Download CHE-06 year 2004

CHE-06
Assignment Booklet
Bachelor's Degree Programme (B.Sc.)
ORGANIC REACTION MECHANISM
Elective Course in Chemistry
CHE-06
School of Sciences
Indira Gandhi National Open University
New Delhi-110 068
2004
Dear Students,
As explained in the programme guide for B.Sc. Programme, you have to do two assignments for this
elective course in Chemistry. Both of these assignments are Tutor Marked Assignments (TMAs).
The block wise distribution of assignments is as follows:
Assignment-01 (TMA) –
Assignment-02 (TMA) –
Blocks 1 and 2
Blocks 3 and 4
Instructions for Formatting Your Assignments
Before attempting the assignments, please read the following instructions carefully.
1. On top of the first page of each TMA answer sheet, please write the details exactly in the following
format:
Enrolment No
: .........................……………
Name
: ........................…………….
Address
: ........................…………….
Course Code : ........................……………
…...………………………..
Course Title
…………………………….
: .......................…………….
Assignment No : ......................…………….
Study Centre : ...........................................
Date
: ………...........................…..
PLEASE FOLLOW THE ABOVE FORMAT STRICTLY TO FACILITATE EVALUATION AND
TO AVOID DELAY.
2. Use only foolscap size writing paper of good quality (but not of very thin variety) for writing your
answers.
3. Leave 4 cm margin on the left, top and bottom of your answer sheet.
4. Your answers should be precise.
5. While solving problems, clearly indicate the question number along with the part being solved.
6. The assignments should be submitted within 8 weeks after receiving this booklet.
Answer sheets received after the due date shall not be accepted.
We strongly suggest that you should retain a copy of your assignments to avoid any unforeseen situation.
Wishing you all good luck.
2
Assignment - 01
(Tutor Marked Assignment)
ORGANIC REACTION MECHANISM
Elective Course in Chemistry
Course Code: CHE-06
Assignment Code: CHE-06/TMA-1/2004
Maximum Marks: 100
Answer all questions.
1.
a)
Write the conjugate bases of each of the following acids and arrange the bases in the order
of decreasing basicity. Explain your answer.
(4)
NH3, HCCH, H2O, CH3OH
b)
Which reagent in each of the following pairs would be a stronger nucleophile in a protic
solvent and why?
i)
ii)
iii)
2.
3.
(6)
CH3NH¯ or CH3NH2
H2O or H3O+
CH3SH or CH3OH
a)
Predict the product and write the reaction of 1, 3-butadiene with HBr showing the
mechanism for the formation of two products at different temperatures. Also draw the
potential energy diagram for the reaction showing both the reaction pathways.
b)
The acid dissociation constant of benzoic acid is 6.310-5. If the substitution constant for
(4)
nitro group at para position is 0.81, find out the acid dissociation constant of p-nitrobenzoic
acid.
a)
Which SN2 reaction out of each of the following pairs would you expect to take place more (4)
rapidly in a protic solvent? Explain your answer.
b)
i)
CH3CH2CH2Br + CH3OH  CH3CH2CH2OCH3 + HBr
or
CH3CH2CH2Br + CH3O¯  CH3CH2CH2OCH3 +Br¯
ii)
CH3CH2I + HO¯  CH3CH2OH + I¯
or
CH3CH2I + HS¯  CH3CH2SH + I¯
Write the mechanism that account for the products of the following reactions.
HO 


H 2O
i)
HOCH2 CH2 Br
ii)
H2 NCH2CH2CH2CH2 Br
HO 


H 2O
3
(6)
(6)
4.
5.
a)
Which in each of the following pairs of SN1 reactions would be faster and why?
i)
CH3Cl + CH3OH CH3OCH3 + HCl
or
(CH3)3CCl + CH3OH  (CH3)3COCH3 + HCl
ii)
(CH3)3CBr + H2O  (CH3)3COH
or
(CH3)3CBr + CH3OH  (CH3)3COCH3
iii)
(CH3)3CCl + H2O  (CH3)3COH + HCl
or
(CH3)2C = CHCl + H2O  (CH3)2C= CHOH + HCl
b)
Starting with toluene outline the synthesis of 1-bromo – 2 (trichloromethyl) benzene and
1- bromo – 4 (trichloromethyl)benzene.
a)
Outline ring bromination and sulphonation reactions of the following compounds. In each (7)
case give the structure of the major reaction product(s). Also indicate whether the reaction
would occur faster or slower than the corresponding reaction of benzene.
i)
ii)
iii)
b)
Conc.H 2SO 4
A

