Okay, so welcome to Lecture 1, Part A of OC2. This is Dr. Soler speaking. And just to give you an overview of what we're going to do in Part A is we're going to introduce you, hello, to alkyl halides. And we're going to describe what are they, the general structure of an alkyl halide, how they're made, and why they're useful. And then we're going to do an overview of the reactions that we can do, and that we will explore in this module with alkyl halides.
So Let's start off with alkyl halides. So let's start with a broader vision. So we have organic halogen compounds.
So these are organic compounds that contain one or more halogens. X is used to indicate halogen, and that's combined with a carbon atom. And there's elements as well.
So if we look here, we have an alkyl group here. But there's two halogens on here. There's a carbonyl there.
Here is, oh, there's an aromatic ring. There's a halogen there, halogen there. And look at this. We've got some aromatic rings here.
It's a big ring structure. And there's a halogen there. So those are organic halogen compounds.
But we are narrowing into an alkyl halide. And these are also known as halogenoalkanes in some cases, in some textbooks. So this is really a subset of this organic halogen compound.
So we're specifically focusing on alkyl compounds. So what is an alkyl group? Well, it's a carbon which has got an sp3 hybridized atom, which you might recall from Professor Jamieson's lecture, and that carbon atom is bound to a halogen atom. Now that halogen could be Fluorine, chlorine, bromine, or iodine. In this module, we are focusing in on chlorine, bromine, and iodine.
We are going to ignore poor fluorine there. We're going to ignore it because the bonds are so strong between that carbon and that fluorine that we're not going to get the reactivity that we want and we're going to need when we're discussing our reactions. So this is the shorthand form of an alkyl halide R for the alkyl group.
X for the halide. And you might want to remind yourself, what does alkyl mean? Well, alkyl group is a functional group. It's like an alkane, but one of the hydrogens has been taken away.
It's missing a hydrogen. So if you have, think about methane, if you lose one hydrogen, you have a methyl group. So we use R to indicate a general alkyl group. alkane, alkyl.
So this could be methyl from a methane, okay, it's methane. Ethyl group, that's ethane that's missing a hydrogen. Isopropyl, isopropane, which is missing a hydrogen. And if you look at each one of those carbons, they're sp3 hybridized. So there's four different things bound to that carbon.
We need to think about the structure of alkyl halides because that's setting us up for what's going to be happening for over the next two lectures. So we have our carbon there. Our carbon is sp3 hybridized.
So there's one, two, three, four things bound to that carbon. That allergen could be fluorine, chlorine, bromine, or iodine, but we're going to ignore fluorine and just focus on those three as stated before. So because it's sp3 carbon.
hybridized, we have this tetrahedral geometry around this carbon, which is 109 degree bond angle, more or less. And if we, let's just explore that carbon-allogene bond. Remember when you have a single line there, that means you're sharing a pair of electrons. I've shown that pair of electrons here.
So we're sharing that pair of electrons, and this is an overlay of that carbon in. sp3 orbital with that p orbital of the halogen and you form that bond and you're sharing that pair of electrons. You've got a little back lobe here and you've got your little back lobe here of that sp3 orbital. This seems irrelevant but it's incredibly irrelevant. So the nature of the beast between this carbon and this halogen and how the electrons are shared between them.
and these back orbitals and what's bound to the carbon is going to direct us into different types of reactions. So how do we make organic halogen compounds? Well, I don't really care.
It's not a topic of my module, but I'm just giving you a quick overview just to remind you. Okay. And this is coming from, I think, Professor Jameson's course, OC1.
But we can add to an alkene, okay, or acetylene, if you wanted to, a triple bond, we can add HDL or HBR across that multiple bond. Okay, so that's one way of making it. It's hydrohalogenation. Or we can add bromine or chlorine to an alkene or acetylene, and that's called halogenation.
So this has been covered before, but if you've noticed, I keep saying addition. We're adding it across that multiple bond, that single or triple bond here, in this case, a double bond. You can also make organic halogen compounds by substituting a hydrogen on an alkane. that's over here, with bromine or chlorine. But this is going through a radical reaction pathway.
We're not covering this. It leads to multiple mixtures. So as I said, not to worry about this. What I want to do is talk about alkyl halides once we have them, because they are very useful compounds. So here's our alkyl halide.
They're reactive compounds. Okay, so once you have an alkyl halide, you can use it to do lots of different types of chemistry. And it's a very special compound because of the nature between that carbon bond and that halogen.
What it means is the alkyl halides are really good electrophiles. Okay, this bond, as we're going to explain to you, is polarizable. So we get a partial positive charge on the alkyl side and a partial negative charge on the halogen side. And this means we can actually break this bond and this forms a really good leaving group as a halide anion.
Okay, this is a lot of words. I'm going to be showing you with pictures what I mean here. So alkyl halides can be treated with nucleophiles or with bases to form products that you desire. So depending on what you want, you can treat it either with a nucleophile or a base.
And we will show you this. And this is why. alkyl halides can undergo a lot of different types of substitution and elimination reactions, not addition reactions. That's what I'm not talking about here. I'm talking about substitution and elimination reactions.
So what we're going to go over in this lecture module is three types of reactions with alkyl halides. We're going to talk about two types of nucleophilic substitution reactions and one elimination reaction. So this lecture, we're going to talk about nucleophilic substitution reactions. And in order to do that, here is your alkyl halide. Okay, when in doubt, look at a name.
Substitution, we're going to substitute with a nucleophile is going to be substituting that halide to form a good leaving group. So it's a nucleophilic substitution reaction. And we're forming a bond between the nucleophile and that carbon.
So we need a nucleophile to do that. Makes sense. Nucleophile is substituting that halogen, and there's two types we're going to cover.
We're going to cover SN2 and SN1. This lecture is focused on SN1. We're also going to explore elimination reactions.
Elimination is different to substitution. In this case, we're going to use a base, and the base is going to interact with your alkyl halide, and you're going to lose both. a halogen and and hydrogen off of the alkyl group here which i've drawn over here just so you can see it okay so both of those are lost and that means if you lose that and that you form an alkene okay there are several types of this we're only going to cover in this course next lecture the e2 reaction so none of these reactions that i'm talking about here are additional reactions we've got substitution and elimination that we will be covering. And that is the end of part one.