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

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

Conceptual Problems in

Cover image: Shutterstock.com

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.

Size : 172x235mm Spine : 19mm ISBN : 9789332517561 Title Sub Title Edition Authors / Editors Name With CD Red Band Territory line URL Price mQuest

SALIENT FEATURES

 Three new chapters on carbonyl pounds, ethers and amines, aromatic com- pounds, and bio-molecules.

com- More than 2750 methodically-designed MCQs

ISBN 978-933-251-756-1

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

Head Office: A-8 (A), 7th Floor, Knowledge Boulevard, Sector 62, Noida 201 309,

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www.pearson.co.in, Email: companysecretary.india@pearson.com

eISBN 978-933-258-207-1

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

This page is intentionally left blank.

HybridizationResonanceAromaticity

Structural IsomerismGeometrical IsomerismOptical IsomerismConformational Isomerism

Chapter 3 SubStituent effeCtS, reaCtive intermeDiateS, 101 – 168

aCiD-baSe anD eleCtrophileS/nuCleophileS

Substituent EffectsReactive IntermediatesAcid-base

Electrophiles/Nucleophiles

Nucleophilic SubstitutionsElimination ReactionsElectrophilic Addition ReactionsNucleophilic Addition ReactionsElectrophilic Aromatic SubstitutionsNucleophilic Aromatic Substitutions

vi n Contents

Chapter 5 alKaneS, alKeneS anD alKyneS 235 – 320

AlkanesAlkenes Alkynes

Chapter 6 alKyl haliDeS anD alCoholS 321 – 410

Alkyl Halides Alcohols

Chapter 7 Carbonyl CompounDS, EtherS anD AmineS 411 – 468

Aldehydes/Ketones

Carboxylic Acids and their Derivatives

AminesEthers

Chapter 8 aromatiC CompounDS 469 – 498

Aromatic Compounds

Chapter 9 bio-moleCuleS 499 – 518

CarbohydratesAmino AcidsPeptides

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

competi-tive 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

ques-tions 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.

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

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

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.

Hybridization, Resonance and Aromaticity

Chapter

1

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b Hybridization generates new set of

atomic obitals identical in size but not

in shape and energy

c Hybridization generates new set of

atomic obitals indentical in energy but not in shape and size

d Hybridization generates new set of

atomic orbitals indentical in shape, size and energy

6 Which of the following statements is true

about hybridization?

a Hybrid orbitals frequently undergo

linear overlaps making sigma bonds

b Hybrid orbitals frequently undergo

lateral overlaps making π-bonds In other words, there are several com-pounds in which π-bonds are formed using hybrid orbitals

c Hybrid orbitals are molecular

4  n   Conceptual Problems in Organic Chemistry

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

16 In which of the following compounds,

C has used sp2 orbital in making C–O bond?

a four sp orbitals b four sp2 orbitals

c four sp3 orbitals d none of these

a Both C-O bonds are formed by sp3-sp3

overlaps

b Both C-O bonds are formed by sp2-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

In this molecule,

a both C-N bonds are formed by sp2-sp2

overlaps

b one C-N bond is formed by sp2-sp2

overlap while the other by sp2-sp3

a C = C = C = C H

H

HH

b C = C = C = C H

H

HH

c C = C = C = C H

H

HH

d C = C = C = C H

H

HH

24 Which of the following compounds has

maximum number of sp-hybridized atoms?

a sp3-hybridized b sp2-hybridized

c sp-hybridized d unhybridized

6  n   Conceptual Problems in Organic Chemistry

d

N = OO

b

O

Hybridization, Resonance and Aromaticity  n   7

1 2 3 4

IV CH2 = CH–C = CH Which of the following is the correct order

l1

l2

Which of the following is the correct order

of spatial distances l1 and l2?

8  n   Conceptual Problems in Organic Chemistry

c more stable canonical structure

con-tributes less than less stable canonical structure

Hybridization, Resonance and Aromaticity  n   9

N+ O–

O

CH –3 N O

OIII

c it has greater length of charge

sepa-ration than if it has lower length of charge-separation

c A canonical structure with negative

charge on less electronegative atom contributes more than a canonical structure with negative charge on more electronegative atom

