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Ch. 16 - Conjugated SystemsWorksheetSee all chapters
All Chapters
Ch. 1 - A Review of General Chemistry
Ch. 2 - Molecular Representations
Ch. 3 - Acids and Bases
Ch. 4 - Alkanes and Cycloalkanes
Ch. 5 - Chirality
Ch. 6 - Thermodynamics and Kinetics
Ch. 7 - Substitution Reactions
Ch. 8 - Elimination Reactions
Ch. 9 - Alkenes and Alkynes
Ch. 10 - Addition Reactions
Ch. 11 - Radical Reactions
Ch. 12 - Alcohols, Ethers, Epoxides and Thiols
Ch. 13 - Alcohols and Carbonyl Compounds
Ch. 14 - Synthetic Techniques
Ch. 15 - Analytical Techniques: IR, NMR, Mass Spect
Ch. 16 - Conjugated Systems
Ch. 17 - Aromaticity
Ch. 18 - Reactions of Aromatics: EAS and Beyond
Ch. 19 - Aldehydes and Ketones: Nucleophilic Addition
Ch. 20 - Carboxylic Acid Derivatives: NAS
Ch. 21 - Enolate Chemistry: Reactions at the Alpha-Carbon
Ch. 22 - Condensation Chemistry
Ch. 23 - Amines
Ch. 24 - Carbohydrates
Ch. 25 - Phenols
Ch. 26 - Amino Acids, Peptides, and Proteins
Ch. 26 - Transition Metals
Conjugation Chemistry
Stability of Conjugated Intermediates
Allylic Halogenation
Conjugated Hydrohalogenation (1,2 vs 1,4 addition)
Diels-Alder Reaction
Diels-Alder Forming Bridged Products
Diels-Alder Retrosynthesis
Molecular Orbital Theory
Drawing Atomic Orbitals
Drawing Molecular Orbitals
Orbital Diagram: 3-atoms- Allylic Ions
Orbital Diagram: 4-atoms- 1,3-butadiene
Orbital Diagram: 5-atoms- Allylic Ions
Orbital Diagram: 6-atoms- 1,3,5-hexatriene
Orbital Diagram: Excited States
Pericyclic Reaction
Thermal Cycloaddition Reactions
Photochemical Cycloaddition Reactions
Thermal Electrocyclic Reactions
Photochemical Electrocyclic Reactions
Cumulative Electrocyclic Problems
Sigmatropic Rearrangement
Cope Rearrangement
Claisen Rearrangement
Additional Guides

Congrats guys, we're almost to the end. But before we finish let's talk cumulatively about thermal and photochemical electrocyclic reactions. 

Concept #1: Two Steps to Predicting Any Electrocyclic Products


In this video we're going to put it all together and talk cumulatively about both thermal and photochemical electrocyclic 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 stereochemistry with thermals and photochemical reactions, electrocyclic reactions but also I kept thinking to myself like there's got to be an easier way, maybe I can 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 Mo's from scratch every time. So, what I've done here is I'm gonna, I'm going to present this cheat sheet to you and it's going to be up to you to figure out how helpful it is or not, if you think that you're going to be doing lots of electrocyclic reactions 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 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 going to be conrotatory or disrotatory, 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 orbitals and then the activation type, either heat or light, and then you can figure out, you can look at the orbitals and you can figure out how they rotate. So, that's already what you're used to doing and that's perfectly acceptable, you can do that every time if you want but I have a shortcut and that shortcut is to use this little summary chart and with the summary chart does is it tells you the rotation the conclusion of the rotation based on either how many pi bonds you're starting or not either but both the number of pi bonds your starting and the type of activation that you have. So, for example, if you happen to have an even number of pi bonds in your polyene and if you're using thermal activation, heat activation then you can just automatically memorize that it's going to be conrotatory and then as you change them the, the conclusion changes. Now, memorizing this whole table I think would be really 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 up called etc. So, you know how you say etc, etc. So, e.t.c is etc. So, you could think that if you have an even number of pi bonds with thermal activation it's going to be conrotatory and that's etcetera and then if any of the other things change then you can just base, what your knowledge off of it etc. 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 numbers thermal activation then that must be disrotatory because I'm changing one thing, if you're changing two things at the same time then it goes back to conrotatory. 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 to a conrotatory, okay? So, just, it's up to you to figure out if you want to use this or not, I am going to 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 Conor tutorial purses disrotatory depending on, which one you use depending on, regardless of the method you know it. Now, step two is to determine the stereochemistry, so the way you determine the stereochemistry is first of all just draw the structure in 3d 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 can totally do that every time if you want to. but I made another chart for this step as 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 going to have to do this semester and what this one says is that it also gives you the conclusion of whether it's going to be cis or trans based on the rotation, which you should have figured out in step one, and then based on one new idea, which is the pi bond either being the same or different. Now, what I mean by same or different is that same means that they're both either cis or they're both trans, different means that one cis and one is trans, right? And again, the conclusion of cis or 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 going to 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, DIS is CIS kind of like DIS instead of this, I'm just pulling out a little bit of my slang here and if it's the same DIS, this disrotatory is CIS. So, you could think about and you could say okay, if I already know it's going to be disrotatory and my bonds are cis to, are both cis then I know it's going to be a CIS or if they're both trans they're still gonna beat CIS because they're the same, but if they're, if they're different or if it's conrotatory they just think it's the other one, okay? So, basically for both of those you have kind of starting point and then you can change your answer based on how many of those variables are 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 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:


  • a. Obtain final structure by drawing 3D-representation + ROTATION —OR—
  • b. Use Electrocyclic Stereochemistry Summary Chart

Practice: Use the summary charts to predict the product of the following reactions. If there is more than one isomer possible, draw them

Practice: Use the summary charts to predict the product of the following reactions. If there is more than one isomer possible, draw them

Practice: Predict the product for the following reaction.