I want to. Yes. >> All right. >> Good afternoon. >> Announcements and reminders before we begin. >> Today. >> Should be a reasonably normal day. Tomorrow and Wednesday, I'm going to get a little bit more interesting. First of all, let me remind you that because I'm going to be tied up in meetings all day. Both of those days, I will not be holding my normal office hours. However, if we will sort of kind of compensate for the address, I remind you that the big thing for tomorrow is since you folks indicated that you could pretty much at least on Tuesdays, coming a little bit early. Tomorrow at four o'clock. This room, you've scheduled an introduction to the wildly plus, which you've already paid for c and a, and we'll find out how to use it with Ms. Natalie Wagner alone as a representative of the Wiley Publishing Company. So that's what we'll do before the usual class period. I'm probably not going to finish today. Talking about everything that you will need to know for your first exam on Wednesday, assuming that's true after the presentation on Tuesday when we resume normal glass operations, I will try to finish up everything you need to know for that. And then whatever time we have a leftover before will be yours for whatever question you have. Pursuant to the first thing we gave out the practice fan before. If you didn't get a copy of that, please don't hesitate to ask for one. Any question you have relating to anything you saw on the practice exam, anything from the textbook or anything that we've talked about here in class. Fair game for that question and answer session. Basically what's going to happen on Tuesday. And then of course on Wednesday, you'll have the entire two hour class period to work on your first date. When you come to class on Wednesday, please sit where the seeding chart says to sit. Obviously a little green circles indicate where Kim, 3-2-1 and Kevin, 3-11 students are supposed to sit. >> And there's a method to the madness. >> If you sit in the spots designated by the green circles, then two things will be true. One is, it'll be a lot easier for me to hand out papers. The other is if you have a question in the middle of the exam, you should be able to get up and come down front and answer questions without having to climb over. Anyone will take advantage of the fact that we have a sizable room here and spread everybody out accordingly so that everybody can do that makes sense. Alright, so the main thing is tomorrow at four o'clock, introduction to wiley plus with Ms. Wagner lot here in this room eating a little bit early. And we gave out this handout about wiley plus cb. Didn't get one of those. Please see me before you leave. There's a reminder on the back, you can go to this for a little tutorial. And there's another one that says, please ask your students to bring their wiley plus registration cards with them when Ms. Wagar launch Joseph. >> So everybody, alright, last time we left off talking about all kinds of different compounds, get their names. >> Last ones, we were talking about alcohol's discussion of alcohol nomenclature in section 4.3 in your textbook we left off about the top of page 149, you can see some other examples of other alcohols and how they get their names there. And we'd actually already talked a little bit about how cyclic alkanes get their names. And you can see that a couple of the examples of alcohols we gave last time also involve rings. We aren't gonna say some more today about how other classes of compounds get their names. And to keep life relatively simple Was it turns out I'm gonna skip around a little bit from the order it's presented in your textbook. >> Right now. >> I'm going to go to Section 4.5 and talk about how alkenes get their names. And of course, alkenes are characterized by the presence of at least one carbon, carbon double bond. I got along a little model of ethane today, and I'll say more about why I brought along the model of epi. >> But suffice to say that ethane, of course, has the formula C2H6. >> That looks something like this. However, the presence of that double bond and an alkene cuts down on the hydrogen count by two. So the simplest possible alkene as the formula C2H4. And you may remember that in general, cn H 2n is the generic formula for an LP. Now the point is, if C2H6 has the name ethane, what would you guess would be the name of the compound with the formula C2H4 >> Yeah. >> Alkenes have names that end in E. >> So the IUPAC name for this compound is FV. >> And of course we can write it in short-hand forms that look, for example, in this case, something like this. Now, as you've already seen, there's the IUPAC name for compounds, and especially for simple compounds like this one. There's what everybody calls it. >> What everybody calls this compound is ethylene, which kinda makes no sense. >> Number one, why use a longer word when a shorter word will do? And number two, technically speaking, there's no Ethel in FOE because as we've seen already, an ethyl group consists of two carbon atoms and five hydrogen atoms. C2h5 is whole molecule, consists of two carbon atoms and hydrogen atoms. >> So technically speaking, that's not an ethyl group. >> Nonetheless, people use the name ethylene to refer to this molecule. >> So just be aware that LG name this compound by any reasonable method. >> Yeah, IUPAC name groping three carbons is probe has to end in E. >> And if there's a double bond in there, so propane, or again, some people call it propylene, but at the same disadvantages, echoing depths named Viscount bad. >> Okay, carbon alkane, butane four. >> Carbon alkene is so name this got bad. >> Yeah, no, yes, yeah. >> Turns out isobutane is something else. The problem is that both of these compounds are beauty consists of a four carbon chain with a double bond in there somewhere. The only difference obviously is the location of the double bond. And the problem is, once the carbon chain gets to be at least four carbons long, you need to show where the double bond is located with a number. The complete name of the first compound is one butane, because the double bond for that compound begins at carbon atom number one. The complete name for this compound is 2Q gene, because the double bond begins at carbon atom number two. So with ethane and propane, you don't need me numbers, but when the carbon gene gets to be for longer, you must show with a number where the double bond is. >> Look, it makes sense. I named this got bad. Yeah, as we did before. >> Number longest chain. And if you feel like it's circle that substituents longest chain is five carbons long. This double bond in carbon number one. >> So that much is called one painting. >> And there's a methyl and number two complete IUPAC name to metal empty name. This compact. >> Yeah. >> The approval. >> Almost one small correction? >> Yeah. >> Yep. Yep. >> To show where the double bond is located. >> Number the longest chain, if you like, circle the substituents. >> Six carbon chain with a double bond beginning at number two, that's two. >> And then the rest is 5-methyl on number two. That actually is the correct name, despite the fact that there is a seven carbon chain in that molecule. Look up here for a moment. >> 1234567. However, this is the correct name because when your name alkenes, what you're looking for is the longest carbon chain that contains both SP2 hybridized carbon atoms. >> So this is the longest chain that contains both SP2 hybridized carbon atoms. Therefore, this is the correct name. >> Makes sense, right? >> Name this cop bad. >> Yeah, God, wasn't there be cyclohexane but as it is cyclohexane name it now. >> Yeah. No, but not a bad dry it certainly di methyl. Yeah. >> Three very dry mouth. >> All one closer. >> It's 33 dimethyl one. Actually, you don't even need but one. So this should all be one word at missiles, but there's a reason you don't need the one. Obviously, in principle, since the ring has no beginning and no end, you could start numbering the ring anywhere you want. But if the double bond is contained in a ray, the understanding is that the two carbon atoms connected by the double bond are number one and number two by definition, that said, we should still number things so as to put the smallest number that you can in the name of the compound. If we had call this number one and the other end must be number two. And then we gotta keep go and 345666 di metal. If