Bond formation or breaking

The dynamic behavior of ring systems is one of the most active areas of MM applications, since the energy hypersurface of a large molecule that does not involve bond formation or breaking can be adequately explored only by this technique. Here again. Dale sum-... 

When a molecule coming from a gas phase adsorbs on a solid surface, it must both cross a gas-phase boundary and form an adsorptive bond when it encounters the solid. Similarly, when a molecule desorbs, it must break the adsorptive bond and enter the gas phase. Although the collision of a molecule with a solid surface can be treated by using either classical or quantum mechanics, the prediction of the rate of bond formation or breaking requires a quantum-mechanical description because this process involves the probability of an event occurring. 

QM/MM methods -which enable one to simulate the core region quantum mechanically, to model bond formation or breaking, coupled with an atomistic level description of the surrounding regions, which include microstructural features and nanoarchitecture, together with continuum methods that effectively extend the material to infinity -while at time of writing are in their infancy, span hierarchical length scales from the electronic structure to a continuum and have the potential to truly Simulate the dirt ... 

Three-dimensional potential energy diagrams of the type discussed in connection with the variable E2 transition state theory for elimination reactions can be used to consider structural effects on the reactivity of carbonyl compounds and the tetrahedral intermediates involved in carbonyl-group reactions. Many of these reactions involve the formation or breaking of two separate bonds. This is the case in the first stage of acetal hydrolysis, which involves both a proton transfer and breaking of a C—O bond. The overall reaction might take place in several ways. There are two mechanistic extremes ... 

Neglect of electrons means that molecular mechanics methods cannot treat chemical problems where electronic effects predominate. For example, they cannot describe processes which involve bond formation or bond breaking. Molecular properties which depend on subtle electronic details are also not reproducible by molecular mechanics methods. 

Simulation of molecules can be done at the quantum mechanical level, as is necessaiy to determine the electronic properties of molecules, to analyze covalent bonds or simulate bond formation and breaking. However, quantum mechanical simulation is extremely computationally intensive and is too time-consuming for all but the smallest molecular systems. 

Conventional presentaticsis of DFT start with pure states but sooner w later encounter mixed states and d sities (ensemble densities is the usual formulation in the DFT literature) as well. These arise, for example in formation or breaking of chemical bonds and in treatments of so-called static correlation (situations in which several different one-electron configurations are nearly degenerate). Much of the DFT literature treats these problems by extension and generalization from pure state, closed shell system results. A more inclusively systematic treatment is preferable. Therefore, the first task is to obtain the Time-Dependent Variational Principle (TDVP) in a form which includes mixed states. 

Developments in computer techniques making it possible to solve complicated fluid motions in a combustion environment that are affected by diffusion and involve complicated chemistry (large numbers of elementary reactions, which individually are not "complex" but quite simple, i.e., most of them involve two reacting species, sometimes three, and the formation or breaking of just one bond), and with a large number of transient intermediates formed in the course of fuel oxidation and pollutant formation. 

The aqua ion Au(H20)4+ has not been characterized either in solution or in the solid state. Most of the substitution studies have involved the halide complexes AuXj and Au(NH3) (Ref. 319). A number of earUer generalizations have been confirmed. Rates are very sensitive to the nature of both entering and leaving ligands and bond formation and breaking are nearly synchronous. The double-humped energy profiles witnessed with Pd(II) and Pt(II) are not invoked the five-coordinate species resulting from an associative mechanism is the transition state ... 

At first it was hoped, that the precise frequency of these new light sources could be employed to selectively excite individual bonds, weakening or breaking them, thus enhancing the formation of one product and discrimi-... 

Chemical reactions are studied in terms of elementary reactions involving only one step for bond breaking, bond formation, or electron transfer. A characteristic of elementary reactions is the molecularity. In other words, if... 

In this chapter the mechanisms of electrode reactions are explained for the most simple case of an electron transfer without chemical transformation, i.e. without formation or breaking chemical bonds. Other more complex cases are also referred to. Comparison with electron transfer reactions in homogeneous solution are made. 

Use three centered dots to indicate association of an unspecified type (e.g., hydrogen bonding, bond formation, or bond breaking). 

Hi) their stereochemistry depending on the total number of n and o electrons involved in the formation or breaking of bonds. 

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