 Mannose (source code)

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= Mannose

<Mannose> is an <aldohexose>, a six-carbon <monosaccharide>. The commonly discussed biological form, D-mannose, has neutral <molecular formula> $\mathrm{C_6H_{12}O_6}$. Like other <sugars>, it can have distinct cyclic forms; specifying D configuration does not by itself identify an alpha or beta anomer.<D-mannose in ChEBI>[CHEBI:16024: formula, D-aldohexose and mannose classification]{ref}

A <Fischer projection> provides an original structural comparison with D-<glucose>. Reading hydroxyl positions from carbon2 to carbon5, D-<glucose> has the pattern right–left–right–right, while D-<mannose> has left–left–right–right. The difference is at carbon2 alone, so they are <epimers>. Reversing all four <stereocenters> would be a different operation, producing the corresponding <enantiomer>.

Changing that one spatial arrangement changes neither the number of <carbon> atoms nor the total <hydrogen> and <oxygen> counts. A molecular-mass measurement therefore cannot, by itself, distinguish the two <sugars>. An identifying experiment must supply additional structural discrimination, for example through an appropriately interpreted <nuclear magnetic resonance> spectrum.

The useful distinction is between composition and configuration. The D label concerns a reference <stereocenter>; alpha/beta labels concern the anomeric center in cyclic forms. Neither label should be read as a direct statement about sweetness or the sign of <optical rotation>.<Nomenclature of Carbohydrates (Recommendations 1996) by Alan D. McNaught>[Carbohydrate configurational conventions and cyclic-form nomenclature]{ref}

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