we number it this way, it comes out 33. >> Dimethyl 13 is smaller than six. >> The buying all this, there are some other examples in your textbook. >> Starting at the bottom of page 151. By the way, you mentioned isobutane before. This is actually the structure of isobutane because there's actually two methyl propane that the common name is isobutane or isobutane. And some of the rules are spelled out in good detail on page 150 to see anything else there should worry about for the time being. >> And we'll come back and see some other examples a little bit later. Okay, let's skip ahead for a moment to page 154, which talks about how L times get their names. >> Of course, the distinguishing feature of an alkyne is the presence of a carbon-carbon triple bond. Here is the simplest possible alkyne. >> If C2H6 is Ethene, C2H4 is what do you think C2H2 is >> That's the IUPAC. Iupac name shorthand structure isn't that much different. But we've seen this compound before, and I don't know if I called it by this name earlier or not, but we'll certainly see this in your textbook. What everybody calls this compound is acetylene, which makes absolutely no sense. Number one, it's not an, it's an high principle, you should call it that. And number two, there's no acetyl in a settling. There is a piece of a molecule that is referred to as an acetyl group. >> And it looks like that, but that's obviously not present in this molecule. >> Again, this is a name that was given to this molecule a long time ago before people knew what the structure was and that name is persistent. >> However, the names of most other kinds are significantly more straightforward. >> How would you name this combat by any reasonable amendment? >> Yeah, except for one thing. >> Yea you gotta show where the triple bond is located too. >> So number the garb and Jane for carbon chain, that's what the u means, this triple bond. >> And that's what the I mean the triple bond between the carbon number one 1B type name this countdown. Yeah, I'll buy the 3x side part. >> And you do have methyls on 25. How do we deal with that? Yeah. >> 2-5 diamond Yes. >> Well, put it this way. If you look at the exam questions, when it comes time to name compounds, The question is usually phrase, provide an acceptable name for the following combat. Iupac nomenclature is always acceptable. >> So in that sense, no. >> So we on the other hand, I will probably refer to this compound is acetylene because I'm an old organic chemist. So the reason for knowing common names is just to know what I'm talking about. And if it doesn't make sense, just raise your hand and say, is it really what people call that compound? >> Or they wouldn't be like on a task, we draw that line. >> Any other questions about where we are so far? >> Alright, let me come back for a moment to one aspect of alkene nomenclature is a combat we saw a few moments ago. >> What's it called? So what's this camp alcohol? >> Ok, the point is, both of these are to beauty, but it turns out that they are not the same thing. As we'll see shortly. >> Single bonds don't present a problem in this regard because you can freely rotate around single bonds without breaking the bond. But the problem is a double bond, as we saw earlier, consists of a sigma bond and a pi bond. You try rotating one set of substituents around a double bond compared to the other set of substituents. Well, you can't do that without breaking the pi bond. In other words, you can't rotate around a double bond the same way you can rotate around a single bond. To get from here to here, you have to actually break bonds and reconstitute the molecule, the double bond in part, some rigidity to the molecule. Well, the point is, if you have to break bonds to get from here to here, that means you have to deal with chemical reaction to get from here to here. Which means those are two different molecules, but they are both to beauty. So how do we deal with this? >> Can get out the cis trans thing again, the original combat I'd really is cis to the other is trans to beauty. And again, if you number the carbon chain, and the question to ask yourself is, as you follow the numbers through the double bond that the kernel through more or less in the shape of a C. >> What does it curl through more or less in the shape of an S, kernels through more or less in the shape of a C. >> It says curl through more or less in the shape of an S. >> Claims in fact, if you were to draw these two compounds in bond line notation, that's exactly what they would look like. C versus grains, if that helps them find. Let's try a somewhat more complex example. Name this column bad, complete with the appropriate stereochemical script. Or as we said before, any compounds that are cis-trans isomers of each other are in fact scare, you. >> Name it, right? >> Again, I'll buy the three part, lets number the carbon chain. So yes, there's a seven carbon chain double bond begins a member three, So a will end in 3MT. >> Now, as you follow the number two carbon atoms, does it go through the double bond? >> More legacy or more like an S? >> Yeah. >> Scissor grants, grants. Now it's tempting to say CIS, and that was why I showed you this example because it's got a sneaky because you see something sticking up over here that looks very much like what sticking up over there. They're on the same sides. You'd say cis, not how it works, follow the longest carbon chain through the double bond, which is why I will suggest that you number the carbons and then follow the numbers the carbon chain, the substituents of course, are indeed methyl and f. All the question is, where are they located? So finish the name. Yeah, and again, I will not nitpicky while an alphabetical order. So people would say it should be for FL3 methyl. >> But Sicer trans comes at the beginning of the name. >> So full IUPAC name for this compound trends for 3M makes sense. >> Okay, let's go back for a moment and look at some of the previous examples. >> You'll notice that when we named this combat, we didn't bother with cis or trans outcome. >> Yeah. >> Well, there's only one substituent, but that's not the crucial point. >> Yeah, yes, carbon number one has two hydrogens on it. >> If either of the carbon atoms that is connected by a double bond has two identical things attached at one end. >> And system trains doesn't mean anything. Same principle here. Might be a little bit easier to see here. >> If we follow the numbered carbon sequence here, we could have called this sis. But then again, we could just as easily call this number one and call this the substituent, in which case it would be trains. Well, the point is it doesn't matter. And if it does matter, it doesn't matter. >> So in that case, cis and trans has no meaning. >> The only time cis and trans matters, let me just give you a generic thumbnail sketch of any old alkene with substituents W, X, Y, and Z as shown here. >> For cis and trans to matter, w must be different from x and y must be different from x_0. >> That's the case we have here. W is an FOX, is a methyl, why is an apple Z is appropriate? So if w is different from x and y is different from Z, then cis trans comes into play. But if either of those things is not true, then cis-trans doesn't matter. So not all alkenes need the cis-trans thing. >> Okay, going back here for a moment, is the double bond in cyclohexane cis or trans? >> Yeah. Okay. >> You're right. >> If you just go follow the carbon chain through the double bond, it is cis or we don't bother putting System the name and there's a reason for that. And that reason is there's no such thing as trans psych LOW pixie. It is possible to have a trans double bond in a ring if the ring is large enough, but typically the ring has to be at least eight carbon atoms big. You get a trans double bond it there. If you think it's possible to have a trans double bond and a six-member ring. Go home and try building a three-dimensional molecular model of what it would look like. Suffice it to say, you will find out in a hurry how much stream there is in that molecule. So in this example, while technically speaking, the double bond is sis, the descriptor is really not needed as advocates. And one last point to ponder here, 25 Dinah for 3x. I looking back at this example, cis or trans? Yes. >> No. Yeah. Yeah. >> The correct answer to that question is no. It's neither sin nor trains. The reason