[Agent-X]

I'm doing a book problem, and I am told to find the most stable stereoisomers of two stereoisomers.
I know it's the one on the left.
I understand what's going on, but I don't understand how the bonds are being referred.
I have a decent grasp of the concepts so far in terms of strain and positioning.

I know how to draw a chair conformation. I understand where the locants are and the position of axial and equatorial bonds are on a chair conformation. But I'm unable to take the concepts of the wedge and dash projection and convert them to a structural conformation drawing.

How do I tell which are axial and which are equatorial?

My previous assumption was to consider one type of wedge as a group (either axial or equatorial), and the other wedges would be trans to that group.

Am I suppose to try out their most probable positions that lead to stability or is there a definite way to interpret these wedges as axial and/or equatorial? Would keeping in mind the 3D visualization of a cyclohexane molecule be a necessity?

*rethinks*

Is the solid wedge "up" and the dashed wedge "down"?

[stevet]

I have found that the easiest was to convert a wedge and dash drawing to a chair with axial or equatorial substituents is to build a model of the cyclohexane ring, then force it flat. You will then be able to see one bond clearly points up and the other down. The add your substituents accordingly, then fold it into a chair conformation, and check positions of groups that way.

Also remember that the positions alternate: on a drawing of a chair, at 1 carbon, there is an upward pointing axial, and a slighly downward pointing equatorial, on the next carbon on the ring, there is a slightly upward pointing equatorial, and a downward pointing axial. All the bonds pointing up or slightly up are cis, and vice versa.

Hope this helps.

[Dan]

Ok, take your molecule and start by drawing the two possible chair conformations.
Then decide which conformation is lower in energy (usually you choose the lowest number of large axial substituents - because axial substituents are subject to 1,3-diaxial strain).
Axial substituents are the vertical ones.

As an example, I have attached alpha-D-mannopyranose 1.

If 1 is converted into chair representations, there are two possible chair conformations: 1a and 1b. In these structures, axial substituents are coloured red and equatorial blue. In the top structure I have labelled the OH groups, on the bottom I have included the H and labelled those.

If we consider 1a and 1b, we can count that 1a has two bulky axial OH groups, whereas 1b has three bulky axial groups. Therefore we decide that conformer 1a is lower in energy, and is the dominant conformation, and that alpha-D-mannopyranoside has two axial OH groups.

So try it for yourself - remember each isomer has two possible chair conformations!

[Agent-X]

Ok, so I have to consider one group of wedges as axial and the other as equatorial. Right? From there, I have to visualize the two possible conformations and determine which one is more stable.

So, a person can't designate the wedges as being "up" or "down."

Alright, thanks for the example.

p.s.

Why did you change the position of the oxygen on the chair?
Does that make anything different?

[Agent-X]

Excuse the double post; I can no longer edit.

I think I'm wrong in the previous post. However, I think I'm right in assuming that I consider one group "up" and the other "down."

For instance, if I consider the solid wedges as "up," which would be relative to the plane of the chair, then things work out. That doesn't mean I'll get the most stable chair conformation, but the conversion of wedge to chair bonds would be converted. After that, I'd need to draw another chair where those considered up are now down.

I see the reasoning for the placement differentiation of oxygen; it causes the CH2OH group to be placed in a different spatial position.

Ok, thanks.