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Cyclohexane: Structure, Formula & Conformations Video

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  • 0:04 Conformation Structure
  • 0:37 Cyclohexane Structure…
  • 1:05 Cyclohexane Conformation
  • 2:10 Hydrogen Atoms
  • 4:12 Lesson Summary
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Lesson Transcript
Instructor: Laura Foist

Laura has a Masters of Science in Food Science and Human Nutrition and has taught college Science.

In this lesson, we'll learn about the conformation that Hermann Sachse developed in order to better understand the properties of cyclohexane. We'll also learn how to draw this cyclohexane conformation.

Conformation Structure

Hermann Sachse was a simple assistant. He wasn't a great chemist and he wasn't well known. But he developed a formula to determine the structure of cyclohexane. But chemists of his time just couldn't understand this structure, which is now known as the chair conformation. He died at the young age of 31, with his ideas being ridiculed. It wasn't for another 25 years that scientists discovered that his ideas were legitimate. Today chair conformations are the most precise way for depicting the conformation of 6-membered rings.

Cyclohexane Structure & Formula

Cyclohexane has the chemical formula of C6H12. It forms a ring, so there are no CH3 ends, instead each carbon is attached to a CH2. The simplest way to draw cyclohexane is simply draw a hexagon. According to this format, each point depicts a fully saturated (with hydrogen atoms) carbon. When cyclohexane is depicted this way, each carbon atom and each hydrogen atom appear exactly the same.

Cyclohexane Conformation

The conformation that Hermann Sachse developed is today called the chair conformation. Although we often draw cyclohexane as a flat hexagon, this isn't the technically correct conformation. Carbon atoms like to form bond angles of 109.5 degrees. This bond angle keeps the carbon atoms as close as possible without them interfering with each other. But if cyclohexane were in a flat hexagon, the bond angle would be 120 degrees. By forming a warped hexagon, the bond angles become the ideal 109.5 degrees.

Drawing the chair conformation takes a little practice. So, give it a try as we are going through the steps of creating this. The method that works quite well is as follows:

  • Draw two slightly offset parallel lines

  • Put a dot above the top line, slightly to the right of the bottom line; put a dot below the bottom line, slightly to the left of the top line; and finally

  • Connect the lines to the dots

So, you should practice drawing the chair conformation several times until it comes naturally.

Hydrogen Atoms

Typically when we draw substituents on the hexagon, or any flat molecule, we use dotted lines to indicate the substituent is pointing down, and we use wedges to indicate that it's pointing up. On this chair conformation, the dotted lines and wedges aren't used. Instead, a line pointing up indicates the substituent is pointing up, while a line pointing down indicates it is pointing down. Pretty straight forward. But each location doesn't only have an up or down position; it is also either equatorial or axial. Equatorial is perpendicular to the original lines we drew, while axial comes at an angle. Both equatorial and axial can be either up or down; in fact, they alternate back and forth around the chair.

Equitorial and axial

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