is, what's the hybridization of the double-bonded carbons and an alkene SP2, which implies what geometry is trigonal planar bond angles of 120 degrees. That's where cis trans isomer ism comes from. That's what allows you to talk about the double bond or the carbon chain growing through the double bond like a C or like an S. What's the hybridization of the triple bonded carbon atoms in this compound SP. What geometry? >> Linear. >> If the molecule is linear at least through here, then it doesn't curl through like a C or like an ethical through like an eye. Cis trans has no meaning. So times this trans has meaning. Well, we saw it has meaning before with cyclic molecules that have more than one substituent. But also for alkenes in which w is not the same thing as x and y is not the same thing as eight, but not for alkyne, not for normal things like that. Make sense? >> Okay, all of this is spelled out reasonably well. >> And your textbook, there is some discussion of cis trans, geometry on page 153. But I think what I'm showing you here covers a few more examples, but what they do in the textbook. So let's go with that for the time being, and now at this point, I'm going to double back to Section 4.4 again. We'd already seen some examples of how to name it, relatively simple psych, LOW alkanes. But Section 4.4 a talks about mottos, cyclic compounds, compounds with only one ray. Section. 4.4 B moves on to bicyclic compounds. And you get some truly interesting stuff going on here. >> Now, as the word suggests by cyclic compounds contain two rings. >> Alright, here's an example of a compound that contains two rings. >> Try naming this belt. Think l'Hopital. >> If I go to my way of thinking, the sensible thing to do would be to treat the larger ring is the main carbon chain, and a smaller ring as the substituent. >> And you can have cyclic substituents just like butane becomes beautiful psych, LOW, butane becomes cyclopedia. Told no reason not to name it that way. How many total carbon atoms are there in that molecule? In a moment, you'll see why I'm asking that question. >> I hope that was reasonably obvious, but the point is that is not the same thing as this cop bad because how many total carbon are, the carbon atoms are there in that top down nine compounds like this one, which have two rings, and those two rings share one carbon atom. >> But what I've indicated with an arrow I refer to as spiral compounds. We will not hold you responsible for the nomenclature of spiral compounds in this course. We will, however old you are responsible for the nomenclature of compounds like this one. And this is the third possibility for a bicyclic compound with a six-member ring, a four-membered ring. But how many total carbon atoms in that molecule? >> Eight. >> The IUPAC name of this compound is by psych, LOW four to 0 octane brackets. >> Four dot two dot 0. >> Close the brackets. Here's what it means. I hope the bi cycle makes sense. >> Touring, I hope the octane makes sense. >> A total of eight carbon atoms in the molecule. What are the four to 0 me? Well, let's think about it this way. The two carbon atoms that I've indicated by making big black dots out of them are obviously the two carbon atoms that are shared by both rings of carbon atoms that are shared by both rings are referred to as the bridgehead carbon atoms. And what the four and the 20 represents is the length of the carbon bridges that connect the bridge hints. In other words, in going from one bridge head to the other, there are three possible pathways we could go. The longest way around 1234. In other words, started for example, this bridgehead go the longest pathway to the other bridge it in the process, you go past 1234 carbon atoms. That's what the four in buy-side glow for 0 octane means. It means those two bridgehead carbons are connected by a four carbon bridge. >> Or we could have gone the second longest path way. That's this two carbon bridge over here. >> That's what the two means. >> And of course, to get from one bridgehead to the next by the shortest possible path way. We could've just gone directly from one to the other by way of a single bond that connects the do. In that context, that single bond is thought of as a 0 carbon bridge. >> That's what the 0 means. >> The terminology makes sense. >> Okay, let's try a couple of other examples. Name this cap bad. First of all, how many total carbon atoms? Like row? >> Let's count carbons just to make sure everybody's on the same page. >> One to bridgeheads first. >> Then as I kept the rest of it, it's 345678. >> So in fact, nine carbon atoms, we buy silos, something, something, something knowing. >> Then all we have to do is figure out the length and the bridges. >> Longest bridge comes first, but numbers are always listed in decreasing order. >> So since the longest rage is a four carbon bridge, we put an A4 second longest branch, two carbons long. >> And the last bridge One cardinal. >> So by psych, LOW 4-to-1 no-name looks reasonable right away. >> You can always kind of double-check yourself on this a little bit because if you've done it right, if you add up the numbers in the box plus two more for the bridgeheads. That should give me the total number of carbon atoms. And the bicyclic system, four plus two plus 0 is six plus due to the bridgeheads is eight octane. Four plus two plus one is seven plus du for the bridgeheads. >> Noting makes sense. >> Let's try this one. >> Yeah, very good. >> Here are the two regions. Longest bridge or carbons long, second longest bridge actually tied for first, also four carbons long. >> Shortest bridge, single bond 0 carbon-rich four plus four plus 0 is eight plus D for the bridgeheads is ten by psych little four, 4-0 following this. Okay, that's the basics for naming system. >> Now let's see what happens when we start putting substituents That's supposed to be a cl. Now before we worry about the substituents, let's name, but by cyclic system, total carbons had we name b by cyclic part of the molecule? >> Yep. >> Okay. It's going to be a bicyclist. >> Something something something no-name? >> Yes. 3331 and no-name. >> Okay. >> Good. >> Three carbon bridge here. Three Garvin Bridge, Year one carbon bridge there. Now obviously the substituents are chlorine, bromine, and iodine. >> But the question is, what's the numbering system? >> Here's the rules for the numbering system. Carbon number one must be a bridgehead. Given that information, which bridgehead would you like to make? Carbon number one. But what were the glory? Not? >> Okay, there's carbon number one. >> Carbon number two has to be next to carbon number one, but you have to lumber the longest bridge first. Now in this case we have a tie, three carbons, three carbons. But which of those three carbon bridges would you like a number? >> First one to the right? >> Because yeah, if we number this 1 first, that we'll put a higher number on the bromine. >> So 234. >> And you keep numbering until you get back to the other Bridget. So in this case, the other bridge head turns out to be number five. Then you number the second longest bridge. Now in this case, it's the same length as the first brave, so we just keep going. >> 678. >> And then finally number, the shortest bridge last night. So to finish off the name, and again, I will not pick nitpick you about alphabetical order. Fluorines are number one, Bromine's number four iodines on number nine. >> So the complete IUPAC name of this compound is one fluorophore, Bravo nine iota by sank lower 3.3.1. >> Nothing makes sense. Well, you could just count the carbon atoms at this point, you can see there's nine of them. Or just if you are numbering it, you could see three carbon bridge three carbon-rich one. Carbon bridge three plus three plus one is seven plus two for the bridgeheads. >> Is mine noting any other questions about this? >> One, it might seem to have a nine in the name someplace, but too bad, that's just how the numbering system works out for this molecule. Let's try this one. >> Now. >> This is one way you will commonly see things like this drawn. >> Let me zoom in on this a little bit and not be obvious, but I mean real tight on this picture because what I'm trying to indicate here is that this bond, one that has the little break in the middle of it is going behind this bond. Is that clear? >> Let me redraw this molecule. A slightly different way, zoomed back out