Okay gang, welcome back. This is part two of chapter three in the Smith textbook where we're talking about functional groups. When we ended the last set of slides, I gave you this list of really interesting naturally occurring, some of them naturally occurring, some are synthetic molecules, but they all have interesting biological activity. So for example, we have dopamine, which is a neurotransmitter.
We have xylitol, which is an artificial sweetener. Morphine, which is a naturally occurring opioid. Codeine is a modified version. We've just put on a methyl group.
That's what that CH3 is on that OH. We've got heroin, which is a derivative of morphine. Propofol, we've talked about before, is this anesthetic that, you know, Michael Jackson used to take, he used to call it his milk.
It is, to get this into you, it's very hydrophobic, and you have to make an emulsion of it with some emulsifiers that are white, and it just basically looks like milk. It literally does. The emulsification does.
The compound itself, it does not look like milk. Anyway, aspirin, acetaminophen, benzocaine. If you have any dentists out there, you'll use this DEET insect repellent.
repellent, ibuprofen, painkiller, right? I can never keep straight, which Tylenol, Advil, which I think Advil is acetaminophen, and I think Tylenol is ibuprofen. Maybe I've got it backwards. I can never remember that, but anyway.
Prozac, methadone, vanillin gives rise to the smell of vanilla, the taste of vanilla. That's because that's in vanilla. That's what vanilla is. Penicillin. cyclic lactam, silica gamut, benzaldehyde, smells an awful lot like almonds because almonds have benzaldehyde in them.
This guy, 2-butene-1-thiol, 3-methyl-1-butane-thiol, these guys are found in skunk scent. I think this one may be in there as well. Diethyl sulfide, diethyl sulfide for Gold plating, testosterone, the hormone that gives rise to male secondary characteristics.
Estrogen gives rise to female secondary characteristics. Ethinyl estradiol, a component of the birth control pill, tricks the female reproductive system into thinking it's pregnant. So you don't ovulate when you're taking this stuff.
Stop, stop, stop. stop taking it then um yeah you just you go on with your menstrual cycle um progesterone um there's another hormone uh this is aspartame uh found in um nutra sweet and i can't see this because of my zoom things covering it so maybe i can move that can i move that yes dodecanoic acid all right cool Alrighty, let's take a look at functional groups. And I'm going to use this pointer.
It's going to be easier, I think, with this pointer. Hopefully the laser, this doesn't go, sometimes this falls asleep kind of when I'm not moving it. Okay, this is a primary amine.
Okay, that's an alcohol. That's an alcohol. Here is an alcohol.
There is an alcohol. There is an alcohol. There is an alcohol.
There is an alcohol. There's a special kind of alcohol called a phenol. I'm not going to hold you to that.
I'll accept you just circling this in exam type setting, call that an alcohol. And later on in 352, we'll worry about the fact that that whole thing is a phenol. Here's an alcohol, a little bit different than that one, because we don't have three alternating rings.
This is a benzene or aromatic hydrocarbon, okay, for our purposes now. Here is an ether, an ROR sandwich. The oxygen is the meat, okay? This is an amine. We have NCH2CH.
Okay. So we have NRRR, three different R groups on that nitrogen makes that a tertiary amine. Okay.
We have a carbon-carbon double bond. We call that an alkenes. Again, we see it again, alkenes, alcohol, ether, ROR, aromatic ether, ROR. I'm not going to ask you to distinguish that as an aromatic ether, but that piece would...
be considered an ether. This would be an aromatic hydrocarbon. This is an amine.
Here is an ester. R, carbonyl O-R prime, okay? There's your R prime group, so that is an ester. Okay, here's another ester, R, carbonyl O-R prime.
Okay, there's your ester. That has two esters in it. We have an alkene, there's the alkene.
Here is an ether, R-O-R, okay? And we have a tertiary amine, R, R prime, R triple prime. This is, we're going to call this an alcohol.
right there and aromatic hydrocarbon, but technically together the two are a phenol. Okay. And I'm not going to pit those two against each other. Okay.
Aspirin, carboxylic acid right there, R-C-double-dun-do-O-H. Here's an ester, R-carbonyl-O-R-prime. Okay. Aromatic hydrocarbon, O-H, technically altogether, this is called a phenol. P-H-E-N-O-L, phenol or phenol.
Okay, right here we have an amide. We have R, carbonyl, N, R prime, and an H. That whole schmear there, that's an amide.
