D- and L-glucopyranose


D-glucopyranose Colour sweetness triangle (toggle) Lipophilicity surface on/off (transparent) Electrostatic surface on/off (transparent) Select two atoms to measure distance Hydrogen bond	L-glucopyranose Colour sweetness triangle Lipophilicity surface on/off (transparent) Electrostatic surface on/off (transparent) Select two atoms to measure distance

Colour coding in sweetness triangle:
yellow = AH, hydrogen bond donor, green= B, hydrogen bond acceptor, purple= X, hydrophobic group.
Surface colours: see scheme below.

Both compounds are almost equally sweet. In fact L-glucose would make a good low calory sweetener, as it is hardly metabolized in the human body. However, it turned out to be too expensive to synthesize. Nature makes the D-form only.

Pressing the 'h bond' button shows an internal hydrogen bond. H-bonds occur between electronegative atoms, one containing a more or less acidic proton (donor), the other one a free electron pair (acceptor). Hydrogen bonds are preferably, but not necessarily, linear (angle A-H...B ~180 °), with an A...B distance of ~ 2.9 Å. They stabilize the system by ca. 4 kcal/mol.
Keep in mind that water molecules participate in hydrogen bonds too, in a dynamic way; i.e. bonds are being formed and broken continuously.

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