Hybridization concepts

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... 

It has been shown that description of bonding based on the bent-bond concept can be just as successful in describing molecular structure as the hybridization concept. We will, however, use the hybridization terminology. 

Utgoff, P., Perception trees A case study in hybrid concept representations. In Proceedings of AAAI88, Vol. 2, p. 601. Morgan Kaufmann, San Mateo, CA, 1988. 

Summary Ab initio calculated bond dissociation energies of silicon compounds will be discussed by means of atomic ionization energies and atomic orbital overlap. Ring strain energies of C- as well as Si-rings are estimated by homodesmotic reactions. The hybridization concept is critically examined in the case of silicon compounds. From the most important results a set of basic rules will be presented. 

The hybridization concept which has been accepted for carbon compounds should not be applied to... 

Let us now sketch the general LCAO-NBO formation of diatomic NBOs from their constituent (N)AOs, employing the donor-acceptor and hybridization concepts developed in previous sections. If we visualize the starting atomic configurations... 

This graduate-level text presents the first comprehensive overview of modern chemical valency and bonding theory, written by internationally recognized experts in the held. The authors build on the foundation of Lewis- and Pauling-like localized structural and hybridization concepts to present a book that is directly based on current ab initio computational technology. 

Heterocyclic systems have played an important role in this historical development. In addition to pyridine and thiophene mentioned earlier, a third heterocyclic system with one heteroatom played a crucial part protonation and methylation of 4//-pyrone were found by J. N. Collie and T. Tickle in 1899 to occur at the exocyclic oxygen atom and not at the oxygen heteroatom, giving a first hint for the jr-electron sextet theory based on the these arguments.36 Therefore, F. Arndt, who proposed in 1924 a mesomeric structure for 4//-pyrone, should also be considered among the pioneers who contributed to the theory of the aromatic sextet.37 These ideas were later refined by Linus Pauling, whose valence bond theory (and the electronegativity, resonance and hybridization concepts) led to results similar to Hiickel s molecular orbital theory.38... 

Hybridization concepts can also be applied to atoms other than carbon. Here, we look at how we can understand the properties of oxygen and nitrogen compounds by considering hybrid orbitals for these atoms. 

These attempts may be called thermodynamic semi-theoretical approaches . They concern mostly the simplest kind of bonding, namely the metallic bond. The underlying hypothesis is that the contributions of different outer orbitals (7 s, 6 d, 5 f) in some chosen thermodynamic or structural property can be linearly combined, the coefficients of this linear combination being related to the degree of participation of the different orbitals in the bonding an approach clearly related to the molecular orbital approach of quantum chemistry and to the hybridization concept, and which had been previously employed in other transition metals and to the rare-earth metallic systems " (for a criticism of this approach, see Ref. 6). The chosen thermodynamic and structural properties are, therefore, bonding indicators , since they will reflect contributions introduced by the fact that the wavefunctions of bonding electrons have mixed orbital characters. 

Another argument that has often been invoked against VB theory and the hybridization concept is the fact that the water molecule has two experimentally measurable ionization potentials, in apparent contradiction with the classical representation of water with its lone electron pairs located in two equivalent... 

The hybrids consist of solid and liquid substances in the same system. The most widely used hybrid concept has a hollow solid fuel grain, much like a solid propellant grain, but with no solid oxidizer present. The fuel grain may contain other. energetic solid substances. The oxidizer is generally a storable liquid propellant such as nitrogen tetroxide or chlorine trifluoride. 

At present, sponsors and CROs do not completely understand, nor do they fully embrace, the SMO and hybrid concepts. The scope of most major clinical development projects often prevents sponsors and CROs from ever using SMOs as one-stop sources for study conduct services. 

A much lesser known contribution of Pauling to the chemical knowledge, is his explicit expression for the momentum representation of the hydrogenic wave function [3]. Momentum space concepts are common among scattering physicists, some experimental chemists and a few theoreticians however, they have not won over the bulk of chemists nearly as efficiently as the hybrid concept. The reason is that they are somewhat counter intuitive and molecular structure is expressed in a rather indirect and (in the truest sense of the word) convoluted manner. 

Two novel hybrid concepts for gas separation using adsorption technology have emerged in recent years. They include (a) adsorbent membranes, and (b) simultaneous adsorption and reaction. 

Figure 10.18 shows a schematic flow diagram for the PSA-SSF hybrid concept for increased H2 recovery using the process scheme described above. The fresh feed to the PSA process is SMROG containing 72.8% H2,22.6% C02, and 4.6% CHi + CO at a pressure of 19.4atm. The PSA process cycle is similar to that for the Poly-bed process except that only two cocurrent depressurization steps are used (eliminate... 

Other reactor configurations and concepts have also been discussed in the technical literature. Most commonly dted are hybrid concepts, where the membrane reactor is used as an add-on stage to an already existing conventional reactor. This particular configuration has a number of attractive features, especially for applications involving conventional type porous membranes, which are characterized by moderate (Knudsen-type) permselective properties. Staged membrane reactors have received mention and so have reactors with multiple feed-ports and recycle. To facilitate the transport across the membrane in laboratory studies one often applies a sweep gas or a vacuum in the permeate side or a pressure gradient across the membrane. It is unlikely that the first two approaches, effective as they may be in laboratory applications, will find widespread commercial application. 

Hybrid concepts combining the principles of selective adsorption with those of membrane technology and reaction engineering have been developed to enhance the overall separation or reaction efficiency. ° Two examples are given below. 

As part of an interdisciplinary study we are working on emission control catalysis for an extended parallel hybrid concept [1-5]. The main elements of the experimental car developed at the Swiss Federal Institute of Technology are the combustion engine, operating in a fixed cycle mode, a flywheel as a short term energy storage device, an electrical machine and a continuous variable transmission. One of the features of this hybrid vehicle is the so called intermittent... 

We have seen that hybridization neatly explains bonding that involves and p orbitals. For elements in the third period and beyond, however, we cannot always account for molecular geometry by assuming that only. y and p orbitals hybridize. To understand the formation of molecules with trigonal bipyramidal and octahedral geometries, for instance, we must include d orbitals in the hybridization concept. 

The hybridization concept can be readily applied to molecules with double and triple bonds, such as those shown in Scheme 1.1. Second-row elements are described as having sp or sp orbitals, resulting from hybridization of the s orbital with two or one p orbitals, respectively. The double and triple bonds are conceived as arising from the overlap of the unhybridized p orbitals on adjacent atoms. These bonds have a nodal plane and are called tt bonds. Because the overlap is not as effective as for sp orbitals, these bonds are somewhat weaker than a bonds. 

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