Ch. 14 - Synthetic TechniquesWorksheetSee all chapters
All Chapters
Ch. 1 - A Review of General Chemistry
Ch. 2 - Molecular Representations
Ch. 3 - Acids and Bases
Ch. 4 - Alkanes and Cycloalkanes
Ch. 5 - Chirality
Ch. 6 - Thermodynamics and Kinetics
Ch. 7 - Substitution Reactions
Ch. 8 - Elimination Reactions
Ch. 9 - Alkenes and Alkynes
Ch. 10 - Addition Reactions
Ch. 11 - Radical Reactions
Ch. 12 - Alcohols, Ethers, Epoxides and Thiols
Ch. 13 - Alcohols and Carbonyl Compounds
Ch. 14 - Synthetic Techniques
Ch. 15 - Analytical Techniques: IR, NMR, Mass Spect
Ch. 16 - Conjugated Systems
Ch. 17 - Aromaticity
Ch. 18 - Reactions of Aromatics: EAS and Beyond
Ch. 19 - Aldehydes and Ketones: Nucleophilic Addition
Ch. 20 - Carboxylic Acid Derivatives: NAS
Ch. 21 - Enolate Chemistry: Reactions at the Alpha-Carbon
Ch. 22 - Condensation Chemistry
Ch. 23 - Amines
Ch. 24 - Carbohydrates
Ch. 25 - Phenols
Ch. 26 - Amino Acids, Peptides, and Proteins

When trying to make alkanes reactive, we must first perform a radical halogenation to add a halogen and allow for further reactions to take place. 

 

The one exception we must remember is that when doing a radical chlorination in particular we can only perform this reaction when a single type of hydrogen is present

Concept #1: Functionalizing Alkanes

Transcript

So the synthetic cheat sheet focused on a few different important rules. Now what I want to do is focus on one of those in particular and that's alkane halogenation. So this is actually a pretty easy rule because we just remember that this is the only way to functionalize alkanes through radical halogenation. It's the only way.
I've already said in past lessons that radical chlorination is really only useful if you have a single type of what in your molecule? Do you remember? Hydrogen. Only if you have a single type of hydrogen will it be helpful. If you don't, then it won't be.
I would love it if all of you guys got this as your retro-synthesis. This first question. How do you turn that alkane into this alkyl halide. Oh my God. It's so easy. You could do this in your sleep. It's just Br2 over heat or light.
So you're thinking man, that would be so awesome. But guess what? Your professor probably isn't going to give you that at least by itself. What you're probably going to get is either this in a multi-step retro-synthesis or it's just going to be harder than that. Because that's too easy. That's just way too straight forward.
So what you're more likely to get is where you have to turn an alkane into an alkyl halide that you can't immediately get in one step from halogenation. For example, we can easily put bromines here. But it's not that easy to just stick a bromine on a random carbon like that or to stick a bromine on a random carbon like that. How do we do that? That's going to require multi-step synthesis. That's going to require us to kind of concentrate and figure out what reagents would it take to transform into that. That's the first thing.
The second thing is that you guys should also know how to take an alkyl halide like this and turn it back into an alkane. It's important to know what reactions could go backwards and take it back to the alkane. So we're going to be practicing all of that here.
Now what I want you guys to do, in particular, is focus on I think two of the easier ones. This is not the easiest exercise here. It's a little bit tricky. But I want you guys to focus on (b) and (d) and tell me what those reagents are because (b) is basically taking – it's not that bad. It's taking this alkane and putting an alkyl halide right there. So you're going to have to figure out in multiple steps, it's not just one step, how you can do that. (d) same thing, we're just putting it in a different place.
So I want you guys to try out both of these. I'll pause the video. I'll pause, you know. And you guys try your hardest to get those syntheses down and then obviously, I'll show you the answer. So let's go for it. And I've already said in past lessons that radical chlorination is really only useful if you have a single type of what in your molecule? Do you remember? Hydrogen. So only if you have a single type of hydrogen will it be helpful. If you don't, then it won't be.

I would love it if all of you guys got this as your retrosynthesis, this first question. How do you turn that alkane into this alkyl halide? Oh my God, it's so easy. You could do this in your sleep. It's just Br2 over heat or light. So you're thinking, “Man, that would be so awesome.”

But guess what? Your professor probably isn't going to give you that, at least by itself. What you're probably going to get is either this in a multi-step retrosynthesis, or it's just going to be harder than that, because that's too easy. That's just way too straightforward.

What you're more likely to get is where you have to turn an alkane into an alkyl halide that you can't immediately get in one step from halogenation. For example, we can easily put bromines here, but it's not that easy to just stick a bromine on a random carbon like that, or to stick a bromine on a random carbon like that. How do we do that? That's going to require multi-step synthesis. That's going to require us to kind of concentrate and figure out what reagents would it take to transform into that? So that's the first thing.

The second thing is that you guys should also know how to take an alkyl halide like this and turn it back into an alkane. It's important to know what reactions could go backwards and take it back to the alkane. So we're going to be practicing all of that here.

Now, what I want you guys to do in particular is focus on I think two of the easier ones. This is not the easiest exercise here; it's a little bit tricky. But I want you guys to focus on B and D, and tell me what those reagents are. Because B is basically taking – it's not that bad – it's taking this alkane and putting an alkyl halide right there. So you're going to have to figure out in multiple steps – this is not just one step – how you can do that. D, same thing. You're just putting it in a different place.

So I want you guys to try out both of these. I'll pause the video, I'll pause, and you guys try your hardest to get those syntheses down, and then obviously I'll show you the answer. So let's go for it.

Practice: Predict the product:

Practice: Propose a synthesis for following transformation: