How can I draw d -glucose in its chair conformation? Why it is the most common aldohexose in nature?

First convert the Fischer projection to a Haworth projection, then convert the Haworth projection to a chair form.

The Fischer projection of glucose is

Convert to a Haworth Projection

Step 1. Draw a basic Haworth projection with the ring oxygen at the top.

##"C-1"## is the atom to the right of the oxygen, and ##"C-5"## is the atom to its left.

Step 2. Draw a ##"CH"_2"OH"## on ##"C-5"##.

Step 3. Draw an ##"OH"## below the ring on ##"C-1"## for the α form (draw it above the ring for the β form).

Step 4. Draw all the ##"OH"## groups on the right side of the Fischer projection on the bottom of the ring. Those on the left go above the ring.

The ##"O"## on C-5 is part of the ring.

You can omit the hydrogen atoms, so the Haworth projection for α-D-glucopyranose is

Convert Haworth to Chair

Step 1. Draw a cyclohexane chair in which the ##"O"## atom replaces ##"C-6"## and the bulky ##"CH"_2"OH"## is in the equatorial position.

Step 2. Put all the ##"OH"## groups that are "down" in the Haworth projection "down" in the chair. All the other ##"OH"## groups go "up".

The chair form of α-D-glucopyranose is

The structure of β-D-glucopyranose is

Prevalence of Glucose

As you move around the β-glucose ring, you see that all the substituents are equatorial.

This is the most stable arrangement possible.

In α-glucose, only the ##"OH"## at ##"C-1"## is axial.

Every other aldohexose would have more axial substituents and be less stable.

Glucose is the most common hexose because it is the most stable.