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Books > Science & Mathematics > Chemistry > Physical chemistry > Quantum & theoretical chemistry
The liquid crystalline state may be identified as a distinct and
unique state of matter which is characterised by properties which
resemble those of both solids and liquids. It was first recognised
in the middle of the last century through the study of nerve myelin
and derivatives of cholesterol. The research in the area really
gathered momentum, however, when as a result of the pioneering work
of Gray in the early 1970's organic compounds exhibiting liquid
crystalline properties were shown to be suitable to form the basis
of display devices in the electronic products. The study of liquid
crystals is truly multidisciplinary and has attached the attention
of physicists, biologists, chemists, mathematicians and electronics
engineers. It is therefore impossible to cover all these aspects
fully in two small volumes and therefore it was decided in view of
the overall title of the series to concentrate on the structural
and bonding aspects of the subject. The Chapters presented in these
two volumes have been organised to cover the following fundamental
aspects of the subiect. The calculation of the structures of liquid
crystals, an account of their dynamical properties and a discussion
of computer simulations of liquid crystalline phases formed by Gay
Berne mesogens. The relationships between molecular conformation
and packing are analysed in some detail. The crystal structures of
liquid crystal mesogens and the importance of their X ray
scattering properties for characterisational purposes are
discussed.
"Imagination and shrewd guesswork are powerful instruments for
acquiring scientific knowledge . . . " 1. H. van't Hoff The last
decades have witnessed a rapid growth of quantum chemistry and a
tremendous increase in the number of very accurate ab initio
calculations of the electronic structure of molecules yielding
results of admirable accuracy. This dramatic progress has opened a
new stage in the quantum mechanical description of matter at the
molecular level. In the first place, highly accurate results
provide severe tests of the quantum mecha nics. Secondly, modern
quantitative computational ab initio methods can be synergetically
combined with various experimen tal techniques thus enabling
precise numerical characterization of molecular properties better
than ever anticipated earlier. However, the role of theory is not
exhausted in disclosing the fundamental laws of Nature and
production of ever increasing sets of data of high accuracy. It has
to provide additionally a means of systematization, recognition of
regularities, and ratio nalization of the myriads of established
facts avoiding in this way complete chaos. Additional problems are
represented by molecular wavefunctions provided by the modern
high-level computational quantum chemistry methods. They involve,
in principle, all the information on molecular system, but they are
so immensely complex that can not be immediately understood in
simple and physically meaningful terms. Both of these aspects,
categorization and interpretation, call for conceptual models which
should be preferably pictorial, transparent, intuitively appealing
and well-founded, being sometimes useful for semi quantitative
purposes."
The Sixth International Conference on Miniaturized Chemical and
Biochemical Analysis Systems, known as /JTAS2002, will be fully
dedicated to the latest scientific and technological developments
in the field of miniaturized devices and systems for realizing not
only chemical and biochemical analysis but also synthesis. The
first /JTAS meeting was held in Enschede in 1994 with approximately
160 participants, bringing together the scientists with background
in analytical and biochemistry with those with Micro Electro
Mechanical Systems (MEMS) in one workshop. We are grateful to Piet
Bergveld and Albert van den Berg of MESA Research Institute of the
University of Twente for their great efforts to arrange this
exciting first meeting. The policy of the meeting was succeeded by
late Prof. Dr. Michael Widmer in the second meeting, /JTAS'96 held
in Basel with 275 participants. The first two meetings were held as
informal workshops. From the third workshop, /JTAS'98 (420
participants) held in Banff, the workshop had become a worldwide
conference. Participants continued to increase in /JTAS2000 (about
500 participants) held in Enschede and /JTAS2001 (about 700
participants) held in Monterey. The number of submitted papers also
dramatically increased in this period from 130 in 1998, 230 in 2000
to nearly 400 in 2001. From 2001, /JTAS became an annual symposium.
The steering committee meeting held in Monterey, confrrmed the
policy of former /JTAS that quality rather than quantity would be
the key-point and that the parallel-session format throughout the
3.
