D-glucose: from Fischer projection, via 3D glucopyranose, to Haworth projection.

Maitland Jones, 2nd ed., § 23.1 p. 1170

The relation between the Fischer projection of D-glucose and the three dimensional structure of beta-D-glucopyranose is shown here in the form of an animation.
The starting structure resembles the Fischer projection. Position the structure in such a way that the carbon chain is vertical, the aldehyde at the top, and the horizontal bonds pointing towards you (conform the definition of the Fischer projection).

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Colour/Uncolour the four oxygen positions that define the type of sugar. The stereochemical position of the green OH group determines the D type of sugar. It is this oxygen that attacks the carbonyl group and ends up in the ring.

To compare stereo-isomers of cyclic compounds, only the relative positions of the substituents matter. The flexibility of the ring doesn't affect cis or trans relations between substituents. Therefore Haworth introduced a projection in which the ring is made flat, and the substituents are pointing either up or down.

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next conformation

The animation shows the relation between the 3D structure of glucopyranose and the Haworth projection. Try to align the structure as in the drawing on the right. Note how the alternating up/down (trans/trans) positions of the substituents stick out clearly now.

Questions

Note: Although the questions are in English, you may answer them in Dutch...
  1. At which stage (conformation number) it is decided whether alpha or beta glucopyranose is formed? What should happen to obtain the alpha isomer?

  2. In pyranose sugars other than glucose, at least one hydroxyl group ends up in an axial position. Which one (#) is it in galactose?

  3. What would be the substituent positions (axial/equatorial) in L-glucopyranose?

  4. What would be the first step in the reverse reaction, the (acid catalyzed) opening of the pyranose ring?

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and your answers!

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