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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157 views

What is the carbon content, by weight, of vegetable oil?

I have only a high school understanding of chemistry, so please bear with me and my ham-fisted question. I’m trying to understand the carbon content in vegetable oil. I get that various oils have ...
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2answers
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What does per-O-acetylated glucopyranoside mean? [closed]

What does per-O-acetylated glucopyranoside mean? Can you please break down the roots?
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1answer
88 views

Pyranose v/s Furanose form of Glucose and Fructose

According to my textbook (Class 12 NCERT Chemistry): Fructose also exists in two cyclic forms which are obtained by the addition of —OH at C5 to the C = O group. The ring, thus formed is a five ...
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0answers
59 views

Can I extract solid sugar from any fruit juice at home?

The goal here is to isolate the sugar from all other compounds in the juice. In this case, I'm using apple juice and grape juice. The sugar does not need to be edible, as it is being used to make r-...
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Carbohydrate Chemistry for Candy Making

I am trying to understand the different behaviors of sugar syrups when it comes to candy making. Specifically, maple syrup vs molasses. In making maple candy, pure maple syrup is heated to soft ball ...
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37 views

Glucose and related aldohexoses are interconvertible with a little base. Does anybody know how much of each sugar is present at equilibrium?

If you add NaOH to D-glucose in water, a mixture of almost all aldohexoses will arise over time, including mannose and fructose. I wonder how much of each will be present and what could explain the ...
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2answers
205 views

Reaction of glucose acetal with acetic anhydride

The following problem was asked in JEE Mains 2020 (Sept 2, Shift 1), Consider the following reactions: $\ce{ (i) Glucose + ROH ->[dry HCl] Acetal ->[$x$ eq. of (CH3CO)2O] acetyl derivative }$ $\...
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1answer
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Sucrose skeletal formula - missing Carbon and Hydrogen [duplicate]

I was reading the Wikipedia article about Sucrose, when I noticed that the skeletal formula was missing some $\ce{C}$ and $\ce{H}$ atoms. The chemical formula being $\ce{C12H22O11}$, I counted the $11$...
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381 views

Oxidation of hydroxyl groups of glucose

In all oxidation reactions of glucose, it seems that the aldehyde group alone gets oxidised and none of the hydroxyl groups. In one reaction with nitric acid, the aldehyde group and the terminal ...
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1answer
134 views

Do all reducing sugars show mutarotation?

Do all reducing sugars show mutarotation? I studied that for a sugar to be reducing it must possess a free aldehydo or keto group. Also, for a mutarotation interconversion between α- and β-forms of ...
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1answer
89 views

what is a sugar unit?

How a sugar unit is defined? I am trying to understand the structure of calicheamicins, and it is noted that They consist of an enediyne headpiece and a modified carbohydrate tail consisting of four ...
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58 views

Where does the beta notation come from in the alpha 1,2 beta glycosidic bond (in sucrose)? [duplicate]

I am confused as to where the beta is coming from (in the alpha-1,2-beta glycosidic bond in sucrose). I understand that the alpha is from the anomeric carbon of the glucose, but I don't see how the ...
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100 views

What is the chemical equation for a Maillard reaction? [closed]

I'm a 10th-grader in my first year of chemistry. We have an assignment to make a brochure about a certain reaction, and I'm studying Maillard reactions. Does anyone know the chemical equation ...
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1answer
530 views

Why are there two structures of L-Glucose in the Fischer projection?

We are told that L-Glucose is an enantiomer of D-Glucose, which would mean that they are mirror images of each other. But then we're also told that the L and D forms is determined by the spacial ...
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1answer
111 views

How is levulinic acid formed from sucrose? [closed]

I came across the following question: Sucrose on treatment with conc. $\ce {HCl}$ produces? The answer is given as levulinic acid. So how exactly does sucrose produce levulinic acid?
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1answer
150 views

Why glucose and other similar carbohydrates are oxidised fully by HIO4?

$\ce{HIO4_{(aq)}}$ requires the vicinal diols to have syn configuration, as it forms a cyclic periodate ester. But glucose does not have syn configuration at C3, and if you consider cyclic forms of ...
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1answer
649 views

Reactions which confirms the presence of cyclic structure of glucose [duplicate]

Are there any reactions that can be explained only on the basis of the cyclic structure of glucose rather than the open chain thus confirming its presence in the solution? Like a reaction that can ...
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Can a per-acetylated sugar anomerize?

So I have a question concerning a reaction mechanism for the reaction below. I know for certain that I get the alfa anomer, but I can't explain it. When I draw out the mechanism it doesn't make sense ...
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1answer
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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
515 views

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
125 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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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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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
486 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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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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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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2answers
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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 ...
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1answer
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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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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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252 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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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
159 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 aldoses and ...
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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
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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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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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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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9k views

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
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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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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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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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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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292 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
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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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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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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
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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
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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 ...