? There's three. That has four degrees of unsaturation. So you have now mastered calculating the degrees of unsaturation or figuring it out. I hope you are, I hope there's an intuitive speed
20:21
at which you can do this. It's, and you might make little mistakes missing some of these numbers, but generally it's pretty intuitive. What you can't see yet is how you're going to use that and again you'll have to hold on with this degrees of unsaturation thing until we get to the spectroscopy chapter. It's really going to help you.
20:40
Okay, so let's keep going. We're going to do the things the other way. So now if I give you the molecular formula, and this is more typical. If I give you the molecular formula, what's important is you can calculate the degrees of unsaturation just from a molecular formula. And so let's practice that. But there's some rules I have to give you.
21:00
And these rules are just going to seem super complex at first. It's like how can I apply all these complex rules when I'm under time pressure on an exam? Practice. That's how you're going to do it. Okay, so here's our rules. So if you have some sort of a C and H compound that has nothing but C's and H's with N carbons,
21:21
and you can figure out how many carbons just by looking in the molecular formula. So here's our example. C3H4. There's three carbons. N equals 3. There you go. It's a three carbon compound. So I'll just write here N equals 3. It's kind of obvious. You just look at C3, C5, C whatever.
21:41
Okay, so how do we figure out the degrees of unsaturation? What we figure out is what's the maximum number of hydrogens you could have on a molecule that has three carbons? Let me just try to sketch it out here. I'll just use a different pen color somewhere here so we don't get in the way. If I had a three carbon alkane like that, how many hydrogens
22:00
at most could that have? Eight. You guys are good at that. Okay, 2N plus 2. That's the maximum number of hydrogens. So if this compound had no unsaturation, had zero degrees of unsaturation, it ought to be H8, but it's not H8. It's actually H4.
22:22
The actual number of hydrogens here, 4, so you can tell it's missing some hydrogens. C3H4 is missing hydrogens. And what we do is we now divide this difference by 2. There's four hydrogens missing somewhere. And if there's four hydrogens, we divide that number by 2,
22:43
8 minus 4 divided by 2. So how did I calculate this? Equals 8 minus 4 divided by 2 divided by, and that equals 2. That's the degrees of unsaturation. And the idea is that it takes two hydrogens to add
23:02
to a double bond, a CC double bond. That's why you divide by 2. Okay, so how do you use this? Later when we do spectroscopy, I'm going to say, here's a molecule with the formula C3H4, and here's a spectrum. What's the structure? And the first thing you need to do is start drawing out some plausible structures that fit C3H4.
23:23
So I can think of two things that have two degrees of unsaturation. There's a third one I'm not going to draw. There's really only three simple alkenes or simple molecules that have this formula. So here's a molecule that has two degrees of unsaturation and fits that formula, two double bonds, or I could have one double bond and one ring.
23:40
So you need some simple way that allows you to quickly draw out plausible structures. And knowing how many rings and how many pi bonds there are in a molecule is the fastest way to help you quickly sketch out some structures. That's why you, how you're going to use degrees of unsaturation. Okay, let's keep practicing here.
24:00
So I've got some special sub rules here for oxygen, halogens, and nitrogen. So the oxygen rule, little add-on rule is ignore the oxygens. They don't affect any of those things I just told you. Okay, so let's come down to a molecule, C3H6O. So here N equals 3, and what's the maximum number of hydrogens,
24:21
number of hydrogens I can have if N is equal to 3? Well, it's still 8. If I have three carbons, the maximum number of hydrogens can be 8, and the number of oxygens you have in there doesn't matter. Okay, how many hydrogens are there on this? Well, I just look, it says H6, there's 6. And so how many degrees of unsaturation are there in this molecule?
24:43
There's one, 8 minus 6 is 2, and I divide by 2. That tells me there's either one double bond or one ring in this molecule. I can very quickly sketch out the possibilities. Once I know there's either one double bond or one ring, that makes it very quick for me to sketch out a bunch of possible structures.
25:02
Okay, halogens are a little bit more complex. Our rule is, so let's start off with this rule again. So here's C3H5CL, there's three carbons. And so the maximum number of hydrogens is still 8. That's always going to be 8 with a C3 compound.
