Cis vs Trans Conformations

Before we can really understand chair conformations, we have to practice drawing them! These tricky little suckers can be hard to get right.  

Method for Drawing Chairs

Concept: How to draw chairs.

2m
Video Transcript

Now that we understand the positions of cyclohexane, I'm actually going to take like five minutes just to teach you how to draw it. I know that sounds kind of juvenile, but once again, there are so many people that struggle to draw this weird shape that it's not even worth it not to go over it. We should just go over it once, make sure that you have at least one solid way how to draw it and then we'll move on from there.
So how to draw cyclohexane. I've actually seen a lot of different explanations in different books, the easiest one that I've found is this. I always just draw two slightly angled parallel lines like that. Then all I do is I cap off both ends. What that means is I use an up cap for the down one and I use a down cap for the bottom one. That one actually came out really nice. You would think I'm like a pro. Well, I kind of am, but they usually come out not that nice.
That's how to draw a cyclohexane. And then obviously if you want to draw the other one, you should be able to draw both. You would draw the slightly parallel lines the other way and then you'd cap them the other way. That one came out okay too. These are totally legit – like this would totally work in a test. I'm sure that some of you girls can draw this way nicer than I can, but whatever. I'm just saying this works. 

  1. Draw two slightly angled parallel lines. 
  1. Cap both ends off

How did you do?

 

It's ok if you didn't draw it beautifully the first time - practice makes perfect!

Cis and Trans

Concept: How to distinguish cis from trans.

1m
Video Transcript

What I want to teach you guys is how to determine cis and trans. Cis and trans is not based on whether your positions are axial or equatorial. That's one of the biggest misconceptions in this chapter. A lot of students say, “Oh, but they're both equatorial so that means that they should be cis. Or one is equatorial and one is axial, so they should be trans.” Wrong. That's not how you decide it at all.
Cis and trans is actually going to be based on whether the groups are facing the same face of the ring. What I mean by face is just top or bottom. What that means is that I'm not going to be looking at positions. I'm going to be looking at direction.

Cis or trans is based on whether the groups are facing the same face (top or bottom) of the ring.

  • It has nothing to do with the axial and equatorial positions!

Example: Is the following cyclohexane cis or trans? 

1m

Example: Is the following cyclohexane cis or trans? 

1m

Not too bad, right? It's as easy as it sounds! Let's move on.

Cis vs Trans Conformations Additional Practice Problems

Match the following chair conformations with the correct wedge and dash drawing.

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For each of the following dimethylcyclohexane derivatives, write in the box below it whether the molecule is a cis or trans isomer. Also, write an a or c in the circle below it to indicate whether the molecule is overall achiral (a) or chiral (c). Write your answers in the boxes and circles provided.

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Determine the IUPAC name for the compound given below. 

a) anti-fluorocyclohexanol

b) cis-3-fluorocyclohexanol

c) syn-3-fluorocyclohexanol

d) trans-3-fluorocyclohexanol

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Draw the geometric isomer, if any, of the following compounds.

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Name the following compound using IUPAC nomenclature. Please include all necessary stereochemisty in the name like R/S or E/Z or cis/trans etc. This question is all or nothing, no partial. 

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Given an IUPAC substitutive name for each of the following molecules.

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Is the methyl group cis or trans to the alcohol group?

A) Cis

B) Trans

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Is the methyl group cis or trans to the chlorine?

A) Cis

B) Trans

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Give systematic IUPAC names for each of the following:
 

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Write a bond-line formula for each of the following compounds: ( j) trans-4-Isobutylcyclohexanol

 

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Give an IUPAC name for each of the following compounds:

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(a) Menthol, used to flavor various foods and tobacco, is the most stable stereoisomer of 2-isopropyl-5-methylcyclohexanol. Draw its most stable conformation. Is the hydroxyl group cis or trans to the isopropyl group? To the methyl group? 

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Name each of the following compounds according to substitutive IUPAC nomenclature: 

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For each pair of compounds below, determine whether they are identical compounds, constitutional isomers, stereoisomers, or different conformations of the same compound:

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For each pair of compounds below, determine whether they are identical compounds, constitutional isomers, stereoisomers, or different conformations of the same compound:

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