Reducing sugars

[MichaelXY]

Okay, I understand that reducing sugars are such that they reduce Cu III to Cu+ ions, as in a Benedict’s solution. This reduction is due to the double bonded =O in the Aldehyde, and Keytone groups. What I do not get is how this reaction occurs when the monosaccharide like say glucose forms a ring which it does when in a hydrated medium. In a ring form the =O gets an H from the #5 Carbon to make =OH. In this configuration I do not see how a reaction can occur. So what gives ?
One more question. Since a starch is a chain of monosaccharides, howcome it does not reduce. I would think the end of the starch chain would behave like a single glucose and react with the Cu.

Thanks

[mith]

1.It's not exclusively in a ring formation, you'll still have linear chains. Microscopic reversibility and equilibrium

2.It does, but only once per molecule only one site available at the ends. Assuming a weight by weight comparison, there's less reactions taking place.

[MichaelXY]

You Da man Mith, Thanks for clearing that up