Question

Question: Glucose is a simple sugar with five substituents bonded to a six-membered ring.

a. Using a chair representation, draw the most stable arrangement of these substituents on the six-membered ring.

b. Convert this representation into one that uses a hexagon with wedges and dashed wedges.

c. Draw a constitutional isomer of glucose.

d. Draw a stereoisomer that has an axial OH group on one carbon.

Short answer

Answer

a.

Most stable chair form of glucose

b.

Wedged and dashed wedged structure of glucose

c.

Fructose, a constitutional isomer of glucose

d.

$\beta -D-glucopyranose$,a stereoisomer with OH on the axial position

Step-by-step solution

Numbering

The numbers are assigned to the atoms in the ring, starting from oxygen.

Numbered ring structure of glucose

Draw chair form and add the substituents

The chair form of the ring is drawn. The atoms at position 1 and position 4 are picked, and one of them is assigned up and the other down positions.

Each atom in the ring has two substituents: one at the axial position and the other at the equatorial position. The axial groups on the up carbon atoms are on the upper side and vice-versa. The remaining positions are the equatorial positions.

Glucose ring in chair form

Arbitrarily assign the groups on the axial and equatorial positions on each carbon. In glucose, the OH groups are present on the opposite sides of two consecutive carbons.

Hence, starting from position 2, the groups are alternatively assigned on up and down positions. In this structure, starting from position 2, the groups are assigned the up alternatively.

The remaining bonds are filled with hydrogen (H) atoms.

Wedges and dashed wedges representation

The groups on the upper side of the ring are represented with a wedge, and those on down the ring are represented with dashed wedges.

Solutions

a. The most stable arrangement of the substituents in the chair form of glucose is represented below.

Most stable chair form of glucose

b. The upper side groups are represented with a solid wedge, and the down groups are represented with a dashed wedge on the hexagonal ring of glucose.

Wedged and dashed wedged structure of ring structure of glucose

c. The constitutional isomer of glucose is fructose. Glucose and fructose have the same molecular formula but different connectivities. Glucose has an aldehyde group, while fructose has a ketone group.

Fructose

d. The stereoisomer of glucose with an OH group on the axial position on carbon one is $\beta -D-glucopyranose$.

$\beta -D-glucopyranose$