LOYOLA COLLEGE (AUTONOMOUS), CHENNAI – 600 034
B.Sc. DEGREE EXAMINATION – CHEMISTRY
SIXTH SEMESTER – APRIL 2008
CH 6603 – SYNTHETICS ORG.CHEM. & ORG. SPECTROSCOPY
Date : 25/04/2008 Dept. No. Max. : 100 Marks
Time : 9:00 – 12:00
PART – A
Answer all the questions. (10 ´ 2 = 20)
- What is the range of Infrared radiations ?What are the units used in IR spectroscopy.
- What is chemical shift ?Why do we choose Tetra methyl silane (TMS) as a standard substance for recording chemical shift values.
- How many NMR signals would you expect from the following compounds i.Toluene ii.Allyl alcohol.
- How will you use the UV- Visible spectral data to distinguish between the following pairs – Ethyl benzene and Styrene.
- What is Nitrogen rule with respect to mass spectroscopy.
- How will you convert diethyl malonate to butanoic acid?
- Complete the following reactions.
- Name the reagents A and B used to effect the following conversions.
- i) CH3-CH=CH-CHO CH3-CH=CH-CH2OH
- Complete the following reactions.
- i) R2CHOH ?
- ii) CH3-CH2-CO-CH2-CH2-CH3 ?
- Explain functional group inter conversion with an example.
PART – B
Answer any Eight questions (8 ´ 5 = 40)
- The Infrared spectrum of methyl salicylate shows the following peaks at 3300 cm-1 , 1700 cm-1, 3050 cm-1, 1540cm-1, 1590 cm-1 and 2950 cm-1 Attribute these peaks to the following features of the molecule.
(i) – CH3 (ii) C = O (iii) – OH group on the ring (iv) Aromatic ring.
- Write sort notes on a. bathochromic shift
- Hyper chromic shift
- What is meant by shielding and deshielding of protons in NMR spectroscopy.
- What is mass spectroscopy ? What is the principle of mass spectroscopy.
- The mass spectrum of 2- pentene shows m/e peaks at 70 , 55, 41, 29 and 27. Write down the different fragments and correlate their m/e values with the m/e peaks obtained.
- Calculate the λ max values for the following compounds . Give reasons for your interpretations.
- Discuss any two methods that are commonly used for protection of alcoholic – OH group during synthesis of a organic compound.
- How will you synthesize acetophenone using umpolung reaction.
- Describe the use of chromic acid in the oxidation of alcohols and ketones. Write the mechanism involved.
- How is NaBH4 prepared ? Write any three synthetic applications of NaBH4.
- What is hydroboration ? Write the reagents and the mechanism involved in the reaction which converts propene to 1– propanol.
- For the Diels Alder reaction predict the major product.
PART – C
Answer any four questions. ( 4 ´ 10 = 40 )
- i). Which one of the following compounds is most consistent with the IR spectrum given in the following figure.? Give reasons for your interpretation. C6 H5 – OH , C6H5 – COCH3 , C6H5 – COOH , C6H5 –CH2OH.
ii). Describe the appearance of the proton NMR spectrum of each of the following compounds. How many signals would you expect to find and how many peaks will each signal be split.
(a) Cl CH2 – O – CH2 CH3 (b) 1,2-dichloroethane (c) p-diethyl benzene.
- i)How does Infrared spectroscopy useful to distinguish between inter molecular H-bonding and intramolecular H-bonding ? Explain using suitable examples.
- ii) A hydrocarbon shows a mass parent peak at m/e 102. It exhibits NMR signals δ 7.4 (5 H ,Singlet) and δ 3.08 (1H Singlet). What is the probable structure of the hydrocarbon?
- i) Describe the working principle of a UV–Visible spectrophotometer using a simple block diagram .
ii)Account for the splitting of PMR signals.
- i) Explain the term umpolung with an example.
- ii) Using 1,3 dithianes , how will you effect the following conversions.
- benzaldehyde to C6H5 CH2CH2 C6H5
- formaldehyde to C6H5 CH2CH2CH2CH2
- i) How are the following groups protected and deprotected during synthesis of organic compounds.
(a) – NH2 gp. (b) – CHO gp.
- ii) Complete the following reactions
(a) CH3-CH2-CHO + CH3-NH-CH3 ¾® ?
- i) How will you synthesize
(a) Succinic acid
(b) Crotonic acid
- Diels Alder reaction is highly stereo specific – Account.
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