Drawing Cyclohexane rings.
Students often complain they are
terrible at drawing organic chemistry structures especially chair
conformations of the cyclohexane rings. Since getting the questions
right often depends on the person marking your papers being able to
interpret your ring correctly I feel its worth spending extra time
getting your ring right.
I will walk you through two methods for
getting a perfect ring. Firstly it is unlikely you will be able to
draw a perfect ring without picking your pen up off the paper.
Please refer to my diagrams when reading the methods
Method 1.
Step 1. Start with a pair of lines
drawn in pencil as guides. Draw a triangle as shown in the picture.
Step 2. Draw a pair of parallel lines
coming off this triangle. Note the lines should not be horizontal
but pointing upwards towards the pencil line. The two top points
should both be on the upper pencil guide line.
Step 3. Close the ring by drawing two
more lines to make another triangle.
Method 2.
The second method makes use of the fact
it is made up of three sets of parallel lines. In my example I have
chosen the middle two lines to draw first, you may prefer the end
two. As you can see in both my examples of have used the same color
for the lines that are parallel.
Step a. I have again started with a
pair of lines drawn in pencil as guides. Although not essential to
draw the lines it is important that the two top points should be on
the upper pencil line.
Step. 2 more parallel lines.
Step c. Close both sides of the ring
with another pair of parallel lines.
Now that you have the perfect ring we
need to place the axial and equatorial bonds. Once the perfect ring
has been drawn its easy to place the axial bonds. They should all be
drawn vertical. I find it easiest to start on a bottom point and
draw a vertical line down, any up points should have a vertical line
up. This is an alternating pattern of up and down. When ever I
answer a problem involving energy conformations I will always start
with a quick diagram of a cyclohexane ring with the axial positions
drawn in.
One common mistake is to start with two
lines horizontal. This makes it difficult to put the axial positions
on correctly as they would no longer be vertical. Another common
mistake is to have the axial position going in the wrong direction
i.e going up when it should be going down. This makes it impossible
for the carbons to be tetrahedral. Do not draw your rings like the
examples in the next two pictures.
Next drawing the equatorial positions.
Notice if the axial position goes down the equatorial position goes
up. This is why I recommend putting the axial positions in first.
The equatorial positions should be drawn parallel to the lines in the
ring. Again in my example I have color coded which line is parallel
with each side. Its worth noticing that there should be 3 sets of 4
lines now all parallel.
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