[a confused chiral girl]

Hello~

I don't know how to determine which one of these would not undergo mutarotation. I know that it won't undergo mutarotation when the anomeric carbon is part of an acetal functional group, but I don't know how to see if it is acetal or not. Can someone please show me which one?

Thank you!!

[a confused chiral girl]

sorry, I have to post the choices one by one...as attachment..
thank you~

[a confused chiral girl]

choice C..

[a confused chiral girl]

choice D..

[Yggdrasil]

Here's how I would go about it.

1)  Identify the anomeric carbon.

2)  Determine whether the oxygens bonded to the anomeric carbon are OH or OR groups.  In a hemi-acetal (or hemi-ketal) one of the oxygens will be an OH.  In an acetal or ketal, both oxygens will be OR groups.

[AWK]

Mutarotation is possible for
   OH
   |
O-C-X
   |
   X
arrangement of atoms in sugar

[a confused chiral girl]

Here's how I would go about it.

1)  Identify the anomeric carbon.

2)  Determine whether the oxygens bonded to the anomeric carbon are OH or OR groups.  In a hemi-acetal (or hemi-ketal) one of the oxygens will be an OH.  In an acetal or ketal, both oxygens will be OR groups.

using your suggestion, I would pick...choice C, is that correct?   

[AWK]

OK
but mutarotation.gif shows hemiketal!

[a confused chiral girl]

OK
but mutarotation.gif shows hemiketal!

actually, it is not choice C.gif? because in order to look for acetal/ketal, both O bonded should be OR and neither should be OH. but in all choices, the anomeric C bonded to the 2 O all have at least one that is OH...

[InPhaseTransit]

Aren't choiceB.gif and choiceD.gif the same?? Both are methyl-beta-D-glucosides. Glycosides don't mutarotate.

[AWK]

OK
but mutarotation.gif shows hemiketal!

actually, it is not choice C.gif? because in order to look for acetal/ketal, both O bonded should be OR and neither should be OH. but in all choices, the anomeric C bonded to the 2 O all have at least one that is OH...

For mutarotation sugar derivative must contain -OH at anomeric carbon

[a confused chiral girl]

sorry, Choiceb.gif and choiceD.gif are the same structures..but I can't delete one of the posts..so please ignore one.

Yggsil said ketal and acetal would have both O as OR groups..and acetal/ketal do not mutarotate...so from the structures, only B has both OR groups at the Anomeric Carbon. Thus, I pick choice B.gif, is that correct? 

[Yggdrasil]

Yes.  B/D will not undergo mutorotation because they are acetals.

[a confused chiral girl]

oh yes 
thank you~  how about ketals? to make sure, acetals and ketals do not undergo mutarotation, while Hemiacetals and hemiketals are able to undergo mutarotation. is this correct?

[kiwi]

oh yes 
thank you~  how about ketals? to make sure, acetals and ketals do not undergo mutarotation, while Hemiacetals and hemiketals are able to undergo mutarotation. is this correct?

yes