Organic-Biochem-Nutrition – 3. Aldehydes, Ketones, Sugars.

Posted: February 14, 2012 in alcohol, Fructose, glycolysis, Learn organic chemistry
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There is one ketotriose, dihydroxyacetone.




  2. majkinetor says:

    So, can we say that sugar is special case of alcohol ?

    Judging from definition (wiki: an alcohol is an organic compound in which the hydroxyl functional group (-OH) is bound to a carbon atom. In particular, this carbon center should be saturated) it is.

    Or we can’t think like that ?

    • rdfeinman says:

      That is not correct. Sugars are polyhydroxy alcohols and ketones and their derivatives. They, of course, have some of the properties of alcohols by virtue of the hydroxyl groups (like the lower alcohols, they tend to be water soluble). The way it is used by Lustig indicates a lack of precision, a lack of commitment to careful chemical practice which compromises, in my view, everything he says.

      On organic chemistry, again, the appeal is its logic and precision. The basic idea is that the chemistry resides in the functional groups. So, a compound with two functional groups is expected to have properties that are the sum of the properties of the different functional group (and possibly some effect of their interaction). So, for example, sugars fold up into 5- or 6-membered rings because the alcohol group (you can say that) reacts with the aldehyde to form a new functional group (called a hemiacetal) which is why you usually see sugars written in the cyclic form.

      So, “sugar alcohols,” or polyols (glycerol is the simplest) are alcohols in some way but again, to be precise, they have a separate name and are generally refered to as diols, triols, etc. although sugar alcohol is acceptable.

      Sometimes the name includes both functional groups. Keto-acids have properties of both ketones and acids. “Ketone bodies” is preferred to just “ketones” since ketones is a real category while ketone boies include a ketoacid and a hydroxyacid (and acetone which is non-enzymatic by-product of ketone body formation).

      If there is more than one functional group on a single carbon, all bets are off and there is a new name. So, a carboxyl group has a carbonyl and a hydroxyl group but its properties are considered completely separate and one only refers to as a carboxyl group (etymologically a combination of carbonyl and hydroxyl but chemically completely different).

      If their are two hydroxyls on one carbon, that is a special case known as a gem-diol (short for geminal-diol) and has special properties, and is, in essence a hydrated ketone.

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