On partitioning the overlap charge density in self‐consistent charge molecular‐orbital calculations

Hillier, Ian H.; Wyatt, J. F.

doi:10.1002/qua.560030110

Cited by 18 publications

(1 citation statement)

References 14 publications

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“…For the purpose of quantifying the double (multiple)-bond character of the CF + bond, we investigated 16 F-substituted carbocations (1-16, Scheme 1) and compared them with some typical CF single bonds in neutral molecules (17)(18)(19). We also included fluoronium ions 20-23 that can be considered the result of a protonation or methylation of fluorides, which lead to divalent F with probably weak CF bonds.…”

Section: Isoelectronic C=fmentioning

confidence: 99%

Characterization of CF Bonds with Multiple‐Bond Character: Bond Lengths, Stretching Force Constants, and Bond Dissociation Energies

Kraka

2009

ChemPhysChem

107

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Isoelectronic C=F(+) and C=O bonds contained in fluoro-substituted carbenium ions, aldehydes, and ketones are investigated with regard to their bond properties by utilizing the vibrational spectra of these molecules. It is demonstrated that bond dissociation energies (BDEs), bond lengths, vibrational stretching frequencies, and bond densities are not reliable descriptors of the bond strength. The latter is related to the intrinsic BDE, which corresponds to nonrelaxed dissociation products retaining the electronic structure and geometry they have in the molecule. It is shown that the harmonic stretching force constants k(a) of the localized internal coordinate vibrations (adiabatic vibrational modes) reflect trends in the intrinsic BDEs. The k(a) values of both CO and CF bonds are related to the bond lengths through a single exponential function. This observation is used to derive a common bond order n for 46 CO- and CF-containing molecules that reliably describes differences in bonding. CF bonds in fluorinated carbenium ions possess bond orders between 1.3 and 1.7 as a result of significant pi back-bonding from F to C, which is sensitive to electronic effects caused by substituents at the carbenium center. Therefore, the strength of the C=F(+) bond can be used as a sensor for (hyper)conjugation and other electronic effects influencing the stability of the carbenium ion. The diatomic C=F(+) ion has a true double bond due to pi donation from the F atom. The characterization of CF bonds with the help of adiabatic stretching modes is also applied to fluoronium ions (n = 0.3-0.6) and transition states involving CF cleavage and HF elimination (n = 0.7-0.8).

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Section: Isoelectronic C=fmentioning

confidence: 99%

Characterization of CF Bonds with Multiple‐Bond Character: Bond Lengths, Stretching Force Constants, and Bond Dissociation Energies

Kraka

2009

ChemPhysChem

107

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Electronic Wavefunctions Analysis

Ciosłowski

1998

Encyclopedia of Computational Chemistry

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Self‐consistent pseudo‐eigenvalue equations in parametric charge‐dependent MO methods

Karlsson

1970

Int J of Quantum Chemistry

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Self-consistent pseudo-eigenvalue equations are explicitly derived for the iterative extended Hiickel method with use of the minimum-energy criterion. It is shown that inclusion of the overlap matrix in the iterative procedure gives equations that are too complicated for the simple model under consideration. An expression for the total energy is derived, and it is shown that if the eigenvalues of the pseudo-eigenvalue equations are interpreted as ionization potentials and electron affinities, then the empirical parameters of the Hamiltonian matrix must be reinterpreted. The connection with the Hartree-Fock equations is mentioned. I t is proposed that minimizing the energy in the VESCF method should be done in a manner similar to the one used in the iterative Huckel methods. Numerical applications to benzene and pyridine have been made.O n a obenu des equations aux valeurs propres "pseudo", auto-cohtrrntes pour la mtthode de Huckel generaliste ittrative B l'aide d u critere de minimum de I'energie. En incluant la matrice de recouvrement dans le proctdt ittratif on obtient des equations trop compliqutes pour le modtle simple en considtration. O n obtient une expression pour I'tnergie totale, et on montre que, si les valeurs propres sont interprttkes comme des potentiels d'ionisation et des afinitts tlectroniques, il est ntcessaire de rtinterprtter les paramttres empiriques de la matrice Hamiltonienne. O n propose de minimiser 1'Cnergie dans la methode VESCF avec le proctdt employe dans les mtthodes de Huckel gintralistes. On a fait des applications numtriques a u benzene et a u pyridine.Es werden "self-consistent," Pseudoeigenwertgleichungen fur die iterative verallgemeinerte Huckelmethode mit dem Minimumenergiekriterium hergeleitet. Es wird gezeigt, dass Einschliessung der Uberlappungsmatrix in dem Iterationsverfahren Gleichungen gibt, die zu kompliziert fur das betrachtete einfache Modell sind. Ein Ausdruck fur die Gesamtenergie wird hergeleitet, und es wird gezeigt, dass wenn die Eigenwerte der Pseudoeigenwertgleichungen als Ionisierungsspannungen und Elektronenaffinitaten interpretiert werden, mussen die empirischen Parameter der Harniltonschen Matrix wieder erklart werden. Es wird vorgeschlagen die Energieminimisierung in der v~s c~-M e t h o d e in derselben IVeise wie in den iterativen Huckelmethoden auszufuhren. Numerische h n nwendungen auf Benzol und Pyridin sind ausgefiihrt worden.

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On partitioning the overlap charge density in self‐consistent charge molecular‐orbital calculations

Cited by 18 publications

References 14 publications

Characterization of CF Bonds with Multiple‐Bond Character: Bond Lengths, Stretching Force Constants, and Bond Dissociation Energies

Characterization of CF Bonds with Multiple‐Bond Character: Bond Lengths, Stretching Force Constants, and Bond Dissociation Energies

Electronic Wavefunctions Analysis

Self‐consistent pseudo‐eigenvalue equations in parametric charge‐dependent MO methods

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