Okay, so acetaminophen is an amide and a phenol, or you can consider that just an aromatic alcohol. Benzocaine, here you have an aromatic amine. NH2 bound to an R group, that's an amine.
primary amine. This is an aromatic hydrocarbon, or you could call it a benzene derivative. A carbonyl, so an R group, carbonyl, O, R prime, that is an ester.
Okay, so I'd circle that piece there as an ester. That piece is an amine. That piece is an aromatic hydrocarbon. Aromatic hydrocarbon, okay, we don't worry about the alkyl groups. We're not going to consider them a functional group, okay?
Although they are, we're going to ignore them because there's just too dang many of them. So we're going to ignore them, okay, for now. All right. R, carbonyl, N, R, R prime.
That is an amine, excuse me, an amide, okay. R, carbonyl, N, R, R prime. That is an amide, okay.
Aromatic hydrocarbon, carboxylic acid, okay. We have R. carbonyl OH.
That's the telltale sign of A. So technically it would be, you know, where do you stop drawing the R group? Could you have the R group go clear out there?
Yeah, sure. Okay. But what you're looking for is something attached to the carbonyl, attached to the OH. Okay. So that is a carboxylic acid.
This is a secondary amine. We have an NH, an R, and an R prime. This piece here is an ether, ROR.
Okay. That's an ether. Here's an aromatic hydrocarbon.
Aromatic hydrocarbon. If you wanted to call that a fluoroalkane or a haloalkane, that would be okay. Technically, I guess it depends on what.
If you have a multiple-choice exam and it's offered as one of the options, go for it as a haloalkane. This has a ketone in it, carbonyl R, R prime. two aromatic hydrocarbons.
Here's one aromatic hydrocarbon. There's the other. This nitrogen is an amine.
We have R group, R group, R group. So it's a tertiary amine. Here we have an aldehyde. Here's your R group attached to carbonyl and an H. There's an aromatic hydrocarbon, carbonyl attached to an H.
Okay. So this is an aldehyde. Yeah. That would be the aldehyde right there. Okay.
And this would be the aromatic hydrocarbon. We also have an ether. Okay, R-O-R, so there's an ether right there, and there's an alcohol. So bottom line is that you can have multiple functional groups within the same molecule.
Okay, many of these, most of these have more than one functional group. Okay, all right, here we have an amide. Okay, carbonyl N-R-N-R-N-R here to attach the carbonyl. This also is an amide, R-carbonyl-N-R.
So there's an amide, there's an amide. This piece right here is basically a sulfide, okay? Right? That is a sulfide, RSR, the sulfur sandwich, okay?
Or sometimes people call it a thioether. This piece here is a carboxylic acid, R-C-L-O-O-H. That's a carboxylic acid.
It is not an amide. That nitrogen must be attached to the carbonyl for this piece to be an amide. Okay, the difference is that we have a...
non-nitrogen thing sandwiched in between the carbonyl and that nitrogen so this is not an amide right there this piece here is not an amide that one is okay So take a look at the amide and verify how that's an amide and this piece is not. Benzaldehyde, you have the aldehyde functional group and the aromatic hydrocarbon. Two butene, one thiol, you have a thiol functional group and an alkene.
Thiol, and we'll just leave it at that, but technically that's an alkane. But if we circle all the alkanes, we're going to be circling everything, so don't worry about it. The alkane is kind of an entry-level organic molecule.
We're going to kind of ignore it for now in this kind of an exercise. All right, aromatic hydrocarbon. Aromatic hydrocarbon with the nitrogen in the ring, that's a special kind of amine. It's called a nitrogen-containing heterocycle. We won't worry about that for right now, but that's coming.
So, again, this is a very complicated topic. We'll get the gist of it as we move on, and you'll become more and more familiar with these, where you just look at these and you go, oh, that's what that is. All right, this is a sulfide, as is this. This one's used in gold plating, apparently. Testosterone has a ketone, RR carbonyl.
It's a ketone. Alkene and an alcohol. We're not going to call the rest of this stuff an alkane because it just clutters things. Think of all these other functional groups as being built on alkane.
So alkane is the introductory class of molecules and the basic, right? And everything else you modify and build on that. So for that purpose, we're not generally going to use an alkane as its own standalone functional group, although it technically is.
