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Questions tagged [carbohydrates]

Carbohydrates are one of three classes of primary metabolites and thus natural products. They are polyhydroxylated hydrocarbons and their derivatives. Colloquially, they are known as sugars. This tag may be applied to all questions that concern carbohydrate species in solution, reaction mechanisms and structures.

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1answer
192 views

Oxidation of fructose with conc. HNO3

I recently studied carbohydrates. I was taught that fructose on oxidation with strong oxidizing agents like concentrated $\ce{HNO3}$ yields glycolic acid and tartaric acid along with trihydroxy ...
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1answer
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Fischer's proof of the structure of glucose

To differentiate between Mannose and Glucose , Fischer developed a series of reactions to make the aldehyde group to alcohol and terminal alcohol to aldehyde. What was this series of reactions ? Even ...
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1answer
66 views

Haworth's research of glucose

Firstly haworth used CH3I/Ag2O with glucose which replaced 5 H by CH3 forming a acetal which locked the anomer and stopped the equilibirium of ring chain tautomerism. Under dilute acidic conditions ...
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0answers
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Question on identification of a compound

Question: Multiple correct answers are possible My Approach: I just found structure Q for all options A, B, C and D for which I have uploaded the structures below with their corresponding options. ...
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1answer
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What is the difference between the sugar in a fresh fruit and the sugar in a juice?

In this paper of the WHO, there is a distinction between intrinsic sugars, who are incorporated within the structure of intact fruit and vegetables, and sugars naturally present in fruit juices. (page ...
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2answers
100 views

What reagents can be used to distinguish pentose and hexose sugars?

I have been asked how I can differentiate D-glucose and D-xylose using the following reagents / reactions: Orcinol Benedict's test Ammoniacal silver nitrate $\ce{FeCl3}$ $\ce{C6H5SO2Cl}$,...
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1answer
309 views

Does cooling a potato change the nature of its carbohydrates?

A talk-show guest of Joe Rogan claimed that cooling a potato after cooking creates "resistant starch" that's better for human consumption https://www.youtube.com/watch?v=niwqfwA2Lb8 The claim is ...
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1answer
1k views

How long would it take for sucrose to undergo hydrolysis in boiling water?

I was reading the book Cocktail Codex and there was a snippet on avoiding boiling sugar and water to make simple syrup that made me a bit skeptical. Here it is: Heat also affects the molecular ...
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1answer
96 views

Will (3R,4S,5R)-1,3,4,5,6-pentahydroxyhexan-2-one tautomerise in nitric acid?

The following question was sent to me .The question is " Which of the following is A ?" The given answer was a,b,c Background If both ends of an aldose chain are oxidized to carboxylic acids the ...
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1answer
253 views

How are glycosidic linkages formed?

Consider glycosidic linkages in disaccharides. I know a condensation reaction occurs, with the loss of water. But which OH is lost? The O in the linkage belongs to which monosaccharide? Example: ...
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0answers
35 views

Fehling's solution - What is the shelf life of the unmixed A & B components?

If you prepare two separate solutions of Fehling's A and Fehling's B, what is the shelf life likely to be? Will the effectiveness of the solution diminish over time? The literature recommends ...
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1answer
76 views

Why doesn't open-chain glucose react with water readily in aqueous solution?

Though the exact number given varies from 0.02% to 3%, it's well agreed that glucose spends a very small percentage of its time in aqueous solution as a linear aldehyde. Glucose's overwhelming ...
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Why the use of MD simulations is less popular for the study of carbohydrates?

In classical all-atom MD simulations, the force fields for proteins, nucleic acids and lipids seem to be more well developed than carbohydrates. It seems to me that the use of MD simulations is not so ...
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2answers
256 views

How does existence of alpha and beta form of glucose prove that it exists as a cyclic structure

My book says that Glucose is found to exist in two different crystalline forms which are named as $\alpha$ and $\beta$. Next it says that This behaviour could not be explained by the open ...
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1answer
69 views

Nomenclature of carbohydrates

In the chapter on Biomolecules in my book, the following points are given regarding carbohydrates. Numbering the C-chain with consecutive rank The C-atom present in the aldehyde group of ...
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0answers
63 views

What would happen if you burned paper with a laser, in a vacuum?

