Intro to Redox

Concept: Concept: General Features of Redox

7m
Video Transcript

Hey guys, now I'm going to introduce a topic that you guys might have heard before from general chemistry, but in organic chemistry, it's going to be significantly different. That topic is oxidation and reduction.
Oxidation-reduction, if you remember way back to gen chem, you guys had to learn these complicated redox equations where you had to do several steps to get the right numbers and it was very quantitative. Honestly, that was a part of general chemistry I didn't like very much. That's part of why I'm tutoring orgo because I don't have to do as much math.
In organic chemistry, oxidation-reduction really boils down to are we adding oxygens, are we adding hydrogens. Instead of looking at these complicated formulas and equations, we're really just going to be able to look at the molecule itself to tell if it's going to be oxidized or reduced. So for those of you that might have struggled with that in gen chem, this is your ticket to really succeed at oxidation-reduction. Let's go ahead and look at the definitions really quick.
An oxidation reaction is really going to be any reaction that involves the increase in the oxygen content of the molecule. You're increasing the oxygen content. You're increasing the oxidation. Now one thing to keep in mind is that doesn't mean that you're adding extra oxygens, that just means that you have more carbons bonded to oxygen. You'll see how we can change that up in a second. There actually is a difference between the two.
A reduction reaction would be any reaction that involves the increase of hydrogen content of a molecule. So as you're reducing something, you're increasing the amount of hydrogens that it has.
So let's look at this little scheme that is kind of a general road map of oxidation-reduction. What you'll notice first of all is that oxidation and reduction are opposites of each other. That is something that even if you completely messed up with those equations in gen chem, you should still know that they're opposites of each other. They're going in different directions.
Let's go ahead and start off with probably the most reduced form or what is the most reduced form of carbon and then we'll move forward. So the most – if I had to say one of these five structures is the most reduced structure, which one would it be? It would be the first one. That first structure is called methane. As you guys can see, methane is the most reduced one-carbon hydrocarbon because it doesn't have any bonds to oxygen. It has only bonds to hydrogen. So methane would be fully reduced carbon.
As we start adding oxygen bonds, this is going to progressively get more and more and more oxidized. Now in this video, I don't want to focus on reagents. We'll do reagents in a little bit, but for right now I just want you to focus on how can I tell if something is more oxidized or less oxidized, something like that.
As we're moving this direction, as we move to the right in this little table here, what you're going to find is that you start having more and more and more bonds to oxygen. So as you guys can see, a primary alcohol would be more oxidized than methane because that primary alcohol only has one bond to O.
Now as we keep going, we can keep making more bonds to oxygen. As you guys can see, here I have an aldehyde. In this case, this is actually formaldehyde. That's the name of it, but I'll just keep it as aldehyde. That's fine. An aldehyde is going to be more oxidized than an alcohol. Is it because it has more oxygen atoms? No. It's because the carbon has more bonds to oxygen. So now it has two bonds instead of one. That would be a more oxidized carbon.
Let's keep going. Now I've got a carboxylic acid. I'm just going to write COH, remember that that is the condensed form of the functional group. A carboxylic acid would be even more oxidized because now what you'll notice it has three bonds to oxygen.
Finally, if I continue to keep oxidizing and oxidizing, notice that I'm getting rid of hydrogens and I'm adding bonds to the oxygen, finally what I get to is fully oxidized carbon which is actually considered inorganic carbon. This is not an organic molecule. Why? Remember that the definition of organic molecules was a carbon bonded to a hydrogen. I'm sorry. I mean, it needs carbons and hydrogens, but there needs to be hydrogens present for it to be organic. So this would be inorganic because there's no hydrogens present. This is CO2 gas. So completely oxidized carbon actually just evolves as CO2 gas. Completely reduced carbon is methane gas.
I just want you guys to get a general feel that we could go either way, either direction on this chart, depending on what the reagent is. Now the reagents that we're going to deal with in organic chemistry one are actually going to be the one that are in this gray box.
Notice I have a gray box that is really only looking at a few of the different structures. We're ignoring the methane. We're ignoring the CO2. Why is that? Because in orgo one, we're not really making a lot of these gasses. What we're really trying to do is we're trying to figure out how we can go from an alcohol to an aldehyde. How we can go from an aldehyde back to an alcohol. Stuff like that. We're trying to make sure that we know these transformations.
As we talk more about reagents in future topics or in later topics, we will focus on reagents that make these transformations possible, not the ones all the way to the extremes. So we're not going to be taking – in orgo one we're not going to be turning methane into CO2. That doesn't happen in orgo one. Cool.
So let's just so some really quick practice. As I said, this is way easier than redox reactions. You can just say are the following transformations an oxidation or a reduction. So I'm going to go ahead and give you guys some time, go ahead and end the video and then you guys will be able to select which one is the correct one. Go ahead and choose if this is going to be an oxidation reaction or a reduction reaction. 

Concept: Example 1: Distinguishing between Oxidation and Reduction

1m
Video Transcript

Alright guys this first one was super easy this is oxidation, OK? And the reason it's oxidation is because I'm adding 2 alcohols or two oxygens to that double bond, OK? Just so you guys know in case you have learned this reaction already maybe you haven't but the name of this reaction was 1-2 Syn Dihydroxylation, OK? And all that means is that you're adding 2 alcohols on a double bond, you're adding them in the same direction, OK? And they are vicinal to each other, OK? Instead of using the 1-2 you could also say that this is Vicinal Syn Dihydroxylation, alright? So that's the first answer go ahead and solve the second problem.

Concept: Example 2: Distinguishing between Oxidation and Reduction

2m
Video Transcript

Alright guys this one was a little bit more challenging but it's still pretty easy this is a reduction, OK? The reason this is a reduction is because if you'll notice these carbons here had zero bonds to hydrogen, OK? After the reaction takes place I have one bond to hydrogen here, one bond to hydrogen here I've effectively added two hydrogens or what we would consider one equivalent of hydrogen whenever I say an equivalent that means you're adding two of them, alright? You may know this reaction or you may not that's fine but I just want to let you guys know that you could have told if you did know this reaction you could tell that it's a reduction just by the name, OK? Because the actual name of this reaction that that is taught in Orgo 1 is dissolving metal reduction, OK? And in dissolving metal reduction what you wind up getting is you wind up getting trans double bonds that's just something that either you know it or you don't but a triple bond turns into a double bond that has a trans stereo chemistry what's funny what's cool about it is that if you remember the name the name says it right there it's a reduction reaction we know that we're adding hydrogens, alright? So let's go ahead and move on to the last question go ahead and figure it out.

Concept: Example 3: Distinguishing between Oxidation and Reduction

1m
Video Transcript

Alright guys so this was obviously also a reduction, OK? Why? Well did we change the amount of oxygens on this molecule? No but we did change the number of hydrogens, OK? Notice that at the beginning this had zero hydrogens this had zero hydrogens, OK? After my reaction takes place I have one hydrogen here and I have one hydrogen here so once again I have added 2 equivalents...I'm sorry I've added 2 hydrogens or 1 equivalent of hydrogen, OK? So just yes know this is actually one of the types of transformations that we learn about with oxidation reduction, OK? So I'm not going to go into exactly what reaction this is right now but you guys should just know that you can use a certain reagent to perform a reducing agent to perform this transformation, alright? So let's go ahead and move on to the next topic.