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This Q&A is a continuation from the following Q&A; What do we get when we joint two α- glucoses via an α1,4 bond?

More straightforwardly, the question may focus on whether the bond represented by the following straight line means equatorial or axial　(Find the OH circled in blue in the following figure).

enter image description here https://www.chemspider.com/Chemical-Structure.388329.html

Above figure is quoted from chemspide. If I understand correctly, the bond or solid line may indicates the anomeric hydroxy group of the alpha-maltose is equatorial, am I right(See the blue circle of the figure, quoted above)?

The chemspide also has figure which may indicates the anomeric hydroxy group of alpha-maltose has axical anomeric hydroxy group, shown as follows. (See the blue circle of the figure, quoted below)

enter image description here

https://www.chemspider.com/Chemical-Structure.6019.html

However, Wikipedia has figures which indicate the anomeric hydroxy group of α-maltose is axial and β-maltose has equatorial one.

enter image description here https://en.wikipedia.org/wiki/Maltose

So, I' very confused.

On the other hand, PubChem has following descriptions, quoted below; this article is titled simply "maltose," but this article also has the description which the "maltose" is synonymous with the "beta-maltose".

enter image description here

However, although the article for the α-maltose titled "α-maltose" but the article also　has the description which indicate the "α-maltose is also synonymous with maltose".

https://pubchem.ncbi.nlm.nih.gov/compound/alpha-Maltose#section=3D-Conformer

If I understand correctly, the structural formulas on PubChem indicates;

  • the anomeric hydroxy group of α-maltose　is axal but　directed Upward
  • the anomeric hydroxy group of β-maltose　is also axial but directed downward.

anomeric hydroxy groups of both A and B in this appear to be axial.

enter image description here https://pubchem.ncbi.nlm.nih.gov/compound/alpha-Maltose#section=Structures

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Maltose [4-O-(α-D-glucopyranosyl)-D-glucopyranose] always has an α-1-O-4 linkage. The bridging oxygen at $\ce{C1}$ is axial. For maltose, there are two anomers. The β-anomer (shown below) has the anomeric hydroxyl equatorial while the α-anomer is axial. These two anomers are interconvertible in aqueous solution.
On the other hand, cellobiose [4-O-(β-D-glucopyranosyl)-D-glucopyranose] always has a β-1-O-4 linkage. It also exists as α- and β- (shown below) anomers, axial and equatorial, respectively.
The diagrams are from here. A good read..


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