Preview D K Singh Conceptual Problems in Organic Chemistry for Engineering and Medical Entrance Examinations 3rd Edition Pearson by D K Singh (2014)

Singh

3rd edition

Conceptual Problems in

D. K. Singh
Conceptual Problems in Organic Chemistry 3/e covers all the essential concepts of
organic chemistry through 2750 multiple-choice questions (MCQs) given in the book.
The MCQs have been designed in a manner to facilitate quick learning. The current
edition, a successor to the highly-appreciated previous edition, has three new chapters to
give aspirants an extra edge to crack the examinations.
SALIENT FEATURES


Three new chapters on carbonyl compounds, ethers and amines, aromatic compounds, and bio-molecules.



More than 2750 methodically-designed
MCQs.

Conceptual Problems in

for Engineering and Medical Entrance Examinations

organic chemistry

organic
chemistry

3rd edition

Conceptual Problems in

organic
chemistry

for Engineering and Medical Entrance Examinations

3rd
edition

D. K. Singh
Cover image: Shutterstock.com

Size :172x235mm

Spine : 19mm

ISBN : 9789332517561

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Conceptual Problems
in Organic Chemistry
[For Engineering and Medical Entrance Examinations]

Third Edition

D. K. Singh

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Copyright © 2014 Dorling Kindersley (India) Pvt. Ltd

Published by Pearson India Education Services Pvt. Ltd, CIN: U72200TN2005PTC057128,
formerly known as TutorVista Global Pvt. Ltd, licensee of Pearson Education in South Asia.
No part of this eBook may be used or reproduced in any manner whatsoever without the

publisher’s prior written consent.
This eBook may or may not include all assets that were part of the print version. The publisher
reserves the right to remove any material in this eBook at any time.
ISBN 978-933-251-756-1
eISBN 978-933-258-207-1
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Fax:  080-30461003, Phone: 080-30461060
www.pearson.co.in, Email: 

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To my mother, for her immense
love, patience and support

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This page is intentionally left blank.

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Contents
Foreword
Preface to the Third Edition
About the Author

Chapter 1 Hybridization, Resonance and Aromaticity


Hybridization



Resonance



Aromaticity

Chapter 2 Isomerism


Structural Isomerism



Geometrical Isomerism

Optical Isomerism



Conformational Isomerism

Chapter 3 Substituent Effects, Reactive Intermediates,


Acid-base and Electrophiles/Nucleophiles




Substituent Effects
Reactive Intermediates



Acid-base



Electrophiles/Nucleophiles

Chapter 4 Reaction Mechanism

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Nucleophilic Substitutions



Elimination Reactions



Electrophilic Addition Reactions



Nucleophilic Addition Reactions



Electrophilic Aromatic Substitutions



Nucleophilic Aromatic Substitutions

vii
ix
x
1 – 28

29 – 100

101 – 168

169 – 234

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vi 

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n  Contents

Chapter 5


Alkanes, Alkenes and Alkynes



Alkenes



Alkynes

Chapter 6

Alkyl Halides and Alcohols

Alkyl Halides



Alcohols

Chapter 7



Carbonyl Compounds, Ethers and Amines
Aldehydes/Ketones



Amines



Ethers

235 – 320

Alkanes

321 – 410

411 – 468

Carboxylic Acids and their Derivatives

Chapter 8Aromatic Compounds

Aromatic Compounds

469 – 498

Chapter 9Bio-molecules

Carbohydrates

499 – 518



Amino Acids



Peptides

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Foreword
Chemistry is an ever-expanding branch of science that is based on well-established concepts.
Most of the concepts are widely accepted and are often experimentally verified. Organic

