: 200
Sucrose: alpha-D-glucopyranosyl-(1→2)-beta-D-fructofuranoside. Both anomeric C locked → non-reducing. Hydrolysis gives invert sugar (rotation inverts from + to -). No mutarotation. Gives positive Seliwanoff (HCl hydrolyzes it, releasing fructose). Maltose: alpha-D-glucopyranosyl-(1→4)-D-glucopyranose. C1 of first glucose (alpha) bonded to C4 of second. Second glucose has free anomeric C1 → reducing. Shows mutarotation. From starch digestion (amylase). Lactose: beta-D-galactopyranosyl-(1→4)-D-glucopyranose. Note BETA linkage (galactose contributes C1 in beta configuration). Free anomeric C on glucose → reducing. Milk sugar. Lactose intolerance = lack of beta-galactosidase. Cellobiose: beta-D-glucopyranosyl-(1→4)-D-glucopyranose. Same as maltose but BETA linkage. Repeating unit of cellulose. Reducing sugar. JEE exam tips: Know the glycosidic bond type (alpha/beta, which carbons). Know which are reducing (free anomeric C). Know the component monosaccharides. Sucrose is THE non-reducing disaccharide — appears in almost every exam.