Reaction Mechanism - Video Tutorials & Practice Problems
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Reactivity
Did you know that not all molecules are reactive? Only certain types of molecules will want to react in a mechanism. Let’s dig a little deeper into this...
Stability and reactivity generally have an inverse relationship. If a molecule is unstable in some way, it will want to react! Here are the 4 signs we can look for that determine reactivity:
1
concept
How to tell if a molecule will be reactive or not.
Video duration:
5m
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Video transcript
Hey, guys. And we're going to get into the part that makes this chapter really fun on. That's the mechanism. All right. So just so you guys know I'm going to teach this section Maurin depth than your professor taught it for this chapter. Why is that? Well, because I realized that mechanisms are such a big part of organic chemistry that if we can learn them as early as possible, it's gonna help you guys so much more later on, okay? You don't wanna be learning about mechanisms for the first time in chapter seven or Chapter eight. That would be organic suicide. Alright, Because you're gonna be very confused and you're gonna toe pick up the pace. Ah, lot. So what we want to do is you want to just use the concept of acids and bases. Thio, introduce what the mechanism is. All right, so we're gonna talk about this in two parts. The first part is I want to talk about the reactivity of Adam's. Why do they even react on? The second part is I want to show you how the react with electron movement. So let's go ahead and begin. So just you guys know, the currency of organic chemistry I've said this before is stability. Okay? Stability. Every atom wants to become more stable. Every molecule wants to become more stable, all right. And it turns out that stability and reactivity, you hear? You hear these words all the time actually have an inverse relationship in verse? What I mean by that is opposite. That means if stability goes up, reactivity is generally going to go down. If reactivity is up, that means stability goes down, get their opposites of each other. Okay, so how can we tell if a molecules reactive or molecules un reactive? Alright. Like I said, this is not a section that's usually covered in your textbook. I have just built this from years of teaching or go and realizing that, hey, there's actually ways that we can predict this. Okay, so there's actually four really common ways that we know that something's gonna be reactive. You guys ready? And you actually know three of these four already? Okay, The first one is formal charges. Guys, remember those. Okay? Formal charges. What? What does that mean? Formal charges mean that an atom is not at its ideal bonding preference. right. It has too many or too few valence electrons. Okay, remember the sticks and the dots. So what that means is that it's going to try to do anything in its power to try toe, go back to its bonding preference. So that means it has a very big reason toe want to react to something else. If it can get rid of some electrons, maybe it can go back to the state that it wants to be in. Does that make sense? So it's the first one. If you see a formal charge, you know that this is going to be reactive. The second one is net die polls. Okay, so net die. Polls have to do with the fact that I have asymmetrical die polls that are not perfectly canceling out. And what that means is that I'm gonna have partial charges in different places. Another way that I could say this is partial charges. Okay, so remember that a partial charge is the result of a net. Typo, if I have a net typo going to the right, that means that I would have a partial negative on one side and a partial positive on the other. Okay, so what I'm basically doing here is I'm saying if you have formal charges a full charge, that's very reactive. But even if you have a partial charge, that's also very reactive. So now let's talk about two other things. The two other things are pi Bonds. Okay, we're gonna find out. Is that pie Bonds? Remember that we went over this in the first chapter. Pi bonds are not as strong. A single Sigma bonds right there, actually, much weaker in terms of the amount of energy that saved. So what that means is that pie bonds are really good source of electrons, okay? And they're gonna be pretty easy to break. Remember, Sigma bonds are almost impossible to break many times, but pi bonds, they're not as stable, so they're easier to break. So pi bonds are gonna also be reactive. I know. I said the word break a lot of times, but and then finally, the fourth one is something you don't know yet, and that is starik effects. Okay, Hysteric effects is something that we're gonna talk about more when we talk about basically cycle al canes and we're gonna talk about a bunch of other stuff a little bit later, but an example of Starik effect. I just wanna tell you would be like something like Ring Strain. So imagine that I have a three member ID ring, and these bond angles are very, very, very tight. Usually, those bond angles would wanna be like 109.5. But instead, they're like, 60 degrees. That's an example of ring straight. And that means that these bond angles air not stable because of the fact that they're, you know, they're just not their ideal position. All right? And that's also gonna make molecules reactive. Now, do you need Thio deal with this one right now? No, but I just want to be comprehensive. And, you know, those were, like the four major things that make organic molecules reactive. Cool. So what I want to do is move onto an exercise and I want you guys to look at these eight different compounds and just go ahead and look at the first box. The first box is literally a check box. I want you to either check off that it is reactive or put an X on it. If it is not reactive. So I want you to go through maybe a through D the first four. And I want you guys to look at those first four and see if you can find any of those four reasons why it would be reactive. If you can't, then that means it's not gonna be reacted.
