Glucosidic bond in sucrose

[anondukie]

Why isn't the glycosidic bond in sucrose! named alpha and beta since it is between two anomeric Cs? (still an open question) Most sources refer to it as being an alpha 1,2 linkage. Also, is it fair to assume that if the higher priority substituents on the anomeric and configurational Cs are cis (as represented on a Haworth projection) the molecule will always be beta and vice versa? (I figured this one out)

Thanks!

Edit: Another quick question. I know that we're effectively flipping the Haworth projection for fructose when we draw sucrose and that this changes the numbering and orientation of the substituents. Will there ever be an instance in which the Haworth projection for glucose is similarly manipulated? I feel like that would be harder to do because the Haworth projection for glucose is less symmetric. (I figured this one out as well)

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[aldol16]

Exactly what are you talking about? Glucose is a monosaccharide and has zero glycosidic bonds.

 

[anondukie]

I meant sucrose!

 

[theonlytycrane]

the linkage is D-alpha(1)-D-beta(2)

Drawing sucrose "upside-down" is just the easiest way to see how the glucosidic bond forms. The numbering (priority) of the carbons on fructose doesn't change.

I think the last part of your question is talking about drawing a D-alpha(1)-D-alpha(1) linkage or something. If you're comfortable with the important sugar monomers and Haworth projections, drawing one unit right-side up and then flipping it upside-down shouldn't be too bad.

 

[anondukie]

Thanks for the answer. We do rotate one of the glucose unit in trehalose and it isn't too bad! My primary concern was what happens when we change the numbering from clockwise to anti clockwise. I've deduced that doing so will change the rule for converting between Fischer and Haworth projections (i.e. right will no longer be down). This is also true when chairs are flipped and numbered differently (like in cellulose).