- Oxidation of alcohols I: Mechanism and oxidation states
- Oxidation of alcohols II: Examples
- Biological redox reactions
- Protection of alcohols
- Preparation of mesylates and tosylates
- SN1 and SN2 reactions of alcohols
- Formation of nitrate esters
- Preparation of alkyl halides from alcohols
Biological redox reactions
Redox reactions of alcohols in biological systems. Role of NADH/NAD+ in these reactions. Created by Jay.
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- i can't understand what's the connection b/w ethanol and NAD in the above reaction.(3 votes)
- NAD⁺ is the oxidizing agent. It oxidizes the ethanol to ethanal. The equation is CH₃CH₂OH + NAD⁺ → CH₃CH=O + NADH + H⁺(5 votes)
- 2:02All the steps I understand - except this one. Why does this happen? What provokes it?(5 votes)
- Ethanol is oxidized from an oxidation state of -1 to +1 (4- 5 for the alpha carbon in the alcohol and 4-3 in the alpha carbon in ethanal). The first hydrogen in the alcohol is first removed while leaving its electrons. These electrons then create a double bond with the alpha carbon. This would give the carbon 5 bonds, so the hydrogen is removed maintaining both electrons from the bond. This H- ion then bonds to the NAD+ ring displacing the electrons within the ring. This effectively reduces the NAD+ to NADH.(1 vote)
- At6:44you say you can use the Jones reagent to oxidize Phenol; however, it does not have a Hydrogen attached to the Alpha Carbon. How is this?(3 votes)
- Ah, but the oxidation of phenols by Jones reagent follows a different mechanism from that for the oxidation of alcohols.(3 votes)
- Just wondering, where do these reactions happen specifically in biology/biochemistry? Jay said something about an electron transport chain, but could someone elaborate?(1 vote)
- The electron transport chain is one of the steps in the process called aerobic respiration otherwise known as the production of ATP (Adenosine Triphosphate). ATP powers most, if not all of the energy needs of the eukaryotic cell and is thus extremely important. Your cells use ATP on everything from transporting sugars across the lipid bilayer, opening the Na and K pumps in your neurons to contracting the fibers in your muscle.(4 votes)
- What is the oxidation state of the carbon in Benzene 1,2 - diol?(1 vote)
- C-1 and C-2 have oxidation numbers of +1. Each C loses both sigma electrons to the O atom, but it retains two electrons from the C=C bond on one side and one electron from the C-C bond on the other side. This gives it 3 valence electrons. C normally has 4 valence electrons, so its oxidation number is +1.
C-2 to C-6 have oxidation numbers of -1. Each C gains two electrons from the less electronegative H, and it has 2 electrons from the C=C bond on one side and one electron from the C-C bond on the other side. This gives it 5 valence electrons. C normally has 4 valence electrons, so its oxidation number is -1.(1 vote)
- What is the difference between Ethanol and Ethanal? Examples...(1 vote)
- ethanol is CH3CH2OH (it is an alcohol with -OH as functional group).
ethanal is CH3CHO (it is an aldehyde with -CHO as fucntional group).(1 vote)
- Around2:57, he states that the extra electrons (2) move off the bond and form a lone pair on the nitrogen. Doesn't the nitrogen already have a lone pair? I thought that nitrogen had five valence electrons, on forming a lone pair.(1 vote)
- If you check that bottom left molecule, nitrogen has 4 bonds so it can’t also have a lone pair (otherwise it would be breaking the octet rule)(1 vote)
- At6:27, Isn't the oxidation from phenol to benzoquinone reversible? Why is that one not reversible and the next one reversible?(1 vote)
- At0:42, Jay said increase in the number of bonds to oxygen is oxidation. Can I also say, because the alcohol molecule losed 2 H+, it was oxidized?(1 vote)
- Jay showed the reduction benjoquinone by a reversible arrow , but reduction of ubiquinone was shown by single headed arrow .Is it not reversible?(1 vote)
- It's not reversible, most likely because the compound it is reduced to is aromatic and thus very stable.(1 vote)
In this video, we're going to look at the biological redox reactions of alcohols in phenols. Over here on the left, we have the ethanol molecule. So this is our 2-carbon alcohol. And the carbon that we're most concerned with is this carbon right here, which has one bond to this oxygen atom. And in the liver, ethanol is oxidized to ethanal. So over here on the right is the ethanal molecule-- a 2-carbon aldehyde. And once again, we're concerned with that carbon in yellow. And so one easy way to tell that ethanol was oxidized to ethanal is to see that, on the left, we have one bond of that carbon to oxygen. And over here on the right, we now have two bonds of that carbon to oxygen. So an increase in the number of bonds to oxygen is oxidation. You could also assign oxidation states to this carbon. And you will see that there's an increase in the oxidation state of that carbon. And then, you could also think about electrons. LEO the lion goes GER-- loss of electrons is oxidation, gain of electrons is reduction. And so if I think about these electrons here in magenta, you can see that those electrons are lost from the ethanol molecule. So loss of electrons is oxidation, ethanol is oxidized. If ethanol is oxidized, something else must be reduced. That's how redox reactions work. What's reduced is NAD+ over here on the left. So this is NAD+, which stands for "nicotinamide adenine dinucleotide." The adenine is hiding in this R portion. And we have a nitrogenous-based ring with an amide functional group over here on the right for the nicotinamide portion of the molecule. Plus 1 formal charge on this nitrogen gives us NAD+. This is nicotinamide adenine dinucleotide-- NAD+. And since ethanol is oxidized, NAD+ must be reduced. So reduction means gaining of electrons. NAD+ is going to gain those electrons in magenta from ethanol. So if we think about a possible mechanism, if I took these electrons between the oxygen the hydrogen and moved them in here, that would form our double bond between the carbon and the oxygen. But there'd be too many bonds to this carbon