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New Types of Low Molecular-Weight Heterosiloxanes.

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New Types of Low Molecular-Weight
Heterosiloxanes
H . Schmidbaur, Marburg (Germany)
Low molecular-weight model substances of well-defined composition were prepared for the first time in connection with an
investigation of the principles of structure and bonding in heterosiloxanes. Examples of such compounds are RiSiOXR:,
(RiSi0)2XR$ (R:Si0)3XR2, and (RiSi0)dX. where X = Si,
Ge, Sn, or Pb, R1 = CH3 or CzHs, and R2 = CH3, C2H5, etc.
Specific heterolytic cleavage reactions with Lewis acids or
nucleophilic reagents, as well as infrared and N M R
spectrosopic examinations carried out on such heterosiloxanes have shown that, within the Si-q-Xgrouping, the
X-0- bond invariably possesses the greater polarity and the
lower proportion of x-bond character. In particular, the regular changes in the chemical shifts and the coupling constants
of the N M R spectra demonstrate that this polarization is in
--
n-
accordance with +Si-O+Xt
and increases regularly in the
order X = Si < G e < Sn < Pb. This result is thus in contradiciton to the assumption that the electronegativities of these
elements alternate [I]. The N M R spectra have particularly
high numbers of peaks as a result of the presence of the magnetically active isotopes IH, 13C, 29Si, 117Sn, 119Sn, and 207Pb.
Heterosiloxanes of the trivalent elements of group V of the
periodic table, which are of the general type RiSiOYRg
(Y = P, As, or Sb) with a lone pair of electrons o n the heteroatom, are very sensitive to hydrolysis and oxidation and
belong to the thermally least stable types of heterosiloxanes. Derivatives of the same elements in the pentavalent
state [RiSiOYR: and (R:Si0)2YR$] o n the other hand exhibit
high thermal stability (in particular if Y = Sb).
Heterosiloxanes of the elements of group 111, RjSiOZRg
(2= A1 orGa), with a n electron deficiency on the hetero-atom
occur exclusively in the dimeric form. The planar four-membered ring systems ( I ) exhibit comparatively high thermal and
chemical stability on account of the stabilization which is
possible with this arrangement.
[Inorganic Chemistry Colloquium, Universitat Marburg
(Germany), December 13th, 1963, and Technische Hochschule
Aachen (Germany), November 19th, 19631 [“B 769/114 IE]
German version: Angew. Chem. 76, 234 (1964)
This system is the aliphatic analogue of a quinone/hydroquinone equilibrium for which the high stability of the semiquinone stage is characteristic. Treatment of PyH with 4
moles of T C N E in acetonitrile and subsequent dilution with
water yield crystalline pyridinium pentacyanopropenide ( I )
in approx. 90 % yield.
~ c o N H NC,
2
I
K
1. Dihydropyridines and Tetracynnoethylene: Reduced diphosphopyridine nucleotide (DPNH) and model compounds
(PyH) reduce tetracyanoethylene (TCNE) to the radical
anion TCNE-Q, which can be detected and determined
quantitatively by its characteristic “coxcomb spectrum”,
which contains twelve maxima between 350 and 500 mp. The
intensity of this absorption depends upon the apparent redox
potential of the corresponding P y @ PyH system [2]. The
transient deep coloration which occurs on mixing PyH with
TCNE can be explained by the formation of a charge-transfer complex. The reduction to a radical is interpreted as a
hydride-ion transfer. This leads to TCNEHQ, which equilibrates with TCNE.
+
TCNEHe -i TCNE
+
2 TCNE.3
+ Ha
-~
[I] Cf. also H.Schtnidbaur,Lecturedelivered at the VII. European
Congress on Molecular Spectroscopy, Budapest 1963, Abstract
“2’
=z
C
,
C-CO
N
LN ‘CN
(1)
2. Cynnoyuinones: Of the six possible cyano-substituted
benzoquinones, the compounds (2)-(6), where X = C1, Br,
I, OH, or OR, were synthetized. The electron affinity of the
halogeno- or hydrogeno-substituted compounds increases
with increasing substitution by C N ; the dissociation of the
hydroxylated quinones and hydroquinones increases correspondingly.
3. Cvanoarenes: Similar changes in the physical properties
are found with increasing substitution of the benzene ring
with cyano groups. Pentacyanotoluene shows high C-H
acidity; it forms a deep blue anion which is unstable in the
presence of water. The pyrene complexes of tetracyanom-xylene, pentacyanotoluene, and hexacyanobenzene [3] are
yellow, red, and blue-green, respectively (color of solution in
acetonitrile). In a differential thermoanalysis, hexacyanobenzene was found to be stable up to 475OC. It sublimes
rapidly without decomposition at this temperature.
[Organic Chemistry Colloquium, Universitat Basel
(Switzerland), November 29th, 19631
[VB 772/115 IE]
German version: Angew. Chem. 76, 275 (1964)
Electron Spin Resonance Measurements on
Irradiated Bacteriophages and Their Nucleic Acids
Recent Developments in Cyanocarbon Chemistry
K. Wallenfels, Freiburg/Breisgau (Germany); experimental
work with G . Bachmnnn, H . Diekmnnn, K. Friedrich, D . Hofmann, and R. Kern
c
A. Miiller, Karlsruhe (Germany)
Bacteriophages are particularly suitable for studying radiation damage because of their primitive organization, high
nucleic-acid content, and great sensitivity to radiation. Radicals were produced in dry bacteriophages and nucleic acid
prepared therefrom, by irradiation with X-rays (50 kr/min) or
y-rays (6OCo; 10 krep/min) and examined qualitatively and
quantitatively by means of their ESR absorption spectra; the
results were compared with measurements on phage proteins
and nucleic-acid components (nucleotides, nucleosides, free
bases).
I n whole phages of strains T I and T 2 , radicals which show
different ESR-spectral types are produced in high yield (G =
2-10) by irradiation. Radicals are formed in comparable
yield from T Z p h a g e nucleic acids and give ESR spectra
which correspond to those observed in whole phages. The
radical concentration in irradiated phage nucleic acid increases with dose according t o a n exponential function up to
a saturation value lying between 1018 and 1019 radicals/g
(63 % of the saturation concentration is reached after doses
of 0.4-1.4 Mr).
p. 86.
121 K . Wollenfels, H . Diekmann, and F. Kubowitz, Liebigs Ann.
Chem. 621, 174 (1959).
Angew. Cliem. internat. Edit. / VGI.3 (1964)
1 No. 3
[3] K . Wollenfels and K. Friedrich, Tetrahedron Letters 1963,
1223.
24 1
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