These reactive trends ARE in order of strength (i.e. a formal charge will typically be more reactive than a dipole).
Using those indicators, let's see if the following molecules are reactive:
2
example
Reactivity of Molecules
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1m
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Video transcript
All right. So a through D Let's go ahead and just start one at a time. Does a have a formal charge? No, it doesn't. It's fine. Um, does it have a partial charge? Actually, it does. Okay, It doesn't have a double bond, and it's not strange. Remember that I told you that hysteric effects are usually just when you have, like, thes small rings, so you don't really have to worry about it. Okay? But a is going to be reactive because the fact that it has a net die poll, So if I were to draw the dye poll here, I'll draw it towards the chlorine. That means I would have a negative and a positive. Okay. And what that means is that this is gonna be reactive because I have partial charges. Is that cool? So far? Cool. We don't know how it's going to react. We just know that it's reactive. Let's look at the second one. The second one was easy. It has a positive charge. That's a formal charge. So this one is definitely going to be reactive. Okay, let's look at this next one. This next one has a ton of dipole moments. It actually has four dipole moments. So you would expect that this would be, like super reactive, right? It's just gonna blow up, right? Actually, no, This turns out to be inert. Do you guys know what inert means? It means it doesn't react at all. It doesn't. It doesn't react with anything. And the reason is because it does not have a net dipole. Remember that you could have dipole moments, but if they're perfectly balanced, it's not going to create a net dipole. So in this case, this one actually would not react with anything because it does not have a net dipole. This is a tetra Hydro, and it's perfectly balanced. All right, then. Lastly. So I'm just gonna put an X. They're not reactive. And then the last one is a double bond. Remember that? I said that double bonds are easy to break in there. Good sources of electrons. Citizens also gonna be reactive as well. So basically I had three reactive molecules and I said for three reactive molecules in different ways and then one un reactive molecule
3
example
Reactivity of Molecules
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1m
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All right. So these next ones, it turns out that they're all gonna be reactive. Okay? Just in different ways. So this one had a negative charge. So negative charges a formal charge, so it will be reactive. That's actually one of the more types of reactive things. F has a net typo going up. So that means that it's gonna have a partial negative and a partial positive. So once again, that's gonna be reactive. Water is water reactive. Actually, it is because it has a net die poll. Okay, any molecule with a net dipole is going to be reactive to some extent. Okay, so water is also reactive. And then finally, this last one's a little bit crazy. Like you don't see lithium a lot. We haven't dealt with lithium a whole lot. But if you just use your election negativity trends, you know that carbon is over here, right? And lithium is like, all the way over here. Okay? Which one's more Electra? Negative. The carbon or the lithium? The carbon is much more Electra. Negative. So I would draw my partial. I'll draw my die poll going towards the carbon, which means that I have a partial negative here. Ah, partial positive there. Does that make sense? So once again, this one also gonna be reactive because has partial charges. Okay, so now we actually understand. Okay. Thes the molecules that are gonna want to react, okay?
Again, we are literally just matching these molecules to the 4 patterns discussed above.
Nucleophiles vs. Electrophiles
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concept
How to tell if charged molecules will react as nucleophiles or electrophiles.
