Organic Chemistry

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16. Conjugated Systems

Pericyclic Reaction

What is a pericylic reaction? Are there certain properties all possess? Is there more common ones I should memorize?


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Properties and Types of Pericyclic Reactions

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Hey, everyone in this video, I'm gonna introduce you to an entirely new class of reactions that you haven't been exposed to yet called Perry Cyclic reactions. So, guys, we're just gonna read this first sentence together, and then I'm going to explain it. Conjugated Pauline's have the ability to react in non ionic concerted cycle ization reactions that we refer to as Perry. Cyclic reactions. Okay, Now, Perry, cyclic reactions are an umbrella term for many different reactions. But the crazy thing or the cool thing is that all of those sub types of reactions all have the same properties in common. So we're gonna go through now is what those properties are that are shared by all Perry cyclic reactions. So the first one is non ionic. What does that mean? What that means is that many times with reactions in organic chemistry, we're used to having some kind of acid in some kind of base, some kind of electron donor and electronic sector. Right. But perry cyclic corrections are unique because there are no ions. There are no partial charges. There's no negative and positive nuclear file electrical. It doesn't exist. So solvents, they're gonna have no effect on them since there are no partial charges. Okay, usually, solvents might have actually influenced the rate of a reaction that has acid and base qualities because there are charges that need to be stabilized. But in this case, there are no charges, so solvents won't matter. They won't change the rate of your reaction concerted. All bonds are created and destroyed simultaneously. There are no intermediates we've seen by now, You might have seen other concern did reactions, but this is gonna be these air. All gonna be concerted cycle is ations all of these mechanisms to be a Perry cyclic reaction. It needs to involve a ring of electrons around a closed loop, forming a cyclic transition states. So remember, keep this in mind. It has no intermediates, but it does have transition states transition states, or what happened for concerted reactions. And since we're these are cycle is ations, they should be cyclic. Transition states reversible. So all perry cyclic reactions are reversible. So that means that we're always gonna want to use our equilibrium arrows to describe them. This principle of reverse ability is also referred to in your textbook as the principle of microscopic reverse ability. That's just a complicated way to say that you can go in the right conditions. You can go from reacting to product and from product to react it. And then finally, all of these Perry cyclic reactions either occur thermally meaning there he activated or photo chemically meaning that their light activated. Okay, so just you're always gonna have those two options to start off your reaction. Okay, Cool. So remember that I mentioned that there are several types of Perry cyclic reactions. What I'm going to do in this video is I'm going to introduce you to the three most common types. There are more than three types of very sick clicks, but the other, like numbers four and five and six are for much more advanced organic chemistry courses. And you're not gonna be responsible for them. If you just know these three, that might be That's probably probably much more than sufficient. In fact, your professor or your textbook may not even teach you all these three. So then in the next video, I'll make sure Onley to include the ones that you need to know. But for right now, I think it's a good idea that you just know what The top three r and then we'll go ahead. And the specific videos you see after this will be specific to the ones that you need to know. Okay, So, Perry cyclic reactions can be easily categorized by the number of pie bonds that are destroyed after the cyclic mechanism. So what I mean by destroyed is going from reacting to two products. Okay, cool. So let's talk about the first one, which is cyclo additions. Okay. Cyclo additions are Paris cyclic reactions in which two pi bonds are destroyed after a cyclic mechanism. So look at our reactions, right. How maney Pi Bonds do we have in the first in the set of reactions Over on the left, we have three total right to on the dying and then one on that al cane. So what I would right here is all right. Three reactant pylons. Now, notice that I'm using an equilibrium arrow and heat to show that through a heat activated cyclic mechanism, I'm gonna form this product here. How many Pi bonds does this product have? Just one. So, how maney Pi bonds were destroyed to this would be a cyclo edition. Any time that you're doing a cyclic heat or light activated mechanism to get rid of two pi bonds, you automatically know what's a cyclo edition. Cool. And there are, by the way, there are lots of different types of cyclo editions underneath that. But in terms of the category, you could just say, Oh, this is a cyclo edition because two pi bonds are gone. Not so bad, right? Let's go to the next type. So the next category is electro cyclic reactions. Electro cyclic reactions are perry cyclic reactions in which one pie bond is destroyed after a cyclic mechanism. Okay, so in this case, this is a very typical Electra cyclic reaction. I have three pi bonds to start off with. Then after I react that with heat in irreversible mechanism, I would get on Lee two pi bonds in my product notice that once again, there was probably a cyclic type of mechanism because I'm forming a ring at the end. And this means that this is an electro cyclic reaction because one pie bond is missing cool. And then finally we have Sigma Tropic Shifts. Sigma Tropic shifts are Perry cyclic reactions in which zero pi bonds or destroyed after a cyclic mechanism. So here notice that we start off with how Maney Pi bonds to and in the product we have. How maney pie Bonn's also to now the pi bonds did switch places and we actually did get a cyclic mechanism. But all that happened was that the pie bonds changed their position. It's not that that the Pi bon is gone completely. So a Sigma Tropic shift would be a heat or light activated mechanism in which you're not losing any pie. Bonn's and guys. The cool thing is that just knowing these three little fax, you would be able to distinguish what psycho edition, What's Electra silk click and what? Sigma Tropic also something that you might have already noticed. But I just want to draw your attention so that you could memorize it easier is that these happen to be in alphabetical order, which is nice. So to bonds, breaking is a cyclo edition. Then one bond breaking is, um, Elektra cyclic reaction and then zero bonds would be a sigma tropic shift. Cool. So they're in order, C. E. S 210 And now you know I've been very general terms. What what are different categories of Paris? I click reactions. And once again, all the properties that we talked about at the beginning applied to these three categories of reactions. Wonderful. So we're done with this video. Let's move onto the next one.

All pericyclic reactions share the following properties, regardless of the type:


Practice Questions:


Identify the type of following pericyclic reaction.


Identify the type of the following pericyclic reaction.


Identify the type of following pericyclic reaction.