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Glucose molecular formula C6H12O6 was established by elemental analysis. Its structure was proven by chemical evidence: (1) Reaction with HI gives n-hexane — confirming a straight 6-carbon chain. (2) Reaction with hydroxylamine (NH2OH) gives an oxime — confirming one C=O group. (3) Acetylation with acetic anhydride gives glucose pentaacetate — confirming 5 OH groups. (4) Mild oxidation with Br2 water gives gluconic acid (monocarboxylic) — confirming the C=O is an aldehyde, not ketone. (5) Strong oxidation with HNO3 gives glucaric acid (dicarboxylic) — confirming C6 is also oxidizable (primary alcohol). (6) Reduction with NaBH4 gives sorbitol (a hexahydric alcohol) — confirming the aldehyde. (7) Glucose forms a cyclic hemiacetal (positive test with Schiff's reagent is slow — some free CHO available but mostly cyclic). (8) Two anomers (alpha and beta) with different melting points and rotations, both equilibrating to +52.7 degrees (mutarotation) — proving cyclic-open chain equilibrium. (9) X-ray crystallography confirmed the chair conformation of beta-D-glucopyranose with all large groups equatorial. This systematic evidence-based approach to structure determination is a model for organic chemistry reasoning.