the normal view. Here's an alternative way of drawing the same molecule just viewed from a different perspective. This helps you visualize what's going on. >> That's fine, but let's try naming this one. >> Let's name the by psych LOW part first. >> Then we'll worry about that. Yes, they glow. >> Okay, it takes a little bit staring at, but here's one bridge edge is a two carbon Bridge is a two carbon bridge, one carbon bridge on top by cycle T2, T1 happening maybe a little bit easier to see in the other girl. >> Okay. >> And then finally, the substituents. >> Yeah, 177 trimethyl. >> One of the bridgeheads must be number one. >> That's that one. >> In this case, it really doesn't matter which two carbon bridge we number first. And then it turns out that the one on top is number seven. So three metals, trimethyl, one of them's on number one, the other two on number 7177, trimethyl by psych LOW two-to-one hip thing. Any questions? >> Yeah. >> Sure. The bridgeheads are number one and number four. Same thing in the other drawing. >> Looks like that. >> Here's the same number. >> It 123456 at number seven hours probably isn't going to really help until you go home and build a molecular model named this cop out now named the bi cycle apart. >> And they'll help you with the rest. >> Yeah, well, I say clue three to 0 or the rest of that. >> Ok. >> Now, for numbering purposes, one of the bridgeheads is number one. Number the longest rich first Then the second longest bridge. And in this case, the shortest bridge is just the bonds. >> Don't worry about that, but the OH, is odd number three. >> Now, of course, with the OH there, what functional group is that? And as we saw previously, alcohols have names that end in OL. What's commonly done in situations like that is to tack on the L part at the end, which is what you would normally do with the number right in front of it by psych load. Three have three all this allows you to focus on the bicycle apart and then worry about where the functional group is. Yeah. Well, it's ten, it's pronounced hep teen. >> Pretend that ease there. >> If the worst thing you do is put an e there, that will be the worst spelling error you make in this course lecture. >> Make sense? >> All right, there are plenty of other examples of this in your textbook. For examples, see review Problem 4.9 on page 151, and try some of those others for practice. As we wrap up the first half of class, let me just point out a couple of other acute examples. >> Name this got bad, which really does exist by the way, by saying hello to 1-0 game, if correct, nobody calls it that. >> What people call it for reasons that should be obvious, is housing. There are other interesting, not just by cyclic but try cyclic Tetris, cyclic, poly cyclic variations, some of which I think people have constructed just for the joy of giving them their name. No one tries to name this compound systematically. >> What it's called is windowpane. >> I'm not making any of this up. >> Let me see if I can draw this last one. >> Somebody the enemy. >> This compound has the formula CH each eight and is known as Q Bain. >> Turns out that certain derivatives of q bane are among the most powerful explosives that have ever been developed. So needless to say, the armed forces are interested in Cuba in chemistry. There's a book that I think we still have and the chemistry library. And if not, it's in Morris library. >> The title of the book is the name game >> Which describes how over the course of many years of research, some of the more interesting and complex organic molecules obtain their names. The authors are Alix ne con from Johns Hopkins University and Ernie silver smiths from Morgan State. I'll just say that if you come across this book, it makes fascinating reading. We talk about the systematic ways in which organic molecules get their names. And it's good to know that, but it's also good to know that there's a lot of exceptions out there. Before the rules that became the system that we use were enforce. People were naming compounds after anything they could think those countries, hometowns, wives, girlfriends, possibly both. >> Check it out. >> It makes for a fascinating reading. However, we will only hold you responsible for IUPAC names before your exam on when I say short break, when we come back, we'll spend a little bit more time talking about other things other than just nomenclature. >> Okay. Yeah. Thank you. I was lucky, very good. >> What I'm going to create the water. At that point, I don't care what yes. Firing rhetoric or time, everyone said, yeah, yeah, great. Yeah. >> Okay. >> Give out handouts today. >> One of them was the seating chart for exams. >> Yet what it looks like this, but our trans fats, fatty acid chain, that trend, Why do people care? >> Schramm one they like they can pack closer, so quagmire, OK. >> You're on the right track. >> Not necessarily for the right reason, but that's the point. >> The point is, the argument has been made that the worst thing we ever did to our food supply is incorporate trans fats into it. >> I'll say more later on about where trans fats come from. >> But suffice it to say that one of the reasons cis trans isomer is a matters as far as alkenes are concern has to do with the presence of trans fats and some of the things that we eat. There's a picture over here to give you an idea of what normal fatty acids look like. Cis lake acid is an example of a normal mono unsaturated fat. Mono unsaturated means there's one double bond. >> And the garb Angie and most of the naturally occurring fats that we can sue if they have double bonds in them, have cis double bonds. >> Or the problem is through some of the processing that we put various foodstuffs through. Sometimes they generate some friends double bonds. >> And the problem is trans fats or trans fatty acids don't get metabolized quite as easily by the body as suspects do. >> Similar, they tend to hang around in the bloodstream, clog up your arteries and contribute to heart disease. Read the article for complete rundown. >> But I think at this point most people know what trans fats are. The answer >> Things that are bad for you. >> But the reason they're called that is because they have a trans double bond. >> So cis-trans isomorphism does matter, not just for that. >> There's a lot of other biologically important reasons as well. >> I'll say more about. Alright, at this point we're up to about Section 4.7 in your textbook, physical properties about Keynes and psycho alkanes. >> We've already talked about these to some extent, but let me just refresh your memory a little bit. >> As we said before, when organic chemists talk about the physical properties of the compounds they're working with. >> Their talking mostly about things like melting points and boiling points, water solubility, solubility, and other solvents, things like that. >> Turns out methane, ethane, propane, and butane are all gases under normal circumstances. Painting is the first of the straight chain hydrocarbons or unbranched hydrocarbons. >> That is a liquid with a boiling point of about 36 degrees Celsius. There's a diagram on page 155 that you can use to look at the boiling points of the unbranched alkanes, you can see that it goes up not quite linearly, but at least there's a reasonable pattern here. >> In general, as you add one more carbon atom to the chain, the boiling point goes up by about 30 degrees. Pentane boils at about 36 degrees. >> Hexane boils at about 67 degrees, obtained boils at about 98 degrees and so on. >> And then as we get above 20 carbon atoms, they become kind of waxy solids that you're familiar with. >> Paraffin wax, that's basically what paraffin wax, it long hydrocarbons, By the way, the physical properties of the alkenes and the alkyne are very similar to the physical properties of the alkanes, where they mostly differ is in their chemical properties. >> That I'll say a lot more about that a little bit later on in the course. >> And as we mentioned before, branching of the carbon chain tends to lower the boiling point. Earlier we looked at the three different isomers of C five H 12 pentane boils at about 36 degrees ISO pentane or two methyl butane about 28 degrees neo pentane or T2 to enough of propane, about ten degrees. This all has to do with the increased surface area with a more elongated molecule. Therefore, there's a greater chance for contact