Ketals

[TheGuru789]

Are Ketals/Hemiketals ever a reducing sugar? I think not, but all I do to judge reducing capability is to look for a free -H. Is this correct?

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[mokamia00]

I think that you should look at the anomeric carbon. And this carbon should be able to give off a free proton. I think that hemiacetals can be reducing sugar because they have the extra H that can be taken off. And I doubt that hemiketals sugar have the extra H in the anomeric carbon to give off.


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[TheGuru789]

Thanks!

 

[theonlytycrane]

The central carbon on the hemiketal can be oxidized as the C-O-H group can be changed to a carbonyl group (C=O). Since the hemiketal can be oxidized, it is a reducing agent (or more specifically a reducing sugar if that is what the molecule is).

The central carbon on the ketal can't be oxidized so it can't act as a reducing agent.

The same idea can be applied to looking at the anomeric carbon on a sugar to see if it can be oxidized. If it can, then the sugar is a reducing sugar. Hope that helps!