Minimum chemical distance

Jochum C, Gasteiger J, Ugi I, Dugundji J (1982) The principle of minimum chemical distance and the principle of minimum structure change, Z Naturforsch 37B 1205... 

Principle of minimum chemical distance 1980 Jochum, Gasteiger, and UgiP... 

Fig. 14 Dependence of relative reactivity on (minimum) interatomic distance between the electrophilic centre and the carboxyl oxygen, for (a) sulphonamides [76] and (b) malonate half-esters [77]. Reprinted with permission from Jager et al. (1984). Copyright 1984 American Chemical Society.

The minimum interaction distance is arbitrarily taken to be 4A except where new chemical bonds are formed. 

In Euclidean cZ-dimensional spaces Flory exponent depends only on d. A good (although not exact) estimation was given by Flory formula, Eq. (9) [7, 8], It is well known [47] that the critical phenomena depend by the decisive mode on various ftactal characteristics of basic stmcture. It becomes obvious, that excepting the ftactal (Hausdorflf) dimension Dj. physical phenomena on ft actals depend on many other dimensions, including skeleton fractal dimension [48], dimension of minimum (or chemical) distance [29] and so on. It also becomes clear, that regular random walks on fractals have anomalous fractal dimension [49] and that the vibrational excitations spectrum is characterized by spectral (fiac-ton) dimension d=2D d [41, 50],... 

Let EM(B) and EM(E) be the initial and final ensemble of molecules of a chemical reaction or sequence of reaction. This chemical conversion determines in a characteristic manner a correlation of the atoms in EM(E) and EM(B). We conjecture that chemical reactions proceed in such a manner that a minimum of valence electrons is relocated. This is criterion for the correlation of the atoms of EM(E) to the atoms of EM(B). We call the number of valence electrons which must be relocated during the transformation from EM(B) to EM(E) with a given correlation of atoms the chemical distance D(B, E) between these EM. 

An attraction between atoms that is too weak to be classified as a chemical bond is often referred to as a van der Waals attraction. The minimum energy distance 7 m is thought to correspond to a situation where the atoms barely touch, and half this distance is referred to as the van der Waals radius of the atom, r, . These radii are listed in the last column of Table 9.2. 

Positioning of the cordon will require careful consideration of the suspected agent involved, its dispersal method and local environmental factors such as temperature, wind speed and direction, and the layout of the surrounding streets and buildings. The aim should be to contain the incident within a fixed area and to prevent any unauthorised entrance or exit from this zone. The inner cordon is required to contain the immediate vicinity of the incident site and suspected edge of the contaminated area. Movement of personnel and unaffected individuals should be able to continue without risk of contamination or injury outside the inner cordon. The second, outer, cordon will be required to contain the entire incident scene and emergency responses. This may contain several separate incident sites or contaminated areas. Estimates of minimum safe distances for several different chemical agents are shown in Table 5.2. 

EMGRESP is a source-term and dispersion emergency response screening tool for calculating downwind contours with a minimum of user input and computational expense in the event of a release of a hazardous chemical. The program provides hazardous contaminant information, calculates toxic concentrations at various distances downwind of a release, and c" the... 

Within the framework of the Bom-Oppenheimer approximation, a diatomic molecule consists of two nuclei that are more-or-less attached by the surrounding electron cloud. Often the specific form of the resulting potential function is not known. However, if a chemical bond is formed between the two nuclei, the potential function displays a minimum at a distance that corresponds to the equilibrium bond length. Furthermore, the energy necessary to break the chemical bond, the dissociation energy, is often evaluated by spectroscopic measurements. It can be concluded, then, that the potential fiinction has the general form shown in Fig. 6. A simple derivation of the Born- Qppenheimer approximation is presented in Section 12.1. 

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