The ' Variable Electronegativity ' Method. III. The Pyrrole Anion and Electronegativity Reversal

1959 ◽  
Vol 12 (3) ◽  
pp. 330 ◽  
Author(s):  
RD Brown ◽  
ML Heffernan
Keyword(s):  
Electron Density ◽  
Electron Distribution ◽  
Ionization Potentials ◽  
Alternative Methods ◽  
Electron Densities ◽  
Tertiary Nitrogen

The π-electron distribution in the pyrrole anion has been evaluated by the VESCF method using two alternative methods of estimating core attraction terms. The results indicate that the π-electron distribution around the conjugated system is very nearly uniform, supporting previous speculations that the relative attracting powers of tertiary nitrogen and carbon reverse when their π-electron densities exceed a certain value, suspected to be not too much greater than unity. The present calculations indicate that the critical π-electron density is around 1.2. The VESCF estimates of ionization potentials of the pyrrole anion are also reported.

The Variable Electronegativity Method. VII. Pyrazole, Its Anion and Cation

1960 ◽  
Vol 13 (1) ◽  
pp. 49 ◽  
Author(s):  
RD Brown ◽  
ML Heffernan
Keyword(s):  
Dipole Moment ◽  
Electron Distribution ◽  
Nitrogen Heterocycles ◽  
Chemical Properties ◽  
Membered Ring ◽  
Matrix Elements ◽  
Electron Densities ◽  
Ring Nitrogen ◽  
Made In ◽  
Tertiary Nitrogen

Results of a VESCF treatment of pyrazole, its anion, and cation are reported. A comparison is made of the chemical properties of pyrazole and those predicted from the calculated π-electron densities. An ambiguity in the comparison owing to the rapid tautomerization of pyrazole is emphasized. The calculated π-electron distribution in the anion supports the suggestion made in previous papers that the relative electronegativities of carbon and tertiary nitrogen reverse when their π-electron densities exceed 1.2. The dipole moment is predicted to be about 2.5 D for pyrazole, in agreement with observations in solution. Theoretical values of ionization potentials are also presented. An analysis is made of VESCF matrix elements and some empirical guides as to suitable values of coulomb and resonance parameters for five-membered ring nitrogen heterocycles are suggested.

scholarly journals Die zeitliche Änderung der radialen Elektronendichteverteilung beim Theta-Pinch

1963 ◽  
Vol 18 (8-9) ◽  
pp. 895-900
Author(s):  
Franz Peter Küpper
Keyword(s):  
Density Distribution ◽  
Electron Density ◽  
Electron Density Distribution ◽  
Electron Distribution ◽  
Radial Symmetry ◽  
Zero Order ◽  
Time Interval ◽  
Interferometric Method ◽  
Density Distributions ◽  
Theta Pinch

In a θ-pinch the radial symmetry of the electron density distribution as a function of time has been measured by a MACH—ZEHNDER interferometer. In a time interval of 400 nsec during a discharge an image converter made three pictures (exposure times of 10 nsec each) . Up to 100 nsec after the first compression, the experimental results show different density distributions for the cases of trapped parallel and antiparallel magnetic fields. Complete radial symmetry of the electron density distribution was not found.Another interferometric method for measuring the radial symmetry of the electron distribution by observing “zero order” fringes is described.

scholarly journals ELECTRON DENSITY STUDIES ON THE REGIOSELECTIVITY OF DEPROTONATION REACTIONS

2014 ◽  
Vol 70 (a1) ◽  
pp. C287-C287
Author(s):  
Juan Van der Maelen ◽  
Javier Cabeza
Keyword(s):  
Electron Density ◽  
Theoretical Calculations ◽  
Density Ratio ◽  
Atomic Charge ◽  
Heterocyclic Ring ◽  
Bond Critical Point ◽  
Electron Densities ◽  
Total Energy Density ◽  
Topological Parameters ◽  
Alkyl Groups