chemistry in particular deals with covalently linked carbon compounds. The stability of
an organic compound in terms of its internal energy and rate of formation/decomposition
can be predicted based on various physical concepts. A fair understanding of the possible
involvement of intermediates and transient species and the kind of interaction among two
or more reactants would enable us to propose a feasible reaction pathway.
Organic chemists have in their arsenal a plethora of reagents and conditions to carry
out various synthetic transformations. Whether or not a reagent is suitable for a specific
transformation can be predicted only through clear understanding of its reactivity. Man has
developed various concepts on reactivity and selectivity by looking at mother nature. Her
ability to generate numerous biomolecules that are indispensable to create and sustain life
on earth has been a true inspiration to man. He cleverly applied those concepts in science
and in everyday life.
Dr Singh has developed an invaluable resource based on concepts in organic chemistry
for the benefit of students who are keen to learn more and prepare themselves for competitive examinations by intense problem solving. Enormous efforts have been expended for
framing this extensive collection of single choice questions. Dr Singh took extraordinary
care to ensure that questions with different levels of difficulty are included in order to keep
the students of all levels interested in the subject. This unique collection of diverse questions enables the students to examine their own comprehension, conceptual understanding,
logical and analytical thinking as well as time management skills. This book is far superior
to many other national level competitive examination guides. The coverage of the subject
is so exhaustive that the students would find every question a learning experience and say
good bye to many guide books/question banks that contain monotonous questions. This is
primarily due to Dr Singh’s penchant for physical organic chemistry. He is well aware that
understanding of theoretical, mechanistic and stereochemical concepts in organic chemistry
is absolutely necessary to logically tackle even synthetic puzzles.

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viii 

n  Foreword

I am certain that a student who succeeds in answering most of Dr Singh’s questions
will be one of the top ranking students in the national level competitive examinations for
undergraduate admission. I consider this book as an outstanding aid and recommend it
wholeheartedly to those aspiring for admission to leading higher education institutions.
This book would be an excellent reference book for postgraduate students and teachers
as well.
Irishi N.N. Namboothiri
Professor
Department of Chemistry
Indian Institute of Technology Bombay
Mumbai 400 076

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Preface to the Third Edition

Organic Chemistry is not a formative science. It requires an interest in the nature and
reaction of molecules. In other words, realization is the best way to learn organic chemistry
because most of the problems are based on application of concepts. Therefore, students
should have a clear concept of the subject and then learn to apply those concepts in solving
problems. While formulating and designing the questions for this book, I had to consider

all angles of each topic included in the syllabus. This book effectively catalyses the process
of learning the subject. In fact, questions are designed to encourage students to learn more
and more of Organic Chemistry. The third edition has been updated and now includes
three new chapters on carbonyl compounds, etheres and amines, aromatic compounds and
biomolecules. I am sure students will find this useful.
I extend my sincere thanks to Mr. Mohammad Ashfaq for his valuable feedback and
suggestions.
I will appreciate your invaluable suggestions and feedback to improve future editions
of this book.

D. K. Singh

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About the Author
Devendra Kaumar Singh trains students appearing for the medical and engineering entrance
examinations in an institute in Patna. He did his post-graduation from the B R Ambedkar Bihar
University in Muzaffarpur, Bihar, and received his doctorate in 1991 from the Indian Institute of
Science Bangalore, under the supervision of Professor S. N. Balasubrahmanyam. Following this,
he worked as a post-doctoral fellow first with Professor Uday Maitra in the same institute for two
years (1991–1993), and then with Professor R. C. Corcoran in the University of Wyoming, USA, for
one year (1993–1994).
Dr Singh’s research interest lies in the area of Physical Organic Chemistry. He has published
three research papers in the Bulletin of the Chemical Society of Japan, Indian Journal of Chemistry and
the Journal of Organic Chemistry, respectively.

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Chapter

1
Hybridization,
Resonance and
Aromaticity


This page is intentionally left blank.


Question Bank







1. Forexhibitingtetravalency,carbonatoms
havetobeexcited.Now,whichofthefollowingstatementsistrue?
a Excitationoccursbeforebonding
b Bondingoccursbeforeexcitation
c Both bonding and excitation occur
simultaneously
d Twobondsareformedfirst,thenexcitationoccursfollowedbyformationof

anothertwobonds







2.







3. Whichofthefollowingstatementsistrue
aboutbondingandexcitation?
a Energyrequiredforexcitationofcarbonatoms(96Kcal/mol)islessthan
energyreleasedinbonding
b Energyrequiredforexcitationismore
thanenergyreleasedinbonding
c Energyrequiredforexcitationisequal
totheenergyreleasedinbonding
d Noneofthese

Bondformationis
a alwaysexothermic
b alwaysendothermic
c neitherexothermicnorendothermic
d sometimesexothermicandsometimes
endothermic

4. Whichofthefollowingstatementsistrue
abouthybridization?
a Onlythoseatomicorbitalscanbehybridizedwhichdonotdiffermuchin
shape.
b Onlythoseatomicorbitalscanbehybridizedwhichdonotdiffermuchin
energy.
c Onlythoseatomicorbitalscanbehybridizedwhichdonotdiffermuchin
size.
d Onlythoseatomicorbitalscanbehybridizedwhichdonotdiffermuchin
overlapintegrals.

