CHM 121 LECTURE - MONDAY

[00:01:57]Good morning all. The early bird always gets all the juicy worms.

[00:02:04]Um, now this is good. 2 minutes to go. We have about 40 almost.

[00:02:17]Ah, that is good. That is good. Um there's someone here Yeah, we will take off nine on the dot so that um the very punctual people do not accuse us of marginalization.

[00:02:41]Um, I see a name here.

[00:02:49]Why can't I?

[00:02:55]Uh, okay. Go that way.

[00:03:14]Good morning.

[00:03:27]You're trying to talk but I can't hear you.

[00:03:32]I want I want to confirm that you're actually here live.

[00:03:36]Can you say good morning?

[00:03:50]You are not at now and mark you didn't put your mic number answered me. So I've confirmed that it's here and he knows why I'm confirming that it's here and I've also confirmed that you can hear me. So, we're going to go ahead and take off.

[00:04:22]Okay.

[00:04:26]So, shall we start with um questions from last class?

[00:04:33]Uh there's none here. Do you have any questions from last class?

[00:04:38]I've told you don't type your name here again. Anyway, since you know how to use the question and answer, I will stop coming here to look at.

[00:04:51]Okay, who prevented you from unmuting?

[00:04:53]Anyway, we'll solve that problem.

[00:04:58]Uh, Calb, good morning.

[00:05:01]Good morning.

[00:06:19]It appears some people are not happy that I'm happy and that they are asking network to shut me out.

[00:06:30]Uh no Jessica, can you hear me now? Or is it when I was shut out?

[00:06:41]EJ Gloria, don't let me use you for example this morning.

[00:06:47]Honorable Jessica, can you hear me now?

[00:06:50]Okay, very good. Uh, somebody tried to cut me off.

[00:06:57]Okay, so no questions.

[00:07:02]Okay.

[00:07:04]What's going on? Okay, you can hear me, but I think maybe the Okay, the slide also went off with that disconnection.

[00:07:14]It's all right. It's all right. I know some people don't like Monday mornings.

[00:07:23]That rap song, Monday morning, making my money.

[00:07:31]Are these children not here?

[00:07:35]Any questions?

[00:07:38]No questions. Okay.

[00:07:43]No questions.

[00:07:46]So last class we started our discourse on ethers.

[00:07:52]We said that we can differentiate them by removing the H.

[00:07:57]That's literally removing the H in RH of alcohol and putting an R where the R could be an alifhatic group or and the right group. We did nlee. I hope you got a chance to look at the naming, understand it, and be able to practice the ones that are there or even more if you go online. And there are so many.

[00:08:28]So today we want to talk about how we prepare eaters.

[00:08:33]Remember I've already said to you that if you know the methods of preparation of a compound and you can write the equation. If you reverse that equation you will get the reactions most times general reactions. You now just be can now add specifics to it. So that makes it easier for you to understand.

[00:08:58]So preparations um we're not looking at uses. It's not as if they are not important.

[00:09:11]important to but okay like it has for instance are that chemical that you see sometimes uh they mix with uh say nail varnishes but because they are very very volatile if you put them on the skin you find out that it cools the skin because as it evaporates it pulls the heat that needs to change from liquid to gas, it needs energy. That energy pulls it from the heat of your body, the hand of the person that is putting that chemical there and then it volatilizes, evaporates and that's why if you have it on your hand, you feel a cooling effect.

[00:10:00]So many of them are carinogenic anyway, suspected carinogens.

[00:10:07]So don't be playing with chemicals.

[00:10:11]But it's uh so that tells you that for instance is a very good solvent especially for nonpolar compounds or non-polar organic compounds. But let's look at the preparation diet. You already know uh it has CH2CH3 on one side and on the other side too.

[00:10:38]Okay. So CH3 CH2 then O then on this side it has another CH2 then CH3 if you remember how we do nomenclature ital on this side ital on this side because there are two of them diil okay so how do you prepare diyl it's from ethanol okay so industrially Diet liter is prepared by using sulfuric acid to catalyze the dehydration of ethanol. Dehydration is removal of water. So if you remove if you bring two molecules of ethanol together you remove water. So you take H from one take O from the other one water. both those two will now combine and give you that ethyl ether.

