Answer: In α-D-glucose and β-D-glucose, the configuration at the first carbon (anomeric carbon, C1) differs. In α-D-glucose, the hydroxyl (OH) group attached to the anomeric carbon is below the plane of the ring (axial position), while in β-D-glucose, the hydroxyl group is above the plane of the ring (equatorial position).
To change the configuration from α-D-glucose to β-D-glucose:
The bond that needs to be broken is the glycosidic bond between the anomeric carbon (C1) and the adjacent hydroxyl group (OH group at C5). Breaking this bond allows the rotation of the anomeric carbon and the change in configuration from α to β.
To convert D-glucose to D-mannose:
D-glucose and D-mannose are epimers, meaning they differ only in the configuration around one carbon atom (C2). In D-glucose, the hydroxyl group at C2 is in the axial position, while in D-mannose, it is in the equatorial position.
The bond that needs to be broken is the C2-C3 bond in the ring structure. Breaking this bond allows the rotation of the C2 carbon, leading to the change in configuration from glucose to mannose.
To convert one "chair" form of D-glucose to the other:
In the chair conformation of D-glucose, the positions of the hydroxyl groups on the ring can be either axial (pointing up or down) or equatorial (pointing outward). To convert one chair form of D-glucose to the other, the glycosidic bond between the anomeric carbon (C1) and the adjacent hydroxyl group (either C4 or C6) must be broken. This allows the ring to flip or invert, resulting in a chair conformation with different hydroxyl positions.