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21 Carboxylic Acid Derivatives -- Part 5
The Tollens reagent must react with the open-chain form of the sugar to be effective.
The sugar does not react with Tollens reagent if the cyclic form cannot open.
The acetal is stable under neutral or basic conditions.
The sugar gives a negative Tollens test if the carbonyl group is in the form of a cyclic acetal.
Because they are stable acetals, they cannot open their open-chain forms.
They are locked in a form.
The Tollens test distinguishes between sugars that are reduced and sugars that are not.
Nonreducing sugars are acetals.
It's called D-fructofuranoside.
ribose is the C2 epimer of arabinose.
An alcohol and a trace of acid catalyst are used to convert aldehydes and ketones to acetals.
The acetals we call glycosides are also converted by these conditions.
Both anomers of the glycoside are formed under these acidic conditions, regardless of the anomer used as the starting material.
The mixture of methyl glucosides is created by the acid-catalyzed reaction of glucose with methanol.
Like other acetals, glycosides are stable to basic conditions, but they hydrolyze in a free sugar and alcohol.
Glycosides are stable with basic reagents and basic solutions.
Methanol is aglycone in a conjugate.
Some aglycones are bonded through an oxygen atom, while others are bonded through a nitrogen atom or some other Heteroatom.
Disaccharides and Polysaccharides will be considered in Sections 23-12 and 23-13.
An aglycone is a group of carbons.
A true acetal is an oxygen atom and a nitrogen atom.
The second part of the mechanism for acetal formation is the same as the first part.
There is a mechanism for the formation of b-d-glucopyranoside.
The mixture of the a and b anomers of ethyl-d-fructofuranoside may be caused by the glycosylation of the proteins.
Draw the beginning of diabetes.
Sugars are insoluble in organic solvents because they contain several hydroxy groups.
Sugars form syrups like honey and molasses because they are difficult to recrystallize from water.
sugars behave like simpler organic compounds if they are alkylated to form ethers.
The ethers are easy to purify by recrystallization and simple chromatographic methods.
The totally methylated ether is given by the treatment of an aldose or a ketose.
Stereochemistry at the anomeric carbon is usually preserved if the conditions are carefully controlled.
The OH group gives the ether.
The configuration at the anomeric carbon is not broken.
The most common method for forming simple ethers is the Williamson ether synthesis.
A simple sugar would isomerize.
If the sugar is first converted to a glycoside by treatment with an alcohol and acid catalyst, a modified Williamson method may be used.
The acetal is stable to base.
The methylated carbohydrate is given by the treatment of a glycoside with sodium hydroxide and dimethyl sulfate.
The ring sizes of sugars can be determined with the help of methylation and hydrolysis.
The five groups are not the same.
There are four different types of ethers, one of which is the glycosidic methyl group of an acetal.
ethers are stable under these con ditions.
Acid hydrolyzes only the acetal methyl group when it is treated.
The six-membered ring of a pyranose can be seen in the cyclic form of b-d-glucose.
When fructose is treated with an excess of silver oxide, show the product that results.
Show what happens when the product of part a is used.
Hydroxy groups can be converted to silyl ethers.
The conversion of sugars to their silyl ethers can be done with the use of chlorotrimethylsilane and tertiary amine.
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