Valence-bond representation

Valence bond representation of the hyperconjugation effect which leads to a lengthening of the C—H bond icetaldeyde. 

Figure 1-1. Limiting valence bond representations of the cation [Fe(H20)6]. ...

In our laboratory we have examined the reactivity pattern of [0s3(y-H)2(C0)10], an unsaturated cluster which can be represented as possessing an osmium-osmium double bond in its classical valence bond representation. We find (2,3) that this compound undergoes a number of reactions with metal carbonyls which in some cases can be formulated as proceeding through intermediates analogous to metal olefin complexes ... 

Valence-bond representations of the (C, Hfchelating ( agostic ) bonding mode in a two-metal-atom site... 

Many other methods, of course, take advantage of invariances with respect to orbital transformations to obtain alternative representations of wavefunctions, such as for example the commonly employed localization procedures for the doubly-occupied MOs from Hartree-Fock calculations [11-15]. We give here a brief account of procedures that particularly seek a valence bond representation of MO wavefunctions. 

For these reasons, a permissive definition of nitrenium ions is chosen. A nitre-nium is any species that can, through valence bond representations, be depicted as having a dicoordinate positively charged nitrogen. Such a definition has the advantage of being readily applied to any species for which a valence bond representation can be depicted. On the other hand, such a definition does encompass a number of species with rather different properties. 

The SnI activation free energies and transition-state stractnre for the series t-bntyl chloride, -bromide, and -iodide in several solvents over a wide polarity range have been examined theoretically. The analysis is accomplished by nsing a two-state valence bond representation for the solute electronic stractnre, in combination with a two-dimensional free energy formalism in terms of the alkyl halide nuclear separation... 

A satisfactory theoretical model for ethylene oxide should take into account as many as possible of the physical properties discussed above, but should be able to predict or explain its chemical properties as well. Three such ogodels have been proposed which are based on molecular-orbital theory s 1-3W.1 ° and two more which conform rather to tho valence-bond representation of chemical structure.1M, W 7 The relative merits of all these models have been discussed in recent reviews.8 7 1301... 

Valence bond representations of the ground and excited states of ethylene... 

These complexes are considered according to the mode of bonding of the hydrazido fragment. The known coordination types are shown in valence bond representations in Figure 15 together with the formal charge, geometry and numbers of valence electrons donated to the metal. 

Figure 2-12. Valence bond representation of the formation of a complex. The left hand form is the ionic representation with no covalent interaction between metal and ligand. The right-hand form shows the charge distribution which results from equal sharing of the lone pair.

Figure 2-13. Valence bond representations of the [Cr(H20)6]3+ ion showing the charge distributions.

Figure 8-16. A valence bond representation of a co-ordinated pyridine. The positive charge is delocalised and the 2- and the 4-positions of the ligand develop electrophilic character.

Valence-bond representation Molecular-orbital representation it bonding and multicenter it bonds Shapes of molecules Coordination compounds Isomerism Bonding in metals... 

D. L. Thorsteinsson, J. Cooper, Gerratt, P. B. Karadakov, M. Raimondi, Theor. Chim Acta (Berlin) 93, 343 (1996). Modern Valence Bond Representations of CASSCF Wavefunctions. 

The molecular structure of S2N2, as shown in Fig. 16.7.2(a), is aZ)2h square-planar ring with S-N edge 165 pm, somewhat analogous to the isoelectronic cation S + (Fig. 16.4.2). The valence-bond representations of the S2N2 molecule are as follows ... 

Thorsteinsson et al. also investigated the transformations of CASSCF functions to modem valence bond representations [10-12], They examined trans-... 

Fig. 2. Dicobaltaboranes (a) possible Co2S2B2 core geometries for Cp2Co2S2B2H2 (3) (b) crystallographically determined structure of 3 (c) crystallographically determined structure of Cp2Co2(/i-PPh2)B2H5 (4) (d) valence bond representation of 4.

Although the molecular orbital description of bonding has some mathematical advantages, simple valence bond representations of structures are adequate for many purposes. The structures of molecules that have only single bonds (and in some cases unshared pairs of electrons on the... 

Figure 7. Valence bond representation of two-electron reduction of neutral square-planar Ni bis(dithiolene) complexes.

Figure 17-11. Valence bond representations of the cytosine-guanine base pair in the relevant electronic states (adapted from Ref. [53])...

The 1,3-diene-metal complexes show a number of characteristic features and will be treated separately. Data for selected compounds, all containing single-c/s-butadiene, are collected in Table VII (50, 53 -60). Early studies (61) concentrated on differentiating between the two valence bond representations 16 and 17, while recent interest has centered on intramolecular rearrangements (62). 

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