вход по аккаунту


Book Review Orbital Symmetry and Reaction Mechanism. The OCAMS View. By E. A. Halevi

код для вставкиСкачать
Society of Synthetic Organic Chemistry has now undertaken
a sort of stocktaking review, with contributions by 60 authors drawn from academia and industry. These mainly very
personal contributions highlight some important developments that have taken place in Japan in synthetic organic
chemistry, and describe the most outstanding research results achieved in recent times.
The first part of the book is devoted to the history of the
development of synthetic chemistry in Japan, with descriptions of some milestones in the areas of the synthesis of
natural products and biologically active substances (Y. Ban,
M. Matsui, M . Yamaguchi), organic synthesis in the pharmaceutical industry (K. Morita), industrial synthesis (Y. Ito),
and syntheses of molecular energy storage media, organic
conductors, and ferromagnetic materials (Z. Yoshida). In a
more general article H. Nozaki discusses the changes that
have occurred over the years in the areas on which synthetic
organic chemistry has concentrated.
In the second part 53 authors (of whom 36 are from universities and 17 from industry) describe their best research
results. The majority of the literature citations belong to the
last ten years. The contributions extend over a wide range of
synthetic organic chemistry, but an emphasis on certain topics is clearly evident. These include the synthesis and modification of complex natural products (e.g., 1-oxacephems,
taxanditerpenoids, 1,3-polyols, macrolides, glycoconjugates,
pyrethroid insecticides), metal-assisted selective transformations (especially those using palladium or the ruthenium(I1)BINAP reagent, and new Lewis acid catalyzed reactions),
syntheses based on organoboranes and organosilanes, and
stereochemically controlled reactions. On the other hand,
some classes of interesting compounds other than natural
products that have been synthesized in Japan are perhaps
somewhat under-represented here. Rather predictably, modern developments in the chemistry of organoheteroelement
compounds are treated only in the context of aids to organic
synthesis (see above), not from the standpoint of the synthesis of the compounds themselves. Looking at the list of authors one can, of course, point to a few notable omissions,
but it is certainly not possible to achieve completeness in a
collection of this kind.
With regard to the future of Japanese organic chemistry as
mentioned in the title, most of the comments are to be found
in the first part of the book, but some of the authors in the
second part also make projections. In academic research
some important future trends are: a) studies aimed at a better understanding of organometallic reactions, especially
with regard to (stere0)selective reactions, and closer links
between inorganic chemistry and synthetic organic chemistry; b) chemical synthesis in combination with methods
based on fermentation and enzyme-catalyzed reactions; c)
the synthesis of molecules with useful photochemical, electrical, or magnetic properties. For industry, Y. Ito predicts that
future objectives will include: a) technologies for protecting
the global environment and conserving natural resourcessuch projects will require cooperation between industry and
universities; b) a strengthening of speculative basic research,
with a willingness on the part of management to take risks;
c) international collaboration in the development of new
chemical technologies; d) a close integration of chemistry,
biotechnology, electronics, and physics a t the molecular level. Many of these future perspectives could apply equally in
Germany, as also could the urgent appeal to policy-makers
to increase investment in education and basic research.
The book has a consistent layout and very attractive presentation, which is greatly helped by the clear and excellently
reproduced formula diagrams. The title page of each contri1220
VCH Verlagsgesellschafl mhH. 0-69451 Weinheim, 1993
bution carries a photograph of the author with a biographical note on his scientific work. Although the book does not
cover the whole field exhaustively, it is certainly an important and valuable source of information on the present state
of synthetic organic chemistry in Japan.
Gerhard Maas
Fachbereich Chemie
der Universitat Kaiserslautern (FRG)
Orbital Symmetry and Reaction Mechanism. The OCAMS
View. By E. A . Halevi. Springer, Berlin/New York, 1992.
