Open-chain glucose: CH2OH(CHOH)4CHO — an aldohexose with 4 chiral centers (C2, C3, C4, C5), giving 2^4 = 16 possible stereoisomers. D-glucose has all OH groups on the right at C2, C4, C6 in Fischer projection (except C3 which is on left).

Cyclic form: Intramolecular hemiacetal between C1 (CHO) and C5 (OH) → 6-membered pyranose ring. C1 becomes the anomeric carbon with a new OH group. Alpha-D-glucopyranose: C1-OH axial (below ring in Haworth). Beta-D-glucopyranose: C1-OH equatorial (above ring). Beta form is more stable (all large groups equatorial in chair conformation).

Mutarotation: Pure alpha form ([alpha] = +112 degrees) dissolves and equilibrates to a mixture of alpha (36%) and beta (64%) through the open-chain form, settling at [alpha] = +52.7 degrees. This proves cyclic-open chain equilibrium in solution.