between molecules, which is what allows the London are van der Waals forces between them to interact well, the more branch to more spherical molecules can only touch at 1. Therefore, the attractive forces weaker, which means the boiling point is lower. >> And of course, hydrocarbons are not soluble in water, or anybody who thinks they are is invited to go take a look at the Gulf of Mexico, but we'll see if we can solve that problem at some future time. >> And cyclic alkanes are similar to the alkanes. >> If you want to look at some of the physical constants for psych well, alkanes. See Table 4.4 on page 156, labor textbook. >> Now a big part of the rest of what Chapter four is all about in your textbook has to do with different conformations of alkenes. And I think the easiest way to show you what I mean by that is by looking at a model. So I'm going to dredge up my little model of ethane again. >> You look at it sitting up here on the tabletop like this, or I can just turn it in slightly different perspective. Let me see if I can get this lined up well with the camera. Okay, something like that. >> Now here's the thing. >> Sp3 hybridized carbon atom. Sp3 hybridized carbon atom. >> The sigma bond between the two is formed by an sp3 orbital from this carbon atom overlapping with an sp3 orbital, this carbonate, but they overlap in an end-to-end fashion. >> When I use my fingers to try to show you this, it's something like this. But the point is I can rotate my fingers relative to each other without causing them to stop overlapping. >> Same thing with the orbitals that make up the sigma bond. >> I can rotate one carbon atom with respect to the other. >> And it doesn't change the fact that we still have the overlap between the orbitals here. >> That bond remains intact. >> But as I rotate one carbon atom with respect to the other, I get a slightly different arrangement of all the other bots. >> In other words, if I hold this model like this and then just rotate this front carbon atom. Just asked a little bit with respect to the back carbon atom. >> Now I have a different conformation of ethane. And if I rotate it a few more degrees, I have it's still different conformation and another, and another and another in essence, since I can freely rotate 360 degrees around its single bond, there is an infinite number of different conformations of this molecule that exist. That's what we mean by different conformations of alkenes, different arrangements of the atoms in three-dimensional space that can be converted one to the other simply by rotating around single bonds And the magic word here is single bonds, because it is not possible to rotate freely around double bonds. >> Because a double bond consists of a single bond and a pi bond. >> You try rotating around a pi bond, you will break the pi bond. >> That's what contributes to the formation of cis and trans isomers. >> But without canes are only going to do is worry about single bonds, which are sigma bonds. >> By definition, there's no problem with rotating one with respect to the other. >> Now, big part of what we're doing for the rest of chapter four, simply showing you how we can draw pictures of the different conformations. >> Obviously, if you really want to see what these things look like in three dimensions, I would strongly encourage you to get out your molecular model kit, built molecular models that look something like this and visualize the thing in three-dimensions. >> But when you lecture textbook, you have two-dimensional pictures to look at there. >> And there are a few little tricks that organic chemists like to play to try to impart to you the three-dimensional nature of the molecules using our two-dimensional surface. >> Some of those little tricks are shown on page 157 and what are called Newman projections and saw horse formulas. >> Let me just describe what is meant by these things. >> And again, I encourage you to think about what the molecule really looks like in three-dimensions as I tried to show you these pictures. >> But let me start by drawing a couple of pictures now. >> One formulation that I already described, He's using the wedges in the dotted line. >> The idea being that the wedge shaped bonds that look like this or like this, or bonds coming out of the plane of the page or out of the plane of the blackboard, or out of the plane of the textbook toward you. >> The dotted lines are bonds that are receding into the plane of the blackboard or into the plane of the page away from you. So if I hold the model like this and do the best I can on screen to get this looking sort of like the picture I just drew. >> The two bonds that I'm indicating that my fingers right now are the regular lines, the ones that are in the plane of the page. These two are the ones that are out toward, you might be hard to see on the left-hand side, it'll bother out toward you. >> And then the other bonds down here are the ones that are away from U. >> Dotted lines make sense? Ok? >> That's one way of representing this picture. >> Now if we simply turn this a little bit and look at it from a slightly different perspective. >> Let me call this the witch dot drawing because it uses wedges and dotted lines to try to show you the three-dimensional nature of the molecule. >> Let me draw something that looks a little bit different just because it's viewed from a different perspective. >> This is the so-called saw horse projection or saw horse formless. It basically just takes that wedge dot growing, which looks something like this, and turns it a little bit, kind of turned it upside down when I drew it. >> So let me just hold it. That's going to make this look that much like the growing as possible. >> While we're not going to work best I can do something like that. >> My hand gets in the way. But I think you get the idea. >> Is it clear that the two pictures and the model pretty much represent the same thing. Okay, again, all we're trying to do is just draw pictures that represent what the model looks like in three dimensions. And then if we turn it still more so that now we're looking down the carbon-carbon bond that it's maybe hard to see on camera, but carbon atom here where my pen is. And then there's another carbon atom down here. >> It's hard to see because we're looking down. >> The carbon-carbon bond by pinpoint, is now moving along the carbon-carbon bond that we're looking down, the picture that is commonly used is something that looks sort of like this. >> And this is referred to as a Newman Projection after a chemist by the name of Neumann at Ohio State University who first proposed that this would be a good way to represent the three-dimensional nature of the molecule. >> Now here's the point Newman projections by definition mean that you are looking down a carbon-carbon bond. >> The circle in the Newman projection represents the front carbon atom, the one that's closest to you. As you're looking down the carbon-carbon bond, the lines that go all the way to the middle of the Newman projection represent the bonds attached to that carbon atom, which in my model is this bond, this bond, this bond. The lines that stop at the perimeter of the circle represent the bonds going to the back carbon atom, which is down here someplace. That's probably gonna be hard for you to see on screen. But that's sort of the point that back carbon atom is behind the front carbon atom. >> And you can't see it all that well. >> And really, if this was a completely correctly draw, a Newman projection, you shouldn't see those back bonds at all because they'd be covered up by the front ball. >> But we're doing the best we can to show you all the atoms that are present in the molecule. >> So the point is, these three pictures represent the same conformation of ethane, just drawn in different ways. Is it clear that all three of those pictures are trying to represent the same conformation of ethane. Don't take my word for any of this. >> Go home, get out your molecular model kit built models. >> Convince yourself that this is true. >> These three pictures represent what is commonly called the eclipsed conformation for butane. If you think about what happens during an eclipse, like, let's say a solar eclipse, for example. That means from our perspective, the moon appears to move between the Earth and the Sun. So if you look at the sun, you're actually seeing the moon. Same principle here. If you