5. Whichofthefollowingstatementsistrue
abouthybridization?
a Hybridization generates new set of
atomicorbitalsidenticalinshapebut
notinsizeandenergy.

b Hybridization generates new set of
atomicobitalsidenticalinsizebutnot
inshapeandenergy.
c
Hybridization generates new set of
atomicobitalsindenticalinenergybut
notinshapeandsize.
d Hybridization generates new set of
atomicorbitalsindenticalinshape,size
andenergy.
6. Whichofthefollowingstatementsistrue
abouthybridization?
a Hybrid orbitals frequently undergo
linearoverlapsmakingsigmabonds.
b

Hybrid orbitals frequently undergo
lateral overlaps making π-bonds. In
other words, there are several compoundsinwhichπ-bondsareformed
usinghybridorbitals.
c
Hybrid orbitals are molecular orbitals.
d Ahybridorbitalbiggerinsizemakes
shorterbond.
7. In 2sp hybridization, 2s-orbital can be
mixedwith
a Only2px
b Only2py
c Only2pz
d Anyoneof2px,2pyand2pz

8. In2sp2orbital,characterof2pzorbitalwill
be
a always33.33%
b always0%
c always66.66%
d either33.33%or0%


4 

n  Conceptual Problems in Organic Chemistry




9. In2sp3orbital
a charactersof2px,2pyand2pzorbitals
are equal to each other but less than
thatof2s-orbital
b charactersof2px,2pyand2pzorbitals
areequaltoeachotherbutmorethan
thatof2s
c charactersof2s,2px,2pyand2pzorbitalsareequaltoeachother
d charactersof2px,2pyand2pzarenot
equaltoeachother

10. Whichofthefollowingstatementsabout
the energy of hybrid orbitals resulting
from mixing of 2s and 2p orbitals is
true?

a E2p>Esp3>Esp2>Esp>E2s

b Esp3>Esp2>Esp>E2p>E2s

c E2p>Esp>Esp2>Esp3>E2s

d E2p>Esp>E2s>Esp2>Esp3
11. Whichofthefollowingstatementsabout
thesizeofhybridorbitalsresultingfrom
mixingof2sand2porbitalsistrue?

a 2s>2p>sp3>sp2>sp

b 2p>2s>sp3>sp2>sp

c 2p>sp3>sp2>sp>2s

d sp3>sp2>sp>2p>2s
12. Shapesofsp3,sp2andsporbitalsarelike


a

c

b




d

13. Which of following statements about
overlapintegralsofthevariousorbitalsis
true?

a 2p>2s>2sp3>2sp2>2sp

b 2p>2sp3>2sp2>2sp>2s

c 2p>2sp>2sp2>2sp3>2s

d 2sp3>2sp2>2sp>2p>2s
14. Energycontentofamoleculewillbeless
if

a bondenergyismore
b bondenergyisless
c magnitudeofovelapisveryless
d noneofthese

15. Which of the following orders is correct
forelectronegativity?

a sp3C>sp2C>spC

b spC>sp2C>sp3C

c sp2C>spC>sp3C

d sp3C>spC>sp2C
16. In which of the following compounds,
C has used sp2 orbital in making C–O
bond?
OH
OH


a

b

OH



c

OH



d

17. TheorbitalsusedbyCinformingC-Hand
C-ClbondsofCH2Cl2are

a foursporbitals b foursp2orbitals

c foursp3orbitals d noneofthese
18. CH2=CH-CN

3
2
1

Cl-C2 bond of this molecule is formed
by
b sp2-sp3overlap

a sp3-sp2overlap
d sp2-sp2overlap

c sp2-spoverlap
19.
O






Inthismolecule,therearetwoC-Obonds.
Whichofthefollowingstatementsistrue
aboutthesebonds?
a BothC-Obondsareformedbysp3-sp3
overlaps
b BothC-Obondsareformedbysp2-sp2
overlaps


Hybridization, Resonance and Aromaticity  n  5





c One C-O bond is formed by sp2-sp3
overlap while the other C-O bond is
formedbysp3-sp3overlap

d BothC-Obondsareformedbysp2-sp3
overlaps

20.



