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2m
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But now, how are they going to react? That's the next question. Okay, what are they going to react as? And it turns out that we can basically categorize all reactive organic molecules. It is important into two different subtypes. Okay. And those two subtypes are basically negatively charged species and positively charged species. Okay, so a negatively charged species. I know you've heard these words before, but I'm just gonna remind you of what they are. A negatively charged species is known as a nuclear file. Okay. And the way that we that I'm going to for this course abbreviate nuclear file is I'm often going to write and you negative, Okay. And that stands for the fact that I have a negatively charged Adam okay? And instead, or a negative charged atom or a negatively charged part of a molecule. And the important thing here is that I'm generalizing because it's going to react about the same way, no matter what type of nuclear fall it is. As long as it's a nuclear fall, it's going to react in certain types of reactions. All right, then, the positively charged ones are going to be known as electro files okay, electro files. I'm gonna go ahead and summarize them using e plus, meaning that it's a positively charged substance. And I also do want to talk with these names a little bit. What does nuclear follow me in an electrified Well, if it's negatively charged, that means that what it wants is positive in order to balance out. Right. So nuclear file literally means it's a nucleus lover or it's a proton lover. Okay, so a nuclear file is gonna want positive charges like protons in order to balance. Same thing with electrified electrified has a positive charge. So it's gonna want electrons, toe bond with or Thio make to react with in order to balance out that positive with a negative. All right, so that's the way we think about it. But if you just want, just think the nuclear follows the negative and the Electra follows the positive. All right, so now we look at all of these re agents, Okay? I gave you eight. And what I want you guys to do is figure out which of these are gonna be react mawr as electro files on which of them are going to react. Maura's nuclear files for a few of these. That's easy for a few of these, we can automatically tell. Okay, so let me go ahead and tell you guys which ones are the easy ones to identify? Okay, B is easy to identify. E is easy to identify and actually, D is easy to identify. Okay, So for these already, just without without knowing the next ruling gonna teach you, you should be able to tell me if he's going to react as nuclear files or Electra files.
Now that we know how to determine if molecules are reactive, we still don’t know HOW they will react! There are two major subtypes of reactivity that we’ll often use in Orgo 1 and 2:
Note that a molecule doesn’t require a negative charge to be a nucleophile, but it needs to have similar properties (i.e. a source of electrons).
That said, try to identify if the following three molecules are nucleophilic or electrophilic.
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example
Nucleophile or Electrophile
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1m
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Video transcript
Let's go ahead and start off with be It has a positive charge. A full positive. So do you think it will be electric file or nuclear file? Good job. I heard pretty much all of you guys say electrical, except that one annoying person that said nuclear file just to, like, piss everyone off. I'm kidding. So no. Yeah, it was an electrical codes. Positively charged. In fact, what you could have done was just looked at the fact that I haven't e positive and my carbon has a positive Perfect. Okay, so let's go to E is probably the next easiest one. So for E. I have a negative charge. What do you think? That's going to be awesome. Wow, you guys air like on fire right now? That's gonna be a nuclear file. Alright? Because that's a negative charge. And nuclear files tend to, like, always have some kind of negative charge and canned or some kind of negative region. All right, so then what about Dee? Why is d easy? It doesn't have any charges. So how would I know if it's a nuclear file or an electrical? And actually, the hint comes from what I said earlier about double bonds. I said that pie bonds are a good source of electrons. Okay, this is just a general rule that I always want you guys to know. Double bonds are really good source of electrons. So if it has a lot of electrons, what does that mean? Does that mean that it's gonna want more electrons or it's gonna want protons? It would want protons that would make it, Ah, good new nuclear file, because it's gonna want the nucleus or the proton. Okay, so basically, you see this This double bond, what you think about is that you could almost think that it has a negative charge, even though it doesn't. That's very wrong to draw. But I'm just having you imagine that those electrons are free Lone pairs, whatever that could attack. Something else does. That kind of makes sense. Just think, anytime you see a double bond, that is a good source of electrons, So this is gonna be a nuclear file. All right,
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concept
How to tell if uncharged molecules will react as nucleophiles or electrophiles.
