Correct Numbering of Sugar Rings

[oxelhs]

---

Members do not see this ad.

Wondering why the numbering in sugars differs.
E.g. in sucrose, the bond is an a1-B2- glycosidic linkage.

Why is the fructose numbered starting at the left going counterclockwise and the glucose the other way around?

 

[Deadlifts]

Wondering why the numbering in sugars differs.
E.g. in sucrose, the bond is an a1-B2- glycosidic linkage.

Why is the fructose numbered starting at the left going counterclockwise and the glucose the other way around?

Draw it as a Haworth projection.

http://o.quizlet.com/n5TxHiavqJYvxDU.sh8HiA_m.png

C1 on glucose bonded to C2 on fructose.

 

[shoehornlettuce]

Wondering why the numbering in sugars differs.
E.g. in sucrose, the bond is an a1-B2- glycosidic linkage.

Why is the fructose numbered starting at the left going counterclockwise and the glucose the other way around?

It's (1-->2) because the anomeric carbon of both glucose and fructose are participating in the linkage. If you look at fructose you'll notice the difference between carbon 2 and carbon 5 (carbon 2 has an OH group bound to it). The absence of this group on the fructose molecule in sucrose tells you the bond must be to the anomeric carbon. So basically the fructose is flipped.