If you hit a piece of paper with a powerful laser inside a vacuum, what would happen? It sounds like it should not "burn" and have a flame spread over the paper, as there is, of course, no oxygen. ...
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1answer
926 views

Clarification in the mechanism for Molisch's test for glucose

Wikipedia says Molisch's test is a sensitive chemical test, named after Austrian botanist Hans Molisch, for the presence of carbohydrates, based on the dehydration of the carbohydrate by sulfuric ...
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1answer
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How can a carbohyrate be hydrolysed?

Polysaccharides and disaccharides if they are neutral how do they undergo hydrolysis? When making a polysaccharide or a dissacharide dehydration synthesis occurs and why does it not get reversed ...
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101 views

Sugar: A molecule or crystal [closed]

Is sugar a molecule or a large crystalline structure composed of many molecules? What do we mean when we say sugar?
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Why does wood burn but not sugar?

Fundamentally, they're both carbohydrates, although the cellulose in wood is essentially polymerized glucose, which combined with its isomer fructose forms sucrose. So why does wood readily burn ...
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1answer
46 views

Can Molisch test be used to separate monosaccharides from polysaccharides?

Do the results of Molisch test on monosaccharides have any differences with when it's done to disaccharides or polysaccharides?
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1answer
585 views

Are Anomers Epimers?

epimers are the class of stereoisomers which differ along configuration at any carbon in a carbohydrate(generally), And anomers are the kind of stereo isomers that differ at the carbonylic carbon, ...
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1answer
39 views

Can sucralose form a syrup?

(Almost) Everyone is familiar with making simple syrup from table sugar and water. I was wondering if pure sucralose is also capable of forming a syrup. I wanted to do an experiment myself, but to ...
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0answers
190 views

What is a reasonable mechanism for the following reaction?

Hello all! I'm stuck on this one question and am not sure how to finish the mechanism. What I did was attack the alkyne first with the N farthest to the left. I'm not sure what do to after that though....
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1answer
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What are the differences between D and L glucopyranose?

I have just studied the concept of cyclotron in carbohydrates. My reference book used Glucose as an example and began by saying we can find D-glucose or L-glucose: Depending on what enantiomer we ...
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1answer
148 views

Can glucose burn in chlorine?

Chlorine is an oxidizing agent, so could it replace oxygen? If so, what would be the products, and how much energy would such reactions release? Do any other carbohydrates burn in chlorine? I cannot ...
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What are the optimal conditions for the complete acid hydrolysis (using HCl) of potato starch? [closed]

I'm hoping someone can provide the specifics on the optimal conditions required for the complete acid hydrolysis (using $\ce{HCl}$) of potato starch? I will be using an autoclave (~$\pu{15 psi}$ @ $\...
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1answer
3k views

Why can't amylase digest glycogen?

Amylase is an enzyme that breaks down starch in the form of amylopectin and amylose. Both amylose and amylopectin are formed by alpha glucose joined together by (1-4) and (1-6) glycosidic bonds. ...
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1answer
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Why are polysaccharides not sweet in taste?

Polysaccharides are defined as polyhydroxy aldehyde or ketone which on hydrolysis yield many units of monosaccharides. I got one answer(to my question above) as: On our tongue, we have things ...
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1answer
658 views

Identifying the D/L form of any aldose or ketose in cyclic form

I understand that the compound above is a ketose because it has a furanose ring. But, how do we know that it is a "D" form? Is there any general rule by which I can identify if any given aldose/...
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1answer
111 views

Carbohydrates: What does “typical nature” mean here?

I am a 12th grader in India. I have understood basic theory on biomolecules. I know about carbohydates (and structures of important saccharides) and $\alpha$-amino acids, proteins, and peptides. This ...
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1answer
721 views

Is it possible to make a disaccharide from two fructose monomers? If so, what is its name?

Maltose is a disaccharide made from two molecules of glucose; and sucrose (table sugar) is made from glucose and fructose. Is it possible to combine two fructose molecules to make a disaccharide? If ...
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0answers
603 views

How can I extract cellulose in plants using acids?

Me and my classmates are doing a research project about the extraction of nano cellulose from plants to form a biocomposite, which can be a material to form an effective biodegradable material. We've ...
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1answer
78 views

Where does the additional hydrogen in the Fischer depictions of glucopyranose come from?