NH

C

23. CH2=C=C=CH2

Whichofthefollowingstructuresismost

appropriateforthismolecule?


H

O
Inthismolecule,
a bothC-Nbondsareformedbysp2-sp2
overlaps
b one C-N bond is formed by sp2-sp2
overlap while the other by sp 2-sp 3
overlap
c bothC-Nbondsareformedbysp2-sp3
overlaps
d bothC-Nbondsareformedbysp2-sp2
overlaps

21. CH2=C=CH2

Inthismolecule(allene)

a allthreeC-atomsaresp2hybridized

b bothterminalC-atomsaresp2hybridizedwhilecentralC-atomissp-hybridized

c bothterminalC-atomsaresp-hybridized while central C-atom is sp2 hybridized

d noneofthese
22. CH2=C=CH2

Whichofthefollowingstructuresismost
appropriateforthismolecule?
H
H

a
C=C=C
H
H
H
H
C
=
C
=
C
b


H
H

H
H

c
C=C=C
H
H
H

H
C=C=C
d
H
H


a
b

H
H
H




H

c

d

H
H
H
H

C=C=C=C
C=C=C=C

C=C=C=C

C=C=C=C

H
H
H
H
H
H
H
H

24. Which of the following compounds has
maximum number of sp-hybridized Catoms?

a (CN)2

b CH≡C–CN

c HC≡C–CH2–CH=C=C=CH2

d CH2=C=CH–CN
25. CH3–O–CH=CH2

Oxygenatomofthismoleculeis

a sp3hybridized

b sp2hybridized

c sp-hybridized

d unhybridized
26. CH3












C=O
CH3
Oxygenatomofthismoleculeis
a sp3-hybridized
b sp2-hybridized
c sp-hybridized
d unhybridized

27. CH3–C≡N

Nitrogenatomofthismoleculeis
b sp2-hybridized

a sp3-hybridized
d unhybridized

c sp-hybridized


6 

n  Conceptual Problems in Organic Chemistry

28. In which of the following molecules, all
atomsarecoplanar?





a

c

b



CH3

C=C

CH3

a

CN
CN

d



CH3

CH3

CH3

CH3

b

29. Inwhichofthefollowingmolecules,–NO2
groupisnotcoplanarwithphenylring?



CH3

a

c

CH3



N
O
CH3



O

CH3

CH3

b
N
O



c I
O

O

N

I

d

CH3
CH3

CH3
CH3

31. In which of the following molecules, all
atomsarenotcoplanar?

O




CH3

a

d

N=O
O

30. Inwhichofthefollowingmoleculesboth
phenylringsarenotcoplanar?

O

O
O



b


Hybridization, Resonance and Aromaticity  n  7



c


O



d
O

32. In which of the following molecules, all
bondanglesarenotsimilar?
CHO
b

a




c

d



33. Whichofthefollowingisthecorrectorder
ofbondangles?

a NH3>H2O>CH4

b H2O>NH3>CH4

c CH4>NH3>H2O

d CH4>H2O>NH3
34. Whichofthefollowingisthecorrectorder
ofbondangles?

a + NH4>H3O + >H2O
+
b H3O + > NH4>H2O
+
c H2O>H3O + > NH4
+
d NH4>H2O>H3O +

35. Which of the following order of bond
anglesiscorrect?


a



b HC ≡ CH >

>

> HC ≡ CH
>

d HC ≡ CH >

36. Which of the following orders of bond
energyiscorrect?

a C–C>N–N>O–O

b O–O>N–N>C–C

c N–N>C–C>O–O

d C–C>O–O>N–N
37.
1
2 3
4

I CH2=CH–CH=CH2




1
2 3
4
II CH3–CH2–CH2–CH3





1
2 3
4

III CH2=CH–CH2–CH3






1
2 3
4
IV CH2=CH–C=CH
Whichofthefollowingisthecorrectorder
ofC2-C3bondlength?
b II>III>I>IV
a II>I>III>IV
c
d
III>I>IV>II
IV>I>III>II




38. CH3CN
CH3CHO
CH3-CH3

I
II
III

Whichofthefollowingisthecorrectorder
of C–C bond length among these compounds?
b III>II>I

a I>II>III
c
d

III>I>II
II>I>III
39. H





H
l1
C=C=C
H
H
l2
Whichofthefollowingisthecorrectorder
ofspatialdistancesl1andl 2?
b l1>l2
a l1=l2
d l2=2l1
c l1

40. H
H



c

>

> HC ≡ CH

>



l1
C=C=C=C
l2

H
H

Whichofthefollowingisthecorrectorder
ofspatialdistancesl1andl2?