The C-alkyl groups of cationic triruthenium cluster complexes of the type [Ru3(µ-H)(µ-κ2N1,C2-EtnMemPyHk)(CO)10]+ (EtnMemPyHk represents a generic C-alkyl-N-methyl-pyrazium species) have been deprotonated to give kinetic products that contain unprecedented C-alkylidene derivatives and maintain the original edge-bridged decacarbonyl structure. When the starting complexes contain various C-alkyl groups, the selectivity of these deprotonation reactions is related to the atomic charges of the alkyl H atoms, as suggested by DFT/natural-bond orbital (NBO) calculations. Three additional electronic properties of the C-alkyl C-H bonds have also been found to correlate with the experimental regioselectivity since, in all cases, the deprotonated C-H bond has the smallest electron density at the bond critical point (bcp), the greatest Laplacian of the electron density at the bcp, and the greatest total energy density ratio at the bcp (computed by using the quantum theory of atoms in molecules, QTAIM). The kinetic decacarbonyl products evolve, under appropriate reaction conditions that depend upon the position of the C-alkylidene group in the heterocyclic ring, towards face-capped nonacarbonyl derivatives (thermodynamic products). Theoretical calculations support the proposal that the selectivity of these deprotonation reactions is primarily determined by the atomic charge of the alkyl H atoms: the higher the charge the easier the deprotonation when the starting complexes contain various C-alkyl groups. On the other hand, although QTAIM results have been obtained here only from theoretical electron densities for the above clusters, comparisons with local and integral topological parameters derived from both experimental and theoretical electron densities for the related triruthenium complex [Ru3(μ-H)2(μ3-MeImCH)(CO)9] (Me2Im = 1,3-dimethylimidazol-2-ylidene) may easily be made.

Anion–π interactions and positive electrostatic potentials of N-heterocycles arise from the positions of the nuclei, not changes in the π-electron distribution

2014 ◽  
Vol 50 (76) ◽  
pp. 11118-11121 ◽  
Author(s):  
Steven E. Wheeler ◽  
Jacob W. G. Bloom
Keyword(s):  
Electron Density ◽  
Electron Distribution ◽  
Electrostatic Potentials ◽  
Anion Binding ◽  
Π Interactions

The positive ESPs that underlie anion-binding by N-heterocycles do not stem from a depletion of π-electron density, as widely assumed.

scholarly journals The Galactic Electron Distribution from a Pulsar Survey

1974 ◽  
Vol 60 ◽  
pp. 87-95 ◽  
Author(s):  
A. G. Lyne
Keyword(s):  
Electron Density ◽  
Electron Distribution ◽  
Statistical Study ◽  
High Sensitivity ◽  
Upper Limit ◽  
The Mean

The recent high-sensitivity pulsar survey at Jodrell Bank has allowed a statistical study of more distant objects. The longitude distribution suggests that many of the pulsars observed have distances greater than 5 kpc, leading to an upper limit of about 0.03 cm-3 for the mean electron density. The electron density averaged over distances of a few hundred parsecs seems to be very constant. The width of the electron distribution in the z-direction appears to be greater than about 600 pc.

A Sporadic Third Layer in the Ionosphere of Mars

Science ◽  
2005 ◽  
Vol 310 (5749) ◽  
pp. 837-839 ◽  
Author(s):  
M. Pätzold ◽  
S. Tellmann ◽  
B. Häusler ◽  
D. Hinson ◽  
R. Schaa ◽  
...  
Keyword(s):  
Electron Density ◽  
Charge Exchange ◽  
Layer Structure ◽  
Electron Densities ◽  
Ionospheric Layer ◽  
Density Profiles ◽  
Mars Express ◽  
Radio Science ◽  
Martian Ionosphere ◽  
Electron Density Profiles