25:22
Sorry, the maximum hydrogens. The actual hydrogens is H5. But we have this special little modifier rule if we have a halogen. We have to add 1 to the actual number of hydrogens for each halogen. Whenever I have a chemical structure and I have a halogen on there, I had to pull off an H in order to add that halogen.
25:44
Chlorides go in the same place where hydrogens do. So in order to back out the degrees of unsaturation, what I need to do here is apply this rule where I add 1 to the actual number of H's, 5 plus 1. Now I can take the difference.
26:02
Now I can take the difference between the maximum number of hydrogens and the actual number of hydrogens. So I say 8 minus 6 is 2, and then 2 divided by 2 is 1. There's 1 degree of unsaturation in C3, H5, CL.
26:22
So now that I know there's 1 degree of unsaturation, I can very quickly sketch out some possibilities that have either 1 ring or 1 double bond. Here's one example. I mean, I could invent all kinds of structures that have either 1 ring or 1 double bond. Here's an example of something that has just 1 ring and a chloride somewhere, and, you know,
26:41
you can draw 3-membered rings, et cetera. So, wait, that's not C3H, sorry. It should be 3 carbons. That's supposed to be a cyclopropane, cyclopropyl chloride. Okay, so I could very quickly sketch out plausible structures that fit that formula that have either 1 ring or 1 double bond.
27:02
Okay, so things can be crazy and complex-looking. Here's a compound that only has 2 carbons, so I'm going to say N is equal to 2. What's the maximum number of hydrogens? It should be 6. Ethane has 6 hydrogens.
27:21
Okay, but now we look at the actual number of hydrogens. It's H4, and I have to use these little modifier rules. Okay, oxygen doesn't matter, so let's ignore that. For each chloride or halide or bromide or iodide that I have, I have to add 1. So I see 1 chloride, so I have to add 1 there.
27:41
But now there's another rule for nitrogen. There's another rule for nitrogen. For each nitrogen I have, I have to subtract 1 from the actual number of hydrogens. And so, overall, my net number for hydrogens is going to be 4, because I add 1 for the chloride, I subtract 1 for the nitrogen.
28:00
And so the difference between these two is now 2 again, and so now this has 1 degree of unsaturation. That tells me that this molecular formula, all compounds that have this molecular formula have either 1 ring or 1 double bond, and so I can quickly sketch out some plausible structures. Okay, so you're not going to use this chapter.
28:22
Well, there will probably be a few sapling problems to get you to practice this. You're going to end up waiting until we get to the spectroscopy chapter, and this is going to be your favorite tool for allowing you to quickly sketch out structures when I ask you to tell me the structure of some molecule that has the formula C2H4NOCl
28:40
and matches this crazy complex spectrum that I'm going to show you. You need some way to narrow down the number of structural possibilities, and that's when this is going to be useful. Okay, so sorry I had to show this to you, but just hold on with this. Yeah? It would belong there, but you, sorry,
29:01
you're never going to see fluorine this quarter. I don't think, yeah. Yeah, but fluorine would fit with the halogens. It's just not common in Chem 51. Sorry, I should have put it there. Okay, so let's talk about nomenclature.
29:23
God, I really want to get to the chemical reactions, and I'm feeling really, okay, so I don't ask IUPEC nomenclature on my exams. Let me just write here on my exams, but I do ask that on the sapling because on the online problem sets
29:43
because the standardized exams ask you questions about nomenclature. So the main thing that I really want you to know is that compounds that are alkenes, if the alkene is the highest priority group in the molecule, will end in ene. As soon as you hear the suffix ene,
30:02
you know there's an alkene somewhere. So here's a polymer. I'm going to, there's four carbons here. Sorry, this is not a very high resolution pen. This is a polymer with four carbons. It just repeats over and over again. And this is called neoprene.
30:23
And so if you went surfing this morning in your wetsuit, it was made out of this polymer. And just from the name neoprene, you know there's an alkene somewhere in the chemical structure of the polymer. And there's also a chlorine atom there. So, you know, that's kind of the level at which I know nomenclature. I hear, I listen for the word ene, and it tells me, oh,
30:40
there's a double bond in there. Okay, but let's talk about this idea of configuration, that double bonds don't rotate easily. I'm going to draw two types of molecules for you. And we'll talk about this nomenclature cis and trans. So here's a four carbon compound.
