Experimental orbital momentum distributions and bonding interactions

Journal of Computational Chemistry, 2007

This paper first comments on the surprisingly poor status that Quantum Chemistry has offered to the fantastic intuition of Lewis concerning the distribution of the electrons in the molecule. Then, it advocates in favor of a hierarchical description of the molecular wave-function, distinguishing the physics taking place in the valence space (in the bond and between the bonds), and the dynamical correlation effects. It is argued that the clearest pictures of the valence electronic population combine two localized views, namely the bond (and lone pair) Molecular Orbitals and the Valence Bond decomposition of the wave-function, preferably in the orthogonal version directly accessible from the complete active space self consistent field method. Such a reading of the wave function enables one to understand the work of the nondynamical correlation as an enhancement of the weight of the low-energy VB components, i.e. as a better compromise between the electronic delocalization and the energetic preferences of the atoms. It is suggested that regarding the bond building, the leading dynamical correlation effect may be the dynamical polarization phenomenon. It is shown that most correlation effects do not destroy the bond electron pairs and remain compatible with Lewis' vision. A certain number of free epistemological considerations have been introduced in the development of the argument. q

Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy, 2015

In this theoretical work, the tetrahydroborate ion (BH4(-)) was used as proton acceptor in the formation of the YCC-H⋯BH4(-) complexes (Y=H, CH3, CCl3 and CF3). Using B3LYP/6-311++G(d,p) level of theory, the results of structure corroborate with the analyses of infrared spectra showing that the changes in the bond lengths are in good agreement with the frequency shifts of the HCC-H, H3CCC-H, Cl3CCC-H and F3CCC-H proton donors. Based on the calculations carried out by the Quantum Theory of Atoms in Molecules (QTAIM), the reductions of electronic density corroborate with the red shifts in the frequencies of the C-H bonds. In addition to that, the C-H bonds are polarized because the contributions of s orbital diminish whereas of p increase. In line with this, the variations on the atomic radii computed via QTAIM calculations show that carbon outweigh hydrogen as follows (ΔrC>ΔrH). This scenario is indirectly supported by the Bent's rule of the chemical bonding. Although the inte...

Ab initio calculations have been accomplished to study the cooperativity between the halogen bond and tetrel bond in the XCNF2COYCN (X = H, F, Cl, Br; Y = F, Cl, Br) complexes. F 2 CO at the same time plays the role of Lewis acid with the π -hole on the C atom and Lewis base with the O atom to participate in the tetrel bond and in halogen bond, respectively. According to the geometry survey, the effect of a tetrel bond on a halogen bond is more pronounced than that of a halogen bond on a tetrel bond and the intermolecular distances in the triads are always smaller than the corresponding values in the dyads. In all cases, the halogen bond and tetrel bond in the termolecular complexes are stronger compared with those in the bimolecular complexes. So, from the intermolecular distances, interaction energies and many-body interactions demonstrate that there is positive cooperativity between the halogen bond and tetrel bond. The molecular electrostatic potential, atoms in molecules and natural bond orbital methodologies are used to analyse the nature of interactions of the complexes.

Journal of Chemical Education, 1999

1. VSEPR Theory 2. Valence Bond theory (with hybridization) 3. Molecular Orbital Theory ( with molecualr orbitals)

The Journal of Physical Chemistry A, 2004

have been studied using valence bond theory (VB). The classic three-structure VB picture changes slightly to account for the increased importance of the VB configuration with both electrons on the donor fragment. When the effects of geometric distortion upon molecule formation are removed, the expected trends in bond energies emerge. Addition of electron-withdrawing (F) substitutents increases bond energy in H 3 N-BF 3 and decreases bond energy in F 3 N-BH 3 . Likewise, addition of electron-donating methyl groups (Me) decreases bond energy in H 3 N-BMe 3 and increases bond energy in Me 3 N-BH 3 . In addition, the effects of adding fluorines stepwise in the series H 3 N-BH 3 , H 3 N-BH 2 F, H 3 N-BHF 2 , H 3 N-BF 3 has been determined. Bond energies are due to the opposing factors of electron withdrawal due to the high fluorine electronegativity and donation into the N-B bonding region by F p lone pairs. VB weights obtained by the method of Chirgwin and Coulson were unstable for coordinate covalently bonded molecules whereas no such problems were found for inverse overlap weights. VB weights in conjunction with bond energy partitioning show that the coordinate covalent bonds studied herein are predominantly charge shift bonds which owe their stability to VB structure mixing rather than any one structure alone. †

Chemistry - A European Journal, 2010

Physical review, 1985

A zeroth-order wave function is constructed as an antisymmetrized product of two-electron group wave functions (geminals) expanded in disjunct but overlapping subspaces of basis orbitals. The geminals are obtained as exact solutions of the two-electron Schrodinger equations within the corresponding local basis sets, and thus give a fully correlated description of the two-electron chemical bonds coupled by inductive (Coulomb and exchange) effects, the latter being taken into account by an appropriate effective core operator. A second-quantized formulation [P. R. Surjan, Phys. Rev. A 30, 43 (1984)] is applied where the wave functions of the individual bonds are represented by appropriate composite particle creation operators. Individual chemical bonds thus correspond to Bose quasipartieles composed of two electrons. Second-order perturbation theory is used for calculating interbond delocalization and dispersion effects. The treatment is based on a biorthogonal formulation [I.

Chemical Physics, 1987

The Journal of Physical Chemistry A, 2010

Ab initio equation-of-motion coupled cluster (EOM-CCSD) one-bond spin-spin coupling constants 1 J(B-N), 1 J(B-H), and 1 J(B-F) have been evaluated for complexes X:BH n F 3-n with X ) N 2 , NCH, NCLi, H 2 CNH, NF 3 , and NH 3 , for n ) 0-3. These complexes can be classified as either covalent or van der Waals complexes, on the basis of their binding energies and B-N distances. 1 J(B-N) for covalent complexes varies significantly from -19 to +9 Hz, whereas 1 J(B-N) is less than 2 Hz for van der Waals complexes. An absolute value of 1 J(B-N) of 3 Hz or greater indicates that the complex is covalently bonded, but a small value of this coupling constant does not necessarily mean that it is a van der Waals complex, in view of the variation among these complexes found for 1 J(B-N) as a function of the B-N distance. Deformation of the boron acid upon complex formation and electron donation by the nitrogen base has opposing effects on both 1 J(B-H) and 1 J(B-F). These effects are relatively small in van der Waals complexes. In covalent complexes, electron donation has the dominant effect on 1 J(B-H), and on 1 J(B-F) in complexes with BH 2 F and BHF 2 , but acid deformation has the dominant effect on 1 J(B-F) in complexes with BF 3 . Values of both 1 J(B-H) and 1 J(B-F) reflect the van der Waals or covalent nature of the B-N bond.