Chemical Reactions of Carbohydrates Flashcards
What are non-reducing sugars?
Non-Reducing Sugars are carbohydrates in which there is no free available Carbon atoms i.e there is no ‘-OH’ group attached to the anomeric carbon, so they can’t reduce other compounds.
In basic aqueous medium, Non-Reducing Sugars don’t generate any compounds containing an aldehyde group. State the reason for this.
This is because they are not oxidized by weak oxidizing agents i.e they are stable with respect to hydrolysis by bases.
All Monosaccharides are Reducing Sugars, true or false
True
Mention the two groups into which monosaccharides are divided
The Aldoses, which have an aldehyde group
The Ketoses, which have a ketone group
What forms of Aldoses can open to reveal an Aldehyde group?
The cyclic hemiacetal forms
What does it take for ketoses to become aldoses?
Ketoses must 1st undergo Isomerization through a series of Tautomeric Shifts to become Aldoses, i.e produce an aldehyde group, before they can act as Reducing Sugars.
Differentiate reducing disaccharides and non-reducing disaccharides
Reducing disaccharides like Lactose & Maltose have only one of their anomeric carbons involved in the glysosidic bond, meaning they can convert to an open chain form with an aldehyde group. On the other hand, non-reducing disaccharides like Sucrose have glycosidic bonds between their anomeric carbons, thus they can’t convert to an open chain form with an aldehyde group; they are stuck in the cyclic form.
How can the reducing sugar components of non-reducing sugars be released? What’s the essence?
Anon-reducing sugar can be hydrolysed using Dilute Hydrochloric Acid in order to release its Reducing Sugar components.
Non-Reducing Sugars don’t react with any of the reducing sugar test solutions, however their reducing sugar components released on hydrolysis with HCl can react positively with the qualitative tests.
Furfural or its derivative is given out during carbohydrate dehydration. True or false
True
What happens when carbohydrates are mixed with concentrated sulphuric acid?
Carbohydrates undergo dehydration with the elimation of 3 Water Molecules.
Furfural (or its derivative) formed during carbohydrate dehydration condenses with ……………. To form coloured products
α-Napitol
…………….. is a general test for all carbohydrates
Molisch test
How do the forms of sugar respond to Molisch test in terms of speed
Monosaccharides give a rapid positive test. Disaccharides and polysaccharides react slower.
The molisch reagent dehydrates hexoses to form ………….
5-hydroxymethylfurfural.
The molisch reagent dehydrates pentoses to form …………
Furfural
