Question

Draw a Haworth projection and a chair conformation for methyl \(\alpha\)-Dmannopyranoside (methyl \(\alpha\)-D-mannoside). Label the anomeric carbon and the glycosidic bond.

Short answer

Question: Draw a Haworth projection and a chair conformation for methyl α-D-mannopyranoside, and label the anomeric carbon and the glycosidic bond. Answer: In the Haworth projection, the methyl α-D-mannoside has a hexagon-shaped ring with the glycosidic bond (-OCH3) on C1 pointing down and the -OH groups on C2, C3, and C4 also pointing down. The chair conformation has a similar arrangement, with substituents in axial or equatorial positions. The anomeric carbon (C1) forms the glycosidic bond with the methyl group (-OCH3), while the glycosidic bond is the bond between C1 and the methyl group.

Step-by-step solution

Understand the structure of methyl α-D-mannoside

Methyl α-D-mannoside is the methyl glycoside of α-D-mannopyranose. So, we first need to understand the structure of D-mannose. It is a monosaccharide (simple sugar) with six carbons in a pyranose (six-membered ring) form. For α-D-isomer, the hydroxyl group (-OH) on the anomeric carbon (C1) is on the opposite side of the CH2OH group on C5 in the Haworth projection.

Draw a Haworth projection for methyl α-D-mannoside

A Haworth projection is a way to represent a cyclic saccharide (sugar) in a flat, planar form. Start by drawing a hexagon with five carbons at its corners, and one oxygen in a ring. The carbons are numbered from 1 to 5, in clockwise order, starting from the oxygen. The sixth carbon, along with the methyl group, is represented as -CH2OCH3 at C5. In the α-D-mannopyranoside, add a glycosidic bond (a bond between C1 and the methyl group, -OCH3) on the C1 carbon, pointing down from the ring. The hydroxyl groups (-OH) are directed down for C2, C3 and C4 while they are directed up for the fifth carbon (C5).

Draw a chair conformation for methyl α-D-mannoside

A chair conformation represents the actual spatial arrangement of carbons and substituents in 3D space. Start by drawing a chair-shaped hexagon (a polygon with alternating long and short bonds) for the six-membered carbon and oxygen ring. Replace the back and front edges of the chair (C1-O-C4 and C3-C6) with bonds to the correct substituents: - On C1, the α-glycosidic bond (-OCH3) is in the axial position and downward-facing. - On C2, the hydroxyl group (-OH) is in the axial position and downward-facing. - On C3, the hydroxyl group (-OH) is in the axial position and downward-facing. - On C4, the hydroxyl group (-OH) is in the axial position and downward-facing. - On C5, the CH2OH is in the equatorial position and upward-facing, while the -OCH3 group is in the axial position and downward-facing. - On C6, the oxygen atom is in the equatorial position and connected to C5.

Label the anomeric carbon and the glycosidic bond

The anomeric carbon is the one that forms the glycosidic bond, which is carbon 1 (C1) in the case of D-mannose. Label it as C1. The glycosidic bond is the bond between C1 and the methyl group (-OCH3). Label this bond as the "glycosidic bond." With these steps completed, you have successfully drawn the Haworth projection and chair conformation for methyl α-D-mannopyranoside (methyl α-D-mannoside), along with the correct labels for the anomeric carbon and glycosidic bond.