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Book Review Chirality Ц From Weak Bosons to the -Helix. Edited by R. Janoschek

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cluded, so that the non-specialist too is given some insight
into the complexities of this field. Methods for detecting and
studying cations are described, devoting special attention
and an appropriately large amount of space to NMR spectroscopy, which is the most important method. It is pleasing
to find that, as a general principle, efforts have been made to
link the experimental data to quantum mechanical calculations (IGLO or geometric optimization methods). In this
connection, however, it is regrettable that the theoretical
methods have not been given a separate chapter. Also, experience has shown that ab-initio calculations offer an extremely useful and precise tool for determining the structures of
carbocations. Apart from this, the introductory chapter is
very appropriate as a readily understandable overview for
the beginner, as well as giving the specialist a survey of the
latest research position.
The main part of the volume covers all the theoretically
conceivable forms of carbocations. After dealing with carbocations that are only of theoretical interest, the discussion
moves on to the carbocation radicals that are important in
preparative electrochemistry. In the chapter on preparative
methods for these (Subramanian; 20 pp.), detailed laboratory recipes for syntheses under electrolytic conditions are
given, supplemented by extensive tables. 1-Alkenyl cations
are treated in great detail (Hanack, Subramanian; 154 pp.);
the authors are the leading workers in this area. The next
chapter (Lenoir, Siehl; 157 pp.) deals with classical cations
having coordination number 3, including alkyl-, cycloalkyland heteroatom-substituted cations, as well as aromatic, homoaromatic and special types of destabilized cations; here
again there is an emphasis on the preparative aspects. The
authors have collected together a remarkable number of reactions that proceed via carbocations as intermediates, in a
presentation that includes numerous tables and selected examples of synthetic methods.
Next there is a short chapter (Siehl, Lenoir; 28 pp.) on
hypercoordinated non-classical cations. The authors have
been remarkably successful in showing the relationship to
synthetic chemistry, despite the fact that these species are
usually only mentioned in passing as “exotic molecules”.
The last two chapters are concerned with di- and polycations
(Siehl, Lenoir; 14 pp.) and with carbocations in organometallic compounds (Lenoir, Siehl; 3 pp.).
The general subject index is very scanty (5 pp.), making it
difficult to search for particular compounds and methods.
Moreover, the system used in the formula index is unnecessarily complicated, causing problems when one is searching
for compounds. An alphabetical arrangement or a listing
according to increasing number of carbon atoms would have
made things much easier. Many of the cations have come to
be generally known by trivial names; such an excellent book
as this should, in my opinion, have been provided with a
comprehensive keyword index.
In conclusion I might mention a few unsightly errors. The
Coates cation appears in two figures (one below the other)
with the different systematic names “Pentacyclo[4.3.0.02~9.03~5.04,8]non-9-yl-Kation”
and “Pentacycio[3.3.1 .02~4.03*7.06~8]non-9-yl-Kation”.
This appears not to
be an accidental error, since it is stated that the Coates cation
is formally a polycyclic derivative of the bicyclo[2.2.l]hept-2en-7-yl cation. Unfortunately the representations of the trishomoaromatic cations are all incorrect at the critical positions. The equations for the reactions leading to the formation of the bishomoaromatic 7-norbornenyl and 7-norbornadienyl cations are also incorrect. The “1” nomenclature
caused me a certain amount of difficulty when I came across
it for the first time, and was unable to find the explanation
800
0
VCH Verlugs~eseilschufimhH. W-6940 Weinheirn. 1992
even after a lengthy search. Also it takes a little time to get
used to the names I-methylethyl cation (instead of 2-propyl
cation) and I-methylpropyl cation (instead of 2-butyl
cation). The convention of showing the cationic center in
bold type is a useful aid to understanding, but has not been
applied consistently. Instead of the adjective “quantenmechanisch” it would be more correct to write “quantenchemisch”, since even ab-initio calculations rely on assumptions and approximations, and therefore fall short of exact
quantum mechanics. The individual chapters are divided up
in a way that is very confusing. It would have been desirable
to keep to a uniform system, and to severely limit the number
of different levels of sub-headings. The figures are up to the
usual high standard found in Houben-Weyl. In a volume
containing over 3000 structural formulas, one can excuse the
few isolated errors-the vast majority of the formulas are
correct. By bringing together a great wealth of data and
presenting the information in a clearly understandable form,
the authors have succeeded in producing a comprehensive
work of reference that will be a valuable aid to everyone
concerned with carbocations. Furthermore, the superb compilation of carbocation reactions will be of great value to the
synthetic chemist. The inclusion of the rather theoretically
and mechanistically orientated topic of carbocations within
the Houben-Weyl series, which is usually associated mainly
with preparative organic chemistry, has proved highly successful.
