Where is the free hemiacetal or hemiketal in maltose?
Is it the hemiaketal with the central carbon being carbon no5?
Is it the hemiaketal with the central carbon being carbon no5?
Locate free hemiacetal or hemiketal in maltose
- Thread starter SaintJude
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All the way to the right: the carbon#1 is anomeric, so it has a connection to OH and OR - hemiacetal. The hemiketal is C1 on the left hand: C-OR and C-OR.
Additionally, this is able to react with Benedict's test (oxidizes sugar) to precipitate red bu reducing Cu2O.
The glucose on the right hand side, for some reason, is beta. Mutorotation can take care of that.
Additionally, this is able to react with Benedict's test (oxidizes sugar) to precipitate red bu reducing Cu2O.
The glucose on the right hand side, for some reason, is beta. Mutorotation can take care of that.
But is it the free one?
For example sucrose does not have a free one. what's the difference then?
Maltose has an aldehyde group that is free to react with Benedict's agent and hence, gives a positive test (orange coulour). On the other hand, Sucrose has an aldehyde group that is tied up and is not free to react with Benedict's reagent and hence, gives a negative test
For example sucrose does not have a free one. what's the difference then?
Maltose has an aldehyde group that is free to react with Benedict's agent and hence, gives a positive test (orange coulour). On the other hand, Sucrose has an aldehyde group that is tied up and is not free to react with Benedict's reagent and hence, gives a negative test
Yes. I wrote some additional information in white for you previous to this, check it out.
Remember that the free group is the anomeric carbon. So sucrose is glu(a1,2)fructose. The anomeric carbon is the one that has the -O- bond. Sucrose's anomer and glucose's anomeric carbon are tied - no mutorotation, no equilibrium with the open chain aldehyde, so no precipitation! Hemiacetals, aldehydes, (ketones?) can undergo Benedict's whereas acetals (locked into mutorotation) cannot.
Remember that the free group is the anomeric carbon. So sucrose is glu(a1,2)fructose. The anomeric carbon is the one that has the -O- bond. Sucrose's anomer and glucose's anomeric carbon are tied - no mutorotation, no equilibrium with the open chain aldehyde, so no precipitation! Hemiacetals, aldehydes, (ketones?) can undergo Benedict's whereas acetals (locked into mutorotation) cannot.
benedict's reacts with a reducing sugar (meaning the sugar can act as a reducing agent. or the sugar can be oxidized). sucrose is not reducing because its anomeric carbon is already occupied being bound to another sugar.
maltose should be reducing because the right most anomeric carbon is free to be oxidized.
Maybe wiki worded it better than me:
A reducing sugar is any sugar that either has an aldehyde group or is capable of forming one in solution through isomerisation.
Benedits reacts with reducing sugars.
maltose should be reducing because the right most anomeric carbon is free to be oxidized.
Maybe wiki worded it better than me:
A reducing sugar is any sugar that either has an aldehyde group or is capable of forming one in solution through isomerisation.
Benedits reacts with reducing sugars.
Ok, what about for the unknown disaccharide below? Will this react with Benedict or not? And how do you know?
Edit:
go to picture: http://www.nd.edu/~aseriann/enediol.gif
Edit:
B/c of enediol rearrangement. The ketose actually converts back and forth into an aldose.
go to picture: http://www.nd.edu/~aseriann/enediol.gif
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That makes sense with what I found online, cool, thanks.
The carbon on the right is anomeric, so yeah, it will. A carbon connected to an O and another OH is anomeric and is free to go into the open chain, allowing it to react with Benedict's.
The carbon on the right is anomeric, so yeah, it will. A carbon connected to an O and another OH is anomeric and is free to go into the open chain, allowing it to react with Benedict's.
Oh, ok I think I understand now.
In sucrose the anomeric carbon, the one attached to oxygen basically is involved in a glycosidic linkage.
But in maltose there is an anomeric carbon not involved in the glycosidic linkage, so it's "free"
In sucrose the anomeric carbon, the one attached to oxygen basically is involved in a glycosidic linkage.
But in maltose there is an anomeric carbon not involved in the glycosidic linkage, so it's "free"
ketones can react?
ok so then the implication is that there is spontaneous tautomerization within sugars? that doesn't sound right.
looking in my notes, it's only possible by adding catalytic acid or base.
so we can say that sugar with a ketone + catalyst can react?
ok so then the implication is that there is spontaneous tautomerization within sugars? that doesn't sound right.
looking in my notes, it's only possible by adding catalytic acid or base.
so we can say that sugar with a ketone + catalyst can react?
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