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2m
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So now we just solved three out of 83 out of eight of them were really easy. Now for the next ones, they're actually gonna be tougher. And we're gonna need to know a new rule because notice all these other ones have both positive and negative regions. So how do I know if it's a nuclear file or an electric file? And that actually is one of the biggest questions that I get when we're in the section. Johnny, how do I know that's a nuclear? How I know that's an electrified And it turns out that there's this rule that we can use to figure out if it's going to react more like a nuclear file or react more like a Electra file. Is that cool? So I'm gonna teach you that rule and what that rule is. This the side of the die poll that has the highest bonding preference can be used to predict the nuclear Felicity or electric Felicity. So what that means is that I agree with you. There are two charges on all of these molecules on the five molecules that are left. There's two charges. There's a positive, and there's a negative. Okay, let's look at a But what I'm gonna do is I'm going to say which of the sides is the one that can make the most bonds. So, for example, the positive charge is on a carbon. How maney bonds can carbon make four. Okay, the negative charge is on a chlorine. How maney bonds can chlorine make? One can't remember. According to bonding preferences. I told you, you're going to keep using bonding preferences all semester. So is this going to react more like a nuclear file or more like an electric file? And the way that I look is I just basically, look at the four. I look at the highest bonding preference and I look at that charge. That's the one that I pay attention to because that's the one that has the highest bonding preference. So the answer is that this is gonna be what this is actually gonna be a really good Electra file. Why? Because the Adam that has the highest bonding preference is the one that is positively charged is not cool. And that's what you're going to use for all of these. So what I want you guys to do is we already figured out B. What about C is C A good nuclear power Electrical. Actually forgot to say this earlier. I should have pointed this out is see a nuclear file or an electric file? This is actually one of the easy ones, too. I forgot. So there was actually four easy ones and four hard ones. CIA's easy. Okay, so I'm gonna highlight this one as well. The answer is that it is none of them. Okay? Because I just told you, it's not even reactive at all. So if it's not reactive, it all. How can it be Ah, Proton lover or an electron lover? It doesn't even it's a nothing lover. It just loves itself. It's a narcissist. Okay, so it's just gonna be inert. It's not going to react with anything. So I wouldn't consider an electrical or a nuclear file. All right, So what that means is that really this has become a lot easier for you guys. All you need to do is identify F g and H and tell me what you guys think in terms of. If they're gonna be Electra files or nuclear files, what do you guys think? So go ahead and positive video now and use that rule to determine these last three
So that wasn’t so hard, but those were the easy cases. What if you have nucleophilic AND electrophilic regions on the same molecule? Is it possible to determine how it will react? Yes it is!
Rule: The side of the dipole with the highest bonding preference (the atom that wants to make the most bonds) will determine how the molecule reacts.
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example
Nucleophile or Electrophile
Video duration:
3m
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Video transcript
All right, so let's go ahead and start off with I'm gonna do f then h and then end off with water. Okay? So f I have two charges. I look at the side with the highest bonding preference. Carbon can make four bonds oxygen can make to bonds. Which one is the one with the higher bonding preference oxygen. So I'm gonna go ahead and look at that charge. So you should have picked that. That one is also gonna be a very strong electric file. Just you guys know I put these ones these molecules here for a reason. A happens to be the most important Electra file of or go one and f happens to be the most important electrified or go to. If you just know these two Electra files, you're gonna be, like, set pretty much set for Aureole won. And to the reason is because in Oracle one we're talking all about ocular Hey, leads what they do and then in or out, or go to We talk about all about Carbonell chemistry. We spend entire, like four or five chapters just talking about carbon deals. Alright at working as Elektra files. So just a little preview. Now, let's go on to H for H. I had lithium. Lithium has can make. How many bonds on Lee One. It's like hydrogen. Hydrogen is happy with one bond cuts in the first column. Okay, then carbon once again, like stuff. Four. So which one has the higher bonding preference? Carbon? So I only look at this charge. That's a negative charge. I mean, this is gonna be a nuclear file is not cool. So this is actually a molecule called an organic metallic. Sounds so scary, right? Organic metallic. What the hell? All it just means is you have an organic Oh, com are an organic part, which is the carbon. And you have a metal, which is lithium. Remember, lithium is a metal. So Organa metallics are actually really common nuclear files. And later on in this course, we're gonna be using these all the time as really important nuclear files. Cool. Awesome. So I've got the last one, and I just want to tell you guys really quickly. Water is an exception. Water can act as both okay, because water, as you guys know, it has a di poll. Okay, But I mean basically what has is it has thes negative electrons so it can accept electrons. Okay. I mean, it could give away electrons, but it can also accept electrons. Waters kind of neutral. So what that means is that water is going to be that one compound that's always going to be able to react as either a nuclear file or Electra file, depending on what the other substance is. Okay, so I just want to say that water is kind of an exception. You can't tell if it's gonna be a nuclear file on Electra file until you see the other re agent and see how that one's reacting with it. Okay, Cool. So with that said, I hope you guys air understanding why molecules react. And I hope that your understanding how, like, in general terms, nuclear phone, Electra file. And now what I wanna do is in the next part, I want to talk about actually drawing out what these reactions look like. So let's go ahead and go for it.
