How to Draw a Proper Chair Structure
A Crystal Clear Chemistry "How To" Tutorial
Although it can be hard to see and draw chair structures at first, by the end of this article, in a few seconds, you'll be able to sketch out a beautiful chair structure, complete with substituents in the axial and equitorial positions. You'll also be able to figure out ring-flips fast and easy.
The Basic Chair Structure: Cyclohexane
The starting point for drawing a chair is to draw plain old cyclohexane. This is essentially a three step process. Read through all of the steps and look at the figures, then practice it yourself.
Step One: Draw two slanted, parallel short lines of equal length, as if you were drawing the short ends of a parallelogram.
Step Two: Then draw two longer, parallel lines from opposite corners so that they extend past each other a bit into the center of the drawing. Again, these two lines should be the same length.
Step Three: Connect the loose ends to make a six-sided chair. The two connecting lines you draw should be the same length, if you've drawn all the other pairs of lines parallel and the same length.
Now you have a nice chair structure! With a bit of practice, this comes completely naturally. If you have non-carbon atoms ("heteroatoms") in the ring instead, just erase a corner and write in the correct atom.
To do the opposite orientation of the chair, just change the slant of the first pair of lines:
Axial and Equitorial Substituents
Drawing the substituents is again a matter of drawing parallel lines. To draw an equitorial substituent, just draw a line the same length as and parallel to the lines that are one atom away from your starting point. In the figure, the line you would draw is in blue, and the lines you have to be parallel to are in red.
Drawing axial substituents is simply a matter of drawing verticle lines in the right places. There are six axial positions in a chair structure, and three of them point up, three of them point down. The "up" positions are on the corners of the chair that point "up", and the same thing for the down positions. Look at the figure to get a better idea. (Note: as a stylistic thing, you can see in the figure below that when the lines cross each other, the line that is supposed to be behind has a slight gap, making it easier to tell which line is going in front.)
Drawing Ring Flips
Chair structures can often rapidly convert between two forms, in which the equitorial substitiuents of one form become the axial substituents of the other form, and vice versa. That's really all that's happening in a ring flip. Still, it takes some practice to be able to draw the alternate chair form when you're given the first form. The main thing to watch out for is to keep the geometric relationship between everything correct; that is, the stuff that is pointing up should stay up, and the stuff that is pointing down should stay down.
There are several common "tricks" to drawing the ring-flip of a chair. We'll use these tricks to flip the following diagram of a chair structure with some pretend substituents.
The easiest way, by far, to flip the chair is to simply move all of the substituents over by one atom in the same direction, switching axial and equitorial positions along the way. Thus, the figure shows the ring flipped version of the previous chair with all of the substituents shifted over one atom.
With a bit of practice, this sort of ring flipping will come quite easily, so, as with every chemistry problem, practice over and over and soon you'll master this essential skill. 