Carbohydrates, Lipids, and Heterocyclic Compounds — DU B.Sc (hons) Chemistry Previous Year Question Papers

Attempt six questions in all. (a) An a-D-methylglycoside X (molecular formula C,H1406) consumes 2 moles of periodic acid (HO 4) to give one mole of HCHO, and the product A. On subsequent oxidation with bromine/HO in the presence of SrCOz, A gives the crystalline salt B. With reactions, arrive at the possible structures for 4. A and B. (6) • Which is the anomeric carbon in fructose? Draw the Fischer projection formula for the two anomeric forms of D-fructofuranose. (c) • What are steroids ? Give an example and discuss its biological importance. What are good and bad cholesterols ? 5,5,5 i pee tad • 1924 2. (a) A carbohydrate P (molecular formula C12H22011) on enzymatic hydrolysis gives D-glucose. P reacts with bromine water, as well as Benedict reagent. When P is subjected to the following sequence of .. reactions Q and Rare obtained as products. Deduce the structure for P, A and B and explain the reaction involved. P (C12#22011) - Biz/ H2O • A (CH3)2504 -2,3,1,6-Trta-O-meihy-D-glucose/ 2,3,5,6-Tetra-O-methyl-D-gluconic acid (b) Electrophilic substitution reactions in furan occur at C-2 position. Show the attack of the electrophile and justify. (c) (i) Write the products for the HIO, oxidation of the open chain form of D-fructose. - (i). Differentiate between amylose and amylopectin based on the =. glycosidic linkage. and the monosaccharide units along with their structures." 5,5,5 3. (a) Identify the two products formed when an aldohexose reacts with excess of acetic anhydride in the presence of sodium acetate. Will the two products obtained react with excess of phenylhydrazine? Explain. (b) How will you confirm the ring size of glucopyranose by the methylation method? Give the reactions involved. (c) An aromatic compound A (molecular formula CH_N) on treatment with n-butyl lithium at 100°C gives B (CgH1gN). B on oxidation with alkaline KMn04 gives C, which on further treatment with PCIs, -followed by NHz gives D. D on Hofmann bromamide reaction gives 2-aminopyridine. Complete the sequence of the reactions giving the structures of A, B, C and D. 5,5,5 4. (a) Distinguish between the following with examples and structures wherever required : (i) Phospholipids and glycolipids (ii) Omega-3-fatty acid and omega-6-fatty acid. (b) How many isomers can be drawn for a D-aldohexose ? Draw their structures. Which of these on oxidation with nitric acid give meso-aldaric acid ? (c) Pyrrole undergoes ring 'expansion on treatment with CHCIs and aqueoûs KOH. Write the complete reaction and mechanism involved. 5,5,5 (a) What are epimers? Suggest the method for the conversion of D-glucose to its epimer. (b) Write the product obtained when phenylhydrazone of acetone is treated with conc. H SO4. Give the name of the reaction and the mechanism involved. (c) Carry out the following conversions,: ="(i) Pyrrole to 2-formylpyrrole - (it) Thiophene to thiophene-2-carboxylic acid. 5,5,5