The daytime martian ionosphere has been observed as a two-layer structure with electron densities that peak at altitudes between about 110 and 130 kilometers. The Mars Express Orbiter Radio Science Experiment on the European Mars Express spacecraft observed, in 10 out of 120 electron density profiles, a third ionospheric layer at altitude ranges of 65 to 110 kilometers, where electron densities, on average, peaked at 0.8 × 1010 per cubic meter. Such a layer has been predicted to be permanent and continuous. Its origin has been attributed to ablation of meteors and charge exchange of magnesium and iron. Our observations imply that this layer is present sporadically and locally.

scholarly journals Mechanisms of the electron density depletion in the SAR arc region

1996 ◽  
Vol 14 (2) ◽  
pp. 211-221 ◽  
Author(s):  
A. V. Pavlov
Keyword(s):  
Electric Field ◽  
Magnetic Storm ◽  
Electron Density ◽  
Drift Velocity ◽  
Recovery Phase ◽  
Electron Densities ◽  
Model Framework ◽  
Vibrationally Excited ◽  
Plasma Drift ◽  
Excited Nitrogen

Abstract. This study compares the measurements of electron density and temperature and the integral airglow intensity at 630 nm in the SAR arc region and slightly south of this (obtained by the Isis 2 spacecraft during the 18 December 1971 magnetic storm), with the model results obtained using the time dependent one-dimensional mathematical model of the Earth\\'s ionosphere and plasmasphere. The explicit expression in the third Enskog approximation for the electron thermal conductivity coefficient in the multicomponent mixture of ionized gases and a simplified calculation method for this coefficient presents an opportunity to calculate more exactly the electron temperature and density and 630 nm emission within SAR arc region are used in the model. Collisions between N2 and hot thermal electrons in the SAR arc region produce vibrationally excited nitrogen molecules. It appears that the loss rate of O+(4S) due to reactions with the vibrationally excited nitrogen is enough to explain electron density depression by a factor of two at F-region heights and the topside ionosphere density variations within the SAR arc if the erosion of plasma within geomagnetic field tubes, during the main phase of the geomagnetic storm and subsequent filling of geomagnetic tubes during the recovery phase, are considered. To explain the disagreement by a factor 1.5 between the observed and modeled SAR arc electron densities an additional plasma drift velocity ~–30 m s–1 in the ion continuity equations is needed during the recovery phase. This additional plasma drift velocity is likely caused by the transition from convecting to corotating flux tubes on the equatorward wall of the trough. The electron densities and temperatures and 630 nm integral intensity at the SAR arc and slightly south of this region as measured for the 18 December 1971 magnetic storm were correctly described by the model without perpendicular electric fields. Within this model framework the effect of the perpendicular electric field ~100 mv m–1 with a duration ~1 h on the SAR arc electron density profiles was found to be large. However, this effect is small if ~1–2 h have passed after the electric field was set equal to zero.

Zur Beziehung von Struktur und Reaktivität cyclischer CH-acider Verbindungen bei der Kondensation mit Orthoameisensäuretriäthylester.

1976 ◽  
Vol 31 (1) ◽  
pp. 95-98 ◽  
Author(s):  
Otto S. Wolfbeis ◽  
H. Junek
Keyword(s):  
Carbon Atom ◽  
Electron Density ◽  
Type A ◽  
Electron Densities ◽  
Active Compounds ◽  
Theoretical Concepts

Condensation of triethylorthoformate with cyclic methylene-active compounds gives rise to ethoxymethylene-, bismethenyl- or triscompounds of type A, B or C resp. An explanation of this different behavior can be obtained by comparing the π-electron densities at the β-carbon atom of the exocyclic double blond of ethoxymethylen- and bismethenyl-compounds, which are calculated using HMO-theory. These calculationes show a limiting electron density, which can be used to explain the lack of further reaction to bis- and triscompounds, when certain heterocyclic active methylenes are used.Reactions of some heterocyclic diketones have been studied and, their behavior found in agreement with theoretical concepts

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