Glucose conformations?

[marpis]

What's the difference between alpha-D-glucose and alpha-L-glucose?
More specifically than just "they have a different conformation"

[Nava2]

For the difference you need to look into the concept of chirality.

Chirality is when a molecule is *not* super imposable onto it's mirror image. It also leads to stereoisomers based on this property.

Uhm, I don't know what more I can say, I can't specifically answer your question because I don't know the chemical structure of glucose off hand.

[tarajunky]

Glucose and other hexose sugars are usually drawn in a "chair" formation. Think of a 6 carbon ring on its side so that you can only see the edge of it. One sugar is on each end, and then two facing you that cover up the two behind them.

This is not a natural conformation, so in order to have the carbon bonds at normal angles you have to move some around. If you move the carbon on the left end up out of the plane of the ring, and move the carbon on the right end down out of the plane of the ring, you have + glucose (could be -, don't remember exactly). If you move the left end carbon down and the right end carbon up, you have the opposite.

And just like Nava said, although they look very similar, these two molecules can never be superimposed over top of each other. They're actually mirror images of each other. Like you can't superimpose your two hands on top of each other, since they are mirror images of each other. Chiral molecules also rotate polarized light as it passes through a solution of the molecules. If you have the + conformation, then the light rotates to the right. If it's in the - conformation, the light rotates to the left.

[marpis]

Thankyou both of you, I had completely forgotten the chair-model! ^^
That helped me a lot, thanks!

[The Claw]

Also: D means it rotates the light right, L left. Dextrose and levoratory, or something.

[Cstrike]

This is technically incorrect, but if you draw a haworth projection of glucose with the 5' carbon having the (CH2OH) facing up [aka the carbon adjacent to the hemiacetal linkage that isn't the epimer], if the OH is on top, we call it 'beta', like it's "Better on top" when unloading your load ;)

Of course if you switch the molecule so that all the groups are pointing the other way, then this rule falls apart quickly...

[marpis]

This is technically incorrect, but if you draw a haworth projection of glucose with the 5' carbon having the (CH2OH) facing up [aka the carbon adjacent to the hemiacetal linkage that isn't the epimer], if the OH is on top, we call it 'beta', like it's "Better on top" when unloading your load ;)

Of course if you switch the molecule so that all the groups are pointing the other way, then this rule falls apart quickly...

Thanks, but I kind of got it clear long ago :)

[Cstrike]

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