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Determination of the Electron Distribution in Solids by X-Rays and its Relation to Chemical Bonding.

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Cleavage of the Pyrimidine Ring with Amines
and Hydrazines
By Prof. Dr. H. Bredereck, Dr. F. Effenberger,
and Dip1.-Chem. W. Resemann
Institut fur Organische Chemie und Organisch-chemische
Technologie derTechnischen Hochschule Stuttgart (Germany)
In the reaction with aniline (R=phenyl), NJV"'dipheny1formamidine was isolated as well as the pyrazolone derivative
(I). 2-Substituted 3-mercaptopyrazolo-[3,4d]-pyrimidinesare
also cleaved, forming the corresponding pyrazolonethiones.
Reactions with hydrazines lead to (11) or (111) depending on
the conditions and the hydrazine derivative used. This novel
cleavage reaction can even be applied to simple pyrimidines.
In the course of our investigations of the heterocyclic series,
we found a new reaction, which, according to our experiences
so far, has general applicability. 2-Substituted 3-hydroxypyrazolo-[3.4d]-pyrimidines[ l ] react with amines and
Whether (IV) or (V) is formed depends only on the arnine.
Aniline (R'=phenyl) yields (1%') ;bemylamine (R'=C~HSCH~)
yields or).
The structural prerequisites for this cleavage reaction are the
topic of further investigations.
E. C . Taylor [2] has reported the cleavage of pteridines by
means of amines and hydrazines.
Received, March 14th. 1962
hydrazines under very mild conditions, evolving ammonia.
Thus, the pyrimidine ring is opened and undergoes partial
237166 IE]
[I] H. Bredereck, F. Effenberger, and W. Resemann, Chem. Ber.,
in the press.
[2] E. C. Taylor, J. Amer chern. SOC.74, 1651 (1952).
H . Witte, Darmstadt (Germany)
larger, while those of ths anions are much smaller. Thus, in
NaCl, the value for Na+ is 0.98 A according to Goldschmidt,
and 0.95 A according to Pauling. The value of 1.19 A,
obtained by Fumi and Tosi, who used Born's approximations, however, agrees well with our own values.
The distribution of the valence electrons particularly influences the diffraction pattern at small and medium glancing
angles. It is, therefore, important to measure such diffraction
intensities as accurately as possible. By means of a combination of measurements on single crystals and on powders
it has, in most cases, been possible to obtain absolute values
for structure amplitudes with an accuracy of about 1 %. By
avoidance of termination effects, Fourier series have been
used to calculate electron distributions along those planes
which permit conclusions concerning the bonding conditions.
Fourier series were also applied to the errors of the structure amplitudes so that both the value of the electron density
and the measurement error function could be reported.
Only in the case of aluminum was no deviation from the
spherically symmetrical charge distribution observed. (The
virtually constant electron density of 0.2 el/A3 between the
ions is in approximate agreement with the expected value of
3 conducting electrons/atom.)
Valence electron distribution strongly influences some reflections in diamond and silicon and, at the same time, the "forbidden'' reflection (222). The same systematic deviations
from the theoretical values of the structure amplitudes have
been found in both substances. (The theoretical values were
calculated according to the method of Hartree on the basis
of a spherically symmetrical charge distribution of free
atoms.) These deviations can be detected in the whole
temperature range between -170 "C and +450 "C.
Determinationof the Electron Distributionin Solids
by X-Rays and its Relation to Chemical Bonding
The deviations from spherical symmetry due to bonding in
NaCl, LiF, and CaFz have little effect on the intensity of the
X-ray reflections. The deviations found are not substantially
larger than the error function. Characteristic for these materials is the bridging between the CI--ions in NaCl or the
F--ions in LiF and CaF2 in which the electron density is
reduced to 0.2 eI/A3. There exists in NaCl an area between
Na+ and C1- which is virtually free of any charge. On the
other hand, the electron densities between Li+ and F- in
LiF and Ca2+ and F- in CaF2 never fall to zero.
If the distances between the points of minimum electron
density on the line joining the cations and anions are compared with the conventional radii according to Goldschmidt
and Pauling, the radii of the cations, thus defined, are much
Angew. Chem. internat. Edit. / VoI. I (19621 / No. 4
All of these deviations cause an increase in electron density
between neighboring atoms. At the midpoint of the line
joining the two atoms values of 1.70 el/A3 for diamond and
0.65 el/A3 for silicon have been found (calculated: 1.16 el/A3,
and 0.35 el/A3, respectively). The density values between
neighboring atoms are virtually independent of temperature.
The experimentally determined electron distribution between
neighboring atoms agrees well with that calculated on a wave
mechanical basis by Ewald and Honl (calculated: 1.50 el/A3,
measured: 1.70 el/&).
[Chemische Gesellschaft zu Heidelberg (German)),
January 23rd. 19621.
[VB 566/19 IE]
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bonding, solids, distributions, chemical, relations, rays, determination, electro
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