My book shows this figure of Fischer formula of D-glucose: I don't understand this figure, and I wonder why the upper carbon atoms in both the right and left formulas have 5 bonds. And from where ...
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1answer
5k views

Why are polysaccharides non-reducing sugars?

My book says that polysaccharides are non-reducing sugars, and they form of condensation of >6 molecules of monosaccharides. The condensation involves the carbonyl groups of the sugars, leaving only ...
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1answer
4k views

Monosaccharides configurations (alpha beta, D L) identification

I am really finding it difficult to identify the correct configuration(s) of a given monosaccharide, in fact my friends and I have been trying to solve this, much to our annoyance. In one of our ...
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4answers
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Why is fermentation of cellulose to produce biofuel and nutrients so difficult?

The formula for glucose is $\ce{C6H12O6}$ and that of cellulose is very similar $\ce{C6H10O5}$. Glucose can be readily fermented by yeast and other micro-organisms to produce carbon dioxide and ...
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1answer
293 views

What is the correct way to notate conformation preferences of polysaccharides?

In some webpages (1 or 2) are found the way to notate the conformational preferences of monosaccharides such as furanose and pyranose. But, it lacks to give a brief description on how to do it with ...
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1answer
3k views

Why is chitin ordinarily insoluble in water, but soluble after deacetylation? [closed]

Chitin is usually insoluble in water. How does its chemical structure explain this? Furthermore, when chitin undergoes deacetylation, it becomes soluble and forms hydrogen bonds with water. How is ...
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1answer
591 views

How do Invert Sugars deter crystallization in Sucrose solutions?

Invert Sugars, by themselves, are notorious for their reputation to crystallize fast (think honey), but their addition to solutions of Sucrose (think simple syrup) deters the crystallization process. ...
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0answers
199 views

Heat and Sugar Syrup Consistency

I make my own sugar syrups and have been observing how heating the syrup to different degrees results in syrups of radically different consistencies, I wonder why. Heating up syrups (4:3 Sugar:Water) ...
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1answer
739 views

Why is methyl α-D-glucopyranoside preferentially formed from glucopyranose in acidic methanol?

According to my textbook Organic Chemistry 2e by David Klein, the formation of a glycoside from glucopyranose favors the α form (see picture below). Why does this happen? Shouldn't the equilibrium ...
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1answer
341 views

Glycoside Formation Reaction

Whenever we add $\ce{H+}$/ Ethanol to glucose in its hemiacetal form, why doesn't pinacone/pinacolone rearrangement take place in place of nucleophillic substitution. The product would lead to ...
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1answer
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Why does the fructose monomer in sucrose appear different from isolated fructose?

I understood that the representation of fructose is: But during the formation of sucrose: How did fructose, whose representation is given in the first picture, turn out to be different in the ...
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1answer
832 views

D/L and +/− labels of glucose

I had just started to read about carbohydrates when I came across D-(+)-glucose. My book says that the '+' sign refers to its optical rotation measured through the polarimeter, and that it could ...
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1answer
175 views

Will mixing methyl 2-cyanoacrylate and cellulose make the cellulose harden quickly?

The other day I was gluing together cotton fabric with methyl 2-cyanoacrylate (superglue) and the fabric started heating up and then eventually began smoking. I have been working on making a 2-part ...
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1answer
350 views

D-Threose: reduction and optical activity

I've bumped into this exercise: Judging by the mechanism of reaction between D-threose and $\ce{NaBH4}$, do you think the final product will be optically active? To me looks like a reduction, ...
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1answer
184 views

Can Cellulose Molecules be Synthesized from Glucose?

I am reading that cellulose may be broken down into glucose. This is usually done with some sort of solvent. Is there any way to 'rebuild' these cellulose molecules from glucose?
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Asking about definitions of word “sugar” in biochemistry

In a lecture about anabolic pathways of sugar, the lecturer was not clear when stating the name of a multiple sugar carrier & it sounded like "dolichol"so is it correct?
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2answers
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2-Deoxy-D-arabinohexose, 2-Deoxyglucose

Aldrich says that these two names are synonyms of one another. Does anyone know the etymology of arabinohexose used in this context?