Table 25.1 Configurational Relationships Among the Isometric D-Aldotetroses, D-Aldopentoses, and D-Aldohexoses CHO H- • HO- CH,OH D-Glyceraldehyde СНО CHO OH Но- H. H H- HO- CHOH CH,OH D-Erythrose D-Threose CHO CHO CHO CHO H- HO- HO H FOH Но H- H OH HO HO H- HO- HO- HO- CH,OH ČHOH ČHOH ČHOH D-Ribose D-Arabinose D-Xylose D-Lyxose СНО СНО CHO CHO СНО СНО СНО CHO ОН НО -H- H- -ОН НО H- H- OH HO- H. -ОН НО- H. FOH H- OH HO H- HO- FOH H FOH HO- H- Но- H- -HO- H- HO- H -HO- H- OH HO- HO- HO H- но- H- HO- HO- H- HO- HO- H- HO- H FOH OH HO- CH,OH ČH,OH ČH,OH CH,OH ČH,OH CH,OH ČH,OH ČH,OH D-Allose D-Altrose D-Glucose D-Mannose D-Gulose D-Idose D-Galactose D-Talose
Carbohydrates
Carbohydrates are the organic compounds that are obtained in foods and living matters in the shape of sugars, cellulose, and starch. The general formula of carbohydrates is Cn(H2O)2. The ratio of H and O present in carbohydrates is identical to water.
Starch
Starch is a polysaccharide carbohydrate that belongs to the category of polysaccharide carbohydrates.
Mutarotation
The rotation of a particular structure of the chiral compound because of the epimerization is called mutarotation. It is the repercussion of the ring chain tautomerism. In terms of glucose, this can be defined as the modification in the equilibrium of the α- and β- glucose anomers upon its dissolution in the solvent water. This process is usually seen in the chemistry of carbohydrates.
L Sugar
A chemical compound that is represented with a molecular formula C6H12O6 is called L-(-) sugar. At the carbon’s 5th position, the hydroxyl group is placed to the compound’s left and therefore the sugar is represented as L(-)-sugar. It is capable of rotating the polarized light’s plane in the direction anticlockwise. L isomers are one of the 2 isomers formed by the configurational stereochemistry of the carbohydrates.
An important technique for establishing relative configurations among isomeric
aldoses and ketoses is to convert both terminal carbon atoms to the same functional group. This can be done either by selective oxidation or reduction. As a specific
example, nitric acid oxidation of d-erythrose gives meso-tartaric acid . Similar oxidation of d-threose gives (2S,3S)-tartaric acid. Given this information and the fact that d-erythrose and d-threose are diastereomers, draw Fischer projections for d-erythrose and d-threose. Check your answers against Table 25.1.
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