CHEMISTRY paper 2 2000


Time Allowed: 3 hours Maximum Marks: 300
Candidates should attempt Question Nos. 1 and 5 which are and any three of the remammg questions selecting alleasl one question from each Section Assume suitable data 1£ conSidered necess3lY and mdieale the same clearly

Answer any three of the following
State the crilena of aromaticity Decide whether each of the followmg compounds is aromahc (il Pyrrole

1,3,5-Hexatriene
5-Cyc1o-heptatriene



18-Annulene Predi cl the pro duct from each 0 f the reactions Give mechamsms m support of your answer


o
[II R-G1y
"
I
NOH
"

(iii R-C·R'
" ...Ui...

Explam Wlttingreaction. Giveitsmechamsm HowwouldyousyntheSize


(il What are SlgmatroplC rearrangements? Give thetr slereochemlSlIy. Say whether 5­methyl cyclop enladine can 0ffer such a rearrangement

Dep1ct Cope and Clasen rearrangements as examples 0f Slgmalrop1c shift


Account for the fact thaltreatment of p-biomotoluene Wlth NaOH at 300 0 )'le1ds a miXture of two products but treatment of m-bromotoluene what NaOH Y1elds a nuxture of three products. Give mecharusm of the reacti on and also giVe ev1dences m supp ort 0f your answer


Predict the pro duct(s) m the followmg reactions Give thea mecharusms
V.
-CH 2



CH,
I
CH, C1-j" OH

CH,



I
0­

(oJ

















Predict the pro ducts from the followmg reactions Give thelr mechall1sms


Ii)




•
R,BH
cu

W­
R_C"O+R

Predict the pro duct from the followmg reactions Discuss the1f mecharu sms
U

il) ._..01-1

NO,



Olit
N
"





...
OM:
Explam the aromatic prop erties of trap olones Give one syntheSis 0f olone
(il In theoty, trans-3, 4-dimethyl cyc10butene can oper by two conrolalal)' paths to give either 4 -hexadiene or 4 2)-hexadiene. Explam why both products are symmelly allowed and then account for the fact that only the 2 4 E iSomer is oblamed m practice
What products would you exp eel to 0blam from the pholochelll1cal cyc1izations of 4 Z 6 -oclatriene and of(2 E. 4 Z 6 2)-octatriene?
(il What slereochemlSlIy would you expect for the product of the Diels-Alder reaction between E. 4 E)-hexadiene and ethyl ene What stereo chemlSlIy would you exp ect 1f E. 4 Z)-hexadiene were used mstead?

4 6 8 E)-Decatelraene has been cyc1ised t07 8-dimethyl-l, 5-cyclo­octatrienePredict the manner of nng closure conrotatory of disrotatory-for both thennal and photochem1cal reactions and predict the stereochemlSlIy of the productm each case


What stereochemlSlIy would you expect to observe 1n these reactions?


A photochem1cal Slgmalrop1c rearrangement


A thermal cycto addition


A thermal Slgmalrop1c rearrangement




Aphotochem1cal cyclo addition Predict the product you would expect to obtam from the followmg reaction Should this shift be a suprafac1al or an antarafac1al pro cess?


O
(5.51
CH,A ,l7

What are the products fonned by Dieckmann Cyclization of diethyl-3 methyl-heptane­dioate? Give its mechanlSm WhatlS Refonnatsky reaction? Show how itlS used for prepanng Give its mechanlSm Predict the productm the followmg reaction. Propose its mecharusm

CH,CD,Es

1. t &Jaw BuOH

2"
CH,CO,fs
3
Predi cl the pro ducts 1n the fall owmg reactions Give thetr mechamsms
o
Ph MH Nl"1.
"

-t-CiCI. NIlOH


SEcnON B
Answer any three of the folloWlng
Propo se a structure for the camp ound Wl th the followmg data MiS (rrJz) 55 (base peak), 90 and 92 (peaks about 113 the Size of90) IR 1642, 990 and 930
'HNMR 1 6 4.5 4.9 6.3 m 17.5 6 19.5 mlegral ratios Unsaturationnumber= 1 Suggest the reaction pro ductCs) and explam its mechamsm



O""m,


CuI,
iiiil
NoBH. 1
2 H,O

Explam the general structure of DNA mc1uding the H -bonding


Predict the pro ducts m the fall owmg reactions and suggest thetr mechamsms


CH, h". 2


0
d
n
n
II

R_C

I.


"
"
Discuss the baSic chemical bonding m a-Keratin mc1uding the H-bonding 0l Describe the deternunation of mol. wt. of polymer by end group analySiS method

Give the syntheSiS, properties and use 0f teJYlene


Predi cl the maJ or products m the photo chenu cal reactions and propo se mechaniSms


Q
rn._ClI,
"
[iil CCl,p
o
Which types of compounds are oXldised by the penodale Give an example 1n each case Mention the roducl fanned by the penodale oXidation of the followmg compound

CD

Describe the reduction of aCId chlondes with lithium alulll1ll1um hydnde and gIVe its mechall1sm What happens when 3 eqUivalents of I-butyl alcohol and LAH are used m this reaction?


How is SeO, used m orgame chemlSlIy? Give two examples and discuss thetr mechamsms


Predict the maJ or product of the photo chelll1cal reaction and gIVe the1f mecharu sms 1 Meth 1but ale





Compound C,HlOO is one of the basiC building blocks of nature. 'HNMR of the compound shows the followmg data j.635(3Hsmglel) 1,70 5 H smglel) 3,835(1 H broad smglelwhich disappears on adding

4155(2 Hdoublet, J=7Hg)
5,70 5 H triplet, J 7 Hg)
Prep are a structure for A



Show the benzene radical amon ES R sp ectrum

Howwould you distingUIsh by MS between 3-heptanone and 4-heptanone?


Phenol1S a weak aCid with pKa 10 0 It has Aw.x 210 nm m ethanol When dil


NaOH is added to the solution, the absorption mcreases to Aw.x 235 nm How do you account for this shift
Calculate forthe followmg

QH





(il How could you use IR spectroscopy to lell1f preparation of 5 choleslen-3-one from
cholestrol by Jones OXI dation is complete?

DistinguiSh between the followmg pam by IR
o
Ii
CH,CNandCll,
(31 CH, G-1-IXli, "rld UI, ClI, CliO