CHEMIETRY

Time Allowed: 3 hours Maximum Marks: 300
Candidates should attempt Question Nos.
Answer any three of the folloWlng (20x3=60)
5-cyc1oheptatriene (not an aromatic compound) reacts with a molecule of bromine to afford a compound having melting point 203°C (decomposition) and is insoluble in nonpolar organic solvents but soluble in water Write and support the structure of the product and rationalize Its formation
Account for the following observations in case of and which are the first and second dissociation constants of the dicarboxylic acids and <img src='./qimages/1151-1a1.jpg'>
Phenanthrene is a tricyclic aromatic hydrocarbon, the structure 0f which iS depicted below it undergoes addition reactions at 10 double bond which iS not a charactenstic reaction of aromatic compound Explain the behaviour of this compound by drawing its various canonical forms <img src='./qimages/1151-1b1.jpg'>
5-dimethyl-l, l-cyciopentanedicarboxylic aCid can be iSolated in two optically inactive compounds and Upon heating gives two isomers of 25-dimethyj cyclopentanecarboxylic acid whereas )'yields only one isomer. Draw the structure of iSomers of and What iS the relationship between the isomers formed by decarb oxylation 0f <img src='./qimages/1151-1c.jpg'>
Propose a rational mechanism for the following transformation

2. arrange compounds in each of the following sets according to the specified order and give reasons for your choice: (15 x 4 60)
Increasing 0rder 0f reactivity toward cationic po1ymerization. Methy1 acrylate, propene, i sobutene, vinyl acetate.
Increasing order of chemical shift is 8 scale of the protons and sho wn in the
following compound. <img src='./qimages/1151-2b.jpg'>
(c)Increasing order of stability of three main different conformations of 2-flouroehtanol.
Decreasing order 0 fhydro1ysis by aqueous KOH.
p-H3COC6H4CH2Cl. C6H.sCH2C1 p-NCC6H4CH2Cl. p-CH3C6H4CH2C1
3.Draw the structure 0f the predominant region/stereoisomer 0f the product in the following reactions. Write the mechanism 0f the reaction and give reasons for your choiceo <img src='./qimages/1151-3a.jpg'>

4. Write the mechanism involved: (15x2=30)
In the chain terminati0n step durin g the cationic ring opening polymeri zation 0f hexach1orocyclotriphosphazin es.
In propagation step during the anionic ring Opening polymerization of octamethylcyclotripho sphazines.
(b)Account for the following: (15x2=30)
In polyamide synthesis by aminolysis of diesters with diamines, phenyl esters are preferred over alkyl esters.
Aniomc polymerization of actylamde uSing BuLi give nylon 3.

SECTION B
Answer any three of the following (20x3=60)
An alpha beta-unsaturated ketone of relative molecular mass 110 has an absorption m U.V at "lamdamax= 215 (sigmamax -10,000). A solution of this ketone showed absorbance A 2.0 with I1cm cell Calculate concentration of keton in the solution expressed in g/l.
U.V viSible spectrum of an alpha,beta-unsaturated carbonyl compound was recorded first in
cyclohexane as solvent what will be the effect on An.xlfthe spectra of the same compound lS taken in ethanol as solvent? Give reasons for your answer

Infra-red spectrum 0f R 3S) 3-dichloro -pentane was recorded. Do you think that this spectra will be identical With the spectra of (2S 3R) 2 3-dichloro-pentane R3 3-dichioro -pentane? Give reasons for your answer
The mass spectrum of ethyl phenyl ether has a prominent peak at m/z 66. Describe mode of formation of the fragment responsible for this peak
A compound having molecular formula, ClOH12o3, exhibited folloWing data In its NMR spectra
51.3 triplet, 3.85 (3H smglet)
4.3 (2H quartet, J=7Hz) 6.9 (2H doublet, 11Hz)
7.9 (2H doublet. 11Hz)
ASSign structure to the possible compound
Methyl chloride and neomenthyl chloride both react with base to lose a molecule of HCl by E2 mechanism. The products are regioiSomers and Identify which product is formed from which starting compound. Also mention starting compound or which will react faster Give reasons for your answer. <img src='./qimages/1151-6a.jpg'>

Account for the following (l5x3=45)
Base catalysed cyc1ization of C2H5OOC -COOC2H5 gives 2­ethoxycarbonyl 6 methyl cyc1ohexanone as the main product and not 2­ethoxycarbonyl-2 methyl_cyc1oheXanone
3-methyl-3 phenyl-cyc1opentanone undergoes methylation with CH3l in tetrahydrofuran using lithium di -isopropylatmde at -78 °C to give predonunant product
7.Acomplish the following transformations
(15 x 4 60)
<img src='./qimages/1151-7a.jpg'>

8. Write the mechanism 0f the following reactions: (15 x
<img src='./qimages/1151-8a.jpg'>

(iii)Dehydrobromination 0f meso and racemic 2-dibromo-1, 2-diphenylethane given cis and trans 1-bromo-1, 2-diphenylethene respectively.
Explain the effect of Lewis acid on the cyc1oaddition of 3-butadiene and methyl acrylate using' Frontier Molecular Orbitals' method