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IGNOU MCH-12 (January 2024 – December 2024) Assignment Questions
1. a) Name the two ways of representing the three dimensional structures of molecules in two dimensions and explain the types involved any one of these. Illustrate your answer.
b) Carry out the following conversions for the structures given indicating the projection of the molecule.
i) Convert into the staggered Newman projection
2. a) Explain the stability of methylcyclohexane with the help of chair conformations and the Newman projections.
b) Write the order of simple axis of symmetry and the plane or symmetry in the following molecules.
3. a) How is the asymmetry observed in allenes or spiranes different from that observed in biphenyls? Explain giving example in both the cases.
b) Explain the method of quasi-racemates for the determination of configuration giving suitable diagrams.
4. a) i) Explain the Re and Si faces in CH3CHO using suitable diagrams.
ii) What is a stereocentre? Does the presence of stereocentres ensure chirality in a compound?
b) i) What is chirotopicity and a chirotopic atom? (2)
ii) Explain the presence of chirotopic atoms in a chiral molecule and an achiral molecule.
5. a) Illustrate Cram’s rule by using open chain model by taking suitable examples.
b) Explain the octant rule using suitable diagram and give rules used for contribution of different substituents.
6. a) Draw the potential energy diagrams (PED) for the following reaction indicating:
i) Step 1 as the rate determining step
ii) Step 2 as the rate determining step
b) How are stereochemical studies helpful in establishing the mechanism of organic reactions illustrate your answer.
7. a) Which is more stable in the following pairs and why? Indicate the carbocations as primary secondary or tertiary.
8. a) Arrange the following compounds in the increasing order of their stability. Give reason for your answer.
Allyl anion, m-Nitrobenzyl anion, ortho Chlorobenzyl anion, Benzyl anion
b) Draw the structures of the two types of carbenes. Explain the stereochemistry of addition reaction on these types.
9. a) Give the evidence which explains the formation of benzyne intermediate during nucleophilic substitution reactions of aromatic halides.
b) Why is bromination by free radical mechanism is more selective than chlorination? Write all the possible chlorination products of methyl cyclohexane by photolysis.
10. a) Compare the nature of nitrenes to carbenes and give two methods of generation of nitrenes.
b) Describe the various redox sources of free radical generation.
