Pericyclic and photochemical reactions

 Pericyclic reactions : electrocyclisation, cycloaddition, sigmatropic rearrangements and other related concerted reactions. Principles and applications of photochemical reactions in organic chemistry.

YEAR JUN-2016 DEC-2015 JUN-2015 DEC-2014 JUN-2014 DEC-2013 JUN-2013 DEC-2012 JUN-2012 DEC-2011 JUN-2011
No.of questions appeared 7 8 6 6 7 6 8 8 4 5 4

1.The major product formed in the following reaction is……….

 

2.The following transformation proceeds through two consecutive electrocyclic processes, which are….

electro-chemical-cyclisation-reactions

(1) 4π conrotatory and 6π conrotatory

(2) 4π disrotatory and 6π conrotatory

(3) 4π conrotatory and 6π disrotatory

(4) 4π disrotatory and 6π disrotatory

 

3.The frontier orbital interactions involved in the formation of the carbocation intermediate in the reaction of isobutylene with HCl are

(1) π of olefin and σ* of HCl

(2) πof olefin and σofHCl

(3) π*of olefin and σ* of HCl

(4) π*of olefin andσofHCl

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Ans (1)

Soln:

Orbital diagram of reaction of isobutyl with HCl are as shown below

perycyclic-csir-net-gate-chemical-science-june-2016

Interaction of π-bond of olefin bond with σ * bond of HCl gives the carbocation

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4.The correct match for the following transfor-mations P-S with the processes I-IV is

Processes:  I. Diels-Alder

II.Norrish Type I

III.photocycloaddition followed by Diels-Alder

IV.Norrish Type II

(1) P-II; Q-IV; R-III; S-I

(2) P-II; Q-IV; R-I; S-II

(3) P-IV; Q-II; R-III; S-I

(4) P-IV; Q-II; R-I; S-III

 

 

5.The correct match for the reactions P-S with the names of cyclizations I-IV is

Names of cyclizations:  I. halocyclization

                                               II.Nazarov cyclization

                                              III. radical cyclization

                                              IV.electrocyclization

(1) P-IV; Q-I; R-II; S-III

(2) P-II; Q-I; R-IV; S-III

(3) P-IV; Q-II; R-III; S-I

(4) P-II; Q-I; R-III; S-IV

 

6.The major products A and B formed in the following reaction sequence are

6-2-perycylic-csir-net-gate-chemical-science-june-2016

 

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