Thank you for the video, it’s wonderful! For MCAT purposes fructose is considered a reducing sugar because of tautomerization into an Aldose… it’s so annoying lol but I agree with you!!
You are welcome. I misunderstood your comment. Fructose is not a reducing sugar. It contains a ketone group that is not easily oxidized by the Cu(2+) ions in Benedict's solution. However, solutions of fructose may react positively in a Benedict's test because they may isomerize in solution to form aldehyde isomers. So, it is not the fructose itself that is the reducing sugar, but the spontaneous isomers formed.
Fructose is not a reducing sugar. Fructose is a ketone sugar. If you go back to your Organic Chemistry, ketones cannot be easily oxidized. Those sugars like glucose, galactose, and mannose that are aldehyde sugars are easily oxidized to the corresponding carboxylic acid derivative, so they reduce other reagents and are reducing sugars.
Is fructose a reducing sugar? Yes. All monosaccharides are reducing sugars. Glucose, fructose, and galactose are monosaccharides and are all reducing sugars.@@projoebiochem
@@projoebiochem technically fructose is not reducing due to the reason you have provided, but in actual experiments it reduces because it's able to isomerize to different aldoses e.g., glucose and mannose in a basic medium.
@@Nangofia Look at my reply to another question from @reality_loser. Under basic conditions fructose can undergo an isomeration reaction to convert the ketone into an aldehyde via an endiolate intermediate similar to that seen in the aldose/ketose isomerases. Because this is a random process in solution, it would create a mixture of glucose and mannose, which, as aldehydes, are reducing sugars. Thus samples of fructose are contaminated by these sugar isomers, so they show positive reactions in simple chemical tests for reducing sugars, even though fructose itself is not a reducing sugar.
Can you kindly clear this thing that, suppose as for glucose, In linear structure, it hase -CHO and the double bond between carbon and oxygen helps to react with other things.. As for cyclic structure, the anomaric carbon has a OH group that can react with other things and thus glucose is a reducing sugar.. Can you tell me if my concept is right?
I'll try. It is the aldehyde form that is easily oxidized, making glucose a reducing sugar. The hemiacetal form (the cyclic form with -OH on the anomeric carbon) is in equilibrium with the aldehyde form, so there is always aldehyde form present to be oxidized, so glucose will always react as a reducing sugar. Does that help?
@@tahsinnawar1908 I'm struggling with your answer. It is the aldehyde (CHO) group that makes glucose a reducing sugar. That is the group that is oxidized (and therefore reduces other reagents) in the reaction. In the open chain form, that aldehyde is free and available to react. In solution the cyclic form is the predominant one, and it looks like it should be blocked, but because the cyclic form is in equilibrium with a small amount of that open chain form (about 1%), that is enough of the -CHO form to give the positive reaction in tests like the Benedict's test.
In the open-chain structure of glucose, there is an aldehyde group on the end of the chain that is free to react with an oxidizing agent. That is the free aldehyde group. I'm using free here to contrast with the hemiacetal structure derived from that aldehyde group. Fructose is the ketose, so it doesn't have that aldehyde group. As a commenter noted, samples of fructose sometimes still react with oxidizing agents because fructose can isomerize into a mixture of glucose and mannose which are aldehyde sugars, so they would react with oxidizing agents, giving a false reducing sugar reaction.
Please look at the other comments where this is explained. Fructose itself is not a reducing sugar. It is a ketone. However, fructose can spontaneously isomerize, especially in basic solutions, to give a mixture of mannose and glucose, which are reducing sugars. So, samples of fructose will often react with reagents like Benedict’s solution because of the buildup of these isomeric contaminants.
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Thank you for the video, it’s wonderful! For MCAT purposes fructose is considered a reducing sugar because of tautomerization into an Aldose… it’s so annoying lol but I agree with you!!
You are welcome. I misunderstood your comment. Fructose is not a reducing sugar. It contains a ketone group that is not easily oxidized by the Cu(2+) ions in Benedict's solution. However, solutions of fructose may react positively in a Benedict's test because they may isomerize in solution to form aldehyde isomers. So, it is not the fructose itself that is the reducing sugar, but the spontaneous isomers formed.
This is so helpful, thanks for this
You’re welcome!
Thank you for this good lecture:)
I'm happy that I could help.
Thank you! I have been struggling to understand this, but you make it easy to understand :>
Fructose is considered a reducing sugar
Fructose is not a reducing sugar. Fructose is a ketone sugar. If you go back to your Organic Chemistry, ketones cannot be easily oxidized. Those sugars like glucose, galactose, and mannose that are aldehyde sugars are easily oxidized to the corresponding carboxylic acid derivative, so they reduce other reagents and are reducing sugars.
Is fructose a reducing sugar? Yes. All monosaccharides are reducing sugars. Glucose, fructose, and galactose are monosaccharides and are all reducing sugars.@@projoebiochem
@@projoebiochem technically fructose is not reducing due to the reason you have provided, but in actual experiments it reduces because it's able to isomerize to different aldoses e.g., glucose and mannose in a basic medium.
@@Nangofia Look at my reply to another question from @reality_loser. Under basic conditions fructose can undergo an isomeration reaction to convert the ketone into an aldehyde via an endiolate intermediate similar to that seen in the aldose/ketose isomerases. Because this is a random process in solution, it would create a mixture of glucose and mannose, which, as aldehydes, are reducing sugars. Thus samples of fructose are contaminated by these sugar isomers, so they show positive reactions in simple chemical tests for reducing sugars, even though fructose itself is not a reducing sugar.
Thank you
Can you kindly clear this thing that, suppose as for glucose,
In linear structure, it hase -CHO and the double bond between carbon and oxygen helps to react with other things..
As for cyclic structure, the anomaric carbon has a OH group that can react with other things and thus glucose is a reducing sugar..
Can you tell me if my concept is right?
I'll try. It is the aldehyde form that is easily oxidized, making glucose a reducing sugar. The hemiacetal form (the cyclic form with -OH on the anomeric carbon) is in equilibrium with the aldehyde form, so there is always aldehyde form present to be oxidized, so glucose will always react as a reducing sugar. Does that help?
@@projoebiochem yes it helped me to understand the case of cyclic one.. what about the open chain one can you explain?
@@tahsinnawar1908 I'm struggling with your answer. It is the aldehyde (CHO) group that makes glucose a reducing sugar. That is the group that is oxidized (and therefore reduces other reagents) in the reaction. In the open chain form, that aldehyde is free and available to react. In solution the cyclic form is the predominant one, and it looks like it should be blocked, but because the cyclic form is in equilibrium with a small amount of that open chain form (about 1%), that is enough of the -CHO form to give the positive reaction in tests like the Benedict's test.
Youre the goat
What is free aldehyde group?
In the open-chain structure of glucose, there is an aldehyde group on the end of the chain that is free to react with an oxidizing agent. That is the free aldehyde group. I'm using free here to contrast with the hemiacetal structure derived from that aldehyde group.
Fructose is the ketose, so it doesn't have that aldehyde group. As a commenter noted, samples of fructose sometimes still react with oxidizing agents because fructose can isomerize into a mixture of glucose and mannose which are aldehyde sugars, so they would react with oxidizing agents, giving a false reducing sugar reaction.
Fructose is a reducing sugar
Read the pinned comment and my reply.
Fructose is a reducing sugar
Please look at the other comments where this is explained. Fructose itself is not a reducing sugar. It is a ketone. However, fructose can spontaneously isomerize, especially in basic solutions, to give a mixture of mannose and glucose, which are reducing sugars. So, samples of fructose will often react with reagents like Benedict’s solution because of the buildup of these isomeric contaminants.