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LOYOLA COLLEGE (AUTONOMOUS), CHENNAI 600 034
B.Sc.DEGREE EXAMINATION -CHEMISTRY
SIXTH SEMESTER APRIL 2018
CH 6609- SYNTHETICS ORGANIC CHEMISTRY AND SPECTROSCOPY
Date: 03-05-2018 Dept. No. Max. 100 Marks
Time: 01:00-04:00
PART-A
Answer all questions (10×2=20)
1. Define the term regiospecificity.
2. What do you mean by a precursor?
3. What is Jones reagent? What is its usefulness?
4. Name the reagents used for the following conversions
CO N CHO
→ RCOOR'
5. Predict the product in the following reactions:
Δ
3-Butadiene+ Acrolein
Δ
3-Butadiene+ Maleic anhydride
6. What is meant by an active methylene group? Give an example.
7. Which will absorb at shorter wavelength region? Why?
Cis stilbene or Trans stilbene
8. Calculate the for the following compounds

9. What is coupling constant?
10. How will you distinguish between ortho and p hydroxybenzaldehyde from their IR spectra?
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PART-B
Answer any EIGHT questions
11. Enumerate the advantages of retro synthetic approach.
12. Write a note on reversal of polarity.
13. What do you mean by functional group transposition? Explain it with an example.
14. What is DIBAL? Explain its usefulness in organic synthesis.
15. Outline the mechanism of Clemmenson's reduction with an example.
16. Write the mechanism of crossed -aldol condensation reaction with an example.
17. Write the mechanism of Keto-enoltautomerism taking ethyl acetoacetate as a reference compound.
18. How are the following compounds distinguished from their IR spectra.
C6H5COCH2CH3and C6H5CH2COCH3
19. An organic compound A with Molecular formula C3H9N shows the following peaks in the IR spectrum.
3012 cm-1 3423cm-1 3236 cm-1 (m)and 1615cm-1
When the compound A is treated with HNO2, we get a compound B which shows a strong peak at 3430 cm-1. What are A and B and explain the reactions involved?
20. What is spin-spin coupling? Explain it with an example.
21. Write the mechanism of McClafferty rearrangement.
22. State and explain nitrogen rule with an example.
PART-C
Answer any FOUR questions (4×10=40)
23. Explain the usefulness of the following in modern organic synthesis.
Activating groups Bridging elements
24. Predict the products in the following reactions and suggest a suitable mechanism.
Zn HCl
Acetophenone
3
NaBH4 H2O
Cinnamaldehyde
25. Write the mechanism of Baeyer Villiger oxidation taking an appropriate example.
Predict the product in the following reaction and suggest a suitable mechanism.
Base
Cinnamaldehyde Diethylmalonate
26. A cyclic ketone A (C5H8O) on reaction with NaOCH3 gives a product B which has the following
spectral properties.
IR: 1740cm-1 1160cm-1
UV: Transparent above 200nm
1H-NMR: δ3.6 δ1.2 (9H
Mass: m/z 116, 85, 59, 31.
Deduce the structure of A and B.
Why is TMS chosen as a reference compound in NMR spectroscopy?
27. Discuss the use of IR spectroscopy in distinguishing between inter and intra molecular hydrogen bonding.
28. How will you distinguish between 3-methyl and 4-methyl cyclohexene on the basis of mass
spectroscopy?
Mass spectra of acetone, propionaldehyde and ethyl methylketone show strong peaks at m/z values of
43, 57 and 57 respectively. Suggest a possible origin for each of these peaks.
Write a note on the concept of see back in organic synthesis.