Atomic and group electronegativities from the electron-density distributions of molecules

Boyd, Russell J.; Edgecombe, Kenneth E.

doi:10.1021/ja00221a014

Cited by 130 publications

(83 citation statements)

References 2 publications

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“…This may be due to the decrease in charge concentration at the bond critical point, so r c has more freedom to move. Boyd et al 19 already showed that (r c ) increases monotonically within each period of the periodic table as the atomic number increases. It can be thus understood that d(r c )/dF decreases along the period.…”

Section: Analysis Of the Bond Critical Point Of Hf And Other Hydridesmentioning

confidence: 94%

A quantum molecular similarity analysis of changes in molecular electron density caused by basis set flotation and electric field application

Simon

Duran

1997

The Journal of Chemical Physics

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Quantum molecular similarity ͑QMS͒ techniques are used to assess the response of the electron density of various small molecules to application of a static, uniform electric field. Likewise, QMS is used to analyze the changes in electron density generated by the process of floating a basis set. The results obtained show an interrelation between the floating process, the optimum geometry, and the presence of an external field. Cases involving the Le Chatelier principle are discussed, and an insight on the changes of bond critical point properties, self-similarity values and density differences is performed.

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Section: Analysis Of the Bond Critical Point Of Hf And Other Hydridesmentioning

confidence: 94%

A quantum molecular similarity analysis of changes in molecular electron density caused by basis set flotation and electric field application

Simon

Duran

1997

The Journal of Chemical Physics

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“…These have the maximum magnitude3 of 6~9 0 as -1.34 Hz, as compared to -1.22 Hz for toluene (17). Another estimate of 6J90 for benzyl silane may be had from the general recent agreement that the Si(CH3), and SiH3 groups are less electronegative than hydrogen (23)(24)(25) To within experimental error, these apparent twofold barriers are the same as those deduced for benzyl trimethysilane (10). It has been suggested that, for analogous tin compounds, methyl substituents should increase, and chlorine substituents decrease, the extent of hyperconjugation (12).…”

Section: Spectral Analysesmentioning

confidence: 95%

Theoretical and experimental approaches to the barrier to rotation about the Csp²—Csp³ bond in benzyl silane. Hyperconjugative stabilization of the perpendicular conformation

Schaefer¹,

Sebastian²,

Penner³

1991

Can. J. Chem.

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. Can. J. Chem. 69,496 (1991). The 'H nuclear magnetic resonance spectra of benzyl silane and benzyl trichlorosilane, obtained in CS2 and benzene-d6 solutions, are analyzed. The long-range coupling constants between the methylene and para ring protons are used to derive apparent twofold barriers about the Csp2-Csp3 bonds of 7.4 2 1.6 and 8.1 + 1.1 kJ/mol for the silane and the trichlorosilane, respectively. These are higher than that for ethylbenzene and are attributed mainly to the stabilization of the perpendicular conformer, that with the C-Si bond in a plane perpendicular to the phenyl plane, by u-IT conjugation (hyperconjugation) of the C-Si bond and the IT electron system. Molecular orbital computations confirm the predominantly twofold nature of the internal barrier in benzyl silane and also for benzyl germane and stannane. The calculated barriers for the silane derivatives are rather higher than the experimental values. The computed barriers have magnitudes that appear to change with X in much the same order as do the hyperconjugative interactions deduced in other ways for CH2X(CH3)3 groups (X = Sn, Ge, Si, C). The angles CCX in benzyl-X (X = CH3, SiH3, SiC13, GeH3, SnH3) are all computed to decrease smoothly as sin2$, where $ is the angle by which the C-X bond twists out of the phenyl plane.Key words: conformations, benzyl silane and trichlorosilane; NMR, benzyl silane and trichlorosilane; MO calculations, benzyl silane and trichlorosilane. Des calculs d'orbitales molCculaires confirment la nature principalement binaire de la barrikre interne dans le benzyl silane ainsi que dans les benzyl germane et stannane. Les barrikres calculCs pour les dCrivCs silanes sont sensiblement plus hautes que les valeurs expCrimentales. La variation des amplitudes des barrikres calculCes pour les dCrivCs silanes avec X semble suivre l'ordre des interactions d'hyperconjugaison dCduites sur d'autres bases pour les groupements CH2X(CH3), (X = Sn, Ge, Si, C). Les calculs indiquent que les angles CCX, des benzyl-X (X = CH3, SiH3, SiC13, GeH3 et SnH,), doivent diminuer doucement comme le sin2$, oh IJJ est l'angle que fait la liaison C-X avec le plan du noyau phCnyle.

