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In general, the name "fructose" is used to refer to all tautomeric forms and enantiomers of D-fructose (according to my teacher). Does this imply that "fructose" is the umbrella term for all of these structures? This is not clear to me because the cyclic forms of "fructose" are uniquely named "fructopyranose" and "fructofuranose" yet even they are included under "fructose". Also, in some instances "fructose" is only used to refer to the D-isomer and its tautomeric forms, as in here:

NCERT

(NCERT for class XII, part II; excuse the bad quality)

Even Wikipedia specifies "open-chain form" (below the structure of open fructose) when referring to the open structure of fructose (suggesting that it refers to a multitude of structures). Due to these inconsistencies I ask, what does "fructose" actually refer to?

Note: This inconsistency in naming is not unique to fructose, it is also shown in glucose and other carbohydrates.

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  • $\begingroup$ The nature of language is such that words have many meanings, but (unless you're punning ;) you use just one at a time. $\endgroup$
    – Mithoron
    Commented yesterday
  • $\begingroup$ related chemistry.stackexchange.com/questions/26309/… $\endgroup$
    – Mithoron
    Commented yesterday
  • $\begingroup$ @Mithoron Language really is a pain, especially english $\endgroup$
    – Mayo
    Commented yesterday
  • $\begingroup$ Gosh, wonder what you'd say about Polish then ;> $\endgroup$
    – Mithoron
    Commented yesterday
  • $\begingroup$ Never heard it, but it cant be worse (efficiency-wise and clarity-wise) than english $\endgroup$
    – Mayo
    Commented yesterday

1 Answer 1

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Fructose refers to the open chain and the two anomers (alpha and beta) of the closed forms (pyranose or furanose). These are at equilibrium in aqueous solution.

For pure fructose (in solid form), you might add which anomer it was crystallized in, if known.

Tautomers are usually included when referring to fructose. They are present at low abundance in fast equilibrium in aqueous solution.

Enantiomers (i.e. a molecule and its mirror image) are not included if you specify D-fructose or if you casually speak of fructose from natural origin. This makes sense because organisms make D-fructose almost exclusively without making L-fructose. On the other hand, if you make fructose by total synthesis and don’t have access to chiral reagents, you would end up with the racemic mixture D/L fructose and call it that.

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    $\begingroup$ IIRC, in solution also the six-membered ring is present is small amounts. $\endgroup$
    – Willy England
    Commented yesterday

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