try to look at the back hydrogen atoms, The problem is you can't really see them because the front hydrogen atoms are getting in the way and the bonds in front, or covering up the bonds in back. >> That's what we mean by an eclipsed conformation in that regard. >> Now what I'm gonna do is rotate one carbon atom 60 degrees with respect to the other. >> If I do get something that looks like this, and let me draw the corresponding pictures for this conformation. Ok, I hope I can make this more obvious from the model, but let's see if we can make this look good on camera. >> It would be hard because my n going to keep getting in the way. But there's more or less, the wedge dot drawing actually should rotate at about 60 degrees to make it look more like what I actually grew, which is right here. >> Here's the saw horse form are the same thing on turn it, so it looks like my drawing source structure. >> And then finally, here's the Neumann picture looking down the bond. And if you want to think of this as sort of being like the face of a clock. The lines that go all the way to the middle, representing the front carbon-hydrogen bonds, sort of like a twelv 48 on the face of the clock, the lines, it stop at the perimeter representing the back carbon-hydrogen bonds to 610 on the face of the clock again, is it clear that all three of these pictures and this model represent the same thing. >> Again, my camera work is not that great, but build models and convince yourself that these things are true. >> This is referred to as a staggered conformation. And the best example I can give you here is to think about what happens during the Olympics. Say for example, when athletes are running around an oval racetrack. Here's your oval racetrack. >> What say the finish line is right about there. >> Suppose the athletes in question are running the 200 meter race. The Standard Track is 400 meters, so they're doing half a lap around the track, which means the starting line is over here somewhere. >> Well, if you lined up all the athletes behind the starting line and you made everybody running their own lanes, that obviously the people on the outside lanes will be at a disadvantage. >> They'd be running a greater distance inside weight. That's why typically for a race like that, you tend to move the athletes and the outer wanes farther up the track so that everybody runs the same distance. That's called a staggered start. >> Big the people in the outer leans up from the people in the inner lanes so that everybody runs the same distance. Likewise, compared with the eclipsed conformation that we showed you a few moments ago. >> If we rotate 60, now we move to front carbons or hydrogens with respect to the back hydrogen. >> That's why it's called a staggered conformation. >> Now these are two limiting cases. >> Like we said a few moments ago, there's an infinite number of different conformations. If I rotate one degree from the staggered conformation, I have a different conformation which is not quite steady. >> Staggered. >> The intermediate conformations are called skew confirmations, SK, UW. But let's just focus on the eclipsed staggered conformations for a few moments and think about something we talked about last week that again, you hopefully heard for the first time in your general chemistry class. >> And that is valence shell electron pair repulsion, or VSEPR theory. >> The idea being that pairs of electrons of all kinds need a lone pairs or covalent bonds should try to get as far apart from each other as they possibly can. >> Compare the eclipse then staggered conformations and tell me in which of those cases is VSEPR theory being obeyed most closely? >> Yeah, I hope it's obvious that the carbon-hydrogen bonds are farther apart from each other and the staggered conformation than they are the eclipsed conformation. >> And that being the case, the staggered conformation turns out to be the most stable conformation for ethane. >> By most stable, we mean lowest in potential energy. >> In general, if you get things that repel each other farther apart, that minimizes the potential energy the repel each other in this case, for the electrons and the covalent bonds. >> So the point is, in any given sample of ethane, you'll find some molecules. >> And the eclipsed conformation, you'll find some molecules in various skew confirmations, but the majority of the molecules will be in the staggered conformation because that's the confirmation that minimizes the potential energy constant. >> Makes sense. >> Ok? >> Now this concept wouldn't be worth much if the only kind of molecule we can apply it to was f-ing. >> But let me just take my model of ethane and take a little red ball here that's going to represent a methyl group. >> Pop off one of the hydrogen atoms, put a methyl group at a place. Now I have propane, and I can draw the corresponding picture for propane. In fact, really on my original pictures, all I have to do, draw the corresponding picture for propane is just change one hydrogen to a methyl group in each of these pictures. >> So my dealings though, I've just drawn the corresponding pictures for programs. >> And in principle, you could do this for any outcome. If I take the original model and pop off a hydrogen atom at each end and replace it with a methyl group. >> Now I have butane. >> Although actually now it gets a little bit more interesting just thinking about Newman projections for a moment. >> And let me just quote the model up here. >> Here is one possible eclipsed conformation for butane. But if I rotate one carbon atom a 120 degrees with respect to the other carbon atom, I get another eclipsed conformation. >> If I turn it this way, it might be a little more obvious. I hope it's obvious that it's not the same as the first eclipsed conformation that I had up there, because the positioning of the two red balls is a little bit different. >> Likewise, here is one possible staggered conformation for butane. But if I rotate one carbon atom is 60 degrees with respect to the other. I now have a different staggered conformation for butane. >> Again, different in terms of the relative positioning of the two methyl groups region. >> Let me just take a moment and draw a picture, actually draw four pictures of those different conformations of butane. >> And for ease of reference, I'm going to label these a, B, C, and D. >> So just to show you this one more time on the model, here's confirmation. A rotate the back carbon atom a 120 degrees Now I have confirmation BY rotate the back carbon atom 60 degrees. >> Now I have confirmation, see it doing the best I can to get it on camera and then rotate again a 120 degrees. >> Now I have confirmation, big hope it's clear what the pictures are trying to show, what the model looks like. >> Which of the four conformations, ABC or D, represents the most stable conformation of butane. >> And why? >> Yeah, because one reason is the two methyls are farthest apart. >> The other reason is, is D an eclipsed or staggered conformation stagger? >> Yeah, turns out both C and D are staggered conformations, whereas a and B are eclipsed conformations. >> So D turns out to be the most stable conformation. >> Which of the others, a, B, or C, represents the least stable conformation for beating a because and yet being eclipsed forces the bonds closer together and as the two metals closer together as one. >> And then between B and C, Which one is more stable? >> See, any staggered conformation is more stable than any eclipsed conformation. Because staggered conformations get the bonds farther apart, which is more consistent with VSEPR theory. The order stability is this for what it's worth confirmation. D is called the anti conformation for butane because the methyl groups are anti or opposite to each other. See is sometimes called the Ghosh confirmation for butane, which is just a word that means the other staggered conformation, but not the most stable version. Now one thing your textbook does, this shows you energy diagrams like this. >> This is on page 159, shows you that when we say one conformation is more stable than another, what we mean is that it's at a lower potential energy than the other potential energy on the y axis here. Here's ethane, showing you the staggered conformation is more stable, lower potential energy than the eclipsed conformation. >> And here's the corresponding sequence of pictures for