8 

n  Conceptual Problems in Organic Chemistry

a l1=l2
c l1
b l1>l2
d l2=2l1

41. Resonanceinvolves

a changeinthepositionsofatoms

b changeinthepositionsofbothσand
πelectrons

c changeinthepositionsofonly π electrons
d

changeinthepositionsofonlyσelectrons
42.CH3–CH=O


I

CH2=CH–OH


II
–
+

CH3 – CH – O


III

Amongthese,whicharecanonicalstructures?
b IandIII

a IandII
d all

c IIandIII
43. CH2=CH–CH=CH2


I
–
+

CH2 – CH = CH – CH2


II
–
+

CH2 – CH = CH – CH2

III

Amongthesewhicharecanonicalstructures?
b IandIII

a IandII
c
d

IIandIII
allofthese
44. Which of the following statements is
true?

a Resonance is an intermolecular process

b Canonicalstructuresareimaginary

c Canonicalstructuresarereal

d Acanonicalstructureexplainsallfeaturesofamolecule
45. Foraresonatingmolecule,realstructure
is






a theresonancehybrid

b thecanonicalstructures
c sometimesresonancehybridandsometimescanonicalstructures
d noneofthese

46. A resonance hybrid is the one which is
contributedby

a allcanonicalstructures

b only the least stable canonical structure

c only the most stable canonical structure

d noneofthese
47. Intheresonancehybrid

a all canonical structures contribute
equally

b
more
stable
canonical
structure
con

tributesmorethanlessstablecanonical
structure
c

more
stable canonical structure con

tributeslessthanlessstablecanonical
structure

d thereisnocontributionofanycanonicalstructure
48. Delocalizationofelectronsincreasesmolecularstabilitybecause

a electrons-nucleiattractionincreases

b electrons-electrons repulsion increases

c potential energy of the molecule increases

d potential energy of the molecule remainsunaffected
49. Resonanceenergyis

a equal to the energy of resonance hybrid

b equaltotheenergyofmoststablecanonicalstructure

c equaltotheenergyofleaststablecanonicalstructure

d equaltothedifferenceinenergiesof
themoststablecanonicalstructureand
resonancehybrid


Hybridization, Resonance and Aromaticity  n  9

50. Resonanceenergyis

a storedinthemolecule

b releasedbythemolecule

c neitherstorednorreleasedbythemolecule

d sometimes stored and sometimes releasedbythemolecule
51. Allcanonicalstructuresofamolecule

a must have different number of unpairedelectrons

b musthavedifferentnumberofpaired
electrons


c mustbealwaysequivalent

d neednotbealwaysequivalentbutthey
shouldnotdiffermuchinstability
52.

–
–
+
+
CH2 – O
CH2 – O
CH2 = O

I
II
III
Which of these structures is practically
notavalidcanonicalstructureofformaldehyde?
a I
b II
c III
d noneofthese

+
53. CH2 = CH – CH = CH – NH3


I
–
+
+

CH2 – CH = CH – CH – NH3


II
+

CH2 – CH = CH – CH = NH3


III

Which of these structures is not a valid
canonicalstructure?
b II

a I
d noneofthese

c III
–
+ O
CH3 – N
O
+ O
CH3 – N
–
O
O
CH3 – N
O

a I
c III

55. Acanonicalstructurewillbemorestable
if

a ithasmorenumberofπ-bondsthanif
ithaslessnumberofπ-bonds

b ithaschargeseparationthanifithas
nochargeseparation

c it has greater length of charge separation than if it has lower length of
charge-separation

d ithaspositivechargeonmoreelectronegative atom than if it has positive
chargeonlesselectronegativeatom
56. Whichofthefollowingstatementsistrue
aboutthecontributionsofcanonicalstructuresintheresonancehybrid?

a Acharge-separatedcanonicalstructure
contributes more than a canonical
structurewithoutcharge-separation

b Acanonicalstructurewithlessnumber
of π bonds contributes more than a

canonicalstructurewithmorenumber
ofπ bonds

c A canonical structure with negative
charge on less electronegative atom
contributes more than a canonical
structurewithnegativechargeonmore
electronegativeatom

d contribution of a charge-separated
canonicalstructurewillbemoreina
polarsolventthaninanon-polarsolvent
O

57.
I

54.