Bond Making
Now we understand which molecules will want to react, and we are getting better at determining If they are nucleophiles or electrophiles, but how to they actually attack other molecules?
Reactive molecules share electrons to become more stable. Arrows are used to show which direction they are going.
Arrows always move from regions of high electron density to low electron density
By that logic, nucleophiles must always attack electrophiles.
Each attacking arrow represents two electrons being shared.
After the reaction is complete, replace that arrow with a new σ -bond
Summary:Molecules with lots of electrons will attack (draw an arrow to) molecules with a positive charge. Let’s get drawing!
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concept
Learning the rules of electron movement
Video duration:
4m
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Video transcript
so that first part was pretty fun, right? We just learned how to tell the difference between a non reactive molecule, which is just inert or reactive molecule, which is actually gonna try to make bonds with other molecules. Okay, on top of that, then we also learned what type of reactivity they have if they're going to react more like an electric file or a nuclear file. Well, now what I want to do is actually wanna learn. I want to teach you guys how to start drawing out these mechanisms. So what that means is we're actually gonna start drawing electron movement, and you guys are gonna be probably the first people in your class to draw as good mechanisms as we're gonna do now. But I'm not concerned. I know you guys are smart, and I think you guys are gonna like this part. So let's go ahead and get started. So reactive molecules are the ones that are going to try toe do something about their reactivity. So what that means is, if you're a non reactive molecule, your inert, you don't care. But if you're reactive, you're gonna try to share electrons with another molecule in order to become more stable. Remember that we talked about that in the first chapter. How we form molecular Orbital's in order. Thio reach a lower energy state. Okay, so it turns out that we're gonna use curved arrows to indicate the direction that these electrons air going and inorganic chemistry. That's actually a huge part of this field. A huge part of this field is just figuring out where these electrons are moving to their start here on they move over here and then what do they do? And then they move over here and those air called mechanisms. Okay, so I'm just gonna tell us right now. Ah, huge part of this course is gonna be drawing arrows and figure out where these electrons moving from. Adam. Adam! Adam. Okay, so I just want to teach you guys are remind you guys a few things about the way that electrons move. And it turns out that these rules that I'm gonna teach you are the same that we learned for residents structures. Why? Because it turns out that resonance structures are the same thing. In terms of that, we're moving electrons from one atom to another. So Let's go ahead and get started. So remember that arrows air always gonna move from regions of high electron density Too low electron density. Okay, so what that means is that we always want to start from the part of the molecule that has the most electrons and moved to a part of the molecule that doesn't have a whole lot. This is the same that we same thing that we did it in residence structures. Okay, but back when we talk about resonance structures, we didn't know about nuclear files and electro files. So now that I've taught you what a nuclear file is and what an electro file is, which one do you think is always going to be the one that starts off the arrow? Because, remember, we always start from the high area. Okay, So do we start off from the nuclear file or from the electro file? And the answer is that we're going to start off from the nuclear file, Okay, because the nuclear follows the one with the negative charge. Right? So we're always gonna have nuclear files that attack Electra files. Okay. And a huge part of organic chemistry can be summed up as saying nuclear files attack Electra files. Honestly, Like when it comes down to it, you could probably explain 50% of the reactions Just talking like that. Okay, so it's a very important point. Okay, So another thing is that each attacking arrow is going to represent two electrons that are being shared. So every time that I draw one of these arrows, that means that I'm sharing two electrons with another atom. And what that means is that after the reaction has taken place, I'm gonna replace whatever that arrow was. I'm gonna replace it with a new Sigma bond. Okay? Why is that? Because remember that a signal bond equals two electrons being shared. Okay, So what that means is that an arrow is really just a fancy way of drawing a Sigma bond in motion. That means I'm creating a new Sigma bond. Does that make sense? So far? I know it's a lot of words such just go ahead and get started. So what I want you guys to do for these reactions is I know that you don't even know what these molecules are. Really. But we do understand nuclear files, and you do understand Electra files, and we also understand how electrons move. Now we kind of know. So what I want you guys to do first of all, is determined the initial direction of electron movement by drawing the very first arrow of each mechanism. Even though we don't know what's going on here, it's okay because you could just follow the general rule of nuclear following Electra five.
