Now you’re finally getting ready to start understanding types of chemical reactions. Oh joy!
Concept: What you need to know about types of chemical reactions.1m
In this chapter we’re going to talk about reactions. And what that means is that your professor is going to want you to be able to recognize basic types of reactions. So you’re not going to need to understand all the reactions that happen in Organic Chemistry yet but there are four major types of reactions that your professor is going to expect you to be able to recognize. So maybe you don’t fully understand it but you can say, hey, based on these general features this must be this type of reaction. Alright? And this could be a multiple choice type of question for you on your exam. So let’s just go ahead and get started.
We’re gonna learn about 4 different types of chemical reactions. You don’t actually need to understand these! Just be able to recognize them for now.
Concept: Recognizing Acid-Base Reactions.3m
As I said there are four major types. And the first one is the easiest one. This is going to be called an acid-base reaction and in most textbooks this is will have its own chapter. So usually we’re gonna have to spend an entire chapter just to talk about acid-base reactions. Now the general features of this that you should be aware of are that molecules of opposite charges are going to react together to exchange a proton. Okay? Now, I used the word “proton” earlier in the first chapter when I was explaining just electrons and protons and stuff and what I said what a proton was, was just H+. Okay? Because remember, that’s a hydrogen. It doesn’t have an electron and it doesn’t have a neutron so it’s just a proton. That’s why we call it a proton. Alright? Now notice that I did put the word “usually” next to it because it turns out there’s going to be some special types of acid-base reactions that don’t exchange a proton. Alright? But we’ll get there. I’ll let you guys know what those are.
So I just want to show you guys this example. This is a very common example where I have basically a negative charge, okay, and that would be one of the charges. And I’m looking at the other molecule and I see well there’s no positive charge. So is this really going to be acid-base? Well, if you think about it we’ve already learned about electronegativity, right? And remember that we learned how to draw dipole moments. So if I were to look at this HO bond right there. Is there a dipole on that bond? And the answer is yes. There’s actually a very strong dipole pulling towards the oxygen. So what that means is that more electrons are there at the oxygen and less electrons are at the hydrogen. Are you guys comfortable with that? That just has to do with the partial charges we assign. Imagine that the O is like a sumo wrestler pulling on that rope and pulling all the electrons towards itself and that H is the puny guy that can’t even keep up. Right? So what that means is that we are going to get an exchange. The opposite charge that I am talking about is this oppositely charged hydrogen. So the opposite charge that I’m talking about is oppositely charged hydrogen. So I have a negative interacting with the positive and what’s going to happen at the end is that remember that I said you’re gonna have exchange. So what that means is that I’m going to redraw this first compound and what I’m going to draw is that now this O gets a negative because before, the other O had the negative. And now this OH over here is now attached to the H that came from the other compound. Alright? So basically what happened was that I switched a negative charge and an H. See how that happened? That’s what we call an acid-base reaction, exchanging protons and electrons. Alright? And then we’d get more in-depth with that later.
In this reaction, two molecules of opposite charges react to exchange a proton. (There are some exceptions that don’t, but we’ll get to this later)
Concept: Recognizing Substitution Reactions.2m
This is an acid-base reaction where an atom (or group of atoms) other than protons are exchanged.
Concept: Recognizing Elimination Reactions.1m
Here, two single bonds (σ) are removed to create one double bond (π).
Concept: Recognizing Addition Reactions.1m
In these reactions, one double bond generates two new single bonds.