Reaction Mechanisms, Pericyclic Reactions, Organic Photochemistry and Stereochemistry

404 Pages·2015·15.1 MB·English

MScCH-06
Vardhman Mahaveer Open University, Kota

Reaction Mechanisms, Pericyclic Reactions,
Organic Photochemistry and Stereochemistry
MScCH-06
Vardhman Mahaveer Open University, Kota

Reaction Mechanisms, Pericyclic Reactions,
Organic Photochemistry and Stereochemistry
Course Development Committee
Chair Person
Prof. Ashok Sharma
Vice-Chancellor
Vardhman Mahaveer Open University, Kota
Coordinator and Members
Coordinator
SANDEEP HOODA
Assistant Professor of Zoology
School of Science & Technology
Vardhman Mahaveer Open University, Kota
Prof L.R. Gurjar Dr. Arvind Pareek
Director Academic Director Regional Centre-Bharatpur
VMOU Kota VMOU Kota
Dr. Anuradha Dubey Dr. Sunil kumar Jangir
Deputy Director,SOST Convener Chemistry
VMOU Kota VMOU Kota
Prof. P.S. Verma (Retd.) Prof. Pahup Singh (Retd.)
Department of Chemistry Department of Chemistry
University of Raj, Jaipur University of Raj, Jaipur
Prof. P.D. Sharma (Retd.) Prof. Ashu Rani
Department of Chemistry Department of Chemistry
University of Raj, Jaipur University of Kota, Kota
Dr. R.L. Pilaliya, (Retd.) Dr. Sapna Sharma
Department of Chemistry, Govt. College Department of Chemistry
Bikaner JECRC,university Jaipur
Dr. Sanjay Kumar Sharma Dr. Sushil Kumar Sharma
Department of Chemistry Department of Chemistry
JECRC,university Jaipur University of Kota, Kota
Editing and Course Writing
Editor
Prof. Ashu Rani Mr. Ankit Sharma
Department of Chemistry Assistant Professor, Department of Pure and
University of Kota, Kota Applied Chemistry, University of Kota, Kota
Writers:
Dr.Sushil Kr. Sharma 1, Dr. Poonam Khandelwal 3, 4, 10,
Assistant Professor, 2,8,11,13,16 Assistant Professor, Department 19
Department of Pure and of Chemistry
Applied Chemistry Mohan lal Sukhadia University,
University of Kota, Kota Udaipur
Dr. Shobhana Sharma 5,15,20 Dr.Vishwajeet Singh Yadav 6
Assistant Professor, Assistant Professor,
Department of Chemistry Department of Chemistry,
S.S.Jain Subodh Uka Tarsadia University
P.G.College,Jaipur Bardoli Surat, GUJARAT
Dr.Renu Hada 7 Mr.Ankit Sharma 9, 14,
Assistant Professor, Assistant Professor, Department 17,18
Department of Chemistry, of Pure and Applied Chemistry
Uka Tarsadia University University of Kota, Kota
Bardoli
Surat, GUJARAT
Dr. Varsha Sharma 12
Assistant Professor,
Department of Chemistry,
S.S.Jain Subhod PG College,
Jaipur

Academic and Administrative Management
Prof. Ashok Sharma Prof. L.R. Gurjar
Vice-Chancellor Director (Academic)
Vardhman Mahaveer Open University, Kota Vardhman Mahaveer Open University, Kota
Prof. Karan Singh Dr. Subodh Kumar
Director (MP&D) Additional Director (MP&D)
Vardhman Mahaveer Open University, Kota Vardhman Mahaveer Open University, Kota

ISBN :
All Right reserved. No part of this Book may be reproduced in any form by mimeograph or any other means
without permission in writing from V.M. Open University, Kota.
Printed and Published on behalf of the Registrar, V.M. Open University, Kota.
Printed by :
MScCH-06
Vardhman Mahaveer Open University, Kota

Index

Unit No. Unit Name Page
No.
Unit -1 Reaction Intermediates - Formation, stability, structure, 1
detection and reaction of carbonium ions, carbanions and
free radicals
Unit -2 Reaction Intermediates-II 24
Unit -3 Molecular Rearrangements-I 48
Unit -4 Molecular Rearrangements – II 71
Unit -5 Elimination Reaction 91
Unit -6 Molecular Orbitals and Their Symmetry Properties 104
Unit -7 Classification and stereochemistry of pericyclic reactions: 137
Classification of pericyclic reactions. Woodward-
Hoffmann correlation diagrams. FMO and PMO approach

