16. Conjugated Systems
Cumulative Electrocyclic Problems
Congrats guys, we're almost to the end. But before we finish let's talk cumulatively about thermal and photochemical electrocyclic reactions.Â
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concept
Two Steps to Predicting Any Electrocyclic Products
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in this video, we're gonna put it all together and talk cumulatively about both thermal and photochemical electricity. Click reactions. So, guys, the reason I put this page together is because one I wanted to just give you an overview of what the expectations are for how to determine stereo chemistry with thermal and photochemical reactions. Electricity corrections. But also, I kept thinking to myself, There's gotta be an easier way. Maybe I could come up with a cheat sheet that will help my students to come up with these conclusions a little faster than having to draw the emos from scratch every time. So what I've done here is I'm gonna I'm gonna present this cheat sheet to you, and it's gonna be up to you to figure out how helpful it is or not. If you think that you're gonna be doing lots of electricity, click corrections this semester. It might be a good idea to learn this sheet if you think that it's just a very small thing that you need to learn how to do. And it's not a huge focus for your class. Then we just stick to the old method of what we're already doing because you know that that works every time. So let's go ahead and just go through the steps. So the first thing you always need to do is figure out the rotation if it's gonna be Conroe Totori or destroy auditory. We already have gone through the process of figuring this out manually, which means that you obtain the Homo through a combination of drawing your molecular orbital's and then the activation type either heater light, and then you can figure out you can look at the orbital's and you can figure out how they rotate. So it's already what you're used to doing, and that's perfectly acceptable. You could do that every time if you want, but I have a shortcut, And that shortcut is to use this little summary chart. And what this summary chart does is it tells you, um, the rotation, the conclusion of the rotation based on either how maney pi bonds you're starting or not either, but both the number of pylons you're starting and the type of activation that you have So, for example, if you happen to have an even number of pie, Bonn's in your Pauline, and if you're using thermal activation, he activation. Then you could just automatically memorized that it's going to be Conroe Totori. And then as you change them, the conclusion changes. Now, Memorizing this whole table, I think would be really, um, just dumb. I don't think that that's a good thing to do, because I think that you're going to mess up and forget it. But I do have a little abbreviation that might help that I thought of called etcetera. So you know how you say etcetera, etcetera. So E. T. C. Is etcetera. So you could think that if you have an even number of pi bonds with thermal activation, it's going to be convert a Torrey, and that's etcetera. And then if any of the other things change, then you could just base What, your knowledge off of it, etcetera. So, for example, let's say that instead of an even number, it's an odd number. But I still have thermal activation. Well, I would think, Okay, etcetera. Odd number, thermal activation. Then that must be disrobe hitori, because I'm changing one thing. If you're changing two things at the same time, then it goes back to convert a Tory's. So if it actually turns out to be odd and photochemical. Then I would say, Well, that's both of them are opposites. That must be back. Thio, Conroe Editori. Okay, so just it's up to you to figure out if you want to use this or not. I am gonna make you practice it one time, But after that, if you never want to do it again, that's fine. So now let's say that you figured out contributory versus discriminatory, depending on which one you used, depending regardless of the method, you know it now. Step two is to determine the stereo chemistry. So the way you determine the stereo chemistry is, first of all, just draw the structure in three D and draw out the rotation and then figure out if they should be going CIS or trans to each other. So that's what we've already done. Perfectly acceptable way to do things. You could totally do that every time if you want to. But I made another chart for this step is well, in case it can help you. And maybe it does. Maybe it doesn't it really. You should determine, based on how many of these you're gonna have to do this semester. And what this one says is that it also gives you the conclusion of whether it's gonna be Sister Trans based on the rotation, which you should have figured out and step one and then based on one new idea, which is the pie bonds either being same or different. Now, what I mean by same or different is that same means that they're both either cysts or they're both trans different means. That one assists and one is trans right. And again, the conclusion of Sister Trans is going to change based on if you change one of those things. So once again, I don't think you should memorize this whole chart because then you're gonna have too many things going on in your head. But you could memorize this one really stupid phrase that I thought of, which is if it's the same. This is CIS kind of like this instead of this, I'm just pulling out a little bit of my uhh slang here. And if it's the same diss diss road disrobe. Hitori is sis. So you could think about it. And you could say, Okay, if I already know it's gonna be dis Rhoda Torrey and my bonds are cysts are both cysts. Then I know it's gonna be a cyst. Or if they're both Trans, they're still gonna be sis because they're the same. But if they're, if they're different or if it's convert hitori, then you just think it's the other one. Okay, so, basically, for both of those, you have kind of a starting point, and then you can change your answer based on how many of the variables air changing. Okay, So, guys, I don't know if this will be helpful or not, but at least I wanted to try to help you guys. And if you just decide to use the old method, that's totally fine. Let's move. Let's move to a practice problem.
Step 1:Determine ROTATION (conrotatory vs. disrotatory)
- a. Obtain HOMO through combination of drawing molecular orbitals + activation type —OR—
- b. Use Electrocyclic Rotation Summary Chart:
Step 2:Determine STEREOCHEMISTRY
- a. Obtain final structure by drawing 3D-representation + ROTATION —OR—
- b. Use Electrocyclic Stereochemistry Summary Chart
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Problem
ProblemUse the summary charts to predict the product of the following reactions. If there is more than one isomer possible, draw them
A
B
C
D
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Problem
ProblemUse the summary charts to predict the product of the following reactions. If there is more than one isomer possible, draw them
A
B
C
D
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Problem
ProblemPredict the product for the following reaction.
A
B
C
D