H

I
II

C

O

II
H

C
+

OH
–
OH

O–

III

Which of these structures is not a valid
canonicalstructureofnitromethane?

b II
d noneofthese

III

H

C

+
OH

10 

n  Conceptual Problems in Organic Chemistry



Among these canonical structures, the
correctorderofstabilityis
b III>II>I
a I>II>III
d II>I>III
c I>III>II




O

58.
I

H

C





Thecorrectorderofstabilityamongthese

canonicalstructuresis
b III>I>II
a I>III>II
c
d
II>III>I
II>I>III

61.
–
O

O
I

–

NH
H

H

O–
II

H

C
+

O

–
O

II

O–
III





C

H

59. I

CH2 = CH – CH = O



+
–
CH2 = CH – CH – O

III

III
Thecorrectorderofstabilityamongthese
canonicalstructuresis
b II>III>I
a III>II>I
d I>II>III
c I>III>II

62.

I



II

N

I

H

C

+

N
–

+

O

60.

H

Thecorrectorderofstabilityamongthese
canonicalstructuresis
b I>III>II
a I>II>III
d III>I>II
c II>I>III

+
–
CH2 – CH = CH – O



–
NH

C

H

–
CH2

III

N–

O–
II

H

C
+

–
CH2

IV

O–
III

H

C

CH2

H

–

O

C

H
O
Among these canonical structures, the
correctorderofstabilityis
b II>I>III
a I>II>III
d II>I≡III
c I=III>II

II

NH

V

N
–

N

+


Hybridization, Resonance and Aromaticity  n  11







Amongthesecanonicalstructuresofpyridine,thecorrectorderofstabilityis
a (I=V)>(II=IV)>III
b (II=IV)>(I=V)>III
c (I=V)>III>(II=IV)
d III>(II=IV)>(I=V)

63.
5

4

3

6

N 2
1
Inpyridineelectrondensityismaximum
on
b 3and5
a 2and6
c
d 3and4
4

65. 4

3

5





N

66.

O

I

N

H
O+

II

N

N

H

H

–
N
+
H

II

IV

–

N
+
H

–

N
+
H
Amongthesecanonicalstructuresofpyrrole,thecorrectorderofstabilityis
a (III=IV)>(II=V)>I
b I>(II=V)>(III=IV)
c I>(III=IV)>(II=V)
d (II=V)>(III=V)>I

–

N+

O
+
I

V

–

H
Theleaststablecanonicalstructureamong
theseis
a I
b II
c III
d allareequallystable

67.

N
+
H

–

O

III


III

2

H
In pyrrole-electron density is maximum
on
b 3and4
a 2and3
d 2and5
c 2and4

64.
I

1

O

+

II

+
O

III

Themoststablecanonicalstructureamong
theseis
a I
b II
c III
d allareequallystable


12 

n  Conceptual Problems in Organic Chemistry

68. 3

3









5
Inthisanion,π-electron-densityismaximumon
a C1
b C2andC5
c C3andC4
d sameoneachC-atom







O

H-C-OH
II

O
H-C-NH2
III

Whichofthesecompoundshasmaximum
π-electron-densityonthecarbonylicoxygen?
b II
a I
c
d
III
Sameinall
p




m
p

m

o

m

o

N

o

O

O
In nitrobenzene, π-electron density is
maximumon
b metapositions
a orthopositions
c
d
paraposition
noneofthese

73. Which of the following compounds has
maximumelectrondensityinring?
NO2
OH
a



O



c

b

–
COO

–



d

74.






Which of following statements is true
aboutthiscompound(biphenyl)?
a Bothringsactasπ donors
b Bothringsactasπ acceptors
c Oneringactsasπdonorwhiletheother
asπ-acceptor
d
Resonance does not occur between
bothrings

75.

I

CH2 = CH – CH = CH – OCH3

II

–
+
CH2 – CH = CH – CH = OCH3

III

–
+
CH2 = CH – CH – CH – OCH3

OH

Inphenol,π-electron-densityismaximum
on
a orthoandmetapositions
b orthoandparapositions
c metaandparapositions
d noneofthese

o

m

–
1

4

71.





2


O



70. H-C-H


I


72.

+1
Inthiscation,π electrondensityismore
on
a C1
b C2
c C3

d π-electron-densityissameoneachCatom.

