mannose mnemonic

[echoyjeff222]

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Is the one given in TBR for L-Mannose? If I make a gun, carbons 2 and 3 are pointing right and carbons 4 and 5 are pointing left ...

 

[BerkReviewTeach]

If you use your left hand while looking at your palm, then yes, it is L-mannose. If you use your right hand while looking at your palm, then it is D-mannose.

 

[echoyjeff222]

I must be doing something wrong, then ...

D-mannose has the C2 and C3 pointing to the left in the fischer, but if I look at my right palm while doing a gun sign, 4 and 5 are coming toward me (which I thought was "left?")

 

[Czarcasm]

I must be doing something wrong, then ...

D-mannose has the C2 and C3 pointing to the left in the fischer, but if I look at my right palm while doing a gun sign, 4 and 5 are coming toward me (which I thought was "left?")

Using your right hand, it should look like this (For left, just the opposite). You want to make sure in both scenarios, the palm of your hand is facing towards you (as if it's a flat fischer projection); basically how it is in the picture:

Personally though, I think the mneumonic for mannose or any other sugar is a bit useless since it's unnecessary info. Glucose is probably the only one worth knowing, and well, the middle finger mneumonic is gold 🙂

 

[echoyjeff222]

But ... 4 and 5 are coming toward me? LEFT?? Lol, I feel like I'm missing something really simple

 

[Czarcasm]

But ... 4 and 5 are coming toward me? LEFT?? Lol, I feel like I'm missing something really simple

I'm confused what you're asking. The very last chiral center represents whether it's D or L. If you want the D configuration, use your right hand. If you want the L configuration, use your left hand (or just use right and realize all the chiral centers are inverted).

In your scenario, if you're trying to find the fischer projection for L-mannose, what I'd do personally is use my right hand (I like to stick to one convention). (Like in the picture above) Using my right hand the -OH's on 2 and 3 point on my left, while the -OH's on 4 and 5 point my right (for the D sugar). For the L sugar, all the chiral centers are inverted. So 2 and 3 OH's should point right while 4 and 5 should point left.

 

[echoyjeff222]

Ohhhhhhhhhhhhhhhhh nevermind lol, the left and right were on different axes when I first looked at them. Ha! Got it now. thanks!

 

[Chrisz]

I like "glucose" lol