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“…The last column in Table 4 contains Si electronegativities estimated by the expression (Boyd & Edgecombe, 1988; …”

Section: Electronegativity and Bcp Propertiesmentioning

confidence: 99%

Electron-density distribution in stishovite, SiO₂: a new high-energy synchrotron-radiation study

et al. 2001

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The electron-density distribution of the high-pressure polymorph of SiO 2 , stishovite [a = 4.177 (1) , c = 2.6655 (5) A Ê , space group P4 2 amnm, Z = 2], has been redetermined by single-crystal diffractometry using synchrotron radiation of 100.42 and 30.99 keV, respectively, in order to obtain essentially absorptionand extinction-free data. Room-temperature diffraction experiments on two samples of irregular shape were carried out on two different diffractometers installed at HASYLAB/DESY, Hamburg, Germany. The structure re®nement on the high-energy data converged at R(F ) = 0.0047, wR(F ) = 0.0038, GoF = 0.78, for a multipole model with neutral atoms and multipole expansions up to seventh order. For each atom, the radial expansion coef®cients of the multipole orders (l > 0) were constrained to a common value. The absence of extinction was indicated by a re®ned correction parameter equalling zero within error limit. The excellent quality of the data is also illustrated by a high-order (HO) re®nement (s > 0.7 A Ê À1 ) yielding R(F ) = 0.0060, wR(F) = 0.0048, GoF = 0.85. Both static deformation electron-density distribution and structure amplitudes compare well with corresponding results obtained from band-structure calculations using the linearized-augmented-plane-wave (LAPW) method. Ensuing topological analysis of the total model electron density distribution revealed bond critical point properties for the two unique SiÐO bonds, indicating a predominantly closed-shell interaction mixed with a signi®cant shared interaction contribution that decreases with increasing interatomic distance. Calculation of atomic basins yielded charges of +3.39 e and À1.69 e for Si and O, respectively, in good agreement with the theoretically calculated values of +3.30 e and À1.65 e. The volumina of the Si and O basins are 2.32 and 10.48 A Ê 3 , corresponding to spheres with radii of 0.82 and 1.36 A Ê , respectively. The results also conform well with correlations between bond length and bond critical point properties reported in the literature for geometry-optimized hydroxyacid molecules. Estimates of the Si cation electronegativity indicate that the change of Si coordination by oxygen from 4 to 6 is accompanied by an increase of the ionicity of the SiÐO bond of about 7%.

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Atomic and group electronegativities from the electron-density distributions of molecules

Cited by 130 publications

References 2 publications

A quantum molecular similarity analysis of changes in molecular electron density caused by basis set flotation and electric field application

A quantum molecular similarity analysis of changes in molecular electron density caused by basis set flotation and electric field application

Theoretical and experimental approaches to the barrier to rotation about the Csp²—Csp³ bond in benzyl silane. Hyperconjugative stabilization of the perpendicular conformation

Electron-density distribution in stishovite, SiO₂: a new high-energy synchrotron-radiation study

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Atomic and group electronegativities from the electron-density distributions of molecules

Cited by 130 publications

References 2 publications

A quantum molecular similarity analysis of changes in molecular electron density caused by basis set flotation and electric field application

A quantum molecular similarity analysis of changes in molecular electron density caused by basis set flotation and electric field application

Theoretical and experimental approaches to the barrier to rotation about the Csp2—Csp3 bond in benzyl silane. Hyperconjugative stabilization of the perpendicular conformation

Electron-density distribution in stishovite, SiO2: a new high-energy synchrotron-radiation study

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Theoretical and experimental approaches to the barrier to rotation about the Csp²—Csp³ bond in benzyl silane. Hyperconjugative stabilization of the perpendicular conformation

Electron-density distribution in stishovite, SiO₂: a new high-energy synchrotron-radiation study