All right, aromatic hydrocarbon, alcohol, alcohol, aromatic hydrocarbon, alcohol, alcohol. alkyne is the only one we've gotten alkyne in you don't tend to see alkynes a lot in nature in fact this is not a natural compound this is synthetic and man-made and uh it's made a lot of people very wealthy because it um is effective it's a it's an effective contraceptive is what it is and it's sold it's been uh i'm not gonna say tons of it actually i don't know the actual quantity but tons probably isn't too off i mean there's probably literally been you metric tons of this stuff sold and a lot of money made off of it. Progesterone is very similar to testosterone, but again, it has a ketone here, an alkene, and another ketone, R, carbonyl R.
Aspartame or NutraSweet is an amide. We have an amide right there. Out here, we have a carboxylic acid. That piece right there is carboxylic acid. This is...
an amine, a primary amine. This piece here is an ester, okay, and this piece here is an aromatic hydrocarbon. Last but not least, dodecanoic acid.
100% certain why I chose that. It is a fatty acid, and one of the acids is found in fat molecules, as you might guess from the name, fatty acid, and it has a carboxylic acid in it, and technically that is an alkyl. alkyl group or an alkane, but again, I said, let's not circle the alkyl groups.
Okay. All right. I think a key is coming up, but before we get to that, here is an iClicker question for you that you can do on your own. Go ahead and pause this and classify the functional group A, B, and C. Okay.
This is dopamine, a neurotransmitter. Okay. So what is A? A is an alcohol.
It's a special kind of alcohol called a phenol, but I'm not giving you a phenol as an option here. Okay. So don't choke and say, well, there's no phenol there. Technically you can, phenol is a special kind of alcohol.
And so if you don't see phenol offered as a choice, don't, don't go for it. Okay. So what the most close thing you can call this as an alcohol.
So A is an alcohol. B is an aromatic hydrocarbon. Okay. So that would be.
aromatic. And C, that is an amine. So the correct answer here is D. We've got an alcohol, an aromatic hydrocarbon, and an amine all in the same molecule dopamine. We actually have two alcohols.
Okay. Aromatic alcohols. Okay.
Groovy. That word dates me. Okay.
You guys will never use that, but I did when I was a kid. Everything was groovy. That's groovy. Okay.
There are the functional groups that I have circled. This key is posted on Learning Suite, and I'd encourage you to take a look at it and just kind of be able to do that in an exam-type setting. Okay? Alrighty-tighty. Let's move on.
Okay. In class, I always ask the question, before I go on to that slide, I say, how many of you have ever smelled natural gas? And I'll wait for a second, and I'll look out in the classroom, and almost always I see about half the class raise their hands. And I chuckle because it turns out that natural gas is odorless. Okay.
Natural gas is methane, CH4. We talked about it. in chapter one quite a bit.
And it is combustible, highly combustible, and doesn't smell at all. But it turns out that in 1937, I think it was a junior high school blew up when natural gas leaked into, there was a natural gas leak, and it leaked into the woodshop class. It was filled the whole. building actually and when they went into the wood shop in 1937 and turned on a saw the saw sparked and it basically ignited the methane and basically look what it did to the school okay so it killed 295 mostly children and so we learned from that kind of like we're learning from the coronavirus right now um and so after 1937 they started spiking methane with something called ethane thiol. Ethane thiol looks a lot like this guy.
This is butane thiol, but ethane thiol only has a CH3 and a CH2 here. So ethane thiol would be that, and that is what you smell when you, and I'm sure most of you have smelled it, right? When you turn on your gas stove or, you know, you're working in a lab, you turn on a Bunsen burner, you smell, it smells, it stinks. And what you're smelling is ethane thiol and it's put in there, I think I've been told it's like parts per billion. The human nose can detect ethane thiol down to parts per billion, so they don't have to put much in.
But so the next time there's a gas leak, you can smell it. And for darn sure, don't turn on your saw or anything else that sparks or you're going to have a disaster. So it's an interesting application of stuff we've been talking about. Okay. Here's a functional group question.
Go ahead and take a look at this. It's an iClicker kind of question. Pull out a sheet of paper and work through this.
I'd pause it and see if you can identify the functional groups. And I'm highlighting them in color. I'll let you work it, and we'll work it together.
All right, let's look at A. What is A? Is that an amine, an ester, thioester, an amide, a ketone?
What is it? It's actually an amide. So A is an amide. B, we have an RSR.
