D-Glucose and L-Glucose

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EECStoMed

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I didn't realize it until today though because I always thought that they only differed in the penultimate carbon but D-Glucose and L-Glucose are actually enantiomers. For some reason TPR and EK only stress that when you look at the Glucuse molecule, just look at C5 and if the -OH is on the left, it's a L molecule and if it's on the right, it's D. I think that's very confusing because if everything else was the same, it would be a diastereomer, which is always what I thought they were, am I missing something here? Did anyone else just find this out as well?

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I didn't realize it until today though because I always thought that they only differed in the penultimate carbon but D-Glucose and L-Glucose are actually enantiomers. For some reason TPR and EK only stress that when you look at the Glucuse molecule, just look at C5 and if the -OH is on the left, it's a L molecule and if it's on the right, it's D. I think that's very confusing because if everything else was the same, it would be a diastereomer, which is always what I thought they were, am I missing something here? Did anyone else just find this out as well?

That is a really common mistake many people make. One thing I try to teach in class is a clever mnemonic for remembering glucose. Start by rotating your hands such that you can see your palms and your middle fingers are barely touching. Then proceed to bend your fingers as if you are flipping someone off. Your fingertips now represent the hydroxyls on the Fisher projection of glucose for carbons 2-5 (pointing right, left, right, and right for your right hand). Your index finger corresponds to carbon 2, middle finger to carbon 3, ring finger to carbon 4, and pinky to carbon 5.

Your right hand represents D-glucose (right-handed sugar if you will) and L-glucose (left-handed sugar if you will). We don't actually print this in our books for politically correct reasons (although it is in our lecture handouts booklet), but it is emphasized in class in terms of clever mnemonics for sugars. There are actually a bunch of these, but they all come back to D- and L- of the same sugar being like your right and left hands: enantiomers.
 
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That is a really common mistake many people make. One thing I try to teach in class is a clever mnemonic for remembering glucose. Start by rotating your hands such that you can see your palms and your middle fingers are barely touching. Then proceed to bend your fingers as if you are flipping someone off. Your fingertips now represent the hydroxyls on the Fisher projection of glucose for carbons 2-5 (pointing right, left, right, and right for your right hand). Your index finger corresponds to carbon 2, middle finger to carbon 3, ring finger to carbon 4, and pinky to carbon 5.

Your right hand represents D-glucose (right-handed sugar if you will) and L-glucose (left-handed sugar if you will). We don't actually print this in our books for politically correct reasons (although it is in our lecture handouts booklet), but it is emphasized in class in terms of clever mnemonics for sugars. There are actually a bunch of these, but they all come back to D- and L- of the same sugar being like your right and left hands: enantiomers.

Thanks for the info. I wonder why they don't state that D-Glucose and L-Glucose are ENANTIOMERS. Omg, if this had appeared on the MCAT, i would have put diasteromer and would have been screwed.
 
Thanks for the info. I wonder why they don't state that D-Glucose and L-Glucose are ENANTIOMERS. Omg, if this had appeared on the MCAT, i would have put diasteromer and would have been screwed.

I'm not sure who the they you are referring to are, but I say you should show them your glucose hand! :hardy:

And in rereading my post it's not as clear as I hoped. Does it make sense? Flip something off using your right hand with your palm facing you and your middle finger pointing left.
 
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I'm not sure who the they you are referring to are, but I say you should show them your glucose hand! :hardy:

And in rereading my post it's not as clear as I hoped. Does it make sense? Flip something off using your right hand with your palm facing you and your middle finger pointing left.

wow that finger trick really works. i wont forget it (hopefully) :rolleyes: Do you have any more tricks that people commonly mix up?

:)
 
Hhaa, I actually can't visualize it but thanks anyways. You have a pic?

I'm not sure who the they you are referring to are, but I say you should show them your glucose hand! :hardy:

And in rereading my post it's not as clear as I hoped. Does it make sense? Flip something off using your right hand with your palm facing you and your middle finger pointing left.
 
wow that finger trick really works. i wont forget it (hopefully) :rolleyes: Do you have any more tricks that people commonly mix up?

:)

Yeah, that's one of my favorites. For sugars, you can also note that manose looks like a gun (a man is apt to use a gun), and ribose is all right.

The sugar mantra is "Ribose is all right, but f@*# glucose." If you rotate your hand by 90 degrees so your middle finger points up, that represents the Haworth projection of hydroxyls 2, 3, and 4. 5 ends up in the ring, so it doesn't matter.