[00:11:39]Okay. So that's the general formula simp simplistically put if we look at this you see that is ethanol for you there is ethanol remember we're using sulforic acid as a catalyst so the HA represents acid Okay.

[00:12:10]And here if you want to balance the equation, you put two in front of that uh ethanol.

[00:12:20]Okay? So that that tells you that you need two molecules.

[00:12:28]Now here is broken down the transition state.

[00:12:33]Uh okay.

[00:12:40]Let's deal with that. [sighs] So here you can see this is one molecule. This is another molecule. Okay. So those are the two.

[00:12:54]Now in the first reaction where it reacts with the acid.

[00:13:05]The acid is H A which reversibly will give you H plus A minus. We're using sulfuric acid. So if you say H2SO4 if it ionizes it's going to give you 2 H+ plus SO4 2 minus. That is the balanced equation.

[00:13:33]Okay. So you can see that this is in excess. So either you use that or use this. One of them will now come to the oxygen of the O of the ethanol.

[00:13:50]The oxygen will donate. Oxygen has two lone pairs of electrons. So it will donate one.

[00:13:57]So in a manner of speaking if you were to write this when it was H3 CO2 H.

[00:14:15]So what you get is that this bond between the oxygen and the O will move to the O so that the O becomes delta negative. this H becomes no let's not even use delta let's use because these ones are not they're not temporary in a manner of speaking the sulfuric acid is actually extracting that proton so um that's not the mechanism that's if this happens if it were breaking but what I wanted to show you is this oxygen has has uh two lone pairs of electron okay on opposite sides. That's why the oxygen hydrogen bond is straight.

[00:15:09]Oh no, it's not straight. Both of them are on the other side. But let's let's put it here just so that it will tally with this to explain what is going on there.

[00:15:18]Okay. So he has a lone pair on this side, a lone pair on this side. So let's say this lone pair will now go to this H+ or if you like use this one since we're using sulfuric acid. Okay. So it donates this lone pair to the proton by a and they form a bond by addative coalency.

[00:15:45]Okay. And so because that oxygen has donated his lone pair to the hydrogen to form that bond. So that lone pair is now under the influence of the nucleus of the oxygen and the nucleus of the hydrogen unlike before when it was only under the influence of the oxygen.

[00:16:09]Now to reflect the fact that the oxygen no longer has sole control over that lone pair, you say that the oxygen has lost its lone pair of electrons. Okay?

[00:16:20]And you signify that by putting a plus on top of the oxygen. So that if you go when the oxygen was on his own in the alcohol, if you go and check the number of protons in the nucleus, it will be equal to the number of electrons. Okay?

[00:16:42]But now that it has given out two electrons it lone pair into the empty orbital of the hydrogen.

[00:16:51]The number of protons in the oxygen is no longer equal to the number of electrons under the influence of the nucleus of the oxygen because that lone pair is now under the influence of oxygen atom and hydrogen atom. So that's how we signify that. And then in terms of arrow moving because that's the form of organic chemistry. The arrow is moving. The arrow moves from where you have electrons to where you do not have electrons for a bond to form. So in this case the oxygen donates it lone pair to the proton or the hydrogen cation which as I'm sure you are aware hydrogen on its own hydrogen atom has one electron.

[00:17:40]When he loses that electron, the proton is now more because there's no more electron. Electron is equal to Z but proton is equal to one. And that is the plus you always see on the hydrogen.

[00:17:52]Okay, showing you that the hydrogen has lost one electron. But when hydrogen is hydrogen atom on its own, you write it as H. Okay, you should go and check the nucleus. Then it will have one proton.

[00:18:06]You check the orbits like you learned in secondary school. We call them orital.

[00:18:12]Now when you're dealing with quantum chemistry, whichever one you want to call it, if you check that one, you see one electron for the hydrogen atom.

