close

Вход

Забыли?

вход по аккаунту

?

Book Review Strained Organic Molecules. By A. Greenberg and J. F. Liebman

код для вставкиСкачать
LiI content in the lower temperature range, while the activation energy falls from 0.80 to 0.53 eV. The pre-exponential
factor of the Arrhenius equation a T = A exp( - E A / k T ) remains approximately constant, i. e. the jump frequency is independent of the composition.
Transfer experiments were undertaken with lithium to establish that the electrolytic current is indeed due to lithium
ions. EMF measurements on lithium concentration cells with
Li, xNtr,C1t,,as electrolyte and Li and Li,TiS2 as electrodes
also confirmed practically pure ionic conduction.
All the ternary compounds lying on the quasibinary cuts
Li3N-LiX are thermodynamically stable towards pure lithium, which can therefore be used as anode in electrolytic
cells. Moreover, all lithium nitride halides decompose only at
low lithium activities. This leads to high decomposition potentials, e.g. more than 2.5 V for Li, xNo4CI,6at 100 “ C (cf.
Table 1). The high thermodynamic stability permits use of
thin low-resistance layers, e. g. in printed circuits.
The free energy of formation of lithium nitride halides
from the elements can be calculated from the decomposition
potentials given a knowledge of the ternary phase diagrams
Li-N-X. Applying the experimental result that all ternary
compounds are in equilibrium with nitrogen and no other
chlorides and iodides occur, the values listed in Table 1 were
obtained. Measurement of the specific heat of Li, xNo4Clo6
gave the standard enthalpy as P ( 2 9 8 K ) - Ho(OK)=9.57
kJ/mol.
Experimental
The lithium nitride chlorides were produced by annealing
tablets pressed from a mixture of finely ground Li3NL4]
and
LiCl [Fluka AG] for 48 hours at 450°C under Nz; the lithium nitride bromides and iodides were prepared analogously by annealing at 300 “C or by 3 hours’ fusion of the binary compounds in tungsten vessels. The conductivity was
determined by AC measurements over the frequency range
of 1 Hz to 150 kHz. The frequency dependence could be analyzed by way of Debye equivalent circuits. The electronic
partial conductivities were determined with DC by blocking
the ion flux with molybdenum electrodes.
Received: September 26. 1979 [Z 375 IE]
German version: Angew. Chem. Y2. 72 (1980)
H. Salllegger, H. Hahn, Naturwissenschaften 51, 534 (1964); Z. Anorg. Allg.
Chem. 379, 293 (1970).
P. Hartwig. W. Weppner, W Wickelhaus. Mater. Res. Bull. 14. 493 (1979)
P. Hartwig, W. Weppner, W Wichelhaus, A. Rabenau, Solid State Commun.
30.601 (1979).
E. Schonherr, G. Muller, E. Winkler, 1. Cryst. Growth 43, 469 (1978).
I. Barm, 0. Knacke: Therrnochemical Properties of Inorganrc Substances.
1973, and I. Barin, 0. Knacke, 0.Kubaschewski: Supplement 1977 SpringerVerlag, Berlin; Verlag Stahleisen. Diisseldorf.
BOOK R E V I E W S
Strained Organic Molecules. By A . Greenberg and J. F. Liebman. Organic Chemistry. A Series of Monographs. Vol. 38.
Academic Press, New York 1978. xi, 406 pages. Bound,
$41.50.
This is a long-awaited book. There has been no monograph on this subject since A . uon Baeyer coined the term
“strain” for angle deformations relative to the tetrahedral arrangement at carbon. The volume and the variety of the material collected is overwhelming; the huge number of strained
compounds being scarcely conceivable.
In accordance with the authors’ claim of aiming somewhere between a textbook for advanced students and a monograph focused on a special field, one would expect a clear
taxonomy of strained compounds from thermodynamic and
kinetic points of view, and portrayal (with examples) of the
types, causes, and chemical consequences of strain.
To be perfectly honest, the book does not live up to all
these expectations. For example, thermodynamic and kinetic
stability are not discussed until the penultimate chapter,
though the lability of many strained compounds is referred
to much earlier. Stability and instability are discussed in
terms of thermochemical concepts-and it is clear that conformational enthalpy differences have been ignored-yet
one becomes suspicious, if the dissociation enthalpy
CH,+CH;+H’ is used as a basis and hence methane
would have 19 kcal/mol of strain. The unsolved problem of
the mean bond enthalpy of a C- -H bond is dealt with by reference to the difference in the bond energy (dissociation energy) in methane and toluene. Not all readers will agree with
a choice of bond and group increments according to which
ethylene and tetrafuoroethylene become strained compounds. Also, one has to get accustomed to the conclusion
that conjugative destabilization of anti-aromatic annulenes
amounts to strain.
Angew. Chem. Int. Ed. Engi. 19 (1980) No. I
The report about the tranformations of strained carbocycles under the influence of transition metals is undoubtedly of
great interest. Other current topics touching upon our concepts of bonding and reactivity in general are only indicated:
the slow isomerization of prismane in solution may be a forbidden reaction according to the Woodward-Hoffmann
rules, but the substance itself is explosive; cyclopropene has a
short and thus stable double bond, but it is highly strained
and reactive as a dienophile; the influence of fluorine substituents on stability and lability; lithium as a “strain-reducing’’
substituent on a carbon atom; and the significance of steric
hindrance for the properties of strained compounds. The importance of quantum-chemical results is not always clearly
recognizable. A sentence such as “Calculational evidence
supporting the intermediacy of ...” (p. 287) is unlikely to
find undivided agreement.
While the book hardly offers a modern treatment of “The
present state of strain theory”[’], it contains what is promised
in the title-a comprehensive catalog of strained and labile
organic compounds.
Reinhart Keese [NB 485 IE]
Luminescence Spectroscopy. Edited by M . D. Lumb. Academic Press, New York 1978. ix, 375 pp., bound, $ 49.75.
The book consists of five independent contributions: 1)
Inorganic Luminescence (G. F. Zmbush, 92 pp.), 2) Organic
Luminescence (M. D. Lumb, 56 pp.), 3) Luminescence Instrumentation (T. D. s. Hamilton, I. H . Munroe, G. Walker,
90 pp.), 4) Magnetic Effects in Organic Molecular Spectroscopy ( N . E. Geacintov, C.E. Swenberg, 60 pp.), 5) Magnetooptical Investigations of Recombination Radiation in Inorganic Crystals (B. C. Cavenett, 70 pp.).
[‘I
W. Huckel, Fortschr. Chem., Phys.. Phys. Chem. 19 (4). 1 (1927)
75
Документ
Категория
Без категории
Просмотров
1
Размер файла
141 Кб
Теги
liebman, book, greenberg, organiz, molecules, review, strained
1/--страниц
Пожаловаться на содержимое документа