Molecules bonding, hybridization description

The hybridization concept can also be applied to molecules containing double and triple bonds. The descriptive valence bond approach to the bonding in ethylene and... 

A crystal structure of FXe0S02F (see Ref. 42) showed the Xe-F bond to be shorter than in XeF2 but not as short as in the (Xe-F)" " salts, thus indicating an important contribution from the (FXe)" S03F canonical form, in a resonance hybrid description of the bonding in the molecule (see Ref. 45). 

A variant of the combined QM/MM approach introduces a hybrid description of the solute. The main motivation for the introduction of this additional approximation lies in computational costs. Combined QM/MM calculations are quite costly, even when all the possible simplifications are introduced in the QM part and in the MM interaction potentials. On the other hand, QM formulation is more reliable than an empirical potential function to describe chemical reactions which involve bond-formation and disruption processes. To temperate contrasting factors, i.e. the need for a QM description and the computational costs, one may resort to the well established fact that, in chemical reactions, the quantum bond-breaking and bond-forming processes are limited to a restricted portion of the molecular system, with the remainder playing an auxiliary role. Hence, it may be convenient to resort to hybrid descriptions, where the active part of the molecule is described at the QM level and the remainder via MM potentials. 

Ollier than 90°, makes the actual 0 value smaller than 90°. With the bond orbital description, the gauche conformation of XChUOH is predicted by simply requiring one hybrid lone pair of oxygen to be antipcriplanar to a x- specifying various conformations of low-symmetry molecules containing OH groups, we will find it convenient to adopt a bond orbital description. 

Application of valence bond theory to more complex molecules usually proceeds by writing as many plausible Lewis structures as possible which correspond to the correct molecular connectivity. Valence bond theory assumes that the actual molecule is a hybrid of these canonical forms. A mathematical description of the molecule, the molecular wave function, is given by the sum of the products of the individual wave functions and weighting factors proportional to the contribution of the canonical forms to the overall structure. As a simple example, the hydrogen chloride molecule would be considered to be a hybrid of the limiting canonical forms H—Cl, H Cr, and H C1. The mathematical treatment of molecular structure in terms of valence bond theory can be expanded to encompass more complex molecules. However, as the number of atoms and electrons increases, the mathematical expression of the structure, the wave function, rapidly becomes complex. For this reason, qualitative concepts which arise from the valence bond treatment of simple molecules have been applied to larger molecules. The key ideas that are used to adapt the concepts of valence bond theory to complex molecules are hybridization and resonance. In this qualitative form, valence bond theory describes molecules in terms of orbitals which are mainly localized between two atoms. The shapes of these orbitals are assumed to be similar to those of orbitals described by more quantitative treatment of simpler molecules. 

MMVB is a hybrid force field, which uses MM to treat the unreactive molecular framework, combined with a valence bond (VB) approach to treat the reactive part. The MM part uses the MM2 force field [58], which is well adapted for organic molecules. The VB part uses a parametrized Heisenberg spin Hamiltonian, which can be illustrated by considering a two orbital, two electron description of a sigma bond described by the VB determinants... 

The concepts of directed valence and orbital hybridization were developed by Linus Pauling soon after the description of the hydrogen molecule by the valence bond theory. These concepts were applied to an issue of specific concern to organic chemistry, the tetrahedral orientation of the bonds to tetracoordinate carbon. Pauling reasoned that because covalent bonds require mutual overlap of orbitals, stronger bonds would result from better overlap. Orbitals that possess directional properties, such as p orbitals, should therefore be more effective than spherically symmetric 5 orbitals. 

The extent to which each hybrid is incorporated into the full bonding description of the molecule will depend on the extent to which 3d orbitals... 

The carbon and nitrogen atoms have a p orbital left over after construction of the. s p hybrids. These two p orbitals are perpendicular to the plane that contains the five nuclei. Side-by-side overlap of the p orbitals gives a jrbond that completes the bonding description of this molecule ... 

Hybrid Orbital Descriptions of the Bonding in Hypervalent Molecules... 

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