[00:18:21]Then I'm sure you know that if you are talking about detium or tritium, then the number of protons there increase from two I mean from one to three, from two to three. But here we're dealing with hydrogen. So all these ones I'm saying just to remind you of things that you should know in case you don't know and then you learn new things. So back to our main issue here. So that's the H+ is now on top of so there's now a bond here. If we were drawing it out like we did the other time, you have your CH3, CH2, O H, another H here. And then you have your plus. That lone pair is still there.

[00:19:14]Okay? But you have your plus because it has lost. And so that's what you're getting here.

[00:19:21]Okay?

[00:19:24]So once that happens, you know now that that oxygen in a manner of speaking is no longer stable because it has lost his lone pair. He wants it back. It's like if you have something and someone collects it from you, maybe a bully, you will keep quiet because maybe you know the bully will pound you into the floor. But if it's someone you know you can, you won't even let the person collect it in the first place. But once they've collected, you'll be restless. You want to get it back. Okay? So that restlessness is what makes this ethanol very reactive.

[00:20:00]Okay? So it is very reactive being very reactive. Now this oxygen that has gone to give his lone pair to hydrogen is now looking for ways to get it back.

[00:20:17]Okay. So in looking for ways to get it back, it will be pulling the electron that it's sharing with this carbon. You know there's a carbon oxygen bond here. Okay? Because ordinarily when it's just carbon oxygen, the inductive effect is closer to the oxygen because the oxygen is pulling it to itself. Okay?

[00:20:49]Now that oxygen has gone to form the bonding with hydrogen. It's more comfortable with hydrogen but that pool is still there.

[00:21:00]So in fact now it's stronger because there's a positive charge. So it's now going to pull more because she wants to take the electron that is sharing here to be able to satisfy it uh return or rather replace the lone pair that it's using with hydrogen. So that means that momentally this carbon will become a delta plus and then this oxygen will be a delta minus because electrons are being put towards it.

[00:21:45]Okay. So once this carbon is negative I mean positively charged it means that it will be looking to be looking for a positively charged entity sorry negatively charged entity.

[00:22:08]Okay.

[00:22:11]Now because this pool is strong that bond between the carbon and the oxygen can break.

[00:22:25]It is momentarily this and this but it can now break so that this can go away as a water molecule.

[00:22:34]Okay. Now because as this carbon here is becoming pos is remaining positively charged is looking for electrons.

[00:22:44]The next the neighbor another acid hasn't reached it.

[00:23:12]We'll be maintaining its uh here the oxygen hydrogen again here the oxygen is pulling towards itself. So that oxygen is delta negative. Let me use another. So this oxygen here is delta negative.

[00:23:43]Okay. So what then happens is that this oxygen because it has we now come to this carbon that is delta positive. So delta positive delta negative they will now form a bond.

[00:24:07]Okay. But see here mechanism is SN.

[00:24:16]Okay. So what is happening is that this you see we're using delta posive and delta negative here because they are not breaking up to form a bond.

[00:24:31]So what then happens is Sorry for the break in transmission.

[00:27:20]Uh sorry for the break in transmission.

[00:27:24]Uh I don't know what's going on.

[00:27:44]Okay. Just want to confirm that uh I think this place is jam-packed. I don't know whether that's what is affecting it.

[00:27:55]Okay, let me just confirm that you can hear me.

[00:28:08]People are dropping in and out. Okay.

[00:28:11]Uh, since I see one hand up, since that was just a break, but the hand is gone.

[00:28:23]Well, so, and it appears I'm Wow, I'm spending too much time on that stuff.

[00:28:36]Okay, so maybe the break was a wakeup call. So we move, we move, we move, we move.

[00:28:44]Okay. So I think I've pretty much explained what's going on. So you can see this uh is an SN2. So both of them are here at the same time. This is this one. This is it here.

[00:29:03]Okay. And then this part is the one that is coming in.

[00:29:10]Okay. So, you see that they're both there.

[00:29:14]And then that's H2+ this this one now leaves.