Two Symposia on speciation in insects held at the Fourteenth
International Congress of Entomology (Canberra, Australia, August
22-30, 1972) are included in this volume. The first, on the more
general topic of Genetic Analysis of Speciation Mechanisms,
includes four papers on speciation in various groups of Diptera and
Orthopteroid insects. The second symposium was devoted to the topic
of Evolution in the Hawaiian Drosophilidae; it deals with the
explosive speciation of a group of flies with specialized
ecological requirements in the complex ecolOgical habitats provided
by a recent tropical volcanic archipelago. The Hawaiian Symposium,
organized by Professor D. Elmo Hardy, is the latest outcome of a
major collaborative research project involving over 20 scientists
and about 125 technical assistants over a period of ten years. Some
recent books on evolution have taken the standpoint that the funda
mental genetic mechanism of speciation is relatively uniform and
stereotyped and, in particular, that the 'allopatric' model of its
geographic component is universally valid. Certainly, this has been
a rather generally accepted viewpoint on the part of students of
vertebrate speciation. Workers on speciation in insects have
tended, in general, to be less dogmatic and more willing to
consider a variety of alternative models of speciation. Thus, in
the present volume, several contributions adopt viewpoints which
are unorthodox or novel. Only time will tell whether their
conclusions will turn out to have been soundly based."
Find out how theoretical calculations are used to determine,
elucidate and propose mechanisms for Pd-catalyzed C-C
cross-coupling reactions in Max Garcia Melchor's outstanding
thesis. Garcia Melchor investigates one of the most significant and
useful types of reactions in modern organic synthesis; the Pd-cross
coupling reaction. Due to its versatility, broad scope and
selectivity under mild conditions, this type of reaction can now be
applied in fields as diverse as the agrochemical and pharmaceutical
industry. Garcia Melchor studies the reaction intermediates and
transition states involved in the Negishi, the copper-free
Sonogashira and the asymmetric version of Suzuki-Miyaura coupling.
He also characterizes and provides a detailed picture of the
associated reaction mechanisms. The author has won numerous prizes
for this work which has led to over eight publications in
internationally renowned journals.
1. R. Carlson, A. Nordahl: Exploring Organic Synthetic Experimental
Procedures 2. S.J. Cyvin, B.N. Cyvin, J. Brunvoll: Enumeration of
Benzenoid Chemical Isomers with a Study of Constant-Isomer Series
3. E.Hladka, J. Koca, M. Kratochvil, V. Kvasnicka, L. Matyska, J.
Pospichal, V. Potucek: The Synthon Model and the Program PEGAS for
Computer AssistedOrganic Synthesis 4. K. Bley, B. Gruber, M.
Knauer, N. Stein, I. Ugi: New Elements in the Representation of the
Logical Structure of Chemistry byQualitative Mathematical Models
and Corresponding Data Structures
In 1965 a book by P. Bartlett appeared under the title "The
Nonclassical Ions" 1). The book is a collection of papers reprinted
from various journals. The many reviews that have appeared since
2-22) are either antiquated (the book published in 1972 12) covers
the literature mainly before 1968) or relatively biased (e.g.,
3.4,10" on brief 2, 7,11). This review attempts to discuss the
various points of view on the "nonclassical" carbocations. The main
point is to establish the relative role of "nonclassical" and
"classical" ions in various chemical processes. The author has
followed P. Bartlett's advice 1) that when setting forth the
achievements of the human mind one should see how we came to the
modern understanding of a given problem (" ... how we know what we
know"). The theory of "nonclassical" ions offers an explanation of
many unique chemical, stereochemical and kinetic peculiarities of
bicyclic compounds. It has expanded our knowledge on chemical bonds
in carbocations by introducing electron-deficient bonds (as in
boron hydrides). It has accounted for many rearrangements of stable
cations. As a "side" result our knowledge has been extended about
ionization processes in a solution, as well as about stereochemical
methods. 2 Main Terms of Nonclassical Carbocations In 1939 Hevell,
Salas and Wilson 23) assumed an intermediate, "bridge" ion 2 to be
formed when camphene hydrochloride 1 is rearranged into isobornyl
chloride 3. This happened 17 years after Meerwein first postulated
the intermediate formation of "carbonium" ions in chemical
reactions.
The French chemist Marcelin Berthelot put forward a classical and
by now an often cited sentence revealing the quintessence of the
chemical science: "La Chimie cree son objet." This is certainly
true because the largest number of molecular compounds were and are
continuously synthesized by chemists themselves. However, modern
computational quantum chemistry has reached a state of maturity
that one can safely say: "La Chimie Theorique cree son objet" as
well. Indeed, modern theoretical chemistry is able today to provide
reliable results on elusive systems such as short living species,
reactive intermediates and molecules which will perhaps never be
synthesized because of one or another type of instability. It is
capable of yielding precious information on the nature of the
transition states, reaction paths etc. Additionally, computational
chemistry gives some details of the electronic and geometric
structure of molecules which remain hidden in experimental
examinations. Hence, it follows that powerful numerical techniques
have substantially enlarged the domain of classical chemistry. On
the other hand, interpretive quantum chemistry has provided a
conceptual framework which enabled rationalization and
understanding of the precise data offered either by experiment or
theory. It is modelling which gives a penetrating insight into the
chemical phenomena and provides order in raw experimental results
which would otherwise represent just a large catalogue of unrelated
facts.