69.




2





–
+
IV CH2 = CH – CH – CH – OCH3
Amongthesecanonicalstructureswhich
oneisleaststable?
b II
a I
d IV
c III


Hybridization, Resonance and Aromaticity  n  13




–

+
IV CH2 – CH – CH = O
Amongthesecanonicalstructures,which
oneisleaststable?
b II
a I
d IV
c III

4

77.
3





1
2
Inthismolecule,π-electron-densityismore
on
b C2andC4
a C1andC3
d C1andC4
c C2andC3


O

c -NH-C-H

b -CONH2
d -NO2

81. Which of the following groups act as πacceptorinresonance?

O
O


b -C-OR

a -O-C-R

O

d -NH2

c -NH-C-H

=

III

–
+
CH2 – CH – CH = O

a -CH=O

=

–
+
CH2 – CH = CH – O






=

II






=



CH2 = CH – CH = O

I

76.

82. Which of the following groups can act
eitherasaπ-donororaπ-acceptordependinguponsituation?
b -OH

a -ph
c
d -NO2

-CH=O
83. Which of the following groups can act
eitherasaπ-donororasaπ-acceptordependinguponsituation?
b -NO2

a -NO
c
d

-O-N=O
-NH2
84. Whichofthefollowinggroupcannotparticipateinresonancewithanygroup?
+
+
b - NH3

a - CH2

O

–
d -NO

c -N + -O

79. Resonanceenergywillbemoreif

a Canonicalstructureshavechargeseparationthanifcanonicalstructureshave
nochargeseparation

b Moleculeisnonaromaticthanifmoleculeisaromatic
c

Canonical structures are equivalent
than if canonical structures are non
equivalent

d π-bonds are nonconjugted than if πbondsareconjugated



80. Whichofthefollowinggroupsactsasπdonorinresonance?

=

4
3
2

1
78. CH2=CH—C=CH2

|


OCH3

In this molecule, π-electron density is
maximumon
b C2

a C1
d C4

c C3

85. CH3COOH CH3COONa CH3CONH2


I
II
III




Among these compounds, the correct
orderofresonanceenergyis
b III>II>I

a I>II>III
c
d II>I>III
II>III>I

86.

I
II





–
HN = CH – NH
–
O = CH – NH

III
O = CH – OH
Amongthesespecies,thecorrectorderof
resonanceenergyis
b II>I>III
a I>II>III
d III>II>I
c III>I>II


14 

n  Conceptual Problems in Organic Chemistry

O

87.

O

I



II
O





91.

O



III
IV
Amongthesecompounds,whichonehas
maximumresonanceenergy?

b II
a I
d IV
c III

88. I CH3COOH

II CH3CONH2

III CH3COF

Among these compounds, the correct
orderofresonanceenergyis
b III>II>I

a I>II>III
c
d

II>III>I
II>I>III
89.

OCH3

I

II

III

OCH3
OCH3

II

I

–
+
CH2 = CH – CH – CH = CH – CH2

III

–
+
CH2 – CH = CH – CH = CH – CH2

Among these three canonical structures,

(thoughmorearepossible)whatwouldbe
theirrelativecontributioninthehybrid?
b III>II>I
a I>II>III
d III>I>II
c I>III>II
CH2 = CH – OCH3

III

Among these compounds, the correct
orderofresonanceenergyis
b II>I>III
a I>II>III
d I>III>II
c III>I>II

–
+
CH2 – CH = OCH3
CH2 = CH – N

II
II

CH2 = CH – CH = CH – CH =CH2

II

I

Amongthesecompoundsthecorrectorder
ofresonanceenergyis
b II>I>III
a III>I>II
d III>II>I
c I>II>III

I




I

93.


90.



–
+
CH2 – CH = OH

Whichofthefollowingstatementsistrue
aboutthisresonatingsystem?
a ContributionofIIismorethanthatof
Iinresonancehybrid

b ContributionofIisincreasedbyapolar
solvent
c
Contribution of II is increased by a
polarsolvent
d Relative contributions of I and II are
independentofsolvent

92.



CH2 = CH – OH








CH3
CH3

–
+ CH3
CH2 – CH = N
CH3

Whichofthefollowingstatementsistrue

aboutthecontributionofIandIIinrespectiveresonancehybrids?
a IcontributesmorethanII
b IIcontributesmorethanI
c BothIandIIcontributeequally
d noneofthese