31:02
It's not butane. It's butene. And one way that I would distinguish these, these two molecules, let me draw the hydrogens there because sometimes the best way for you to keep track of alkenes and whether they're cis or trans is to look at the hydrogens that aren't drawn for you.
31:21
That helps you to keep your focus on the fact that both sides of the alkenes are different. Okay, so here's two alkenes, two butenes. That's two butene. And they have different double bond configurations. One of these is trans. And that means that the two alkyl groups are on opposite sides. The two highest priority groups are on opposite sides.
31:45
And it's a description of the overall molecule. If a molecule has only one double bond, I could say, oh, that trans butene over there, and it's totally unambiguous what I'm talking about. If there's only one double bond and I say it's trans, that means the two highest priority groups are on opposite sides.
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If I say that cis molecule and there's only one double bond, or if I say that cis double bond, I'm talking about the double bond where the two highest priority groups are on the same side. Okay, the problem comes if I have more than one double bond in a molecule. I can't say, oh, if there's more than one CC double bond,
32:23
I can't say that trans alkene because you don't know which one I'm talking about. And that's where IUPAC nomenclature comes in. So IUPAC nomenclature works. It uses these descriptors. It doesn't use trans and cis. It uses E and Z to distinguish these. And it's useful even if there's multiple, multiple double bonds in your molecule.
32:42
So according to IUPAC nomenclature, so let me write this above here, that this isomer is the trans isomer, and this isomer over here is, I would call this the cis isomer. I might, the way I might also use these descriptors, I might say, oh, that's a trans double bond,
33:00
and the other one is a cis double bond. I might focus in on the functional group and describe the double bonds that way. Okay, but now let's switch over to IUPAC. And that E and Z thing. This makes perfect sense if you're a native German speaker. But if you're not, then the use of the term, of the letters E
33:23
and Z probably is not so obvious. The IUPAC name for this is that it's not butane. It's a butene, and specifically it's E to butene. What does that mean? E tells you that that double bond has a
33:41
trans configuration. That's what E means. And for this other isomer over here, it's also butene, and the double bond is at the two carbon, two and three, so it's two butene, and this one has the two highest priority groups, cis to each other. So we call that, and I can't do it here with a pen,
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but those are italics font, the E and the Z. So E to butene for the trans isomer, Z to butene for the cis isomer. And every time I have a double bond in there, I have to describe that double bond as either E or Z, and I'll show you an example down at the bottom. So what do these things mean?
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E stands for Entgegen in German. Entgegen means opposite, meaning they're on opposite sides. Z stands for zu zammen, which means together, and that means these are together on the same side. You're going to need some sort of a simple, well, here's a simple way if you're not a native German speaker
34:41
to know this. Some people say this, oh, on the same side. You don't need to speak German to remember that. Okay, so typically, right, the kinds of compounds
35:03
that you will be exposed to typically will not be nameable by you using the rules we give you in Chem 51. Here's one of the most important molecules in lipid signaling. A biologist would call this 5-HP, because they don't want to say the whole IUPAC name, which is 5-hydroporoxy, 6E, 8Z,
35:22
11Z, 14Z, acosa tetraenoic acid. Nobody wants to say that, but this would be an example of a super complex but important biological structure. It's important in inflammation, prostanoid signaling, where you can go back and decipher what they're
35:42
talking about. So this is a carboxylic acid. I can see it ends in oic acid, and I don't expect you to know the name of this or how to name something this complex, but I want you to see how this E and Z nomenclature works. I can't simply say, oh, there's that lipid molecule. It's a trans isomer. Well, there's more than one double bond.
