Q.What is the action of conc. HI with glucose ?

Glucose is an optically active aldohexose (C₆H₁₂O₆) with four asymmetric carbons, prepared by acid hydrolysis of either sucrose or starch. Its open-chain structure was built up from eight lines of evidence: molecular formula from elemental analysis; HI/red-phosphorus reduction giving mainly n-hexane (proving an unbranched 6-carbon chain); reaction with NH₂OH/HCN (proving a carbonyl group); mild oxidation with Br₂ water giving gluconic acid (proving a terminal aldehyde) versus vigorous oxidation with conc. HNO₃ giving glucaric/saccharic acid (proving a primary alcohol at the other end); reduction of Tollens'/Fehling's reagents (confirming the aldehyde); a penta-acetate with acetic anhydride (proving five -OH groups, one per remaining carbon); resistance to easy dehydration (proving no two -OH groups share a carbon); and finally Fischer's own spatial assignment, giving D-(+)-glucose. …