Question Bank for Racemic Modification

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Explain Racemic modification with example. What is racemic modification? Give methods of formation of racemic modification. What is racemic modification? Give formation of racemic modification by synthesis. Bromination of propionic acid by the Hell-Volhard-Zelinsky method gives equal molecule of (+) and (-) α-bromopropionic acid 5. Explain addition of hydrogen cyanide to acetaldehyde to give equal numbers of molecules of the two enantiomeric forms of lactonitrile 6. Explain formation of racemic modification by Racemization method. i. Explain formation of racemic modification by thermal racemization method. ii. Explain formation of racemic modification by anion formation method iii. Explain formation of racemic modification by cation formation method 7. In Mandelic acid base induced racemization occurs whereas in Anthrolactic acid no base induced reacemization occurs. 8. Compound A undergoes base indused racemization where as compound B fail to same.

A B 9. Explain racemization of α-phenethyl chloride by means of antimony pentachloride and of 2-phenylbutane by aluminum chloride 10. Explain racemization of α-phenethyl chloride by means of antimony pentachloride and by Reversible Formation of Stable Inactive Intermediates 11. Explain formation of racemic modification by Reversible Formation of Stable Inactive Intermediates. 12. Racemization of alcohols in the presence of sodium or aluminum alkoxides. 13. Write a note on Walden inversion. 14. Explain Walden inversion in racemic modification formation. 15. Explain epimerization of an optically active compound does not involve racemization. 16. Epimerization of Menthone and isomenthone in racemic modification. 17. Give the properties of Racemic Modification. 18. What is racemic Mixture? Give its properties. 19. What is racemic Compound? Gives its properties 20. What is difference between racemic mixture and racemic compounds 21. Explain racemic solid solution.

22. Write a note on Resolution of racemic modification. 23. Give resolution method of racemic modification by Mechanical separation of Crystals. 24. What is meant by resolution? Give methods of resolution of racemic modification. 25. Explain of racemic modification by formation of diastereoisomer. 26. What is resolving agent? Give the condition of good resolving agents in resolution. 27. Give the common resolving agents for resolution of acids and bases. 28. Method of resolution of amino acids 29. Amino acids are resolved in the form of their acyl derivatives. 30. Explain method of resolution of (±) alanine 31. Amino acids cannot resolve by formation of their formyl derivatives. 32. Explain resolution alcohols 33. Resolution of Alcohols by half ester method 34. Explain resolution via molecular complexes formation. 35. Use of tri-o-thymotide in resolution of racemic modification 36. Resolution by chromatography 37. Second order asymmetric transformation in resolution of racemic modification 38. Explain resolution by equilibrium asymmetric transformation 39. Resolution by asymmetric transformation 40. Write a note on Kinetic method of resolution 41. Explain Asymmetric destruction in resolution of racemic modification 42. Biochemical kinetic resolution method for amino acids. 43. What are criteria of optical activity 44. Methods for determination of optical Purity. Problems based on optical Purity Q. (S)- -2-bromobutane will have an observed specific rotation of +23.10. What is the optical purity, enantiomeric excess and % composition of a mixture whose specific rotation is -9.20. Ans. Specific rotation of [α] of (S)-2-bromobutane is +23.10 Therefore its enantiomer (R)-2-bromobutane is have equal and opposite specific rotation Specific rotation of [α] of (S)-2-bromobutane is -23.10 The mixture shows -9.20; it means that (S) enantiomer is dominant / excess over (R) enantiomer due to negative specific rotation.

[α] of mixture / sample = -9. 20 and [α] for pure (S) enantiomer is -23.10

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% Optical purity =

-9.2 -------- x 100 - 23.1

% Optical purity = 40 % This indicates that (S) enantiomer excess over (R) enantiomer by 40 % i.e. Enantiomer excess = 40% Percentage composition of each enantiomer: If the mixture has a 40% enantiomeric excess, 40% of the mixture is excess S enantiomer and 60% is a racemic mixture. Half of the racemic mixture plus the amount of excess S enantiomer equals the amount of the S enantiomer present in the mixture. Thus, 70% of the mixture is the S enantiomer and 30% is the R enantiomer. Q. (S)- -2-bromobutane will have an observed specific rotation of +23.10 and (R)- -2bromobutane have of -23.10 . What is the optical purity, enantiomeric excess and % composition of a mixture whose specific rotation is +18.40. Q. a reaction which gives mixture of (+) and (-) 2-phenyl pentane shows [α]D specific rotation about -12.960. The known specific rotation for pure detro-rotatary enantiomer of 2-phenyl pentane is 14.910. Calculate optical purity and percentage of each enantiomer in mixture. Q. (+) Mandelic acid has a specific rotation of +1580. What would be the observed specific rotation for mixture contain 50 % optical purity of (-) Mandelic acid? Q. (-) Mandelic acid has a specific rotation of -1580. What would be the observed specific rotation for 70 % optical purity of (-) Mandelic acid? Q. Naproxen is the active ingredient in Aleve. Naproxen has a specific rotation +660 of in chloroform. One commercial preparation results in a mixture which shows specific rotation of +63.360. How much the mixture is optically pure? Q. Q. The chromatographic purification of 1 g of (−)-ethyl lactate with an enantiomeric excess (ee) of 85%yields, without any loss of material, the optically pure (−)-enantiomer. How many g of the (+)-enantiomer were separated?