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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In the Haworth projections of D and L glucose, is the stereochemistry at every carbon except the anomeric carbon just inverted?

I'm having a bit of trouble grasping sugar stereochemistry. Using glucose as an example, if you cyclize D and L glucose, is the stereochemistry at every carbon just inverted from the other form? ...
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Reducing sugars and redox potential

I am wondering if reducing sugars are those that can act as reducing agents, and they act as such with Tollens and Fehling reaction, then what's the redox potential here? And is it a reversible ...
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Dextrose equivalent values (DE) of the most common sugars

What are the dextrose equivalent values (DE) of lactose, and other common sugars? Some data like the values for sucrose (0), maltodextrin (x<20), maltose (52), and glucose (100) can be found at ...
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Does Br2/H2O oxidize all aldehydes including carbohydrates?

In many books, it is mentioned that aldehydes are easily oxidized even by mild oxidizing agents. However, I have never seen bromine water explicitly mentioned. But in the carbohydrates chapter, it is ...
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Hydrophobicity of Polysaccharides

Are polysaccharides generally considered to be hydrophobic and/or hydrophilic? My reasoning is that although they have polar groups/electronegative atoms, the polymeric nature of polysaccharides ...
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230 views

Ring Flip of glucose

I have recently read about mutarotation of glucose specifically I am familiar with how cyclic structures like substituted cyclo-hexanes exist in an equilibrium of both their chair conformers. The ...
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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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How do you identify reducing / non-reducing sugar by looking at structure?

Identifying reducing / non-reducing sugar been confusing me for a while now , I know that reducing sugar contain aldehyde or ketone group . It's easy to identify them in monosaccharides but this ...
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189 views

"Synthetic wood" from cellulose and lignin?

Is there any research into making wood from its constituents? From what I know, wood is composed of cellulose, hemicellulose, and lignin. We can extract these from raw wood, but is there any way we ...
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Why does α-ᴅ-glucose form at a lower temperature than β-ᴅ-glucose?

β-ᴅ-glucose is more stable than its α-anomer due to the fact that all the −OH groups occupy the equatorial position. If this is the case, then why does α-ᴅ-glucose predominate at 30 °C while β-ᴅ-...
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Looking for a compound that when mixed with sugar will burn when a drop of water is added

Years ago, I watched a Johnny Carson episode where a guest on the show mixed a compound with ordinary table sugar and added a drop of water and the mixture burst into flames. I went and bought the ...
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Why is maltose a reducing sugar but not sucrose, even though they're both disaccharides?

I came across this on Wikipedia: Many disaccharides, like cellobiose, lactose and maltose, also have a reducing form, as one of the two units may have an open-chain form with an aldehyde group. ...
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D and L configuration of monosaccharides

I got this question in the last week's test from Organic Chemistry. I am a bit confused in assigning D and L configuration. Help me understand the topic of D and L configuration and help with this ...
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Can sugars dissolve in liquid ammonia?

Can monosaccharides and disaccharides dissolve in liquid ammonia due to hydrogen bond formation? My rationale is that these sugars may be able to form hydrogen bond with ammonia ($\ce{NH3}$).
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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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Phase of reaction between glucose and potassium cyanide to form amygdalin

I'm trying to write a detective-fiction novel, and I was wondering if potassium cyanide reacts with sugar only if the glucose for the amygdalin to form is dissolved in liquid or does it react even if ...
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Find the number of water molecules "embedded" in sucrose

Recently I got a question as follows: How many molecules of water are joined with 12 atoms of carbon in a molecule of sucrose ? (A) 12 (B) 11 (C) 6 (D) 10 I am unable to ...
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135 views

Haworth structures of sucrose and lactose

The haworth structures of lactose and sucrose is My question is regarding the glyosidic linkage, in lactose it is represented as a zig zag and in sucrose it is a "V". What does that mean. ...
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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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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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501 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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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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A non-life process making glucose from carbon dioxide and water using electricity or light?

update (Sept. 2018): Here is a bit of news that someone might be inclined to cite in a "No, not yet, but..." answer. NASA has announced a CO2 conversion challenge! Get out of your element! ...
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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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Why do other sugars melt whereas sucrose decomposes?

Sucrose decomposes at 186 °C. It doesn’t melt but when it reaches decomposition temperature, sucrose decomposes into fructose and glucose. After cooling and hardening it is no longer sucrose. Am I ...
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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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Why do polysaccharides consisting of alpha-glucose have helical structures?

Why do the polysaccharides consisting of alpha-glucose such as starch and glycogen have helical structure, while the one such as cellulose consisting of beta glucose don't display such structures? The ...
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4answers
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Why is it important that glucose’s third OH group points to the left?

My question pertains to the location of the OH group on the 3rd carbon in a glucose molecule. If atoms can rotate freely around single bonds, then why is this important? Why can't glucose be drawn ...
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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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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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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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Fischer to Haworth projection: which carbon connects to the oxygen?

For D-erythose, carbon 4, (the last carbon), connects to the O which connects to Carbon 1. However, for D-glucose, carbon 5 (the 2nd last carbon) attaches to the O which attaches to carbon 1. Why ...
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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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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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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
441 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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The proper formula of sucrose: why both forms are correct and how one is transformed into another? [duplicate]

During preparations for my exam I've stumbled upon a tormenting question how it happens that the formula of sucrose is written in two different forms: the vertical and the horizontal ones: The ...
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1answer
985 views

Why does lactulose turn dark?

Why does the standard 10gm/15ml lactulose solution turn dark when exposed to heat above 30 degrees Celsius? This is probably a simple question. It is funny that the warnings/important information on ...
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What the balanced chemical equation for the conversion of starch to dextrin by dry heating?

This question is related to the toasting of bread. When we toast a slice of bread, the starch in it breaks down into dextrin. I want to know the balanced chemical equation for the process.
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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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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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Can paper burn without oxygen or air?

If you put a paper inside an oven vacuum packed and go beyond $250~\mathrm{^\circ C}$, will it burn? There's no oxidizer. If not, what will happen?
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Identifying chiral carbons

Looking at this structure, I would say this molecule has five chiral carbons. However, its IUPAC name (3R,4R,5S,6R)-3-amino-6-(hydroxymethyl)oxane-2,4,5-triol suggests that there are only four. Which ...
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Fructofuranose vs fructopyranose

What's the difference between the two molecules? I can always read about β-D-fructofuranose in the chemistry books, but unfortunately, I've never found any info concerning β-D-fructopyranose. Is there ...
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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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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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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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Why is H bonded to C5 drawn below the plane in Haworth formula for D-glucose?

I have always seen the hydrogen atom bonded to C5 drawn below the plane as in the following figure. Shouldn't it be drawn above the plane since it is drawn on left side in Fischer projection?
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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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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 ...