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Book Review Zur Konformation des Cyclohexans. (Ostwalds Klassiker der exakten Wissenschaft Band 274.) By H. Sachse and E

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The many new results and the greatly extended knowledge that have been gained in this field during the last
eight years (including publications u p to the beginning of
1987) have been incorporated into this considerably enlarged new edition, maintaining the same high standard.
Since new facts and views concerning the solvents themselves have also come to light, the title has been extended
to take account of this.
The original division into seven chapters has been retained, but the relative emphases have shifted considerably. The book begins with a chapter on “Solute-Solvent Interactions” (45 pp., 303 references), in which those currently held concepts that are of general validity are summarized. In addition important effects such as solvophobic
interactions and micelle formation are discussed. “Classification of Solvents” (26 pp., 171 references) deals with their
classification according to their various physical and
chemical properties (e.g. acids and bases). Also included
here are specific solvation effects, and recent attempts using multivariant statistical methods (chemometrics) to arrive at a rational classification of solvents.
The chapter on “Solvent Effects on the Positions of Homogeneous Chemical Equilibria” (41 pp., 229 references)
covers not only the classical effects o n acid-base and ketoenol equilibria (including the most recent data, with also
gas phase data for comparison), but also solvent effects on
conformational, valence isomerization and electron transfer equilibria. The next chapter on “Solvent Effects on the
Rate of Homogeneous Chemical Reactions“ (171 pp., 769
references) has undergone the greatest enlargement, as is
evident from the remarkably large bibliography alone.
Qualitative observations, quantitative measurements and
theories are discussed, with examples from a very wide
range of reaction types, and effects produced by external
pressure, molecular sieve action and liquid crystalline
reaction media are described.
The important topic “Solvent Effects on Absorption
Spectra of Organic Compounds“ (53 pp., 434 references)
has also been updated to the latest situation. In addition to
the classical effects o n UV-VIS and IR spectra, solvent effects on ESR and N M R spectra are also described. The
final chapter “Empirical Parameters of Solvent Polarity”
(66 pp., 287 references) has been rewritten because of the
large number of new papers that have been published. The
description of the now well-known Y , Z and ET scales has
been enlarged to include also some newer characteristic
quantities, and properties specific to the solvents, e.g. acceptor and donor properties. The comparison of different
empirical scales and the detailed discussion of the controversial multiparameter relationships is especially helpful.
There is a welcome addition in the form of an appendix
which contains numerous tables listing the properties of
solvents, methods for purification, and areas of use in
spectroscopy and synthesis; information on toxicities is
also included.
It can already be seen from this brief description of the
contents of the book that one could scarcely imagine any
other monograph which would treat the whole field of solvent effects so comprehensively without becoming unacceptably long. One gets the impression that the literature
has been very carefully reviewed and evaluated. The well
chosen examples enable the reader to quickly understand
each type of problem, and the detailed bibliography allows
him to extend his reading both in breadth and depth. Anyone wishing to learn about solvent effects or to investigate
them, o r who wishes to find typical examples of effects on
equilibria and reactions, will find this book to be good valAngew. Chem. In(. Ed. Engl. 28 (1989) No. I
ue. For these reasons it belongs not only in every library
but also at the chemist’s bench, and an economical paperback edition of the book would be a very welcome addition.
Siegfried Hiinig [NB 937 IE]
Institut fur Organische Chemie
der Universitat Wiirzburg (FRG)
Zur Konformation des Cyclohexans. (Ostwalds Klassiker
der exakten Wissenschaft, Band 274.) By H. Sachse and
E. Mohr. Akademische Verlagsgesellschaft Geest & Portig, Leipzig 1987. 152 pp., paperback, DM 21.00.--ISBN
3-321-00025-3
In 1885 Adolfvon Baeyer assumed in his strain theory
that all cycloalkanes had a planar ring of carbon atoms.
This view was challenged five years later by Hermann
Sachse, who proposed non-planar chair and boat structures for the important case of cyclohexane. He also correctly recognized the possibility of chair inversion in cyclohexane, yet overestimated the strain requirements, and
concluded that inversion could not occur at room temperature. This led him to describe the cis- and trans-cyclohexane- 1,4-dicarboxylic acids as conformational rather than
configurational isomers. As a corollary of this, he further
concluded that for monosubstituted cyclohexanes one
should expect two stable and separable isomers with axial
and equatorial orientation of the substituent respectively.
Since this could not be backed by experiment, and probably also as a consequence of the eminent authority of von
Baeyer, the work of Sachse gained no recognition and fell
into oblivion for many years to come. It was not until 25
years later (1915), long after Sachse’s premature death in
1893, that Ernst Mohr again took u p the cyclohexane problem, and made it clear that “no objection whatsoever”
could be raised against Sachse’s ideas regarding the nonplanar structure of cyclohexane, provided the inversion
barrier is low enough. A breakthrough in favor of the nonplanar structure of cyclohexane eventually came from the
firm conclusion reached by Mohr in 1922 that both stereoisomers of decalin should exist, followed almost immediately (1923) by Walter Hiickel’s experimental verification
of this prediction. O n this matter, Mohr had engaged in a
controversy with Richard Willstatter, one of von Baeyer’s
former students and late supporter of a planar structure of
cyclohexane, who shortly earlier (1921) had declared transdecalin could not be made due to excessive strain.
