SEcnON A
1. Answer any three of the foll0wi ng (20 x
(a)Alcohols react with thionyl chloride to yield the unstable chiorosulfite which reacts further to give the alkyl chlorides and So2. In dioxane, the product B with retention of configuration is formed but if pyridinium hydrochloride is present, the configuration is inverted to give C in this reaction. Explain the observations:
<img src='./qimages/1088-1a.jpg'>

(b)Identify aromatic compound from amongst the fo11owing.Enumerate the properties 0f the compound selected by you that would suggest aromatic character. What makes a compound anti-aromatic?
<img src='./qimages/1088-1b.jpg'>

(c)Suggest an explanation for the fact that the order of reactivity of the halides towards n-butyl brosylate in acetone of cl>Br>I when (C4 H9)4N+ is the cation 0 f the halide but the order is Br >cl when Li+ is the cation.
(d)Explain the observed pKa of the fo11owing compounds:
<img src='./qimages/1088-1d.jpg'>


Explain the relative magnitudes of the following pairs of B-deuterium isotope effects (per deuteriurm) for solvolysis:
<img src='./qimages/1088-2a.jpg'>


(b)Explain why treatment of l-chloronaphthalene with ethoxide ion gives no reaction but treatment with it gives
<img src='./qimages/1088-2b.jpg'>
ProPose a mechanism for the fo11owing transformation, explaining the migration 0f carboethoxy group in preference to phenyl group despite having a lower migratory aptitude: 15
<img src='./qimages/1088-2c.jpg'>
Explain why carbene does not react with cyclohexene in a manner 0f ordinary carbenes but does react with dimethyl fumarate and maleate to yield spiropentanes
<img src='./qimages/1088-2d.jpg'>

Identify the maj or product in each of the following reactions. Give mechanisms of the reactions involved and stereo structure, if any:
<img src='./qimages/1088-3a.jpg'>

(b)What is a symmetry forbidden reaction? Explain the process by taking one example of an alkene.
4. a)How will you carry out the following transformations in good yie1ds? Indicate the reagents used, conditions employed reasons there of:
<img src='./qimages/1088-4a.jpg'>

(b)What are sigmatropic shifts? Give one example each of 3-and 5-sigmatropic shifts in organic reactions while explaining the logic behind such migrations.
SEcnON B

5. answer any three of the following: (20 x 3
(a)Compound given below dissolves in acetone to form a brightly coloured solution whereas in ether, it remains colourless. The proton NMR at room temperature shows a broad signal at delta 1.88 which on cooling to -50°C resolves into two signals at delta 2.07 and delta 1.29 Explain
<img src='./qimages/1088-5a.jpg'>

(b)How many vibrational degrees of freedom will be observed for gaseous acetylene (C2H2) and which of these will be infrared active?
Calculate the probability of a polymer formed by condensation of monomers consisting of 25 monomers when the reaction is 75% complete. What is the value of number average degree of polymerization under these conditions? Determine the extent of reaction in order for the number of degrees of polymerization to exceed 25.
Explain why on heating cis-3, 4-dimethylcyclobutene gives 4-diene while its trans-isomer gives only the 4-diene. What happens when the same sub strates are irradiated with UV light?

Indicate in each of the following pairs as to which compound would undergo the mentioned rearrangement faster and why. Write main products of the rearrangement reactions:
<img src='./qimages/1088-6a.jpg'>

(b)How will you use IR and NMR spectroscopy to distinguish 0-and p-hydroxyacetophenones?

Explain the formation of citral through the following reaction sequence via sigmatopic shifts:
<img src='./qimages/1088-7a.jpg'>

(b)Arrange the fo11owing in order of increasing magnitude of coupling constant between HA and HB in the NMR spectrum. Give reasons for your answer.

<img src='./qimages/1088-7b.jpg'>

Experimental attempts to prepare the acid chloride of A by treatment with thionyl chloride gave B instead. Explain what might have happened:
<img src='./qimages/1088-7c.jpg'>

(d)Identify major products A and B that might be formed in the following reaction sequence:
<img src='./qimages/1088-7d.jpg'>
Give mechanisms of the reactions involved.

How would mass spectral studies help you to distinguish the following? <img src='./qimages/1088-8a1.jpg'> If mass spectrum is not appropriate, can the job be accomplished by IR UV or NMR? How?
How can NMR/IR be used to estimate enol content of the following?
<img src='./qimages/1088-8a2.jpg'>

(b)Using the indicated spectral determination,how the following pairs of isomeric compounds can be differentiated?
PhCOCH2CH3 and PhCH2COCH3 UV spectrum
PhCH2C=CH and PhCH=C=CH2 IR spectrum
PhOCH2CH3 and PhCH20CH3 NMR spectrum
<img src='./qimages/1088-8b3.jpg'>
<img src='./qimages/1088-8b4.jpg'>


6-Trimethyl benzoic acid (mesitoic acid) undergoes acid catalysed esterification very slowly. However when it is dissolved in concentrated H2So4 and the solution is poured into excess of alcohol, good yields of mesitoic esters are obtained. Explain.
Identify A and B in the following reaction. Give reasons for your identification

<img src='./qimages/1088-8c2.jpg'>