That is a sulfide. Okay, so we have amide sulfide. C is a carboxylic acid. We'd actually want to include that, but I couldn't get that yellow. The tool that I used here wouldn't allow me to capture that carbon in yellow, but that's part of the functional group.
That's the carboxylic acid, and this pink one here is... also an amide. We have R, carbonyl N, R, R. And I couldn't get the pink over all of the atoms, but anyway, that is an amide. So we go amide, sulfide, carboxylic acid, and amide.
So what is it? Amide, sulfide, carboxylic acid, and amide. So E is the correct answer. Okay.
All right, we're going to change. Gears here just a tad I'm not sure why I put that in there again but we've seen this when change gears just a tad and show you this slide and Ask you if you've seen something like this before used to be in an earlier edition of the textbook they had this I think they've removed it from the fifth edition that we're using now I don't remember for sure but turns out that this is a gecko. Okay, and geckos can climb up surfaces as slick as glass and basically just hang there using these toes, okay, spread out. Now, I always ask the class, what's going on here?
Are these suction cups? Are these, you know, like little suction cups that the thing, you know, plasters and you hear, you know, popping as it walks up the glass? Turns out the answer is no, they're not suction cups. This guy is sticking to the glass through what we call Vanderwall's interactions. Okay, Vanderwall's.
Now, Vanderwall was a... Dutch chemist and I don't know anything maybe physicists, but I don't know anything other than the fact that that name is Dutch And what he noticed is that for any given Molecule, it's not charged and not polar there can be what we call momentary dipoles to our momentarily One end of the molecule can take on one charge and the other the the opposite charge and this little Delta sign that means partial. That's not a full plus charge and that's not a full negative charge You know as a zero point one parts of the plus charge or zero point two or zero point three or zero point four You know the answer that is yes. I Don't know. It's just not a full plus charge.
Okay, it's partial partial plus partial negative Or the other end. Okay, the left hand end can be partial negative and the right hand and partial positive Well, it turns out that these things form momentarily, and they will align themselves to where the temporary or momentary is what I call it, rather than temporary. Momentary or temporary dipole, the partial plus end of one will align itself against and attract the partial negative of the other, and these things attract one another. And that is how the gecko apparently sticks to the glass.
Okay, you get momentary dipoles forming on molecules along these little ridges. They're not suction cups. And those will align themselves with the molecules in the glass, which also take on momentary charges.
And there's this electrostatic kind of interaction between the opposite charges. And that's how that thing sticks to the glass. Isn't that cool?
It makes me wonder how mountain goats climb cliffs. It can't be the same, I don't think. but I don't know, maybe.
You ever seen a mountain goat climb what looks like a vertical straight up cliff? They are amazing. It's just amazing.
Okay, so there's a bunch of momentary dipoles lined up with alternating negative seeing positive, positive seeing negative, negative seeing positive, blah, blah, blah. And in the vertical direction, positive seeing negative, positive, negative seeing positive. There's electrostatic interactions between all these opposite charges and the net result, you get enough of them. there can be a very strong attraction between all those different molecules.
Okay, so keep that in mind. Okay, here's a question. What would you guess about the boiling points of the noble gases? Noble gases being the gases in the right-hand column of the periodic table.
Start with helium and then neon, and then I think go to argon. I'm just recalling this from memory. As you go down... the periodic table from helium to neon, and then I think it's argon, you're going from a smaller and lower molecular weight noble gas to a larger one and larger still.
As we move down the periodic table, if we're thinking about periodic tables, we move down a periodic table, we're going from a lower molecular weight to a higher, to a higher, to a higher, etc., etc. So if that is a backdrop, what would you guess about the boiling points of the noble gases as we go down a column like that? Think about that for a second. I can see you're thinking. You're going to start swinging your feet.
Let's see. Well, here they are. You've got helium, neon, argon, krypton.
Not kryptonite, which is Superman's gas, right? Xenon, radon. And helium boils at minus 269, so it's a gas at room temperature.
They all are, okay? But notice the boiling points get higher and higher and higher as the gas gets bigger and bigger and bigger. Part of this is just that it's a larger atom, okay?
But part of that is also due to van der Waals attractions, okay? Same thing can be seen in... F2, Cl2, Br2, I2, and Acetine 2. In terms of the boiling point, we go from minus 188 to minus 35 to plus 58 to 184 to 337. We're going from smaller to bigger to bigger to bigger to big S.