Using those rules, let's draw the mechanisms for the following reactions
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example
Drawing Electron Movement
Video duration:
51s
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Video transcript
So in this case, I have a negative charge and I have a positive charge. Where do you think my arrow is going to start from my arrows going to start from the negative charge? Because remember that we always start from the nuclear fault or the area of high density. So what that means is that my arrow starts from the negative. Where do you think it's going to go to? Well, it's going to go to the area of least electron, So that means that it's gonna actually try to attack that carbon right there. Because what's going on is that the negative has too many electrons. And it's saying, Hey, I want Thio, Go ahead and and link up to a positive charge in order to neutral out and to balance out. Does that make sense? So the first arrow of mechanism is negative to positive. Does that make sense? So far, that's very similar to what we did in resonant structures. Except now I have a full negative in a full positive, Okay?
10
example
Drawing Electron Movement
Video duration:
1m
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So for this next one, I also have a negative charge, but I don't have a positive charge. So can you guys tell me where you think the arrow is going to start from? The arrow should start from the negative charge. That means it should start from the end. Okay, Now the question is, where is it going to attack in the first one? It was really easy. My electro file was really easy to figure out because it just had a positive charge. But in this case, I have water. Now, remember that water is an exception where it can act as either a nuclear file or is an electric file depending on what it's reacting with. So where do you think it would attack here? I'm gonna give you a hint. The only way to know that is by drawing out die polls. So what I want you to do is draw the dye pulls on this molecule and figure out where the partial positive charge is. Once you figured that out, then you can draw the rest of this arrow. So go ahead and pause the video. Try to find the partial positive, and then draw the arrow directly touching that. Positive. I mean, directly attacking that positive. So go for it. All right, so let's just draw draw the dye polls. I had these die polls from the lone pairs. I also had these die polls pulling up towards the Oh, what that means is that the O has a partial negative because it has thes electrons moving up towards it. And then both of these ages are partial. Positive. Does that make sense? Because they're getting electrons pulled away from them. So if I were to complete this arrow, where do you think it would attack? What it's gonna attack is one of the H is because the H is the thing that has the most positive charge on the entire molecule. Does that make sense? So now that h is what's acting as my Electra file? Isn't that interesting?
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example
Drawing Electron Movement
Video duration:
1m
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Video transcript
So now it's going to see. So for See, I don't have any charges. So now this is getting harder and harder. Okay, where do you think I could react on? See, where do you think I would want to start from? I'm gonna want to start from the thing that is most has the most electron density, the highest electron density. So is there a nuclear file here that we learned from the previous page? Yes, there is. Remember that I told you, is that double bonds are good nuclear files. Okay, so what that means is that even though I don't have a charge, I can still say that my arrow is going to start off from the double bond. Why? Because the double bond is a good source of electrons for reaction. Now, all I need to do is figure out which Adam on the HCL is going to react with. Okay. Is it gonna act with the H or is it gonna react with CL? The only way to know that for right now is to draw the dye poll. So let's go ahead and draw the dye poll. Which one is more electro negative? Chlorine So let's go ahead and do that. That means I have a partial negative. Ah, Partial Positive. Good. Okay, So now where is that negative charge you're gonna want to attack? It's going to attack the H. You guys see that? Because once again, the H is the thing that has the positive charge. And you can consider that the dull bon pretty much has a negative charge. Because as those free electrons that are very easy to donate, does that make sense? So far? I hope so. I hope that what you're seeing is that we're just always following a trend of nuclear file attacking the Electra file. Sometimes the Electra files really obvious, like in problem A. But sometimes we have to draw die polls in order to know what the electrified is. Cool. So far, awesome.