36:01
Some of the double bonds are trans, and some are cis. I can't just say trans or cis. This is where we have to use that E and Z thing. So you don't know what acosa tetra means, tetraenoic acid. You just need to know that there's a lot of carbons in there, but if we number this thing by using the IUPAC numbering,
36:22
the carboxylic acid would get the highest priority number, one, and I'll keep counting down the chain here, three, four, five. Here's carbon six. That's our first double bond, and look at this. It says 6E. That means you know that the double bond that starts at carbon six is a trans isomer,
36:42
and then I keep going over here. I get to carbon eight. There's carbon eight down there, and sorry, my pen doesn't have high resolution, and you can see that carbon eight is 8Z on the same side. It's a cis double bond, and the two substituents on there are on the same side. You can keep going. So you can see how the IUPAC nomenclature
37:01
in this EZ stuff works, and this is a typical molecule where you have so many double bonds, and you need to keep track of which double bonds are cis, which double bonds have the Z configuration, which double bonds have the E configuration. I won't ask you anything that complex. That would be crazy. I don't ask IUPAC nomenclature on my exam, but someday
37:21
if you're working in some biochemistry lab and somebody flashes you this complex structure, you might be able to sketch something out that would tell you something about configuration. Okay, so typically the way I expect you to know nomenclature on my exam, I might ask a question that would say something like, draw the Z product
37:44
of the following reaction, and you wouldn't have to name the molecule, but you need to know what a Z isomer is, or an E isomer, and I expect you to know cis and trans. Okay, here's another, there's all these other sections
38:03
in this chapter that they stick in the front to slow down how quickly we can get to the chemistry. Here's sections 10.4, 5, and 6. It's about physical properties like what's the boiling point of an alkene? What are some structures of interesting alkenes, and what are some alkenes that you find in lipids?
38:22
These are all very cool ideas, but I'm not going to put these on my exam, but the only thing I could really do is ask you true, false questions, and I don't do that on my exams. I ask you to draw out structures and stuff. But let's talk about why should you care about alkenes? Why should you care about degrees of unsaturation? And I think the most important reason that you might care
38:42
about things like degrees of unsaturation, how many double bonds there are on a molecule might relate to nutrition. If you look now on the back on the label of every single food item that's sold aside from fresh produce and meats and things like that, they now summarize for you the unsaturation
39:01
and the double bond content of the fats that are in the food that you're eating. So let me just remind you of the structure of a fat versus a lipid. So up above here I have a lipid molecule, and it's got esters, ester functional groups, two of them, carboxylic esters, and then it has a phosphate ester on there.
39:22
And these are attached to a three carbon unit called glycerol. So that's a basic lipid, and that makes up the outside membrane of all of your cells. Now you also have inside of your adipocytes, you have a fat molecule that looks very similar to a lipid.
39:41
And the difference is that with a fat molecule, you've got three esters, and there's no phosphate or polar head group on that molecule. But what I've drawn here with these squiggly lines are some very long chain carboxylic acid groups. So all of these little squiggly lines that I've drawn here look something like this.
40:01
They either look like this long chain with two double bonds. You can have as many as four double bonds in these long chains. You can have as few as zero double bonds in those long chains, or you can have one double bond in those long chains. And so the main thing that you need to know is that the saturated fatty acids that have zero degrees
40:22
of unsaturation tend to be waxy solids. When you have fats that have no double bonds in there, those tend to be solids. If you go to the grocery store and you want to buy some kind of a fat that's a solid, lard, butter, shortening, Crisco shortening, those are all composed
40:41
of saturated fatty acids. If you want a liquid fat, vegetable oil, vegetable oils is soybean oil. They just don't want to tell you soybean. So soybean oil, safflower oil, corn oil, those all have double bonds in them and lots of double bonds. The more double bonds, the more thin the liquid,
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the more liquidy the liquid. And so that's the distinction that you need to know. So you don't want waxy solids to deposit. This is a sectional view of a clogged artery where you can see there's very little space in here for the blood to flow. You don't want the waxy fat deposits
41:20
to start building up in your arteries. There's this whole process that starts. Your immune system starts glomming onto that and it occludes the arteries. And once you occlude the arteries to your brain or your heart, it's a bad situation. So they now tell you on the food packaging, just how many saturated fats there are in that food or the percentage of saturated fats.
41:41
They tell you that. They're telling you chemical information. You know, for years they grouped trans-alkenes like this one here with the good fats, the liquidy ones, which is weird to me because when I look at the structure of that trans-alkene, I just happen to know it's going to adopt a configuration that looks like a saturated alkene. And it seems like only about ten years ago people started
42:02
to say, you know what, that needs to be grouped with saturated fatty acids. You can't just have any old alkene in a fat molecule and have it be liquidy. It has to be a cis-alkene. So I think about ten, maybe eight years ago, they started to tell you not just how much saturated fat
42:22
but also how much trans fats there are because those are going to clog your arteries and you don't want to clog your arteries. That's a bad thing to do. Okay, so unsaturation is on every food packaging. They're telling you about how many double bonds are on the molecules of the fats that you're eating.
