Basic Concepts of Organic Chemistry — DU B.Sc (hons) Chemistry Previous Year Question Papers

Attempt four questions in all. All parts of a question should be attempted together. Giving reasons arrange the following : (a) In order of increasing acidity : (b) In order of increasing basicity : (c) In order of increasing stability (d) In order of increasing stability: (i) But-2-ene (it) But-1-ene (e) In order of increasing stability 2. (a) Giving suitable examples differentiate between : (i) Inductive and Electrometric effect (ii) Homolysis and Heterolysis. (b) Which of the following species behave as a nucleophile, an electrophile, both or neither : (c) Gve the major product formed when Ph-CH = CH-CH3 reacts with HBr in absence of peroxides. Explain the mechanism of the reaction. 5×3 Compare the SN1 and SN2 mechanisms for nucleophilic substitution reaction of alkyl halides. Account for the aromaticity observed in : (i) 1, 3-cyclopentadienyl anion but not 1, 3-cyclopentadiene. (ii) The heterocycles pyrrole and pyridine. Assigning priorities, determine the configuration E/Z for the following compounds : Give the R/S configuration to both the Chiral Centers of Meso-2, 3- Write the contributing resonance structures and delocalized hybrids for : (i) Carbon dioxide CO2 (ii) Isocyanic acid NHCO. (c) How can Propan-1-ol be prepared using Hydroboration-oxidation reaction ? Explain giving mechanism. 5×3 5. (a) Differentiate between : (ii) Racemic Mixture and Meso Compound. (b) (i) Calculate the percentage of isomers expected from monochlorination of Propane. The relative reactivities of 2° and 1° H atoms are 3.8 and 1.0 respectively. (ii) Write the product/s formed when cis-but-2-ene reacts with (c) Halogens are deactivating yet ortho, para-directing in electrophilic aromatic substitution reactions. Explain. 5×3 Write short notes on any three of the following : (a) Hoffmann and Saytzeff mode of elimination (b) Free Radicals (c) Biological dehydration reactions (e) Friedel-Crafts alkylation reaction. 5×3