d contribution of a charge-separated

canonical structure will be more in a polar solvent than in a non-polar sol-vent

I

II

III

–

10  n   Conceptual Problems in Organic Chemistry

Among these canonical structures, the

C

NHO

C

––

The correct order of stability among these canonical structures is

N

+–

+N–

Hybridization, Resonance and Aromaticity  n   11

NH

–

+

NH

–

+

NH

–+

NH

–+

345

In pyrrole-electron density is maximum on

a 2 and 3 b 3 and 4

c 2 and 4 d 2 and 5

66

NI

OH

NII

OH

+–

NIII

O

H+

–

The least stable canonical structure among these is

O +II

O+III

The most stable canonical structure among these is

a I

b II

c III

d all are equally stable

12  n   Conceptual Problems in Organic Chemistry

68

1

23

–COO

CH = CH2 – CH = CH – OCH3

CH2– CH = CH – CH = OCH3

C = CHH2 – CH – CH – OCH3

+–

a I b II

c III d IV

Hybridization, Resonance and Aromaticity  n   13

c Canonical structures are equivalent

than if canonical structures are non

=

c - NH - C - H d - NO2

81. Which of the following groups act as acceptor in resonance?

a - ph b -OH

c - CH=O d - NO2

83. Which of the following groups can act either as a π-donor or as a π-acceptor de-pending upon situation?

a - NO b -NO2

c - O - N = O d - NH2

84. ticipate in resonance with any group?

O = CH – NH–II

O = CH – OHIII

Among these species, the correct order of resonance energy is

a I > II > III b II > I > III

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

14  n   Conceptual Problems in Organic Chemistry

OCH3II

OCH3III

Among these three canonical structures, (though more are possible) what would be their relative contribution in the hybrid?

II

C = CHH2 – N

+

CH2– CH = N–

a I contributes more than II

b II contributes more than I

c Both I and II contribute equally

d none of these

Hybridization, Resonance and Aromaticity  n   15

94. Heat of hydrogenation of cyclohexene

Examine these dienes and their heat of

hydrogenations Now, what will be the

pounds will be in the order as

Examine these canonical structures of naphthalene Now, which of the following statements is true about C1-C2 and C2-C3 bond lengths?

d It is not possible to judge the bond

length because given structures are tautomers

16  n   Conceptual Problems in Organic Chemistry

101 I

2 1

65

The correct order of C-N bond length

CH3O - CH = CH2

II

CH2 = CH2 III Which of the following orders of C-C bond lengths is correct among these com-pounds?

107. Among the following compounds, C1-C2 bond is shortest in

Hybridization, Resonance and Aromaticity  n   17

IIBr

Ionization of these compounds produces

Br– and

a same anion b different anions

c same cation d different cations

18  n   Conceptual Problems in Organic Chemistry

CH3– C – N CH3

CH3+III

a I b II

c III d same in all

121. rect proposition given by kekule regarding the structure of benzene?

Hybridization, Resonance and Aromaticity  n   19

On moving from cyclohexene (I) to

1,3-cyclohexadiene (II) one C=C bond is

increased This is turn, increases heat

of hydrogenation from –28.6 to –55.5

kcal/mole Similarly, on moving from

b On moving from I to II stability

in-creases while on moving from II to III stability decreases

a In the process of becoming aromatic,

creases while in the process of becom-ing antiaromatic, π-electron energy increases

π-electron energy of the molecule de- b In the process of becoming aromatic

creases while in the process of becom-ing antiaromatic, π-electon-energy of the molecule decreases

π-electron energy of the molecule in- c In the process of becoming either

aromatic or antiaromatic, energy of the molecule increases

π-electron- d In the process of becoming either

aromatic or antiaromatic, energy of the molecule decreases

20  n   Conceptual Problems in Organic Chemistry

130.

–+

a

OO

b

OO

Which of the following species is not aro- a

+O

O–

138. Which of the following π-molecular orbital energy diagrams is correct for benzene?

Hybridization, Resonance and Aromaticity  n   21

139. Which of the following π-molecular

orbital-energy diagrams is correct for

140. Which of the following π-molecular

orbital energy diagrams is correct for

π-molecular-+

(Tropylium cation)?

22  n   Conceptual Problems in Organic Chemistry

143. Which of the following π-molecular

obital-energy diagrams is correct for

a p-orbital b sp-orbital

c sp3-orbital d sp2-orbital

147. Lone-pair of electrons on nitrogen atom

trons because

of pyridine is not delocalized with π- elec- a it is in p-orbital

b it is in sp3-orbital

c it is in sp2

orbital which cannot over-lap with p-orbitals on adjacent carbon atoms

Oxygen atom of furan is

a sp3- hybridized b sp2-hybridized

c sp- hybridized d not hybridized

151. Which of the following statements is true about furan?

a One lone pair of electrons is in sp2

-or-bital while the other is in p-orbital