High-throughput screening and combinatorial chemistry are two of
the most potent weapons ever to have been used in the discovery of
new drugs. At a stroke, it seems to be possible to synthesise more
molecules in a month than have previously been made in the whole of
the distinguished history of organic chemistry, Furthermore, all
the molecules can be screened in the same short period. However,
like any weapons of immense power, these techniques must be used
with care, to achieve maximum impact. The costs of implementing and
running high-throughput screening and combinatorial chemistry are
high, as large dedicated facilities must be built and staffed. In
addition, the sheer number of chemical leads generated may
overwhelm the lead optimisation teams in a hail of friendly fire.
Mother nature has not entirely surrendered, as the number of
building blocks that could be used to build libraries would require
more atoms than there are in the universe. In addition, the
progress made by the Human Genome Project has uncovered many
proteins with different functions but related binding sites,
creating issues of selectivity. Advances in the new field of
pharmacogenomics will produce more of these challenges. There is a
real need to make hi- throughput screening and combinatorial
chemistry into 'smart' weapons, so that their power is not
dissipated. That is the challenge for modellers, computational
chemists, cheminformaticians and IT experts. In this book, we have
broken down this grand challenge into key tasks.
The liquid crystalline state may be identified as a distinct and
unique state of matter which is characterised by properties which
resembles those of both solids and liquids. It was first recognised
in the middle of the last century through the study of nerve myelin
and derivatives of cholesterol. The research in the area really
gathered momentum, however, when as a result of the pioneering work
of Gray in the early 1970's organic compounds showing liquid
crystalline properties were shown to be suitable to form the basis
of display devices in the electronic products. The study of liquid
crystals is truly multidisciplinary and has attached the attention
of physicists, biologists, chemists, mathematicians and electronics
engineers. It is therefore impossible to cover all these aspects
fully in two small volumes and therefore it was decided in view of
the overall title of the series to concentrate on the structural
and bonding aspects of the subject. The Chapters presented in these
two volumes have been organised to cover the following fundamental
aspects of the subject. The calculation of the structures of liquid
crystals, an account of their dynamical properties and a discussion
of computer simulations of liquid crystalline phases formed by Gay
Berne mesogens. The relationships between molecular conformation
and packing are analysed in some detail. The crystal structures of
liquid crystal mesogens and the importance of their X ray
scattering properties for characterisational purposes are
discussed.
1. R.G. Pearson Chemical Hardness - An Historical Introduction 2.
P.K. Chattaraj Density Functional Theory of Chemical Hardness 3.
J.L. Gazqu z Hardness and Softness in Density Functional Theory 4.
L. Komorowski Hardness Indices for Free and Bonded Atoms 5. N.H.
March The Ground-State Energy of Atomic and Molecular Ions and Its
Variation with the Number of Elections 6. K. Sen Isoelectronic
Changes in energy, Electronegativity, and Hardness in Atoms via the
Calculations of 7. P. Politzer, J.S. Murray, M.E. Grice Charge
Capacities and Shell Structures of Atoms 8. R. F. Nalewajski The
Hardness Based Molecular Charge Sensitivities and Their Use in the
Theory of Chemical Reactivity 9. B.G. Baekelandt, R. A.
Schoonheydt, W.J. Mortier The EEM Approach to Chemical Hardness in
Molecules and Solids: Fundamentals and Applications 10. J.A.
Alonso, L. C. Balbas Hardness of Metallic Clusters
This book presents the most comprehensive analysis of bonding in
polyoxometalates and related oxides based on classical bonding
concepts and the bond valence model. Numerous tables and figures
underline and illuminate the results, making it a valuable
resource.
Over the past 40 years, Rotational Isomeric State (RIS) models for
hundreds of polymer structures have been developed. The RIS
approach is now available in several software packages. The user is
often faced with the time-consuming task of finding appropriate RIS
parameters from the literature. This book aims at easing this step
by providing a comprehensive overview of the models available. It
reviews the literature from the first applications of RIS models to
the end of 1994, comprises synthetic as well as naturally orccuring
macromolecules, and tabulates all the pertinent features of
published models. It will help readers, even when not very familiar
with the method, to take advantage of this computationally
efficient way of assessing the conformational properties of
macromolecular systems.
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