(C 6 H 6 S 2 O 8 )
60 65C
Conc.HNO3
B


(C 6 H 5 NS2 O10 )
Conc.H 2SO 4
OH
(3)
.H 3O  , H 2 O
C
 (C H NO )
6 5
4

a)
Give an example where primary carbocation is more stable than secondary carbocation.
Explain why it is so?
(2)
b)
Rearrangement is the characteristic of carbocation, explain this characteristic of
carbocation with an example.
(2)
c)
Explain the following:
i)
ii)
iii)
7.
(4)
anisole
nitrobenzene
ethylbenzene
Propose structures for compounds A, B and C.
OH
6.
(6)
a)
(23)
Hydroboration follows Markovnikov’s rule.
Diels-Alder reaction is stereospecific.
Ozonolysis reaction gives the position of the double bond of the original alkene.
Arrange the following in the increasing order of reactivity towards nucleophilic reagents:
(2)
CH3CHO, C2H5CHO, NO2CH2CHO, ClCH2CHO
b)
Explain the following:
i)
ii)
(4)
2-Pentanone does not react with sodium bisulphate
Methanal reacts faster than propanone
4
c)
Predict the product and give the mechanism of the following:
(4)
OCH3
i)
CH3CH + H2O
OCH3
ii)
8.
a)
H2O, H+
Starting with appropriate alkylhalide and base outline synthesis that would yield each of
the following alkenes:
i)
ii)
b)
C2H5CHO + CH3MgBr
(4)
1-Pentene
2, 3-Dimethyl-1-butene
Arrange the following alcohols in order of their reactivity toward acid-catalysed
dehydration.
(2)
1-Pentanol, 2-Methyl-2-butanol, 3-Methyl-2-butanol
9.
10.
c)
Discuss the significance of ‘isotope effect’ and ‘hydrogen exchange’ in elimination
reactions.
(4)
a)
Explain the term oxidation and calculate the oxidation number of carbon, oxygen and
hydrogen atoms in glucose molecule.
(4)
b)
Name a reagent which selectivity oxidizes primary alcohol into an aldehyde. Explain
with suitable example.
(3)
c)
How would you reduce the ethanenitrile (acetonitrile) and nitromethane to its
corresponding primary alcohol.?
(3)
a)
What is Diels-Alder reaction? Discuss its utility and stereochemistry.
(2)
b)
Give the mechanism of the following reactions:
(24)
CH3
i)
Cl
CH3CH2CH2CH2C  CH(CH3)2
CH3CH2CH2CH2CCH=CH2 + HCl
CH3
CH3
OH
CHCH2CHO
CHO
ii)
iii)
+ CH3CHO
CH3CH2S+(CH3)2
C2H5O
CH3CCH3
CH2=CH2 + S(CH3)2
OH
O
iv)
OH
+ LiAlH4
H+
5
CH3CHCH3
Assignment - 02
(Tutor Marked Assignment)
ORGANIC REACTION MECHANISM
Elective Course in Chemistry
Course Code: CHE-06
Assignment Code: CHE-06/TMA-2/2004
Maximum Marks: 100
Answer all questions.
1.
a)
Describe any two common methods for the generation of each of the following
reaction intermediates:
i)
ii)
iii)
iv)
2.
Carbenes
Nitrenes
Benzynes
Free Radicals
b)
Give any two methods of free radical detection.
a)
Complete the following reactions:
(2)
(18)
nBuLi
i)
Cyclohexen eCH 2 Cl 2  

ii)
Benzene  N CHCO C H
iii)
hυ
Phenylazid e 

iv)
Anthracene benzyne 
v)
CH CH CH  NBS 
vi)
C H N  Cl   CuCl 
vii)
oBromoaniso le
2
2
2 2
hυ
5

3
HCl
6
5
2
KNH2

NH
vii)
(24)
3
Δ or
t Butylazide 

hυ
3.
b)
Give reason for the stability of triphenylmethyl radical.
a)
Write the mechanism of the following reactions.
i)
ii)
Addition of HBr to propene in the presence of peroxide
Oxidation of 1,2-glycols with lead tetraacetate.
6
(2)
(23)
4.
b)
What will be the product in the reaction of 1,1-diphenyl-2-aminopropanol with
nitrous acid? Explain the mechanism.
a)
Give the mechanism and expected products in the following reactions:
(4)
(33)

b)
i)
2,3-Diphenyl-2,3-butanediol H
ii)
Benzil 
iii)

CH3CH2CONH2  
OH
NaOH/Br2
Complete the following reaction:
(1)
i) NH OH/HCl

C6H10CO  2  
ii) H 2 SO 4
5.
6.
7.
8.
a)
Explain why in (4+2) cycoladdition, diene is activated by electron donor substituents
and dienophile by electron withdrawing susbtituents.
(3)
b)
What are terms conrotatory and disrotatory? Explain both the terms by taking suitable
example.
(4)
c)
Draw bonding and non bonding molecule orbitals of Hexatriene.
(3)
a)
What is sigmatropic rearrangement? Write its mechanism by taking an example.
(5)
b)
What is photosensitization? Illustrate its use in photochemical reaction.
(5)
Define the following terms:
(25)
a)
b)
c)
d)
e)
Flurescence
Phosphorescence
Vibrational relaxation
Internal conversion
Intersystem crossing
a)
Complete the following reactions:
(15)
hυ
i)
CH CH CH CH COCH 
3 2 2 2
3
ii)
(C H ) CO  (CH ) CHOH 
6 5 2
3 2
iii)
(CH ) CCH  (C H ) CO 
3 2
2
6 5 2
iv)
Malonic ester + Urea
v)
CO2 + RMgX
hυ
hυ
NaOC2 H 5 /C 2 H 5OH
    

383 K
b)
What do you understand by the term ‘activating and deactivating’ groups? Explain
them with the help of examples.
7
(5)
9.
10.
(2½ 4)
Define the following terms:
a)
b)
c)
d)
Synthone
Precursor
Chemoselectivity
Regioselectivity
a)
Classify following polymers as chain growth, step growth or copolymers:
i)
ii)
iii)
iv)
b)
(4)
Teflon
Polyvinyl acetate
Dacron
Butyl rubber
Classify dyes on the basis of their chemical composition and give one example for
each class.
8
(6)