How To Draw A Cyclohexane Chair

by James

Now that we’ve had an aerial tour of the cyclohexane chair, we’re going to move on to a very important skill: how to properly draw one of these beasties.

This takes practice. Your first few attempts in drawing a cyclohexane chair from memory might see you end up with one of these “variations”, which in their own way are less than optimal. At the bottom, I’m including a video that shows how to reproducibly draw a serviceable cyclohexane chair every time using a very simple method.

But first, a “rogue’s gallery” of 4 ways to screw up drawing a cyclohexane chair (and don’t feel bad – we’ve all done it . The trick is to make all the necessary mistakes before you take your midterm).

Bad Chair #1: Crow’s Foot

Screen Shot 2014-05-20 at 2.02.28 PM What’s wrong?  The axial and equatorial positions on the circled carbon are drawn in the wrong direction, leading to the carbon having a “crow’s foot” appearance. Bond angles in this carbon is not properly tetrahedral – furthermore, the adjacent carbons are eclipsed, not staggered!How to fix: Flip the groups on the carbon. The “axial down” group should be drawn as “axial up” and the “equatorial up” group should be drawn as “equatorial down”. Remember, the axial groups alternate “up, down, up, down, up down” throughout the ring.

Bad Chair #2: Crow’s Foot (slight return)

Screen Shot 2014-05-20 at 2.11.59 PM What’s wrong? Another crow’s foot, although drawn on the “head rest” of the chair.How to fix: switch “axial down” to “axial up” and “equatorial up” to “equatorial down”. Then you’ll see that your axial groups now alternate up down up down up down again (like they should)

Bad Chair #3: “The Lightning Bolt” [h/t Chemjobber]

Screen Shot 2014-05-20 at 1.47.22 PM What’s wrong? The axial and equatorial positions are drawn in properly, but the chair is drawn so thinly that the front carbons obscure the groups on the back carbons.How to fix:  The angles at the “headrest” and “footrest” are too acute; open them up a bit. Also, stagger the two front carbons and the two back carbons so that they’re not directly in front of each other.

Bad Chair #4: “Ol’ Fatty”

Screen Shot 2014-05-20 at 1.47.28 PM What’s wrong? Though all the axial and equatorial positions are drawn properly, this diagram strains the imagination for a cyclohexane supposedly consisting of six equal sides.How to fix: Pretty straightforward – just don’t draw the vertical bonds so long!

 

How To Properly Draw Your First Cyclohexane Chair

There are several techniques for properly draw a cyclohexane chair. In this video, I walk through what I consider to be the most completely idiot-proof way to draw a chair, by first drawing a parallelogram (something you should already know how to do). Using this as the “base” of our chair, we then draw flaps moving up and down (representing the head and footrest), then put in the axial and equatorial groups.

Importantly, we can use this method to draw a chair in either the “left hand” or the “right hand” version of a cyclohexane chair, which becomes important, once we learn about chair flips (that’s next!)

In time and with a little bit of practice, you won’t need to draw the parallelogram to guide you. Think of it as a set of training wheels that you will later discard once you don’t need them anymore.

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