D and L sugars

[rockets32]

Anyone know how to tell the difference? These questions always seem to get me and I think the answer has something to do with the location of an OH group.

Thanks

 

[dat_student]

Anyone know how to tell the difference? These questions always seem to get me and I think the answer has something to do with the location of an OH group.

Thanks

L sugars have the hydroxyl group at the lowest stereogenic center pointing to the left in Fischer projection (Remember: L >> Left)

D sugars have the hydroxyl group at the lowest stereogenic center pointing to the right in Fischer projection. Most naturally occuring sugars are D sugars.

The ring forms are usually represented using the Haworth projections. -OH on the right in a Fischer projection is up in a Haworth projection. -OH on the left in a Fischer projection is down in a Haworth projection. For D sugars the terminal -CH2OH group is always up in Haworth projections whereas for L sugars the -CH2OH group is down.