Quantum Chemistry of Organic Compounds: Mechanisms of Reactions

280 Pages·1990·6.874 MB·English

by  Professor Vladimir I. Minkin, Professor Boris Ya. Simkin, Dr. Ruslan M. Minyaev (auth.)

Y.I.Minkin, B.Ya. Simkin, R.M.Minyaev
Quantum Chemistry
of Organic Compounds
Mechanisms of Reactions
With 66 Figures and 35 Tables
Springer-Verlag
Berlin Heidelberg New York London
Paris Tokyo Hong Kong Barcelona
Professor Vladimir I. Minkin
Professor Boris Ya. Simkin
Dr. Ruslan M. Minyaev
Institute of Physical and Organic Chemistry
Rostov University
344711 Rostov on Don/USSR
ISBN-13 :978-3-642-75681-8 e-ISBN-13 :978-3-642-75679-5
DOl: 1O.l007/978-3-642-75679-5
Library of Congress Cataloging-in-Publication Data
Minkin, V.1. (Vladimir Isaakovich). Quantum chemistry of organic compounds:
mechanisms of reactions!
V.1. Minkin, B.Y. Simkin, R.M. Minyaev. p. cm.
Includes bibliographical references and index.
ISBN-13: 978-3-642-75681-8
1. Quantum chemistry. 2. Chemistry, Organic. 3. Chemical reaction,
Conditions and laws of. I. Simkin, B. IA. (Boris IAkovlevich)
II. Miniaev, R.M. (Ruslan Mikhailovich) III. Title.
QD462.M56 1990 547.l'28-dc20 90-10109 CIP
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© Springer-Verlag Berlin Heidelberg 1990
Softcover reprint of the hardcover 1st edition 1990
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Typesetting: Thomson Press (India) Ltd, New Delhi
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"Erst die Theorie entscheidet daruber,
was man beobachten kann"
Albert Einstein
Foreword
Chemistry is the science of substances (today we would say molecules) and their
transformations. Central to this science is the complexity of shape and function
of its typical representatives. There lies, no longer dependent on its vitalistic
antecedents, the rich realm of molecular possibility called organic chemistry.
In this century we have learned how to determine the three-dimensional
structure of molecules. Now chemistry as whole, and organic chemistry in
particular, is poised to move to the exploration of its dynamic dimension, the
busy business of transformations or reactions. Oh, it has been done all along,
for what else is synthesis? What I mean is that the theoretical framework accom
panying organic chemistry, long and fruitfully laboring on a quantum chemical
understanding of structure, is now making the first tentative motions toward
building an organic theory of reactivity.
The Minkin, Simkin, Minyaev book takes us in that direction. It incorporates
the lessons of frontier orbital theory and of Hartree-Fock SCF calculations;
what chemical physicists have learned about trajectory calculations of selected
reactions, and a simplified treatment of all-important solvent effects. It is written
by professional, accomplished organic chemists for other organic chemists; it
is consistently even-toned in its presentation of contending approaches. And
very much up to date. That this contemporary work should emerge from a
regional university in a country in which science has been highly centralized
and organic chemistry not very modern, invites reflection. It is testimony to the
openness of the chemical literature, good people, and the irrepressible streaming
of the human mind toward wisdom.
Cornell University Roald Hoffmann
Preface
The principal notions and conceptual systems of theoretical organic chemistry
have been evolved from generalizations and rationalizations of the results of
research into reaction mechanisms. In the sixties the data from quantum
mechanical calculations began to be widely invoked to account for and predict
the reactivity of organic compounds. In addition to and in place of the notions
derived on the basis of the resonance and mesomerism theories that earlier had
been treated semi quantitatively by means of correlation equations, novel
research tools came to be employed such as reactivity indices, perturbation MO
theory, or the Woodward-Hoffmann rules. It is very characteristic of these
approaches, which have now taken firm root in the field of theoretical chemistry,
that they, on the whole, imply an a priori assumption of the mechanism and
probable structures of the transition states of reactions.
The current stage of theoretical research into reaction mechanisms associated
with direct calculations of potential energy surfaces (PES) and reaction
pathways, with precise identification of transition state structures, has developed
in the wake of amazing progress in computing technology and the development
of the methods of quantum chemistry. Analysis of the PES and reaction
pathways furnishes unique information as to the detailed mechanism of chemical
transformation which can, in principle, be obtained by none but the calculational
methods. Such an analysis forms the basis for the so-called computer experiment
providing for modelling of the reactions and structural situations which are
hard or even impossible to realize empirically. Apart from being a correct
explicative method, the quantum mechanical calculations of PES's are becoming
a means by which mechanisms of chemical reactions may be predicted. This
makes them all the more important for the broad community of organic and
physical chemists engaged in studying reactivity and reaction mechanisms.