42:44
Okay, so let's have a review. Let's review some of the stuff that you've already seen in chapters six. God, I just can't get away from this stuff. Seven, eight, and nine. I'm just going to retell you the stuff that I just finished telling you on Monday because why not?
43:03
Let's talk about the ways that you know for how to make alkenes. You already know how to make alkenes, to synthesize them. And so it's just a review, I can't review everything but I'll review a couple of my favorite ways. So some of my favorite ways to make alkenes are E2 elimination reactions.
43:22
Oftentimes, so let's practice some abbreviations. Oftentimes I'm going to abbreviate CH3 groups, methyl with the letters ME. It's just a stylistic preference. It looks a lot cleaner on a page because I don't have to write subscripts. You'll find that many synthetic chemists and organic chemists abbreviate CH3 groups, methyl groups as ME.
43:41
And so you have to get used to that. So here's a methoxy group at the end of my alkane. And so here would be an example of how I might like to make an alkene. I have some sort of a leaving group here. So here's two oxygen derivatives, a methoxy group and a tosylate group.
44:01
One of those is an outstanding leaving group. And that's the tosylate leaving group. And I want you to start getting used to using that because you spent so many chapters now talking about halogens, get away from that. Tosylates are much easier to, you're going to see them much more commonly. So if I throw a strong hindered base in here,
44:22
you know most alcoc, there's not a huge difference between the most hindered and least hindered alkoxides but t-butoxide is the one that's most hindered. So here's another abbreviation that I'm going to start using, t-butyl. So this is the same as what the book writes. The book writes it like this.
44:46
So that's the way you're used to seeing it from the book. I'm going to start writing o-t-butyl. And you just need to know that that's the same as this potassium tert-butoxide. So when I come along and I say, oh I'm going
45:01
to take this tosylate here. Notice my, I didn't call it an ether. I want to focus your attention on the most reactive part. So I say, oh see that tosylate over there? Let's throw in some t-butoxide base. So I might draw it like this, t-bu-o minus potassium plus. Or I might leave out the minus and the plus
45:22
and just draw it as a molecular formula kind of style. And so this is going to do an E2 elimination. There's beta protons that are beta on the beta carbon that will get pulled off. And this would allow you to make, oh I can see I'm reorienting my carbon chain there, but that's okay. So I had started with three carbons.
45:40
I still have three carbons. And I introduce a new double bond. So I expect you to know E2 eliminations. They're great reactions. They're useful. So let's go ahead and talk about the alternative. And you typically have a halogen leaving group or a tosylate leaving group. You need good leaving groups for E2 eliminations. By the way, E1 and E2 are not the most common elimination
46:03
mechanism in organic chemistry. You're going to have to wait until chapter 23 before we show you the most common elimination mechanism in organic chemistry. It's not E1 and it's not E2. And wish they showed it to you earlier, but we'll just have to leave that as a secret until you get to those chapters.
46:22
Okay, so what's another way other than E2 eliminations to make alkenes? Let's take a tertiary alcohol just as an example. We showed you E1 processes as a way to do elimination reactions.
46:41
So if I take this tertiary alcohol and I treat that with pachyl 3 and pyridine or strong acid and do a dehydration, I can very easily dehydrate this. I'll use the sulfuric acid approach here. So if you use sulfuric acid, not HBR or HI because I don't want nucleophiles like bromide and iodide in there.
47:02
Sulfate is not a good nucleophile so you don't get SN1 reactions. This will very easily make an alkene. And again, pH, I'm sort of trying to get you to practice my abbreviations and again, it's not just mine. The book will start using them more and more. That stands for a benzene ring, a phenyl group.
47:21
And there's two of them on here. So you should be starting to get a lot of practice now with these reagents that we just learned in the alcohol chapter, chapter 9. Dehydration with strong acids, et cetera. Okay, so those are ways that I like to make alkenes. You should know how to make them. So when we come back on Wednesday,
47:43
I'm going to show you a bunch of reactions that you can do with alkenes, where the alkene attacks something.