XXII, 310 pp., hardcover DM 68.00.-ISBN 3-540-50 164910-387-50 164-9
When, in 1992, someone writes a book about the relationship between orbital symmetry and reaction mechanism, it
can be assumed that it is not so much an account of the latest
results as a review and appraisal of a line of development
that extends back at least to 1965. It was then that Woodward and Hoffmann, with their principle of the conservation
of orbital symmetry, initiated a revolution in chemistry that
is almost without equal. This book leaves no doubt that the
stimulus generated by that simple idea could not have come
about without the existence at that time of a receptive intellectual climate, characterized by a lack of the fundamental
knowledge needed to understand reaction mechanisms. The
author does not assume that the reader will be satisfied with
a superficial argument; instead he adopts a rigorous approach
that is a continuous theme throughout the book. He starts by
noting that it would be very convenient if one could make
predictions about a reaction mechanism on the basis of symmetry. The second stage is to determine whether or not the
system goes beyond the range of validity of the molecular
orbital (MO) theory; in other words, one has to distinguish
between MO, configurational, and state correlation. The
third stage is concerned with the rigorous description of the
transition structure in energetic terms, from which one can
decide whether a symmetry argument is to be accepted or
The author takes considerable care to prepare the ground
by explaining aspects of symmetry that are needed later. The
uninitiated reader is gently “led by the hand” through the
necessary stages, and the reader with previous knowledge
will probably not start with any special advantage. The unconventional approach in which symmetry and symmetry
reduction are treated simultaneously is certainly very convincing, but the combining of this with the illustration of the
behavior of atomic p-orbitals in a magnetic field relates only
to an imaginary experiment and not to the actual situation.
Because of the electron spin the 2p state undergoes not a
threefold but a fourfold splitting. The treatment of the Zeeman effect without including the electron spin is a dubious
approach, and should at least have been preceded by an
explanatory note. Considering that fundamental aspects o f
d-orbitals are discussed in some detail, it would have been
appropriate to explain that there is an infinite number of
legitimate ways of choosing a set of five d-orbitals. In fact the
discussion is always confined to the one set that can easily be
generated from the complex functions for spherical symmetry, and which is easy to handle in the case of octahedral
symmetry, where the axes can be chosen in accordance with
the ligands. Thus even the equivalence of the functional
forms is abandoned. On the whole this first third of the book
covers all the most important preparative material for what
is to follow. This includes molecular orbitals and normal
057O-0833/93/0808-1220$ I0 00+ ,2510
Angew. Chem. In[. Ed. Engl. 1993, 32, N o . 8
vibrations, as well as orbital correlation diagrams for diatomic molecules. The two fundamental rules, namely the
non-crossing rule and the Walsh rules, are only briefly mentioned, and the reader is apparently expected to understand
these already.
The next I00 pages are devoted to classical thermal reactions. These are analyzed from the OCAMS (orbital correspondence analysis in maximum symmetry) standpoint that
the author has himself developed. Compared with the Woodward-Hoffmann rules this has the advantage of providing a
rigorous formalism that leads directly to the thermally favored
reaction mechanism. avoiding the need to consider all conceivable mechanisms in turn (and perhaps to overlook the
one that is of most interest). The information that OCAMS
gives about a mechanism is of a relative nature, and is conceptually related, in a broad sense, to the Walsh rules. It
therefore undoubtedly comes nearer to the truth than topological considerations. About 40 topical examples are described in detail and clearly illustrated.
It is only in the final third of the book that the electron spin
is introduced. Spin-forbidden processes are incorporated into
the OCAMS approach, and examples that involve intersystem crossing are described. About a dozen carefully chosen
examples of reactions involving electronically excited states
are described. At the time when the Woodward-Hoffmann
rules were being applied to photochemical reactions without
sufficient care, inappropriate mechanisms were assumed in
many cases. Only four examples from inorganic chemistry
are described, and from these one can conclude that the
orbital symmetry approach is best reserved for carbon compounds, since there is always doubt as to whether the condition of kinetic stability is satisfied for inorganic compounds,
so that no reliance can be placed on results from symmetry
considerations. The appendix contains character tables and
group correlation tables that are a valuable aid in studying
the examples.
The text is excellent in both its intellectual content and
style, and the book provides ample evidence of the author’s
rich fund of experience.
Rudolf Janoschek
Institut fur Theoretische Chemie
der Universitat Graz (Austria)
Science as Writing. By D. Locke. Yale University Press, New
Haven, 1992. X, 237 pp., hardcover $30.00/& 18.50.ISBN 0-300-05452-1
The author of this book, David Locke, started as a chemist.