[00:29:34]Uh where is this stuff?

[00:29:43]So this now leaves me.

[00:29:47]This now leaves and in leaving it takes this along.

[00:30:01]Okay. So either you rational is that way or you go the way we were going before where this is coming in there and this is now going to go off.

[00:30:25]Okay, I think we've spent too much time here.

[00:30:30]all the all the others will not enjoy this.

[00:30:33]Okay. And then you have your your ether in this case till ether and then you have your hydrogenium ion. Okay. And this as I'm sure you are aware let me let me go back to my red ink.

[00:30:53]Hydroium ion is your water plus your proton.

[00:31:01]That is why the sophorical seeding apologies. My network is really bad today and um I have to go and change the settings of these things. Someone who has a stronger network keeps knocking me off.

[00:37:14]If you knock me off again, I just go and sit down. Can teach yourselves.

[00:37:20]So once this thing goes off again, I don't even think you can see the number of participants.

[00:37:30]Anyway, let's uh let's get back to it.

[00:37:40]Uh, okay. Let's use the opportunity to answer some questions.

[00:37:49]Anybody who doesn't get in here, I think that's Please tell all the others.

[00:37:54]anybody who isn't here.

[00:38:00]Uh 5 And it's Um anyway, uh this is this is a flaw that I did not think of.

[00:53:25]So it will be corrected next class.

[00:53:29]Obviously you guys have no way of knowing when the class is full. So you just keep trying wherever you are and then I will change the settings don't worry so that that won't happen again.

[00:53:50]I think I gave you guys some rights so that you can participate well where it seems to be affecting us. Okay. Epoxites are cyclic eaters. So we've been looking at it as the ones that are alifhatic or stretched when they are in a ring form.

[00:54:28]this person that keeps knocking me out.

[00:54:32]It's not Oh, maybe it's my network cuz ah see now this is just 250.

[00:54:41]My network is really bad today.

[00:54:45]Uh but you guys will suffer with me. Maybe I shouldn't be happy. That's what today that I'm happy. Now this network is just misbehaving. Okay.

[00:54:58]So that's cyclic eaters. They are called epoxides.

[00:55:05]Okay. And you can see two examples here.

[00:55:10]Okay. There are sometimes also called auxans.

[00:55:17]And can see here see this one now and we're supposed to be moving forward the preparation of cyclics. This example here is ethylene. Okay, that's another name I hope you know for this.

[00:55:40]Okay, if you use that that's also correct is a common name. So if you oxidize it with oxygen gas in the presence of silver oxide at 300° centigrade, you're going to get an epoxide which is ethylene oxide.

[00:56:01]This some of you might have come across is a monomer for polyethylene oxide.

[00:56:08]>> [clears throat] >> Poly ethylene oxide is the a polymer that finds use in so many places industrially from lubricants to grease to cosmetics.

[00:56:24]Okay.

[00:56:27]So it is a cyclic or rather a monomer for polymers.

[00:56:38]You can also prepare by using a per a peroxy acid or a peroxide.

[00:56:50]This is an example.

[00:56:54]Okay. Presence of CH2 CL2 is dchloromthane.

[00:57:01]Okay. Some of you might have heard of that is the younger brother of chloroform.

[00:57:05]Okay.

[00:57:08]Chloron say younger brother I I know you probably know chloroform chloroform will be CH C3 okay so this is another way of preparing epoxides another example here so you find that epoxide are easily prepared where there is a carbonarbon double bond if you oxidize that carbon it to form an epoxide.

[00:57:42]You add chlorine, gas and water.

[00:57:46]Okay?

[00:57:49]It gives you a chloro cylo alcohol.

[00:57:55]Then you add base sodium hydroxide still in water.

[00:58:00]Then it will give you your one two epoxy cycllohexane.

[00:58:09]Say if you compare [clears throat] this to the Williamson synthesis, okay, you see that the similarity is just that this one has the Williamson is happening on a cyclic system, but you see that it's not giving you an EPO.