And that's not just due to the molecular weight. It's also due to Van der Waals attractions. Kind of like the gecko, okay? And again, the stronger the interactions between molecules, the harder it is to boil something, and the harder it is to boil something, the higher the temperature it takes to make it boil.
Okay, so let's take a look at two organic molecules. This one here is pentane. One, two, three, four, five carbons, okay? This one here is an isomer. What's called an isomer of pentane.
also has five carbons, but I think you can tell by looking at them, those are different molecules. They're slightly different colors, that's true, but notice that in the pentane, all the carbons are kind of laid out in this almost linear fashion. This is very rod-like.
This one has a CH3, CH3, CH3, CH3, and a carbon, okay? So this actually is very spherical, okay? And so with that as a backdrop... which would you guess would be more likely to have the higher boiling point? We kind of alluded to this back when we were talking about methane versus pentane in a boiling point.
But now we have something that has exactly the same molecular weight. It has five carbons and I can't show you, but it has the same number of hydrogens as this one does. They have exactly the same molecular weight.
So which would you expect would have the higher boiling point and why? The answer to that is, we'll see in a minute, this one. But first I want to show you the stick drawing or the skeletal drawing for this. This is called neopentane, neo meaning new, or you've heard the neo prefix, right?
But that's what it's called, neopentane. It's got five carbons, one, two, three. four, five, or one, two, three, four, five, depending on how you want to count them. You see them here. One, two, three, four, five.
Yeah. Here's the ball and stick drawing. Okay.
And that's a space filling model. So it has the same molecular weight, same formula as straight chain pentane, but it's an isomer of pentane, which means it's not pentane. It's different than pentane, but it has the same molecular formula.
And here's a normal pentane with One, two, three, four, five, and kind of a zigzag orientation. One, two, three, four, five. One, two, three, four, five. That's the skeletal drawing.
Here's the space filling. Okay? All right.
Well, there they are, the two of them right next to each other. And I think it's easy to see that two of these are going to have less surface area contacting than two of these. Look how much more surface area that has than those two.
And so if you have a whole bunch of them, okay? They're going to be undergoing van der Waals interactions, just like we saw before about the gecko, right? And so anyway, the boiling point of pentane actually is 36 degrees centigrade or about 97 Fahrenheit. Okay, let's have a drum roll. Can I have a drum roll, please?
Let's get ready to see the next slide, which I think, as I recall, shows the boiling point of neopentane. Let's take a look at it. ta-da okay 9.5 it has the same molecular weight as pentane okay but the boiling point of pentane is 36 and that four if i'm doing my my times table is right i think that is four times nine right four times nine is 36 yeah so um this guy boils nine times higher okay that temperature is is nine times higher, the boiling point temperature is nine times higher than neopentane.
And the reason for that is that there is less surface area for the Van der Waals interactions, and so it requires less energy to break those interactions, and it boils at a much lower temperature. Okay, all righty, a take-home message. The more spherical a molecule is, I mean spherical, okay, not branched, spherical, Okay, that's important.
There's a question, I know there's a question we typically have in exams where I give you a branched molecule, but otherwise it's pretty rod-like. You've got a really rod-like thing with a branch out here and a branch out there. We're not talking about branching necessarily making the difference.
It's not that this is more highly branched, it's more spherical. See how this is more spherical than the Pantene? That's more linear or rod-like, and these guys are more. spherical or kind of ball-shaped.
The more spherical, the lower the surface area and the lower the boiling point because the fewer the van der Waals interactions. Okay, let's ask a question about melting point. Which one do you think would have the lower melting point and why?
Well, if life were easy, we would expect it to be neopentane. This is more spherical than that one. You would expect the melting point to be lower if life were easy, okay? Well, it turns out that melting is different than boiling, okay? Because in melting, you're breaking apart.
crystals, okay, or crystalline solid material, and it turns out that generally speaking, and I'm sure there's exceptions to every one of these rules, but we're not going to go there. We've got to start somewhere, so we're going to make some simplified assumptions or statements, and the simplified statement or rule of thumb is that the more spherical a compound is, the more of them you can get packed into the crystalline lattice. It's a little bit like if you had a box and you're trying to get a bunch of balls, little small balls into a box as opposed to a bunch of rods, okay, the balls will fill the box better than the rods.
So you get a bunch more of these in the crystalline lattice. It actually takes a higher temperature to melt the more spherical molecule. It's exactly backwards, okay, from the boiling point.
