LOYOLA COLLEGE (AUTONOMOUS), CHENNAI – 600 034

B.Sc. DEGREE EXAMINATION – CHEMISTRY

SIXTH SEMESTER – APRIL 2012

CH 6609/CH 6603 – SYNTHETICS ORGANIC CHEMISTRY AND SPECTROSCOPY

 

 

 

Date : 23-04-2012              Dept. No.                                        Max. : 100 Marks

Time : 1:00 – 4:00

 

PART – A

Answer all questions:                                                                                                       (10X2=20)

 

1. What do you mean by umpolung?
2. What are synthons? Give an example.
3. Complete the following reactions
4. Name the reagents used for the following conversion.

 

 

 

 

5. What is meant by an active methylene group? Give an example.
6. Give an important condition for a ketone to undergo Aldol condensation.
7. Calculate the λ_max for the following molecule:

 

 

8. How will you distinguish the following pair of isomers from their IR spectra?

 

 

9. Define the term chemical shift.
10. State nitrogen rule in mass spectra.

 

PART – B

Answer any EIGHT questions:                                                                                            (8×5=40)

 

11. Write a note on convergent synthesis.
12. Explain the various types of intermediates that are formed in organic reactions.
13. What are activating groups? Explain their usefulness in organic synthesis.
14. Write the mechanism of Wolf-Kishner reduction.
15. What is DIBAL? Explain its preparation and usefulness.
16. Write the mechanism of Aldol condensation.
17. Complete the following reactions

 

 

18. Explain the following with suitable examples:
19. a) Bathochromic Shift
20. b) Hyperchromic Shift
21. How is IR spectroscopy useful in detecting the H-bonding in organic compounds?
22. Explain the Proton NmR spectrum of ethyl alcohol contaminated with a little HCl.
23. Write the mechanism of McClafferty rearrangement with reference to mass spectroscopy.
24. Explain why cyclohexane gives only one peak at room temperature while it gives two peaks

at-100°C.

 

PART – C

Answer any FOUR questions:                                                                                        (4X10=40)

 

23. a) write a note on retrosynthetic analysis.   (5)
24. b) What are protecting groups? Explain the usefulness of them in organic synthesis.  (5)

 

24. Starting from acetoacetic ester, how will you prepare the following?

(i) Acetone (ii) succinic acid (iii) antipyrine   (iv) 4-methyl uracil (v) acetic acid.                  (10)

 

25. a) How will you distinguish the following pairs of compounds using IR Spectroscopy? (4)

(i) CH₃-CH₂-OH and CH₃-O-CH₃

(ii) maleic and fumaric acids

1. b) An organic compound of molecular formula C₉H₁₀O₂ showed three peaks in the PMR

spectrum as given below.

δ1.96 (S,3H)

δ5.0 (S,2H)

δ7.2 (S,5H)

Identify the structure of the compound.                                                                                   (6)

 

26. a) write a note on coupling constants.   (4)
27. b) A cyclic ketone (C₅H₈O, A) on reaction with NaOCH₃ gives a product B which has the

following NMR signals.

δ 3.6 (S,3H)

δ1.2 (S,9H)

Deduce the structures of A and B.                                                                                           (6)

 

27. Deduce the structure of the compound C₉H₈O which exhibited the following spectral data:

UV: λ _max(EtOH) : 285 nm (ε 45000)

IR: ۷_max (KBr) : 3090,2820,2750,1685,1630,1610,970 cm^-1

NMR: δ 6.62(1H, dd) J= 16 and 7 Hz, 7.41 (1H,d), 7.4 (5H, m), 9.66 (1H, d)

MS: m/z 132,131, 103, 91,77 and 51.

 

28. a) Discuss the instrumentation of IR Spectrometer with the block diagram. (6)
29. b) How are the following groups protected and deprotected during organic synthesis.  (4)

 

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