[00:58:33]instead is giving you an ether because there's no double bond to start with.

[00:58:40]Okay, there has to be a double bond where the the ring can form across and you can see that none of this is made by breakage of any cyclic system so that you don't confuse them.

[00:59:03]Okay, this is the mechanism for this when you make epoxide from halo hydrins.

[00:59:15]Halo hydrins. This one here uh where is my is a hall hydr.

[00:59:26]Okay.

[00:59:32]They have they have uses industrially.

[00:59:34]So they have the common name.

[00:59:37]You can have a look at this.

[00:59:41]See if you understand the mechanism.

[00:59:45]If you do, it will help you remember it better. If you don't, don't worry yourself about it.

[00:59:51]At this level, what you need to know is that here if you add any of these reagents, you get this product. Because in a test or in an exam, you can find that the examiner can draw the structure and leave this blank where you have to fill in the reagents or put in the reagents and ask you to give the product.

[01:00:15]All those things are possible. It is legal.

[01:00:20]Okay. So this is still expanding on the halo hydrants should understand them. They are important in terms of reactions for cyclic eaters or epoxides.

[01:00:34]You can also add the greener reagent which you came across when we were dealing with alcohols.

[01:00:43]They rbr general formula. So if you add that to an epoxide, the epoxide will open up the ring.

[01:00:53]Okay? And of course give you an alcohol.

[01:00:57]If you recall, greenard reagents are used to produce alcohols.

[01:01:04]So if you react them with if you react them with why is this thing cut off?

[01:01:14]I have to do this again and show you.

[01:01:16]It's it's an alcohol an O that's at the other end. Okay. So maybe you can put it yourself so that I don't have to do the slide again. Maybe that's the benefit of coming to class. So here is O.

[01:01:31]The idea of this reaction is that it takes everything before the Mg here and adds it to everything here without uh everything on the pox side.

[01:01:46]adds it to that and then adds H to the end.

[01:01:51]Okay. So in a manner of speaking this breaks up uh say this breaks up. Okay, that bond between the oxygen and the carbon. So that this oxygen takes delta negative, the carbon takes delta positive. Here this breaks up here. This takes delta positive.

[01:02:22]This takes delta negative. Okay, take note of this. Wherever you have Brinard reagent the carbon will be negatively charged unlike what you are used to when you have helides and all that. Okay. The general thing is for it to form a carbonium a carbanion that's C++. Okay. But wherever a metal is connected to it, if that bond breaks up, that carbon will go with a negative sign. Okay, that's uh a carbanion.

[01:03:05]Okay, carbanion is negative, carbonium or carocation is positive. C++.

[01:03:14]So please take note of that. So this carbon here is going to have a delta negative. Okay? And like we said, this one has delta negative. This carbon has delta positive. So the delta negative and the delta positive will react to form a bond. And then this this delta negative here will react with hydrogen to now form the O. Okay, so this reaction basically combines the two reactants and puts O at the end. That's basically what you take away from this. And that's an easy way for you to remember it.

[01:04:00]Okay, this crown eaters, they are cyclic eaters, but they these ones have more than one oxygen and they are they can be very big.

[01:04:14]Okay, this one you can read. You see they are usually named 18 crown six eater where the 18 will be talking about the number of carbon atoms in the ring and then the six at the end will be the number of oxygen atoms.

[01:04:40]Sorry. Number of atoms in the ring is the first one and then the second one.

[01:05:03]Okay. Well, our time is up. I don't know. Today has just been one hiccup after the other.

[01:05:13]Um, someone said we can't hear you at 9:40.

[01:05:19]It's one of the hiccups.

[01:05:22]Can't hear at 9:46. All those ones were breaks.

[01:05:27]Uh, apologies for that.

[01:05:32]Okay.

[01:05:34]uh ask your class reps. They will send you the recording and the slides.

[01:05:49]Oh, I think yeah, I've sent you the slide already. So, you already have that. Okay. Um apologies for all the hiccups. We'll try and do better next time. See you on Wednesday.

[01:06:01]Good morning.