In the boiling point, the more spherical one boils lower, okay, but in the melting point, the more spherical boils higher. And so we got to look at these and see that the melting point, the more spherical one, melts higher. Okay. Look at these temperatures. And minus 17 is actually higher than minus 130. And so B is going to melt at the higher temperature than this one does.
So it's exactly the opposite from boiling point. So beware of that. Okay. Yeah. Too bad life isn't easy.
And we're going to see later on, especially in... chapters 7 & 8 there are so dang many exceptions you're going to be pulling your hair out so this is the first one all right here's some important forces you should be aware of the hold molecules together and the need to be broken when you either melt or boil these are things that need to be overcome so Vander walls which we already discussed they are momentary dipoles that interact and form momentary electrostatic interactions dipole to dipole interactions these are actual you know when you have polar bonds in a molecule hydrogen bonding and electrostatic or ionic as we go from one to two to three to four these bonds are getting stronger and stronger and stronger okay dipole-dipole interactions are stronger than mandrill walls hydrogen bonding stronger than the dipole-dipole ionic or electrostatic true electrostatic bonding between them plus charge, a full plus charge, and a full negative charge, that is a stronger or higher energy than these others. Okay. Alrighty then. Here's an example of dipole-dipole interactions.
So when you have two atoms of differing electronegativity, okay, that makes the bond polar between them. Okay. So oxygen is more electronegative than carbon.
I know that because oxygen is up in the right-hand corner of the periodic table. Carbon is towards the left. Anything towards the left of another atom is less electronegative.
And as we go kitty-corner, and I don't have a periodic table, let's pretend this is a periodic table, okay? As we go from the bottom of the left-hand corner of the periodic table and move towards the right, upper right-hand corner, we go from less electronegative to... more electronegative.
So down here, less electronegative, more electronegative. O's up here, carbon's over there. So it's carbons to the left of oxygen.
Therefore, oxygen is more electronegative and that bond is polar. You can think of this electronegative almost like a magnet sucking electrons towards it in that double bond. And so these electrons are not shared equally.
That's the point. Okay. The oxygen hogs them, pulls them towards the O.
and puts a partial negative charge on the O and a partial plus charge on the carbon. That happens for every carbonyl. This is an acetone, but it could happen in any ketone, any aldehyde, any ester, any amide, any carboxylic acid.
You have a polar. These bonds are said to be polar. And these are dipoles.
And when these encounter one another, they line up such that the partial negative charge on the O Is drawn towards the partial plus charge on the carbon and so forth. There's just these things this lineup in All three dimensions. So here we're showing it in two dimensions We have them stacking out this way and those have to be overcome when you try to boil a Ketone, okay those electros those dipole-dipole interactions The hydrogen bonding we've seen before where a lone pair on an oxygen coordinates with a hydrogen. The reason that happens is there is a partial plus charge on the hydrogen because the O here is more electronegative than the hydrogen. Again, if this were a periodic table, hydrogen is up over here, oxygen is over there.
As we go from the lower left-hand corner of the table up towards the right, we're going from... less electronegative to more electronegative. Hydrogen is clear over here.
It really is not electronegative at all, hardly. So it is much less electronegative than oxygen, but it's over here on the right-hand side of the periodic table. And so in terms of the OH bond, we have a partial negative charge on the O, a partial plus charge on the H, partial plus charge on the carbon, partial negative on the O, and that's shown like so. Okay, so lone pair will be irresistibly drawn towards the partial plus charge on the H and will form this hydrogen bond. And this hydrogen bond network is almost like Velcro.
So bottom line is alcohols tend to have very high boiling points, much more so than a ketone. And hydrogen bond is stronger than the dipole interaction. So a ketone will require less energy to boil than an alcohol will. And alcohols tend to have very high boiling points.
Okay, so here's an example of the kind of question you might see on an exam. All right, so here we have three molecules that have more or less the same molecular weight. We have this 1, 2, 3, 4 carbon alkane, 1, 2, 3 carbons in an OH, 1, 2, 3 carbons in a carbonyl, okay, carbonyl oxygen. These have almost exactly the same molecular weight.
They're not exactly, they're very close, okay? Here are their ball and stick depictions. So, in the middle here, these are the same molecules on the right. These are the space-filling models.
And notice how similar they are. They look just about as spherical as each other. There's not a lot. You can't say that this one's more rod-like than that one. You can almost drop that on top of it.