As for other tricks/mnemonics,etc..., I would be typing for days to list them all, because many are visual and hard to explain in words. Maybe I'll list a couple each time I log on.
 
D-Glucose :thumbup:

d_glucose.gif



L-Glucose :thumbdown:
l_glucose.gif


Yeah, I'm still a little confused...if my palm is facing me and my middle finger is pointing left, doesn't that mean my finger's broken..? :horns:

Berk, there are same plain-old mneumonics HERE...I would love to know some visual ones...
 
D-Glucose :thumbup:

d_glucose.gif



L-Glucose :thumbdown:
l_glucose.gif


Yeah, I'm still a little confused...if my palm is facing me and my middle finger is pointing left, doesn't that mean my finger's broken..? :horns:

Berk, there are same plain-old mneumonics HERE...I would love to know some visual ones...

That is A CRAZY LIST!!! Thanks a lot. GOOD HONEY TASTES SWEET! I love that one.
 
Yeah, I had a lot of time that day (procrastinating) :laugh: ...
I linked it on the mneumonics sticky as well, but the .doc is here.

Haha, I just copied and pasted that link's stuff into a word doc before you linked the doc file. Btw, you seem like you've prepped for this stuff for a while, have you taken the MCAT yet? If so you must have scored HELLA HIGH.
 
Berk, I would love to know some visual ones...

If I posted the picture, I'd likely be banned. So I'll try words again.

Just flip something infront of you off using your right hand. That's it. If your middle finger is pointing up, then your fingers represent carbons 2-4 in the Newman projection (2-down, 3-up, and 4-down which correlates to index finger(2)-down, middle finger (3)-up, and ring finger (4)-down).

If you rotate your hand by 90 degrees counterclockwise so that you can still see your palm and your middle finger now points to the left, your fingers represent the hydroxyl positions in the Fisher projection (2-right, 3-left, 4-right, and 5-right which correlates to index finger(2)-right, middle finger (3)-left, ring finger (4)-right, and pinky (5)-right).

I never realized how hard it is to put this into words... I usually just flip the class off. :(
 
Haha, I just copied and pasted that link's stuff into a word doc before you linked the doc file. Btw, you seem like you've prepped for this stuff for a while, have you taken the MCAT yet? If so you must have scored HELLA HIGH.

God if only that were true. I take it on July 13, and all I've done is some review; I haven't memorized the important equations - not even the ones I spent hours typing - or taken any practice tests! And time management is a huge problem for me. No, my showy HTML skills only serve to mask my deep and justifiable insecurity...+pity+

Thanks for the vote of confidence anyway, though..! :oops:
 
I think I understand it now... thanks Berk.

When do you guys take the test?
 
Just remember that D-glucose has all of the hydroxyls equatorial when drawn as a chair. All of the deviations start from there.
 
God if only that were true. I take it on July 13, and all I've done is some review; I haven't memorized the important equations - not even the ones I spent hours typing - or taken any practice tests! And time management is a huge problem for me. No, my showy HTML skills only serve to mask my deep and justifiable insecurity...+pity+

Thanks for the vote of confidence anyway, though..! :oops:

I'm taking mine on July 13th also!
 
If I posted the picture, I'd likely be banned. So I'll try words again.
No, you won't be infracted as long as you're flipping people off for educational purposes and not because you're fighting with them. ;)

Thanks for sharing your mnemonics. I hadn't ever heard those, and they're good ones. Would you mind writing up a single post about stereochem of monosaccharides that I can add to the organic reference thread in the subforum? If you're willing, you can post it here and I'll copy it and move it to the subforum. Please do insert the flipping off pics if you can figure out how to do it; I think it will make it easier for people to understand if they can see the pics. :laugh:
 
:eek: WWHoaa careful...on that website link with the mneumonics, for "GARLIC CLOVES SMELL EXQUISITE", it says SECRETIN targets the stomach - that is wrong. Secretin targets the pancreas to release bicarbonate and the other pancreatic juices. :idea: :thumbup:




QUOTED: Berk, there are same plain-old mneumonics HERE...I would love to know some visual ones...
 
When in doubt draw the Fisher structures and determine the R/S configuration for each chiral center. If all the chiral centers switch configurations then it's an enantiomer; if only one chiral center changes configuration, then it's an epimer i.e. a diastereomer that differs only at one chiral center when a molecule has multiple chiral centers.
 
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