Bond Breaking
So now we know how to make bonds. Do we ever have to break bonds? How do we know if we do or we don’t?
12
concept
Why we need to break bonds sometimes.
Video duration:
1m
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Video transcript
Now, what I want to talk about is what we just did was what I call Bond making. Okay, All of this was forms of bond making where I am. Basically, all these arrows indicate the sharing of two electrons. Right? And I said that after the reaction, you're going to replace that arrow with a Sigma bond. Okay, so that means that all of these arrows that I just drew are eventually going to become little sticks that I draw off of each of these atoms. So that's gonna be a stick. That's gonna be a stick. And that's going to be a stick. I hope that you understand that what I'm saying is that arrow is just a really long way of drawing a single bond that's gonna be formed. Okay, Now, what I want to talk about is bond breaking. Okay? So bond breaking is sometimes required okay? In mechanisms, but it's on Lee required when it's needed to preserve octet. It's so what that means is that just like resonant structures, remember that sometimes we would want to make a bond, but that bond would break the octet of a certain Adam. So then what would we do to fix that, we would also break upon. We would make a bond, and then we would break a bond in order to preserve the octet of that atom. So in the same way, we're gonna want to break bonds in order to preserve octet of atoms that are getting attacked, okay?
Bond breaking is sometimes required in mechanisms, but only when it is necessary to preserve octets.
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concept
The two ways to break bonds.
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1m
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Now, there's actually two ways to break bonds there. And I just want to teach you as this really quick. There's hetero Olynyk cleavage. Which hair Olynyk cleavage means that you get ions. Okay, You get, like, a cat eye on on one side, and you get an an eye on on the other. Okay. Hetero Olynyk. Hetero means different. So that just means that you get different amounts of electrons on both. Okay, Notice that for a hetero Olynyk cleavage, I use a full arrow. Okay, well, then, the other option is that I have home Olynyk cleavage. Home Olynyk cleavage means that each of the atoms, when once the bond breaks, gets the same amount of electrons. So each of them get a radical, okay. And home Olynyk cleavage is done with half arrows. Notice that the head of that arrow is a little bit smaller. It's like Onley big on one side. Okay, I know that my head's right in the way of radicals, but you're gonna get radicals. Okay? So what I want you guys to know is that for most for this entire chapter, we're really just going to be dealing with hetero lyric cleavage We're not going to get into home Olynyk cleavage until we talk about radical chemistry, which is coming up in a few chapters, so you don't have to worry about it yet. Cool.
Out of these two different ways, we will stick to heterolytic cleavage for the foreseeable future (we won’t discuss radicals for a few more chapters).
Identify if the following reactions require bonds to be broken. Draw the products.
14
example
Identifying Bond Breaking
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1m
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So what I want you guys to do now is we already talked about which bonds would be made. What I want us to do now is figure out which bonds would also have to be broken in order to but not violate octet. Basically, I want you guys to finish these mechanisms on your own. Okay? I know that sounds rough, but let's go ahead and look at the look at a Okay, So for a in my first step, I went ahead and I made a bond to this carbon. Okay, now that I made a bond to that carbon and my violating its octet, the answer is No, I'm not. Because check it out. This carbon had how many? I'm sorry. Had how many electrons? A 4246 How many total electrons can carbon have 88 Okay, so if I add tomb or is that gonna break the octet? No. So that means that in this mechanism there's gonna be no bond breaking. That mechanism is over. So my final product would look like this. Oh, okay. So I just read through the original now for where? That original. Where that curved arrow was Now I'm just gonna draw a single bond. That single bond represents the two electrons that are being shared. And now I'm going to draw that connected to what was on the other side. So that's gonna be attached to a C with three inches. Isn't that interesting? That's my final product. So basically, all I did was I made a bond, but then I never violated the octet. So that's my final product. Okay. And once again, that new blue bond comes from the arrow. Okay? The arrow turned into a bond.
