 Okay, so this is an addition reaction. We are going to learn it much later in the course of a few chapters from now, actually but I Want you to help me out drawing the mechanism, okay? So what type of molecule is this here? It's an acid. So what kind of reaction are we going to have first? Acid base. So what's the base going to be? The alkene, okay, and where are the electrons from the base going to be coming from? The double bond, okay So notice, where does the hydrogen go? Where does this hydrogen, this proton go on this molecule here? Does it go to this carbon? Or does it go to this carbon? To the left. Why do you know that? Because it became a methyl group. So this is tetrahedral, right? And this is what's the geometry around this thing? Pardon? Trigonal planar, right? Trigonal planar, carbocation, let's have trigonal planar arrangement around molecular geometry. So how are we going to draw this mechanism? So oftentimes you'll see in these organic chemistry books where they just take the pi bond and move the electron. I don't want you to do it that way. I want you to actually show me which carbon it's being attached to because it will make your lives much easier when you're trying to do these on your own because you won't have these products eventually. You'll have to figure out what the products are, okay? So in this particular one, the hydrogen is going here. So what I want you to show is that arrow going through that particular carbon there, as opposed to going to the other carbon, okay? Because that hydrogen could have gone on either one of those carbons. Do you guys understand what I'm saying? So we want to kind of show exclusively which carbon it's going to. Is that the only arrow of this mechanism? No, we have to do one other thing, right? What? So what did we form? One sigma bond and we broke another sigma bond. So we definitely performed a what? Chemical reaction, right? And what about this step? What's the second step of the reaction? Oh, I guess I shouldn't have said that. How many steps does this reaction have? Two steps, okay? So if I were to think about my reaction diagram, how many peaks would I have on my reaction diagram? Two. And how many valleys in between those peaks? One. That valley, what is at the bottom of that valley? The intermediate. And in this case the intermediate is a what? Carbocation. So carbocations are often you'll see as intermediates in chemical reactions, okay? What are the things at the top of the peaks called? Transition states. So are they shown in any of these pictures here, the transition states? No, remember it's kind of those half bonds. You can almost think of the transition state as being what you're drawing as the mechanism. It's more like drawing half or dashed bonds to everything though as opposed to showing the electron flow, okay? So let's just go ahead and finish the second step. What would the arrows look like? Yep, so the lone pair electrons from the chlorine to the positive, like that. So let's remember in organic chemistry, we like to identify nucleophile electrophiles. So let's go over here and identify a nucleophile electrophile. Which one is which? The carbocation, the electrophile. Electrophile. Why would you say that? Because they receive electrons. You see it likes electrons, right? So this is the electrophile and this is the This thing here has a functional group in it. You see the chlorine? All these alkyl halides. This is a way to make alkyl halides. So you can take an alkene reacted with HCl and you can make an alkyl chloride. So this is one of your first reactions that you can understand making something from something else. So the organic chemistry is all about this making stuff. Nope, this is only the one arrow on this one. So if we were to draw another arrow, we would be breaking a sigma bond. Because look, what's happened here? We've got two reactants and they made one thing. So they must be a combination way. So there can only be the one one. Not necessarily. You just got to go through, we'll go through a bunch of reactions and maybe you can find some kind of, I don't know, idea as to generalize, okay?