His mentor was S. William Pelletier, with whom he synthesised atisine, an alkaloid. The work was published in the
Journal of the American Chemical Society in 1959. At
present, David Locke teaches English at the University of
Florida. He is thus able to describe science as an insider.
When he refers to style in science, the example he brings
forward (who else?) is that of Robert B. Woodward. This
issue of scientific style is one that elicits considerable current
interest. A whole periodical, Science in Context, is devoted to
the question of style in science, not only on the part of an
individual, but within a field of science or a national tradition. This book is well-researched and jargon-free. It puts to
rest our cherished notion of science as methodically built
from the objective gathering of facts. It has other uses also. It
will help to devise an efficient rhetoric for one’s scientific
discourse. It should help to restore to science a measure of
personal style, as opposed to the fastidiously repetitive hyperspecialization that masquerades in its stead.
AIIFW. Chrm. Int. Ed. End. 1993. 32, No. H
Locke brings to bear on his precious little book an in-depth
understanding of the scientific process. The third chapter contrasts expressionless, humorless writing, as seemingly required
in publications, both with shop talk in the laboratory, and
with the emotional involvement in their work by eminent
scientists such as Charles Darwin. This empathy for one’s
brainchild is beautifully exemplified by Barbara McClintock’s animation of the genome; it is for her a living entity.
Locke deals next with the rhetoric of science, of which The
Origin qfSpecies is a prime example. He shows convincingly
that the lack of impact of Mendel’s discovery, even though
the contemporaries knew of it, stems from a revolutionary
finding having been presented in the language of normal, runof-the-mill science. He uses Einstein’s introduction of relativity theory to demonstrate the importance of story-telling
to conveying a novel world-view. In a chapter with the felicitous title “The Art of Artless Prose”, the author focuses on
the irony that permeates great texts, such as Galileo’s Diulogues o r The Double Helis. He draws attention also to the
virtue of understatement, as a device to prepare for the hardhitting punch line (such as that, one may add, in Woodward
and Hoffmann’s The Conservation of Orbitul Symmriry:
“Exceptions? There are none.”) The book throbs with vital
insights. In Chapter 5, on “The Putative Purity of Science”,
Locke comments perceptively on the existence of a scientific
oligarchy, in between decision-makers and the scientific
community: “ultimately, it determines what is scientifically
thinkable, until the unorthodox idea thrusts its way into the
arena, with the force of scientific genius, skillful rhetoric, and
iron determination behind it.”
The main virtues of Locke’s book are his intimate familiarity with living science: the smooth readability buoyed by a
constantly pleasing style and by recourse to major texts,
known by everyone, for its examples; the constant criticism
of the myth of science as an objective and neutral process.
These qualities are sometimes drawbacks. One might argue
that to focus on scientific revolutions and masterpieces is too
selective. Normal science is also to be considered advantageously as writing. One might also argue, on a different tack,
that scientific advances can be uncoupled from ideological
hangups: Jacques Loeb (p. 154ff.) is remembered for the
study of tropisms, more than for his obsession with getting
rid of free will.
Deconstruction has been a slogan during the post-modern,
post-structuralist period from which we are emerging. This
debunking movement has helped to jettison the myth of science as the progressive buildup of the laws of nature from
objective facts. Its own mythological view of science nevertheless borders on the ridiculous and, to this writer, is unacceptable. It rests on microsociological studies of laboratory
life. They find that science is akin to a power play: its conclusions would be, according to this critical analysis, merely a
negotiated settlement between the human participants.
Locke’s essay is far above such ultrasimplifications. He uses
various complementary approaches so as to provide a realistic, multidimensional view of science. His metaphor of science as writing is much more productive, and he pushes it to
all its implications without ever forcing the evidence to conform to his model.
Pierre Laszlo
Laboratoire de Chimie
Ecole Polytechnique, Palaiseau (France)
New Books
see next page
VCH Verlu~.~~esellscliuft
mhH. 0.69451 Wemheim. 1993
o57o-0833193joH08-1221 $ /0.10+ ,2510
Без категории
Размер файла
306 Кб
symmetry, ocams, book, reaction, mechanism, view, review, orbital, halevi
Пожаловаться на содержимое документа