right here. So the electrons in magenta are going to move to this carbon down here on NAD+, to this carbon. That would push these electrons over here, and that would push these electrons here off onto the nitrogen. So if we showed what happened with the movement of all of those electrons over here on the right-- this carbon right here at the top already had a hydrogen bonded to it. And it gained another hydrogen with two electrons. The two electrons were the ones in magenta right here. This hydrogen right here is this hydrogen. And the electrons in magenta move over there to our ring. And then, we would also have pi electrons moved over here. And then, we had a lone pair of electrons move off onto the nitrogen. Like that. And then, we still had some pi electrons over here on the right. This molecule is called NADH. So it's a gained the equivalent of a hydride-- hydrogen with two electrons. And so we can see that NAD+ gains two electrons. And gaining electrons is reduction. So NAD+ is reduced to NADH. Since NAD+ is reduced, it allows ethanol to be oxidized. And so we would refer to NAD+ as an oxidizing agent. It is the oxidizing agent for ethanol, even though it itself is being reduced. So that's something that confuses some general chemistry students sometimes. All right. So now over here, we have the NADH molecule. And this reaction is catalyzed by an enzyme, and the enzyme is alcohol dehydrogenase. OK. So this is catalyzed by the alcohol, dehydrogenase enzyme. Like that. And this reaction is reversible. So if we think about the reverse reaction, we think about ethanal being reduced to ethanol. And so if ethanal is reduced to ethanol, NADH would be oxidized to NAD+. And so let's think about a mechanism where we could oxidize NADH and reduce the ethanal. If I took this lone pair of electrons in the nitrogen and move it back in here, that would push these electrons off over here. And now, the electrons-- in magenta on this bond right here-- would attack this carbon right here. So the electrons-- in magenta-- we could think about the electrons as being right here. And you could think about that as being a hydride-- so a hydrogen with two electrons, giving it a negative 1 formal charge. And even though we've seen in some earlier videos that hydride isn't necessarily the best nucleophile. You could think about this as being a nucleophilic attack, if it makes it easier for you, because this carbon right here would be partially positive. The negatively charged electrons would attack that carbon. And in doing so, that would push these pi electrons off to then grab this proton here. And that would give you your ethanol molecule, and that would convert NADH back into NAD+. So you could think about NADH as being oxidized. It is losing two electrons-- the electrons in magenta. Loss of electrons is oxidation. And since NADH is the agent for the reduction of ethanal to ethanol, you would say that NADH would be the reducing agent for this example. And the best way to remember that NADH is the reducing agent is-- it is the one that has the hydrogen on it. So it has the hydride, which is capable of being the agent for the reduction. So therefore, NADH is the reducing agent. This NAD+, NADH conversion-- and vice versa-- is extremely important in biochemistry. This happens in numerous biochemical reactions. And so it's important to understand what's happening with those electrons on these molecules. Let's look at another biochemical example of redox. And here, we have on the left, phenyol. Right? So this is our phenol molecule. And once again, we're most concerned about this carbon, the one that's attached to this oxygen. And there are many ways to oxidize phenols. So if we oxidize phenol with something like the Jones Reagent-- with sodium dichromate, sulfuric acid, and water-- would be capable of oxidizing phenol to this molecule over here on the right, which we call "benzoquinone." This right here is a benzoquinone molecule. And just real fast, you could see that this carbon right now has two bonds of carbon to oxygen so it has been oxidized. So phenol can be oxidized to benzoquinone using numerous organic reagents. Once you make benzoquinone, you could reduce that to this molecule over here on the right, which is called "hydroquinone." There are several, again, organic reagents that can reduce benzoquinone to hydroquinone. Let me change that spelling there. And then, from hydroquinone, you could oxidize hydroquinone back to benzoquinone pretty easily. And so once again, in organic chemistry, there are lots of reagents that can do these redox conversions. And in the body, you're usually talking about the NAD+, NADH system. So we've just studied that. And if we look here at this molecule, you can see it's a quinone. Right? So you can see the benzoquinone portion of this molecule. And this is called "ubiquione." "Ubi" referring to the fact that this is ubiquitous. This compound is found everywhere. It's found in all the cells in nature. And the other name for this would be "coenzyme Q." This is a very important part of the electron transport chain. And if we look at ubiquinone-- going to this molecule over here on the right-- you can see this is like a hydroquinone analog here. So this is ubiquinol. These carbons are being reduced from this chemical reaction that I've drawn here. So ubiquinone is being reduced to ubiquinol. If ubiquinone is being reduced, something else must be oxidized. All right. So the NADH is being oxidized to NAD+. The NAD is the one that has this hydride on here, which can serve as the reducing agent. So here NADH is acting as the reducing agent-- the agent for the reduction of ubiquinone to the ubiquinol molecule over here on the right. And so this is just an oversimplification of part of the electron transport chain where you're transporting electrons, which eventually leads to oxidative phosphorylation and also ATP synthesis, which, of course, gives us energy. This isn't meant to be an exhaustive detail of those biochemical processes, but it's just to show you how you can analyze biochemistry using a simple knowledge of organic chemistry and the importance of NAD+ NADH in biological systems.