That's almost superimposable. But it turns out they have vastly different boiling points. So, the question is, which one of these things will boil higher? Which one will boil with the next highest temperature in which one will have the lowest boiling point? So let's rank them that way.
Okay, so take a second write that down who boils highest and then Next and then next we're talking the temperature to boil. Here's the data Okay, they all have about the same molecular weight 60 versus 58 versus 58 there almost the same molecular weight but look at this this guy has a boiling point of 82.6 centigrade this 157 and this one minus 12 okay so alcohols always boil a higher temperature than the ketone which will boil or an aldehyde which will boil higher than an alkane again this washes out of the fact that all this has is van der Waals interactions this one has van der Waals and dipole-dipole interactions. And this one has Van der Waals dipole-dipole and hydrogen bonding.
Okay, so it gives it a boiling point of 82 versus 57 versus minus 12. Kind of cool. Okay, let's do this one. And then let's stop and break this into another part.
And this may be a perfect stopping point. We've got four different molecules. A, B, C, and D. One is an alcohol, one's an alkane, one's a ketone. Oh, and here's a second alcohol.
Okay, so think about it. How do those two differ? Do they differ? Basically, they both have OHs, so they're going to have the highest boiling points, but D is actually a little bit...
bigger. It's got another methyl CH3 group out here. So it's going to have a higher molecular weight.
So it will have greater van der Waals attractions than this one does. But in terms of the dipole-dipole interactions, it ties, the hydrogen bonding, it ties. Okay.
But this is just a little bit more rod-like. And so D will require a higher temperature than this one. We're going to arrange them in terms of decreasing boiling point.
Okay. So So D will boil higher, a higher temperature than A, okay, which will boil at a higher temperature than B. This has dipole-dipole interactions. okay and c is an alkane and so it'll have the lowest boiling point of all so there's your answer d boils at a higher temperature than a and b and c okay very quickly just let me point out that um carboxylic acids have this really funky um tendency to undergo a dimerization to where The carbonyl of one carboxylic acid acts as a hydrogen bond acceptor from that H.
This one acts as a hydrogen bond donor. They form these dimers. And this will actually boil at a much higher temperature than an alcohol with about the same molecular weight. So this asks, what would you predict about the boiling point of acetic acid relative to other compounds with the same molecular weight?
The answer is this guy's going to boil way higher. I think I show that in the next slide. We'll show these.
call it a day on this. Let's call it a wrap. So we compare this alkane to that ketone, that alcohol, and that carboxylic acid. They have about the same molecular weight, 60, 60, 58, 58. So they tie in terms of molecular weight.
But take a look at the boiling points. This guy boils at 118 compared to that at 83. It's hydrogen bonds, but it can't form that dimer like this one does. This one forms a dimer like I just showed. That gives it a much higher boiling point. And so, yeah, it's higher than this one.
This one will be higher than that one. This one is higher than this one because the ketone has a dipole-dipole bond, partial negative charge there, partial plus. And the dipole-dipole interaction is stronger than van der Waals. This just has van der Waals, so it boils at minus 12. That goes up 57. That goes at 83. That goes at 118. Okay, kind of cool. I think my last slide just shows the different depictions of this carboxylic acid.
This is acetic acid, the carboxylic acid found in vinegar. This is the ball and stick model. This is the structural drawing. This is the skeletal or line drawing. And that's the space filling.
If you shunk yourself down, this is what the molecule would look like. Okay, and it has a much higher boiling point than an alcohol with about the same molecular weight. Here I show them right next to each other. The alkane, the ketone, the alcohol, the carboxylic acid. Okay, note that their shapes are darn near the same, right?
So neither one of these is more rod-like than the other. So the Vander Waals attractions are not what's contributing to the difference in boiling point. It's not Vander Waals here. Again, this one washes out of the fact that the carboxylic acid forms the dimer. This one washes out of the fact that the alcohol can undergo hydrogen bonding.
This one washes out of the fact that that carbonyl is polar. And this washes out of the fact that that molecule is not polar. And all you have is van der Waals attractions, which are not very great because this is more or less spherical.
Let's go ahead and leave it at that. And we'll call it a wrap. And let me...
Click out of this. Oops, I'm trying to click out of it. And here we go. So we stop recording.
I'll let you look at this. And the next one, we'll start up with it. And we'll answer the question as to which of those will have the lowest boiling point and which will have the highest.
And let me go ahead and stop recording.