Unit -8 Analysis of Electrocyclic Reactions 155
Unit -9 Analysis of cycloaddition: Cycloaddition, antarafacial, 175
suprofacial additions, 4n and 4n+2 systems. 2+2 addition
of Ketenes, 1,3-dipolar cycloadditions & cheletropic
reactions
Unit -10 Analysis of Sigmatropic Reactions 198
Unit -11 Electronic Transitions 217
Unit -12 Photochemistry of Carbonyl Compound 231
Unit -13 Photochemistry of Alkenes and Dienes 247
Unit -14 Photochemistry of Aromatic Compounds: Isomerisation, 263
additions and substitutions
Unit -15 Miscellaneous Photochemical Reactions 293
Unit -16 Conformations of Some Acyclic Molecules 307
Unit -17 Confirmation of some cyclic molecules Cyclobutanes, 321
Cyclopentane and Cyclohexane and Monosubsituted
Cyclohexane
Unit -18 Conformations of Di-Substituted Cyclohexanes 342
Unit -19 Conformations of A Few Other Monocyclic and Bicyclic 361
Systems
Unit -20 Conformation and Reactivity 381
MScCH-06
Vardhman Mahaveer Open University, Kota

Preface
The present book entitled “Reaction Mechanisms, Pericyclic Reactions, Organic
Photochemistry and Stereochemistry” has been designed so as to cover the unit-
wise syllabus of MScCH-06 course for M.Sc. Chemistry (Final) students of
Vardhman Mahaveer Open University, Kota. The basic principles and theory have
been explained in simple, concise and lucid manner. Adequate examples,
diagrammes, photographs and self-learning exercises have also been included to
enable the students to grasp the subject easily. The unit writers have consulted
various standard books and internet as their reference on the subject and they are

thankful to the authors of these reference books.

----------------
Unit – 1
Reaction Intermediates - Formation,
stability, structure, detection and reaction
of carbonium ions, carbanions and free
radicals
Structure of unit
1.0 Objective
1.1 Introduction
1.2 Carbonium ion
1.2.1 Formation
1.2.2 Stability
1.2.3 Structure
1.2.4 Reactions
1.3 Carbanions
1.3.1 Formation
1.3.2 Stability
1.3.3 Structure
1.3.4 Reactions
1.4 Free radicals
1.4.1 Formation
1.4.2 Stability
1.4.3 Structure
1.4.4 Detection
1.4.5 Reactions
1.5 Summery
1.6 Review Questions
1.7 Reference and suggested reading
1
1.0 Objective
An organic reaction mechanism is the detailed study of the actual steps by
means of which a reaction takes place. Thus is tell us about the number of steps
involved and their sequence. Actual isolation of one or more intermediates is
the most concrete evidence one can obtain the mechanism of the reaction.
1.1 Introduction
In a chemical reaction, reactants may be converted into product in one step or in
more than one step. When a reaction occurs in a single step no intermediates are
formed. Intermediate lies between two highest energy states and has lower
energy than both of the high energy states.
In intermediate the bonds are completely broken in the reactants and hence the
system has definite geometry. It can be isolated in same cases.
1.2 Carbonium ion
An organic species which has carbon atom bearing only six electrons in its
outer most shell and has a positive charge is called a carbocation or carbonium
ion.
R
|
RC R = H or alkyl or aryl group.
|
R
Carbocations are of three types –p, s and t or 1o, 2o, 3o. Depending upon which
type of carbon atom carries the positive charge, it is correspondingly denoted as
p, s or t carbocation. For example, if the positive charge is present on primary
carbon atom it is called p or 1o-carbocation, and so on. Various examples of
carbocations are :
Primary-Carbocations
   
CH CH CH CH CH CH CH CH CH CH
3 3 2 3 2 2 3 2 2 2
Methyl ethyl propyl butyl

2
CH3 CH3
| |
   
CH  C HCH CH  C CH C H CH CH CHCH
3 2 3 2 6 5 2 2 2
|
CH3

Isobutyl neopentyl benzyl allyl
Secondary-carbocations
 
CH CHCH CH CH CHCH
3 3 3 2 3
Isopropyl s-butyl
 
CH  C CHCH C H CHC H
3 3 6 5 6 5
|
CH3
s-isoamyl benzhydryl

Tertiary-Carbocations

  
CH  C CH CH  C CH CH C H  C C H
3 3 3 2 3 6 5 6 5
| | |
CH3 CH3 CH3
t-butyl t-amyl trityl

1.2.1 Formation of carbonium ion
(i) By the protonation of unsaturated compounds: Olefins, carbonyl
compounds and nitriles when dissolved (treated) with a proton-donating solvent
or Lewis acid form carbonium ions.
3