The following polyunsaturated fat, which does not exist in nat...

Question

The following polyunsaturated fat, which does not exist in nature, is oxidized at a rate similar to oleic acid (Table 11.14), despite having two cis-alkenes. Why?

Accepted Answer

All right. Hi, everyone. So this question says that nine Z 16 Z the DEA 916 dienno acid does not exist naturally. It has the same rate of oxidation as Oleic acid even though it has two. This why. Now here we have four different answer. Choices labeled A through D as to why this is the case. Now, it's worth mentioning that all of the explanations described or proposed describe factors that stabilize the radical formed. This includes the inductive effect and resonance as possible reasons. Now recall the oxidation of fatty acids like the one shown here on the screen can occur through a radical chain reaction referred to as auto oxidation. Now, auto oxidation refers to a natural process in which oxidation occurs in the presence of elemental oxygen at room temperature. Now, the reason why we describe this as a chain reaction is because after the substrate gets oxidized, an incredibly reactive species is produced, the reactive species then attacks other molecules of the substrate to repeat the process that's being described. Hence the term chain reaction. Now, all of this begins by the abstraction of a hydrogen to create a radical. And so the susceptibility of a given fatty acid to oxidation is a question of how stable the associated radical happens to be, right? If a given radical is more stable, then it's more likely to form. Meaning auto ation is more likely to take place. Now, for the purposes of this question, I'm not going to go ahead and redraw a full fatty acid because those structures are quite complex. But I'm going to simplify this a little bit by imagining the following carbon chain, right, let's say I have a seven carbon chain with two sis or kings, one in between carbons, two and three and the other in between carbons five and six. The stability of a radical can be predicted by how unsaturated it happens to be actually let me rephrase that the stability of a given radical on a fatty acid is determined by how unsaturated the fat happens to be. Now, when we discuss un saturation, we refer to how many double bonds are present in the hydrocarbon chain. Because the more unsaturated a fatty acid happens to be, the more resonant structures can be created after the radical has been produced, right. So greater un saturation causes greater stabilization of the radical via more resonant structures. And so the more stable the radical is because of resonance, the weaker the carbon hydrogen bond is going to be and therefore the easier that radical can form. So going back to the hydrocarbon that I drew previously, I want to consider first this carbon for right, that's between the two double wants. If I were to remove a hydrogen from carbon pho, then I would create a radical in between the two double bonds. And because it's in conjugation with the two double bonds, meaning both entities are separated by one single bond in between the radical. Here can participate in residence on either side of it, which results in quite a few resonant structures. This means that it's considered double or doubly a lilic. We can compare this with a carbon chain that has only one double watt because a radical that forms adjacent to one double bond can only participate in resonance with the one double bond. So even though it's stable, it does create less resonant structures when we're dealing with only one double wand. Now Oleic acid, if you recall is a fatty acid that contains only one this alkene. So why then does the molecule provide it have the same rate of oxidation? And therefore the same reactivity as Oleic acid even though there are two akines? Well, consider the number of carbons in between both double bonds. In the example that I drew previously, there was only one carbon in between both double bonds. Whereas here we have 123 or five carbons in between both cis or keen. This means that the lytic positions of either all keen meeting the carbons directly next to the double bonds are relatively isolated from each other, which means that they cannot participate in resonance with the other double bond. So in other words, the radical formed is only stabilized via resonance with the one adjacent A. And so our answer is going to be option B in the multiple choice because nine Z 16 Z Octa DEA 916 dienno acid has the same rate of oxidation as Oleic acid because it's two cyst orens are separated by several ocho groups and the radical formed is only reson stabilized by its one adjacent A and there you have it. So if you stuck around until the end of this video, thank you so very much for watching and I hope you found this helpful.

The following polyunsaturated fat, which does not exist in nature, is oxidized at a rate similar to oleic acid (Table 11.14), despite having two cis-alkenes. Why?

Key Concepts

Polyunsaturated Fats

Oxidation of Fatty Acids

Cis vs. Trans Configuration

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