Acid-Base nature of Sugars

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Water as an Acid

Water, the course, is both one acid and a base. The is in equilibrium v solvated proton (acid) and solvated hydroxide (base). Water is deprotonated by strong bases and protonated by solid acids.The water dissociation equilibrium is different from the mountain dissociation equilibrium the water and they have various constants.In general, because that the dissociation of an mountain HA: HA + H2O H+(aq) + A-(aq)Keq = /Ka = Keq x = /For the mountain dissociation that water as an acid:H2O + H2O H+(aq) + HO-(aq)Keq = /Kw = 10-14 = Ka = Kw/Water thickness = 1 g/mL = 1000 g/L or 55.56 mol/LKa = 10-14 / 101.74 = 10-15.74Very solid bases (stronger than HO-) react completely with the weak mountain water.

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+ H2O
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NH3 +

Alcohols as Acids

Water and alcohols are comparable as Bronsted acids and they likewise have similar acid dissociation constants.
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The conjugate basic of one alcohol is referred to as an alkoxide. Above we see the dissociation the methanol to a solvated proton and the conjugate base methoxide.The Ka of one alcohol varies v the nature that the alcohol. You deserve to see below that the extent of mountain dissociation to reduce (pKa increases) as methyl groups replace hydrogen atom on methanol. Why is this?
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What makes an mountain stronger?

The hydrogen is a small less electronegative than the carbon so a C-H shortcut is slightly polarized with an ext electron thickness on carbon. Overabundance electron thickness on a carbon nearby to a negatively charged oxygen atom (in the alkoxide) destabilizes the conjugate base and also makes the mountain a small weaker.
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Any aspect that stabilizes the conjugate basic of an acid makes the mountain stronger. Anything that destabilizes the conjugate base renders an mountain weaker.We can see a much bigger impact with substituted carboxylic acids. Electron-withdrawing teams stabilize the conjugate basic while electron-donating groups destabilize the conjugate base.

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Can you explain the differences in the acidity of formic acid, acidic acid and also phenol?
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Protonated Aldehyde

Water, alcohols, and aldehydes have actually oxygen atoms v non-bonding electron pairs. These space Bronsted bases in that they can accept a proton. Protonated water, protonated alcohols, and also protonated aldehydes space all very strong acids though.
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Acidity of Glucose

Glucose is more acidic than simple alcohols through a pKa of around 12 (Ka = 10-12). Compare this come methanol v a pKa the 15.5 (Ka = 10-15.5). The electronegative oxygen atom in the molecule traction electron thickness away indigenous the carbon atom bearing the negatively fee oxygen in the conjugate base, stability it.Glucose is a polyprotic acid through 5 five groups. Among the protonation/deprotonation equilibria for direct glucose and also one of the 6-membered ring isomers is shown here.
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Deprotonation of an alcohol team in glucose have the right to facilitate the cyclization reaction since the conjugate basic (alkoxide) is a lot stronger nucleophile. It much more rapidly adds to the electrophilic aldehyde carbon.BackCompassTablesIndexIntroductionNextProfessor Patricia Shapley, university of Illinois, 2012