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What's the difference between the two molecules? I can always read about β-D-fructofuranose in the chemistry books, but unfortunately, I've never found any info concerning β-D-fructopyranose. Is there a big difference between them (apart from their ring structure)? And where can the furanose and the pyranose form be found in nature?

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    $\begingroup$ While I don't have time to write up a full answer, I've always found it interesting that the reason you don't use honey as a sweeter in baking is because of the poor control of sweetness which is caused by the furanose-pyranose interconversion at high temperatures. You can read more about it at biochemislife.wordpress.com/2013/03/15/… $\endgroup$
    – chipbuster
    Sep 7, 2016 at 22:30
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    $\begingroup$ @FelipeS.S.Schneider I think you removed a part of the original post..? The extra question was in the edit, which was rejected anyway. You may check the revision history :) $\endgroup$ Jan 28, 2020 at 14:04
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    $\begingroup$ @WilliamR.Ebenezer You're absolutely right, my fault. I just added the question again. Thanks for spotting that one out :) $\endgroup$ Jan 28, 2020 at 19:59

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They are isomers. Both of them have the same molecular formula ($\ce{C6H12O6}$) but different structures.

β-D-fructopyranose

Structure of β-D-fructopyranose

β-D-fructofuranose

Structure of β-D-fructofuranose

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    $\begingroup$ Could do with some elaboration, I suppose. $\endgroup$ Sep 8, 2016 at 9:53
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Fructopyranose is the free form of fructose. When fructose is attached to another glucose forming sucrose or attached to other fructose making fructans, it does so in its furanose form. When invertase breaks down sucrose into glucose and fructose, the furanose form of fructose that occurs in sucrose, is now a pyranose form that can be metabolized in the liver by fructolysis.

I hope this helped you!

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