Help Request: carbohydrates, ring form of.

[DieselPetrolGrl]

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Blah ! Excuse me for starting a second thread but I didn?t want to mix this question with my last, as they don?t really correlate.

I have read two conflicting texts (I am currently in ochem so pardon the reference to texts) one of which states that hydroxyl groups to the right of the chiral centers of a carbohydrate ( as seen on paper) are oriented downwards when sketching the ring conformation of the molecule whereas those appearing to the left are drawn pointing upwards? I feel this is correct.
But in another book it says ? right side up and left side down?.I have an exam in class coming up so would someone be so kind as to clarify which is true?
Thank you


~PS: Sorry if I sound defensive but this does apply to MCAT ? saw it on Kaplan #7FL BIO I believe.!~ 😛

 

[willthatsall]

Right = down, as far as I know.

 

[premedgeek]

Blah ! Excuse me for starting a second thread but I didn?t want to mix this question with my last, as they don?t really correlate.

I have read two conflicting texts (I am currently in ochem so pardon the reference to texts) one of which states that hydroxyl groups to the right of the chiral centers of a carbohydrate ( as seen on paper) are oriented downwards when sketching the ring conformation of the molecule whereas those appearing to the left are drawn pointing upwards? I feel this is correct.
But in another book it says ? right side up and left side down?.I have an exam in class coming up so would someone be so kind as to clarify which is true?
Thank you


~PS: Sorry if I sound defensive but this does apply to MCAT ? saw it on Kaplan #7FL BIO I believe.!~ 😛

Right = down
Left = up

Also for anomeric carbon
OH up = Beta
OH down = alpha

 

[premedgeek]

wow, quick turn around time for a question. 🙄

 

[DieselPetrolGrl]

Thanks .. i feel better believing that because its from McMurry 6th and the "right side up" if from an old feisendeen &feisendeen textbook

Willsallthat: Also thank u for the kaplan/PM help! Hrm your always comming to my rescue!

 

[DieselPetrolGrl]

Right = down
Left = up

Also for anomeric carbon
OH up = Beta
OH down = alpha

uh oh Anorememme..who! alpha & beta..is that just relivant to weather they are cis or trans to the newchirality center?

While we are on the topic ..is mutarotation just the conversion between alpha and beta..key term i dont think its MCAT worthy though...

 

[PRamos]

My review book and the inclass carbohydrate handouts have some good mnemonics.

Sugars are "downright uplefting" meaning that the Fisher-to-Haworth conversion involves OH groups on the left being up and OH groups on the right being down.

ABC = anomeric beta cis

L-sugars in the Haworth projection look like an L if you out line C-5 and the C-6 group (with hydroxyl)

"Flip off glucose" If you use your right hand to flip off the page (with your palm side facing you and your fingers pointing to your left side), your finger tips correspond to the position of the hydroxyl groups in D-glucose. Index finger folded and to the right, so C-2 is to the right. Middle finger is extended and to the left, so C-3 is to the left. Ring finger folded and to the right, so C-4 is to the right. Pinky finger folded and to the right, so C-5 is to the right. To get L-glucose, you use your left hand, because just like your left and right hands, D-glucose and L-glucose are mirror images (enantiomers).

There are a bunch more, but these are the ones I have found most useful so far.