Peter Buzek, Paul von R a p 6 Schleyer
Institut fur Organische Chemie
der Universitat Erlangen-Nurnberg (FRG)
Chirality - From Weak Bosons to the a-Helix. Edited by R.
Janoschek. Springer, Berlin, 1991. XI, 246 pp., hardcover
DM 168.00.-ISBN 3-540-33920-4
It is hard to think of a property more fundamental, more
ubiquitous, more fascinating than the one that gives rise to
the distinction between an object and its mirror image. That
property is handedness, or chirality, and it arises whenever
an object is not invariant under improper rotation. Such an
object must then necessarily exist in two, and only two, isometric but nonsuperposable forms, one “right-handed” and
the other “left-handed”. Chirality, in its many and varied
manifestations, permeates all branches of the natural sciences and of the arts. The present volume is a collection of
articles designed to provide an interdisciplinary overview of
a small part of this vast subject. Considering the range of
subject material covered, the authors have succeeded remarkably well in meeting their objective, that of writing “for
anybody with a sound scientific education”, and “not [just]
for specialists in their respective fields of research”.
The discovery, in 1956, that parity is not conserved for the
weak interactions governing P-decay has led to our presentday understanding that matter is inherently chiral at the
most fundamental level. In the introductory chapter of this
collection, Latal describes the nature of elementary particles,
develops the Dirac equation and the theoretical basis for the
idea that particles and antiparticles possess opposite helicities (as in left-handed electrons and neutrinos, and righthanded positrons and antineutrinos), and shows how the
unified theory of electromagnetic and weak forces (involving
weak neutral bosons) leads to the prediction of parity-violating effects in atoms. Thus, all atoms are in principle optically
active, although the effect is tiny and has so far been observed only in heavy atoms (e.g., Pb, Bi). Translated from the
oS?o-0X33~92ji)606-0XOO
$3.50+ ,2510
Angew. Chem.
hi.Ed. Engl. 3f (1992) No. 6
atomic to the molecular level, the parity-violating weak neutral current perturbation lifts the degeneracy of space-inverted enantiomers. The energy difference is only approximately
lo-’’ kJmol-’, and corresponds to an excess of just one
molecule of D- or L-alanine in a racemic mixture of loi7
alanine molecules in thermodynamic equilibrium at terrestial temperatures. Ab initio calculations indicate that the
predominant isomer has the L configuration. Janoschek argues that this minuscule bias, appropriately amplified, is
responsible for the fact that all metabolically functional biopolymers are monochiral, both at the monomer level (L-aamino acids, D-sugars) and in the helical polymer conformations (right-handed polypeptide a-helix, B-DNA), i.e., that
the monochirality of the molecules of life has its origins in
the systematic chiral bias of the elementary particles. Various
amplification mechanisms are described in support of this
thesis. However, the reader is cautioned that “any hypothesis on long term processes such as homochirality evolution
will most probably remain experimentally unproven for
ever.”!
After a brief discussion of Kauzmann’s “principle of pairwise interactions”, Derflinger gets to the heart of his subject:
a vigorous critique of the theory of chirality functions developed by Ruch and Schonhofer that focuses on the concept of
“qualitative completeness”. He thus revives a controversy
that had erupted briefly in the pages of Theoretica Chimica
Acta in 1978. Because only one side of the story is told in this
chapter, the reader needs to be made aware of two rebuttals,
neither of them cited here, by Ruch (Theor. Chim. Acta 1978,
49,107) and by Mead (Theor. Chim. Acta 1980,54,165).The
discussion of two other controversial concepts, “qualitative
supercompleteness” and “hyperchirality”, is equally partisan in tone. The chapter concludes with a description of a
method for enumerating enantiomeric pairs.
Snatzke reports on various methods that are employed to
specify the sense of helicity in molecules, points out ambiguities (a short path of a three-dimensional curve can be approximated by either a right- or a left-handed helix), and
discusses rules designed to correlate the absolute structures
(configurations) of chiral chromophores with the signs of
appropriately chosen circular dichroism bands. Surprisingly,
there is no reference to the excellent review on helical molecules in organic chemistry by Meurer and Vogtle (Fortschr.
