Skip to main content
Pearson+ LogoPearson+ Logo
Start typing, then use the up and down arrows to select an option from the list.

Organic Chemistry

Learn the toughest concepts covered in Organic Chemistry with step-by-step video tutorials and practice problems by world-class tutors.

10. Addition Reactions

Addition Reaction

Now we’re going to discuss a new type of organic mechanism called addition. There’s tons of these to keep track of, so let’s get right into it!


Features of Addition Mechanisms.

Play a video:
Was this helpful?
Hey, guys. So at the very beginning of the semester, in those first few lessons, I taught you guys that most of organic chemistry can just be summarized by the reaction of nuclear files with Elektra files. And we've already seen a few examples of how negatively charged species are usually nuclear vials. All right, But in this section, what we're going to study is that double bonds can also be really good nuclear files because they're good sources of electrons. All right, And these reactions categorically are called addition reactions. All right, so let's go ahead and get started. So the general mechanism for an addition reaction is any reaction that's gonna take one pi bon. Okay. And it's gonna break it and form to new signal bonds. Alright, We call that addition because you're basically taking one bond and you're making to later. Okay, so that makes sense. It's addition. You're basically adding to the number of bonds in the molecule has. All right, now, this is actually gonna be the inverse of a reaction that you may have already learned or about to learn, and that's called the elimination reaction. Okay, The elimination reaction is actually the exact opposite. All that means is that for an elimination you would take to signal bonds and we'd make one pie. All right, But in this case, what we're gonna do is gonna take that pie are going to make to signal bonds. All right, so let's just look at the general mechanism, see where the arrows would flow here. Okay. All the rules for mechanisms that I taught you in the past still apply to this mechanism. So where do you think the arrows would start from? Remember that we always want to start from the negatively charged species or the thing that's electron rich to thing. That's electron poor. So we're gonna start from this double bond. The double bond is the source of electrons. In this case, that is the nuclear file. So when a drawn arrow coming from that double bond Now, maybe the more challenging part is figuring out where does this arrow go? Okay, In this case, I have an h and an X, and I'm trying to find the Electra Filic portion because I want to find what's the most positively charged thing on the map. All right, so how could we figure that out. Do you guys know what we could uses? Die polls? Okay, that's what we've been doing for a lot of molecules in this course we've been saying, Okay, where is the DI poll going to pull? And in this case, X stands for any of the religions. So we know that X is always gonna be more Electra negative than the H. So if I'm pulling electrons away from the H, that means I would get a partial positive here in a partial negative here. Okay, Now we know what the electrical it portion is. The electrical portion is going to be the H. So when I draw this mechanism, I'm going to draw it straight to that age. All right? Now, can you just end there? Are we done? No, we're not done. Because remember, hydrogen hates toe have to bonds, and that new arrow represents a new bond that would be created. So if we make upon, we have to break upon. And the bond that we would break is to the X. Okay. What this is going to create is a new molecule that looks like this where I now have basically a double bond and I'm gonna have a new H on one side now. No, there is something that you have to realize here. These carbons right here already had How maney hydrogen. They each had one. This had one hydrogen. This had one hydrogen. Is that cool? Because each of those carbons needed to have four bonds, Obviously. Well, those hydrogen, they're still there. The only difference is that now I'm adding one more h. So let's go ahead and add one more h to one of those bonds. Okay? So I'm just gonna add it right here, in case that's the new age that's coming from my H X. Okay. What about the bond at the bottom? Notice that I used to have a double bond on both of those carbons, and now I don't anymore. So what that means is that if I get a H on one side, I'm gonna wind up getting a carbo cat ion on the other. Now, just remember, a carbo Catalan is the name that we give to a carbon that's missing an electron. Okay, Instead of having four electrons, valence electrons, it only has three. Okay, It's not about this car. Will Catalan and trying to figure out what to do with it. Is there anything that it could react with? Yes, We'll check it out. I've actually gotten X minus hanging around. I've got a spare. An ion. Okay, so what do you think this next arrow is gonna come from the X and I'm gonna go ahead and attack the caramel cat I in. Do I have Thio draw another arrow? Now I'm done. I actually am done because remember that when you make a bond, you only have to break a bond. If you're violating the octet of that atom by adding the X to the carbon, I'm actually going to complete the octet. Okay, So what that means is, I don't have to break anymore, Bond. This is actually the mechanism is final drawn the way it is here. So what that means is that I'm going to get a product, and that product is gonna be my addition. Product. What is gonna look like is that now I'm gonna have let's just say to h is here, and then I'm gonna have an X here. Does that make sense? So far? Cool. So the reason we called this edition is because check it out. I started off with one pie, and at the end, I got to new signals out of it. Okay. Now, by the way, I drew all those ages just to be thorough, but you wouldn't need to draw all of them. In fact, you could just draw the product like this a cyclo hexane with an ex. Okay, because I know that the X is gonna attached to one side or the other. Okay, So just letting, you know That's the general mechanism. And it turns out that for this section, we're gonna be using the same mechanism over and over, gonna use it least very similar mechanisms to this, okay?

Addition reactions are ones in which 1 π-bond is broken and 2 new σ-bonds are formed.

They are the opposite of elimination reactions (if you haven’t learned about these yet don’t worry). 


Provide the mechanism

Play a video:
Was this helpful?
Let's go ahead and get started. The double bond is the source of my electrons. So I'm going to go ahead and grab the H, Remember, because the H is the positively charged species on that H x. OK, if I make that bond, I have to break a bond. So I'm gonna go ahead and draw an arrow on the X, making it leave. Okay, What that's going to give me is it's going to give me an H on one side, a new H, and it's going to give me a Carvel Catalan on the other. Now, does it matter which side that I picked? Like, for example, if you put the car will carry on the top, would you be wrong? No, it doesn't matter. They're both exactly the same. So if you went ahead and you put the h at the bottom and the car will carry on at the top, you're doing great. It's the same exact thing because both of those carbons are identical. Okay, Now it's gonna come and make that Karl O'Callaghan kind of like more stable, the anti on, right? So when you take my ex, I'm gonna attack. I don't need to break any bonds, because now I'm actually completing the octet of that carbon. So my final product would just look like this. Okay. And like I said, if you drew the exit the top, that would have been the same exact thing. So so far, this mechanism isn't that bad, right? It's not super scary.