butane, page 161. >> Here's D, the most stable conformation, the anti conformation. >> Here are two possible, gosh, conformations which are only slightly higher in energy. And then the various eclipsed conformations, including confirmation a, the least stable are up there at relatively high potential energies. One thing I will caution you about right now, section 4.9 a, for the time being at least, and maybe forever ignore all references to conformational stereo isomers. >> I'll say more later on about why I think you should do that for the time being. I'll just say that I think this discussion only creates more confusion than it solves. >> So stay away from section 4.98 and use pictures like this as visual aids if they helping you see what's going on in terms of one conformation being more stable than another. But here's another way of thinking about all of this. >> And it's discussed beginning in Section 4.10, which talks about the relative stabilities of cyclic alkanes. >> There's a discussion on page 162 of the different kinds of strain inorganic molecules. >> And let me just summarize this by saying that there are three kinds of molecular string. >> And the point is, if you can minimize strain or a molecule, that's another way of saying that that molecule is relatively stable. >> Molecules that have a lot of strain not quite so stable. >> The three kinds of strain referred to as torsional strain, steric strain, and angle string. >> And here's what they mean. Torsional strain is what happens when covalent bonds are forced to close together. A few moments ago, we said that any staggered conformation is more stable than any eclipsed conformation. The reason that's true is that for the most part, staggered conformations minimize torsional strain because the bonds are as far apart from each other as they possibly can be. By definition, eclipsed conformations forced the bonds closer together, therefore creating a repulsion between those bonds. >> That's what we mean by torsional strain. >> The reason any staggered conformation is more stable than any eclipse conformation. >> Staggered conformations minimize torsional strain. >> Steric strain is what happens when atoms get too close together. The atoms themselves, of course, consist of a nucleus of the atom is surrounded by a cloud of electrons. >> And if those clouds of electrons start bumping into each other, that's not good because those electrons want to repel each other. A few moments ago, you told me confirmation a was the least stable conformation of butane, and that's correct. >> Well, let me just show you something on the models. >> I turn the model like this. I hope you can see that if I hold it like this, I hope it's obvious that that's confirmation. A laid down like this will like the wedge dot form. >> Now I use the little red balls to represent the methyl groups just to make it easier to visualize the confirmation. >> But at this point, let me replace those red balls with some of these black things that actually represent sp3 hybridized carbon atoms. Because I want to show you something. >> And by the way, if you have a molecular model kit like this and you're having trouble working with it, come see me and we'll show you how to use the molecular molecule. But the point is, here's the same molecule in confirmation a, but with a methyl groups fully in place. >> And let me go ahead and put couple of hydrogen atoms on here, representing the hydrogen atoms in methane, or excuse me, in beating. >> And the point is, if you put the molecule and confirmation a, then these two hydrogen atoms are actually pretty close to each other. >> In fact, the model is a little bit misleading. They actually do kind of bang into each other a little bit. >> Steric strain atoms bumping into each other may not be immediately obvious when you draw it like this, where you draw it as CH3CH2OH, CH2, CH3. But those hydrogen atoms are bumping into each other in that conformation. >> But that's what's going on. >> So confirmation a is the least stable conformation for two reasons. It suffers from torsional strain because the bonds are too close together. And it also suffers from steric strain because those Talia and hydrogen atoms are actually a lot closer together than they walk. >> Concepts make sense so far. >> The third kind of strain, angle. >> Strain comes about in situations where the bond angles in molecules become distorted from what you would expect them to be based on the hybridizations of the atoms. >> That question, this is usually not a big deal for regular alkanes, but does become a bit of a problem. >> We're psycho alkanes, especially those that have relatively small rings. >> And to emphasize the point, Let's talk about the smallest ring, which is of course cyclopropane. >> Now, earlier when we showed you what cyclopropane looked like, a picture that looks something like this. And penciled in the hydrogen atom is, but I'm going to pencil in the hydrogen atoms and a little bit more detail right here. >> And I think you'll see why in a few moments. Now, of course, the other way we can represent cyclopropane in bond line notation. >> It just by drawing a triangle. >> And that's fine. >> But the point is in alkanes, the carbon atoms are all sp3 hybridized. What bond angles do you normally associate with sp3 hybridized atoms? About a 109 degree angles. On the other hand, from your high school geometry course, if we assume that the three carbon, carbon bonds in cyclopropane are all the same length. Then what we have here, these three carbon atoms located at the corners of an equilateral triangle. What's the measure in degrees of the interior angle of an equilateral triangle, 60 degrees. >> That's angle. >> Sprayed molecule wants to have a 190 degree bond angles. What is constrained by the laws of geometry to have 60 degree bond angles. >> Now in reality, cyclopropane does, to try to compensate for that is create sigma bonds that are maybe not quite as strong as other normal sigma bonds. >> Normally in a sigma bond or the orbitals overlap end-to-end rate between the atoms in question. >> But in cyclopropane, neither are the sp3 hybrid orbitals from the carbon atoms where they actually tend to overlap is sort of outside the lines a little bit. >> This is sometimes referred to as bent bonds because the overlap is not occurring directly between the atoms. And perhaps not too surprisingly, isn't there's not quite as much overlap there. >> Those bonds are not quite as strong as normal sigma bonds. >> Ok, let's cyclopropane does the best it can to compensate for the angle strain problem. >> Is this another problem? >> We figured out what it is. >> What's the other kind of strain that we have in cyclopropane. >> Yeah, for torsional strain. >> If you build a model of this thing, which I really can't, because if I tried to do with my models, I break them. >> But it turns out these two hydrogens right here are eclipsing each other and the two that are away from you or eclipsing each other. And these two are eclipsing each other and so on. >> As you look down the carbon-carbon bonds and cyclopropane, there's a lot of torsional strain there, and there is absolutely nothing that cyclopropane can do about that. >> It therefore should not come as a huge surprise to find that cyclopropane is the most strained of the cycle out games it as both angle strain and torsional spring. >> Things get somewhat better as we go to cycler butane for starters, even if we assume that all four carbon atoms, encyclopedia butane lie in the same plane corners of a square. >> Now, what's the angle in degrees for a square? >> Everybody 90 degrees of course. Now right away, that's less of an angle screen problem than cyclopropane had. 60 degrees versus a 109 degrees is 49 degrees worth of angle strain 90 versus a 109 is only 19 degrees worth of ankles, right? So angle strain is less of a problem. >> But what the problem really is, and let me see if I can put a model together real quick without damaging the model all that much. >> I can build cycle abusing without too much difficulty. Years looks like. >> What do you think looks like if you look down this carbon-carbon bond over here, I think it becomes more obvious that those carbon-hydrogen bonds are eclipsing each other. So the problem is, if you have the four carbon atoms lying flat, you eat a lot more torsional strain right here. >> What's cyclical butane has