Chem. Forsch. 1985, 127, 1). The theme of absolute configuration is also featured in a chapter by Kratky, in which
anomalous dispersion of X-rays is described as the method,
pioneered by Bijvoet, used to determine the sense of chirality
of molecules in crystals with respect to a macroscopic (absolute) reference frame.
The need for enantiomeric purity is particularly acute in
pharmacology and medicinal chemistry. This explains why
four of the ten essays in this collection are devoted to strategies for the production of enantiomerically enriched (and, in
the limit, enantiopure) compounds. Faber and Griengl describe the use of enzymes as efficient, cheap, and highly
enantioselective biocatalysts in the preparation of optically
active alcohols, amines, and acids (e.g., enzymatically catalyzed asymmetric reductions of ketones and hydrolyses of
meso diesters). Winterfeldt distinguishes, and illustrates with
examples, three general methods for achieving enantiomeric
purity : by resolution of racemates, by reactions whose
educts are enantiopure natural products, and by enantioselective reactions or asymmetric syntheses. Brunner discusses
the use of chiral transition metal complexes as catalysts in
asymmetric syntheses (e.g., hydrogenation of olefins with Rh
complexes of Diop). Strategies for the separation of enantiomers by liquid column chromatography are the subject of
Angew. Chem. I n [ . Ed. E n d . 31 (19921 N o . 6
a chapter by Lindner. The nature of chiral recognition between the mobile and stationary phases determines resolution efficiency; column packings are classified, and compared, according to type : derivatives of biopolymers (e.g.,
microcrystalline triacetylcellulose), chiral synthetic polymers
(e.g., Okamoto’s helical poly(trity1 methacrylate)), and chiral monomers (e.g., cyclodextrin derivatives).
Although it would be asking too much to expect complete
coverage of all aspects of this subject, given its enormous
scope, it was nevertheless disappointing to find no mention
of topological chirality (the chirality of trefoil knots, catenanes composed of orientated rings, Mobius ladders, and so
forth) in synthetic and naturally occuring molecules. I was
not able to make much sense of the essay by S. Hoffmann,
which I found to be intellectually impenetrable. Most texts of
this nature are plagued by errors, and the present volume is
no exception (e.g., on p. 171 the “symmetry elements” of
ethylene are given as ‘‘30, 3C,, and i“).Despite such shortcomings, however, this volume deserves to be read by anyone interested in this important topic.
Kurt Mislow
Department of Chemistry
Princeton University, Princeton NJ (USA)
Wood and Cellulosic Chemistry. Edited by D. N . S. Hon and
N . Shiraishi. Marcel Dekker, New York, 1991. VIII,
1020 pp., hardcover $234.00.-ISBN 0-8247-8304-03
Wood is one of the most important renewable raw materials and energy media. The growth of wood in forests makes
a significant contribution to reducing the amount of carbon
dioxide in the atmosphere. The carbon dioxide produced
from fossil and living carbon sources by burning and respiration can, over long periods, be transformed back into organic compounds. For this reason alone, it is clear that wood
chemistry and the use of wood as a chemical raw material is
currently of great importance.
Research in wood chemistry now involves many different
fields of science, and the published results are often widely
scattered; surveys that aim to bring together this knowledge
in an ordered way are therefore very useful. The book reviewed here is largely successful in achieving that objective.
The authors, 18 Japanese and four American scientists,
are all recognized experts in their fields. The book is divided
into three main sections, containing 21 chapters altogether.
Part 1, “Structure and Chemistry”, starts from the structure
and mode of formation (lignification) of the woody tissue of
the cell wall in plants, and goes on to describe in turn the
chemical properties of each of the wood constituents that are
bound together in the natural polymer structure-cellulose,
hemicellulose, lignin, and substances present in the wood.
Separate chapters are devoted to the chemistry of the bark,
and to the chemical characterization of wood and its constituents. This part could have been even further improved
by devoting a separate chapter to the biochemistry of wood
formation.
In Part 2, “Degradation”, some of the chapters deal with
topics that have not previously been treated in monograph
form, such as coloration and discoloration, and the photochemistry of wood. The degradation of wood by chemical,
microbiological, enzymic, and pyrolytic mechanisms is described in a detailed and highly informative way. However,
it is disappointing that this part does not also deal with the
gasification and liquefaction of wood.
(0VCH Verlagsgese/lsrha/fmbH, W-6940 Weinheim, 1992
0570-0S33!92!0606-0801 $3S0+.2Sj0
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