Chair Flip - Online Tutor, Practice Problems & Exam Prep

When comparing chair conformations, focus on three key aspects: the distance between groups, the cis/trans configuration, and equatorial preference for asymmetrical chairs. Regardless of how the chair is drawn, as long as these elements match, the structures are equivalent. For example, a 1,2-cis configuration with groups in the same orientation indicates identical compounds, even if drawn differently. Understanding these principles aids in recognizing conformers and their relationships, enhancing your grasp of stereochemistry and molecular interactions.

The 3 important factors when drawing chairs

So, I found that one of the hardest things about teaching this section as a tutor is that everyone draws their chairs differently. Some of you guys are going to have really bubbly chairs, and some are going to be really flat. Some are just going to be ugly. Some people are going to prefer drawing the left-hand chair more, and some will prefer the right-hand chair. And what that means is that I get inundated with lots of questions like, "Johnny, is my chair the same as yours?" or "Did I draw the right chair?" That's why I created this whole new section that isn't in your textbook, just to explain to you what's important about comparing chairs. It turns out that there are probably hundreds of different ways to draw the same chair, and they're all right. You just have to figure out what's important so you'll know what to look for and what you can ignore. Alright?

So, when we're drawing equivalent chairs, what we want to worry about is just three things. Your chair could be to the right, my chair could be to the left, yours could be upside down, yours could be way more flat looking than mine, but there are only three things that really matter. The three things that matter are the distance between the groups, cis versus trans, and, for chairs that are asymmetrical, the equatorial preference.

Let's break it down:

• The first thing is the distance between the groups, which has to do with how far they are from each other. For example, if the first one is at your one position and the second one is next to it, that would be called 1,2. If they're two carbons apart, that would be called 1,3. If they're three carbons apart, that would be 1,4. As long as the distance is the same, we're off to a good start.
• The next important thing is cis versus trans. Maybe you wrote one equatorial and I wrote one axial, but at the end of the day, if the cis and trans are the same, then these are going to be the same chair.
• For asymmetrical chairs, meaning they have two different types of groups, equatorial preference is important too. Maybe I drew the same chair as you, but I drew the other conformer. Maybe I had a 1,2 cis and you had a 1,2 cis, but you drew it with the big group in the axial and I drew it with the small group in the axial. Are those identical? Well, they are the same molecule but they're called conformers, meaning that they can be equilibriums with each other.

What I want to do here is, you know what, I'm actually going to do a free response just so you guys can see what I mean. So, imagine that I'm drawing an answer and I show you guys that the right answer has CH₃ here and CH₃ here. But you draw chairs differently than me, and you like to draw the other chair. So, you were drawing the other chair and you draw it slightly differently. So basically, this is my answer. I said this is the right answer. And then this is yours, and you're thinking, "Wow, did I draw this right? Do I have the right answer or am I just completely wrong?" The way that we would compare these is instead of freaking out and saying "I must have gotten it wrong. I don't know what I'm doing," just say, "Okay, is the distance the same? Is the cis and trans the same?" First of all, what's the distance between these two groups? Well, if this is my one, you can pick anything to be your one, then this would be 2, 3, 4. So this is going to be a 1,4 dimethyl. Now let's look at yours because this is the one that you drew. You wrote 1, 2, 3, 4. Look at that, you also drew a 1,4 dimethyl. Alright, so you weren't that far off. Now let's look at the cis and the trans. This one, they're both facing up, so this one was cis. This one, they're also both facing up, so this one was cis. So guess what? These are the same compound. They're drawn differently, but they're the same compound, so both of them are correct ways to draw this. I know one just looks messier and one looks still kind of messy, but at the end of the day, they're the same thing. That's what I'm trying to help you guys see because I get asked all these questions like, "Is mine the same as yours?"

Let's go ahead and do some practice identifying the following chairs. Are they identical, conformers, or different? Go ahead and try to answer this and then go to the next video once you think you know.

Determine if the following pair of chairs are identical, conformers or different.

• A. Identical
• B. Conformers
• C. Different

Determine if the following pair of chairs are identical, conformers or different.

• A. Identical
• B. Conformers
• C. Different

Determine if the following pair of chairs are identical, conformers or different.

• A. Identical
• B. Conformers
• C. Different

Here’s what students ask on this topic:

What is a chair flip in organic chemistry?

A chair flip in organic chemistry refers to the process where a cyclohexane ring undergoes a conformational change, converting one chair form into another. During this flip, axial substituents become equatorial and vice versa. This process is significant because it affects the stability and reactivity of the molecule, with equatorial positions generally being more stable due to less steric hindrance.

How do you determine if two chair conformations are equivalent?

To determine if two chair conformations are equivalent, focus on three key aspects: the distance between substituent groups, the cis/trans configuration, and the equatorial/axial positions for asymmetrical chairs. If these elements match, the structures are equivalent. For example, a 1,2-cis configuration with groups in the same orientation indicates identical compounds, even if drawn differently.

What is the significance of cis/trans configuration in chair conformations?

The cis/trans configuration in chair conformations is crucial for determining the spatial arrangement of substituents. 'Cis' means that the substituents are on the same side of the ring, while 'trans' means they are on opposite sides. This configuration affects the molecule's physical and chemical properties, including its stability and reactivity.

How does equatorial preference affect chair conformations?

Equatorial preference affects chair conformations by influencing the stability of the molecule. Substituents in the equatorial position experience less steric hindrance compared to those in the axial position. This makes the equatorial conformation generally more stable, especially for larger substituents. Understanding equatorial preference helps in predicting the most stable conformation of a cyclohexane derivative.

What are conformers in the context of chair conformations?

Conformers are different spatial arrangements of a molecule that can be interconverted by rotation around single bonds. In the context of chair conformations, conformers refer to the different chair forms that a cyclohexane ring can adopt. These conformers are in equilibrium with each other and can have different stabilities based on the positions of substituents (axial vs. equatorial).