15
example
Identifying Bond Breaking
Video duration:
2m
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Now, let's look at this next one. Okay? So I'll probably just have you guys do the last one on your own. Okay? So for n notice, that end went ahead and it grabbed the H right here. So now I have to ask you guys, how maney bonds does hydrogen like to make Remember, bonding preference? What does it like to make Onley one bond? Right, We'll check it out. This hydrogen already has a bond to the oxygen. Now, what I'm doing is I'm making another bond to the nitrogen. That's my second bond. So is that hydrogen gonna be happy making to bonds? No. Is it gonna satisfy the octet? No. Remember that Hydrogen wants to have two electrons in its octet. If I make to bonds to it, it will actually have four electrons in its octet. That sucks. So in order to make this bond, what must I do? I have to break upon. Okay. So what that means is that I'm going to delete these die polls because we don't need them anymore. We don't need those anymore. Okay. In order to make that bond, I'm gonna have to break upon and the way that I break upon is I just take two electrons from the bond and I give them to the Oh, so if I make a bond, I break a bond, okay? And what that means is that now my final products are gonna look like this. I'm gonna get a H within. Oh, but now that o instead of having to lone pairs, it has three because it has the two old lone pairs that it used to have. But now it has that extra lone pair that came from the single bond. Does that make sense so far? Cool. Then finally, I have plus my ring structure with the end. But now notice that the end made a new bond to that H. So I'm just gonna draw that Now there's a stick attached to the H. Does that make sense? Where now that h came from what was attached to the O. Now the only thing we have to do is we have to add formal charges. So are there any formal charges here? Yeah, it turns out that O has too many electrons. So would have a negative charge. Okay. And in the end, already has a lone pair. It did from the beginning. So the end is perfect. The end likes its situation. Okay, so notice that in this reaction I actually exchanged Ah, hydrogen and a negative charge. This is actually an acid based reaction. But you guys just throughout the entire mechanism yourselves. So you guys, like, honestly deserved, like a pat on the back. Or you could give me a pat on the back if you want. All right. Hopefully, that wasn't too confusing. We're just doing the same thing over and over again. We're doing the first step is nuclear file to Elektra file? The second step is to break if you need to.
16
example
Identifying Bond Breaking
Video duration:
2m
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Alright, guys. So the answer was that just be, like be you do need to break this bond. The reason is because once again, hydrogen on Lee wants to have one bond not to. It already has a bond. I'm gonna delete these die polls again. It already has a bond to the chlorine. This arrow is gonna be the second bond. That's not good for hydrogen. So in order to make this bond, I have to break a bond. So I'm gonna take these two electrons and give them to the chlorine. Okay, So what that means is that at the end, I'm now gonna have a square that doesn't have a double bond anymore. Why? Because the two electrons from that double bond are what became the Red Arrow. Okay, then I'm gonna have a stick. That stick is the red arrow. The electrons that were shared and that stick is going to be attached to a hydrogen. Okay, awesome. So now that stick is attached to a hydrogen, and now we just have to figure out what's left. Well, I have a chlorine that used tohave. How maney lone pairs. How maney did it used to have one to three. Okay, so it used to have three lone pairs. Now, how Maney doesn't have Well, it still has those three lone pairs. But then it also gained an extra lone pair from that bond. So this is four. So now that chlorine is gonna have a negative charge, does that make sense? Because it has eight electrons instead of seven. Now, we're almost done. But the problem is that, I mean, we're pretty much done. But the problem is that we have one more thing we have to watch out for, which is that any time you break a double bond, you're breaking the amount of electrons that to Adams had. So this Adam up here, this carbon had one h and this carbon had one. H r. You guys cool with that? So far now that it reacted the top carbon still has that blue H, but now it has a new red h attached to it. The red H came from the HCL. Okay, so basically, what I'm saying is this h is the original one from here. And then this h is now the new one that came from there. Okay, but the bottom one still only has one H because it never got it. Never attacked another H. So what that means is that the bottom is now going to get a positive charge. Because now Carbon wants the four bonds, but it only has three. Okay, so this is actually your final product for this step. Okay? And it turns out that this is actually gonna be reaction that we explore a lot more in future chapters. But I'm just helping you guys to see how we can use nuclear files on Electra falls to figure these things out, even if you don't know the reaction, Okay. And it also turns out that if you have a good understanding of nuclear falls and Electra files, even if you forget reactions in organic chemistry, you can still figure them out because you know these things, All right?