something that it can do about that. >> That cyclopropane doesn't have. The laws of geometry dictate that any three points must lie in one plane. >> So the three carbon atoms in cyclopropane must lie in the same plane. >> They have no choice. >> There is no corresponding law geometry that says that four points must lie in one plane. So there's no law that says the four carbon atoms encyclopedia, I'll have to lie in the same plane. >> And in fact, they don't, I don't know how well I'm going to be able to do this on the camera, but let me just hold the model. >> Something like this might be that the best I'm going to do, what I'm gonna do is twisted this model a little bit. >> Remember, all this really constitutes is rotating around carbon-carbon single bonds. >> So here's about the best I can do. Now, let's look down that seen carbon-carbon bond we're looking at a few moments ago. >> And I'll try to get my hand out of the way as best I can. The model in place that's probably isn't going to be the best picture that do the best we can. Carbon-hydrogen bonds more like staggered or more like eclipsed. >> Yeah, I'm not doing a good job showing you this model. Let me see if I can do it any better on this other corpora. >> Let's try it over here about now as you look down the carbon-carbon bond, yeah, that's better. >> It's not perfectly staggered, but suffice it to say that in this twisted or pucker geometry, the carbon-hydrogen bonds are a lot farther apart than they would be if all four carbon atoms relying in the same plane. So it turns out the site little butane can actually minimize the torsional strain between the carbon-hydrogen bonds by adopting a pucker geometry that looks something like this. There's a better picture of it on page 163 in your textbook. But the point is this pucker geometry for psych well, butane is sometimes referred to as the butterfly conformation because it reminded somebody of a butterfly flapping its wings. >> It's a little imagination, but let's consider site. Well, pentane for a few moments that you may know offhand what the measure in degrees is of the interior angle equilateral pentagon. >> Just thought I'd ask, that's not one of the big ones they hammer on a geometry class, but it turns out to be a 108 degrees. >> Now that means that by the time we'd gotten to this point, angle strain pretty much disappears. Alternate versus a 109. There's hardly any ankle sprain their belt. But again, this assumes that all five carbon atoms lie in the same plane. And if they do, you're going to have some torsional spring problems. >> Let me just slap this model together real quick here. >> Cycle of painting. >> And it'll be put all five carbon atoms in the same plane. >> And if you look down the bond where I have the blue and the white to the green and the red balls, we can see that they kind of overlap each other. >> There's a lot of torsional strain there. >> But again, we can combat this problem because there's nothing that says that all five carbon atoms have to lie in the same plane. >> So the molecule can twist itself a little bit to get into a different conformation. >> And in a different conformation, you can see that these bonds are a lot farther apart than they were somewhat closer to being staggered, which minimizes torsional spring. >> And again, there's a picture of what this looks like in your textbook. >> Again on page 163. >> Picture looks something like this. Better picture, top of page 163. >> Better still, go home and build models of it and see what it looks like. >> But this is sometimes called the envelope confirmation because it looks sort of like an envelope with its flaps sticking up. You do know what an envelope is, right? >> Everybody sends email these days. Just want to make sure you let me see pictures of the envelopes on your street. Just wanna make sure those are non-polar bits. Ok, moral story is the reason molecules like cycler, butane, and pentane adopt these pucker conformations is to minimize the torsional strain. >> Between the carbon-hydrogen bonds. Since we're almost out of time for today, let me just say this about what's coming next time. The bulk of the rest of chapter four talks about the different conformations of cyclohexane. >> And part of the reason we spend as much time as we do talking about cyclohexane, is that it turns out that cyclohexane is actually the most stable, that is to say the least strain of the small cycle allow kings. >> By small psych, LOW alkanes, I mean those with fewer than ten carbon atoms are, it turns out it's even more stable than cyclohexane. It's like little octane, if not necessarily the case that the bigger the ring is less strained it, part of the reason for that is that again, by adopting a twisted or pucker geometry, cyclohexane can almost perfectly stagger. It's carbon-hydrogen bonds and can get into a geometry that pretty much minimizes back, pretty much eliminates torsional strain. That confirmation is, call it the chair conformation. But we'll say more about the chair conformation and the boat conformation at some of the ramifications of the different conformations of cyclohexane. We'll stop here for today. Now remember what the schedule is for tomorrow. We're going to get started a little bit early at four o'clock is Weidner law will be here to demonstrate wildly plus 430. >> Class begins like usual. >> And when I'm done yammering, actually at the tail end, the class will be for whatever questions you have about your exam coming up on Wednesday. St. >> John on me because I was actually very interested in is constantly getting around here because I get yourself on a plane and he gives you think, you know, much like really just watch the night graduate work. I, I mean, I know that sounds like you really appreciate that many attacks are eating a theta may or may not be close if you'd like to find out plenty to cover sport if they feel they really want you to do to build your model. Thinking, I think shrink up here. Well, you saw, I hope I said, would it be okay if you get 5.5? >> So instead of two hours, you get 34 >> Would you be willing to meet me at my office and say 20-30 days just because I think it'll be a lot easier than having to do a lot of problems. We can make it that. >> Just shoot the DSS Phillips an email. >> Just tell them to play by Chapters one through four saying it ain't. And Plato gave me every, every, everything we did here. Also, you get the practise it if I take out the practice exam. But the point is all of the stuff that we're talking about today, she'll be able to go upstairs as well in the chemistry library reserves day and night the dish. >> So that's the previous edition of this textbook. >> Coverage is pretty much the same thing might be a better answer. >> Russia that torsion. Okay, I could do it easiest on a model. >> Let's get a little feeling. >> In this conformation. >> You see how this bond overlaps this bump. >> That's torsional stress, okay? If you rotate to a different conformation. >> Now the bonds are about as far apart as they can be that minimize the torsional strain. >> Definition of torsional strain is the electrons in this bond are too close to the electrons in this bond. >> The electrons tend to repel each other. >> So in this conformation, they're farther than that, are different than the atoms. >> Yeah, well, the word torsional strain has nothing to do with, say, the hydrogen atom. And the hydrogen atom, it has to do with the bonds and the other one, okay, steric strain, the atoms getting too close together. >> Then I hope it's obvious what angle scrapings, right? >> Okay. Is everything that we're doing tomorrow awesome? >> I'm an exam or does it end? Well? Probably. >> It depends on how long it takes us to do things tomorrow. >> But yes, there are some things in chapter four I haven't got to yet. >> So certainly some of what we do tomorrow, possibly all of it will be on the exam, but again, I'm only gonna be talking for about an hour tomorrow. >> They're going to save the last hour for whatever questions you have, okay? >> Okay. >> Fine. >> If you get the practice exam. >> I got the practice exam once their handouts for Thursday and see what I can do about the bottom line. >> Go through well, tell you what that's a question that you addressed. >> Mm-hm. Yes. Yeah.
Lecture from Jun 14, 2010
From Dana Chatellier March 03, 2020
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