Reactive Intermediates of Organic Chemistry — DU B.Sc (hons) Chemistry Previous Year Question Papers

REACTIVE INTERMEDIATES OF ORGANIC B.Sc. (Prog.) Industrial Chemistry Q 1. a) Differentiate between classical and non-classical carbocation with .suitable examples. b) Explain how neighboring group participation proceeds through sigma bond and phenyl ring? c) Discuss the various factors affec.ting the stability of carbanion. Arrange the following carbanions in the order of increasing stability and justify your answer. Q2. Complete the following reactions, identify the name reaction and reactive intermediate involved. Q3. a) Write the structure of following bicyclic compounds (i) Bicyclo [2.3.1] octane (il) Bicyclo [2.2.i] heptane (iv) Spiro [2,3] hexane (v) Spiro [2.2] heptane b) An alkene is formed when phosphorus ylide reacts with a carbonyl compound, whereas a sulphur ylide yields an epoxide on treatment with a carbonyl compound. Explain with mechanism. Q4. (a) Describe methods of generation, structure with hybridization and geometry of carbene. (b) Outline the mechanism of the Beckmann rearrangement. Use a suitable example to demonstrate the anti-periplanar migration of the substituent group. (c) Define Bredt's rule. Explain the reactivity and limitation of bridge head carbocation Q5. a) What are the starting materials and the main product of the McMurry coupling reaction? Briefly state the role of low-valent titanium in this transformation. b) State the HSAB principle and classify the following species as hard or soft: Ht, CHst, NH3, and I. Explain how HSAB helps predict the preferred site of electrophilic attack in conjugated systems. c) Define Baldwin's rule. What are the three criteria's used by Baldwin for ring closure Q6. Write short note on any three of the following a) Hoffmann rearrangement b) Baeyer Villager oxidation c) Schmidt rearrangement d) Barton deoxygenation and decarboxylation