Haworth projection

[Bacchus]

Real simple question biochem peeps, since I didn't have sugars in organic. If you are not told your monosaccharide is D or L in addition to not being told if it is alpha or beta, you can ultimately still determine the "D or L" by looking at the Fischer projection. However, if you aren't told the structure is alpha or beta, is it appropriate to draw the hydroxyl group either up or down on the anomeric carbon? Also, does it matter if your CH2OH group of the terminal carbon is pointing up or down? Trying to finish some study guides and my notes don't specify.

---

Members don't see this ad.

 

[geogil]

Real simple question biochem peeps, since I didn't have sugars in organic. If you are not told your monosaccharide is D or L in addition to not being told if it is alpha or beta, you can ultimately still determine the "D or L" by looking at the Fischer projection. However, if you aren't told the structure is alpha or beta, is it appropriate to draw the hydroxyl group either up or down on the anomeric carbon? Also, does it matter if your CH2OH group of the terminal carbon is pointing up or down? Trying to finish some study guides and my notes don't specify.

This will probably get moved out of pre allo, but I'll answer now:
alpha/beta: beta is up for the OH, alpha is down.
D/L this is where the terminal carbon matters. L is up, if I remember correctly. Think of turning a fischer projection 90 degrees to the right so that the line is now horizontal. This is the relative position of all the groups when you close the ring. I'm not sure how to interpret your question about not being specified if it's alpha/beta.

 

[Bacchus]

Here's the question that is "plaguing" me. You have your compound's fischer projection and the terminal CH2OH points down, thus not having an orientation of "right" or "left." Does it matter in the corresponding Haworth if it is up or down?

 

[0Complications]

I just found this on the Berkeley review website. It looks like it might answer your question, if I'm reading it right.

"Be able to interconvert between Fischer and Haworth Projections. Some passages and questions will assume that you can translate between structures. For instance, the Fischer projection may be given in the passage, but the question may center around the structure in a Haworth projection. In translating structures, there are three separate points to observe. The chirality of the anomeric carbon is dependent on the direction of the attack. The chirality of the penultimate carbon (carbon five in aldohexoses) is constant according to the D or L status, and the backbone carbons will go from left in the Fischer projection to up in the Haworth projection."

 

[Bacchus]

It helps, thanks. It appears that L's have CH2OH pointing down and D's have it pointing up. Thanks a bunch folks, now get cracking on those finals. 😉

 

[Phoenix.]

This is not the proper place for homework/study guide help (and asked and answered anyway). Closing.