Why is D-glucose the most common aldohexose in nature?
D-Glucose is the most common aldohexose in nature because in its cyclic form it is the most stable of all the aldohexoses.
We normally write the structure of D-glucose as
But we must remember that D-glucose exists as a cyclic hemiacetal.
Let's re-draw this as a cyclohexane chair.
Now we see why glucose is so stable.
Every substituent is in an equatorial location!
Every other aldohexose must have at least one substituent in a less stable axial location.