It is primarily these readers to whom the present book is addressed. Its first
part (Chaps. 1-5) discusses the main characteristics of PES as well as the
methods useful in its calculation and analysis. Particular attention is given to
the question of adequacy of the calculational method to the character of a given
problem determined by the specificity of structure and the type of transfor
mation. Since most organic reactions are carried out in solution, up-to-date
schemes are examined for taking the solvation effects into account. Any exact
X Preface
calculation starts from the selection of the most likely configurations of the
reacting system. The theory of orbital interactions has proved very effectual for
ascertaining these and determining the reaction paths. The notions of isolobal
analogy rooted in this theory permit a unified conceptual approach to the
reactions of both oganic and organometallic compounds.
The second part of the book (Chaps. 6-12) is devoted to the analysis of
calculation data on the mechanisms of principal organic reactions. Chapters 7,
8, and 10 review the results of theoretical research into mechanisms of the
hetero- and homolytic substitution and addition reactions in the gas phase as
well as in solution. Owing to these results obtained over the last 5-10 years,
some questions of stereo- and regiospecificity of the above reactions have been
clarified and numerous structures calculated of transition states, ion pairs,
unstable intermediate biradicals, and n-complexes as to which only vague
conjectures had been possible before. In Chap. 9, it is shown how this
information may be utilized for target-oriented structural modelling of the
dynamic systems in which fast intramolecular rearrangements take place.
Chapter 11 moves on to examine the reactions of electron and proton transfer
as well as the role of steric and energy factors and the tunnelling mechanism
in the realization of these important transformations. A brief analysis of
pericyclic reactions concludes the book. The PES calculations have enabled a
much more detailed insight to be gained into the workings of their mechanism.
The authors hope the present publication may invite a still greater attention
to very interesting potentialities inherent in the quantum chemical analysis of
reaction mechanisms and encourage more researchers to engage in further
development of this promising field.
Rostov, June 1990 Vladimir I. Minkin
Boris Y. Simkin
Ruslan M. Minyaev
Table of Contents
Chapter 1
Potential Energy Surfaces of Chemical Reactions . . . . 1
1.1 Introduction. Mechanism of Chemical Reaction and Quantum
Chemistry. . . . . . . . . . . . . . . . . . . 1
1.2 Choice of a Coordinate System and the Representation of a PES 2
1.3 Topography of the PES and Properties of a Reacting System. 6
1.3.1 Critical Points . . . . . . . . . . 6
1.3.2 The Regions of the Minima on the PES . . . . . . 8
1.3.2.1 Vibrational Spectrum of Molecules . . . . . 9
1.3.2.2 Calculation of Thermodynamic Functions of Molecules 11
1.3.2.3 Topological Definition of Molecular Structure 13
1.3.2.4 Structural Diagrams. . . . . . . . . . . 18
1.3.3 Saddle Points on the PES. Transition States. . . . . 20
1.3.3.1 Localization of the Transition States on the PES. 21
1.3.3.2 Symmetry Selection Rules for Transition State
Structures . . . . . . . . . . . . . . 23
1.3.3.3 Calculation of Activation Parameters of Reactions
and of Kinetic Isotopic Effects 27
1.3.4 Pathway of a Chemical Reaction. . . . . . . . . 30
1.3.4.1 Ambiguity of the Definition. . . . . . . . 30
1.3.4.2 A More Accurate Definition of the MERP and the
Reaction Coordinate . . . . . . . . . .. 31
1.3.4.3 Symmetry Demands on the Reaction Path. . .. 34
1.3.4.4 Chiral and Achiral Pathways of Degenerate Reactions. 36
1.3.5 Empirical Correlations of the Reaction Pathways . . .. 39
1.3.5.1 Molecular Vibrations and the Reaction Coordinate. 39