The present booklet is preceded by an introduction by
editor Horst Remane, describing some elements of conformational analysis (9 pages): present-day significance, some
basic facts, historical developments. Biographical details
and an account of the scientific achievements of Hermann
Sachse and Ernst Mohr follow (13 pages). Mention is made
here of both pioneers’ grave personal lives overshadowed
by serious illness. Sachse died at an age of only 31, Mohr at
53. The central part of the book is, of course, taken u p by
the reprints of Sachse’s two key publications and three relevant papers by Mohr:
1) H. Sachse: Uber die geometrischen Isomerien der Hexamethylenderivate, Berichte der Deutschen Chemischen
Gesellschaft 23 (1890) 1363-1370.
2) H. Sachse: Uber die Konfigurationen der Polymethylenringe, Zeitschrgt f u r Physikalische Chemie I0 (1892)
203-241.
105
3) E. Mohr: Die Baeyersche Spannungstheorie und die
Struktur des Diamanten, Journal fur Praktische Chemie
98 (1918) 315-353.
4) E.Mohr: Zur Theorie der cis-trans-Isomerie des Decahydronaphthalins, Berichte der Deutschen Chemischen
Gesellschaft 55 (1922) 230-23 1.
5) E. Mohr: Zwei spannungsfreie Cycloheptanmodelle,
Journalfur Praktische Chemie 103 (1922) 316-328.
The original papers are annotated with comments by the
editor, which make u p the last 13 pages, including an author index.
Some critical comments follow concerning the editing of
the little book. The introductory section on fundamentals
of conformational analysis appears somewhat drab and
outdated. The origin of the rotation barrier in ethane (p. 8)
is actually pretty clear (R. M. Pitzer, Acc. Chem. Res. 16
(1983) 207). It is rather disconcerting to detect just in this
text that the characterization of the stationary points of the
inversion process of cyclohexane has not been gotten right
(p. 10, Fig. 5).
The editor has taken much care in supplementing the
old nomenclature by more recent conventions, but in my
view has gone a little too far, as the present historical context demands a tender approach indeed. For example, on
page 14 it is noted expressis verbis “. .. Jod [Iod, H. R.]”; un
peu de trop, it seems to me! Again, wherever the name
“Hexamethylen” occurs in the original papers, and this
happens frequently, of course, the reader is invariably and
relentlessly instructed that the glorious modern term is
“Cyclohexan”. In favor of the editor, let us assume that the
editing program of a computer has performed its stubborn
task here! I found the alteration of “Benzol” in the original
papers to “Benzen” very irritating, since even modern German usage on the whole still prefers the old “classical”
variant. The editor had indeed better avoided this inept interference, especially since he ultimately refrained from introducing the new word in the titles of the cited publications (see, for example, the bizarre situation on p. 82, ref.
12).
As the original papers have not been directly reproduced, but have instead been newly type-set and annotated, some errors have naturally crept in here and there.
For example, in connection with note [5] o n p. 30 the
proper spelling is “Kohlenstoffatome.” It is to be hoped
that the numerous analytical relationships in Sachse’s second paper have not suffered; one error at least is perceptible in the first expression on p. 54. In Fig. 1 and, more
particularly, Fig. 2 of the first paper by Mohr, the perspective is wrong, while Figs. 4, 6 and 20 are turned upsidedown.
On p. 144 it is stated in note [42] that the twist forms of
cyclobutane interconvert by pseudorotation. In actual fact,
this process is to be referred to as a ring inversion, since
the planar four-membered ring allows only a single type of
non-planar deformation (normal coordinate), which necessarily cannot be degenerate. A pseudorotatory degree of
freedom corresponds to a double degeneracy, which is
only possible in rings with five or more members.
Despite all this criticism, it is to be welcomed that the
publishers of the series “Ostwalds Klassiker” have devoted
a volume to the history of elucidation of the cyclohexane
structure, and thereby also to the core of conformational
analysis. The booklet is recommended to everyone interested in the history of the development of basic concepts
of modern chemistry, especially as the price is within reach
of even small purses.
Otto Ermer [NB 921 IE]
Institut fur Organische Chemie
der Universitat Koln (FRG)
Rrg,srr3red names. rrademarks, elc used in rhis journal, even when nor marked as such, are nor lo he considered uiiprorecred by law.
0 VCH Verlagsgesellschalt mbH, D-6940 Weinheim, 1989
Printed in the Federal Republic of Germany by Zechnersche Buchdruckerei, Speyer/Rhein.
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Angew. Chem. Inr. Ed. Engl. 28 (1989) No. I
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