1.3.5.2 The Principle of Least-Motion. . . . . . .. 41
1.3.5.3 Structural Correlations of the Pathways of Chemical
Reactions . . . . . . . 42
1.4 Dynamic Approach. . . . . . . . 45
1.5 Tunnelling Effects in Chemical Reactions 49
1.6 Description of Nonadiabatic Reactions. 53
References . . . . . . . . . . . . 58
XII Table of Contents
Chapter 2
Quantum Chemical Methods for Calculating Potential Energy Surfaces 61
2.1 General Requirements upon the Methods for Calculating
Potential Energy Surfaces . . . . . . . . . . . 61
2.2 Nonempirical (ab initio) Methods. The Hartree-Fock Method 62
2.2.1 Closed Electron Shells. . . 62
2.2.2 Open Electron Shells . . . 64
2.2.3 Basis Sets of Atomic Orbitals 66
2.2.4 Electron Correlation . . . 69
2.2.5 The Problem of Stability of Hartree-Fock Solutions 75
2.3 Semiempirical Methods . . . . . . . . . 76
2.3.1 The Extended Hiickel Method. . . . . 78
2.3.2 Semiempirical Selfconsistent Field Methods 78
2.3.2.1 The CNDO/2 Method. 78
2.3.2.2 The MINDO/3 Method 80
2.3.2.3 The MNDO Method 82
2.3.2.4 The AMI Method 85
References . . . . . . . . . . 86
Chapter 3
Effects of the Medium 88
3.1 A General Scheme for Calculating the Solvation Effects . 89
3.2 Macroscopic Approximation . . . . . . . . . . 90
3.2.1 General Theory. . . . . . . . . . . . . 90
3.2.2 Model Hamiltonians in the Macroscopic Approximation . 92
3.2.2.1 Model Hamiltonian in the Kirkwood Approximation 93
3.2.2.2 A Model Hamiltonian Based on the Born Formula.
Scheme of Solvatons. . . . . . . . . 93
3.2.2.3 The Scheme of Virtual Charges. . . . . 95
3.2.2.4 The Theory of Selfc onsistent Reactive Field 96
3.3 Discrete Representation of Solvent Molecules. Model
Hamiltonians in the Microscopic Approximation.. . . 97
3.4 Specific Features of the Supermolecular Approach in Studies
of Solvation Effects. . . . . . . . . 100
3.5 Statistical Methods for Studying Solutions 102
References . . . . . . . . . . . . . 104
Table of Contents XIII
Chapter 4
Orbital Interactions and the Pathway of a Chemical Reaction 106
4.1 The Role of Frontier Orbitals. . . . . . . . . . 106
4.2 Theory of Orbital Interactions. . . . . . . . . . 108
4.3 Components of the Interaction Energy of a Reacting System
in a Transition State 111
4.4 Isolobal Analogy 113
References . . . . . 115
Chapter 5
Substitution Reaction. 116
5.1 Nucleophilic Substitution at a Tetrahedral Carbon Atom. 117
5.1.1 The SN2 Reactions. . . .. . . . . . . . 118
5.1.1.1 Stereochemistry of the Reactions . . . . 118
5.1.1.2 Reaction Coordinate and the Structure of the
Transition State . . . . . . . . . . . 119
5.1.1.3 Energetics and Stoichiometric Mechanism of the
Gas-Phase SN2 Reactions. . . . . . . .. 121
5.1.1.4 Effect of the Solvent. . . . . . . . . .. 125
~.1.1.5 Reactions with Retention of Configuration of the
Carbon Atom. . . . . . . . . . . . 128
5.1.2 The SN1 Reactions. . . . . . . . . . . . .. 130
5.2 Electrophilic Substitution at the Tetrahedral Carbon Atom.. 132
5.3 Nucleophilic Substitution at the Carbon Atom of the Carbonyl Group 134
5.3.1 The Stoichiometric Mechanism. 134
5.3.2 Homogeneous Catalysis . . . . . . . . . . .. 138
5.3.3 Stereochemistry of the Reaction . . . . . . . .. 142
5.3.3.1 The Direction of Nucleophilic Attack and Orbital
Steering. . . . . . . . . . . . . .. 142
5.3.3.2 Stereochemical Control of the Breakdown of the
Tetrahedral Adduct. . . . . . . . . . 144
5.4 Aromatic Electrophilic Substitution Reactions . . . . . 147
5.5 Nucleophilic Substitution at the Nitrogen, Phosphorus, and
Sulfur Centers . . . . . . . . . . . . . . . 154
5.5.1 Substitution at the Nitrogen Atom of Nitroso- and
Nitro-Groups . . . . . . . . . . . . . 154
5.5.2 Substitution at the Dicoordinate Sulfur Atom . . 156
5.5.3 Substitution at Tricoordinate Sulfur and Phosphorus Centers. 158
5.5.4 Substitution at Tetracoordinate Phosphorus . 159
5.5.5 Substitution at Pentacoordinate Phosphorus. . . . . . . 161