Atoms bonding interactions between

The origin of a torsional barrier can be studied best in simple cases like ethane. Here, rotation about the central carbon-carbon bond results in three staggered and three eclipsed stationary points on the potential energy surface, at least when symmetry considerations are not taken into account. Quantum mechanically, the barrier of rotation is explained by anti-bonding interactions between the hydrogens attached to different carbon atoms. These interactions are small when the conformation of ethane is staggered, and reach a maximum value when the molecule approaches an eclipsed geometry. 

It is noteworthy that it is not obligatory to use a torsional potential within a PEF. Depending on the parameterization, it is also possible to represent the torsional barrier by non-bonding interactions between the atoms separated by three bonds. In fact, torsional potentials and non-bonding 1,4-interactions are in a close relationship. This is one reason why force fields like AMBER downscale the 1,4-non-bonded Coulomb and van der Waals interactions. 

Interatomic potentials began with empirical formulations (empirical in the sense that analytical calculations based on them... no computers were being used yet... gave reasonable agreement with experiments). The most famous of these was the Lennard-Jones (1924) potential for noble gas atoms these were essentially van der Waals interactions. Another is the Weber potential for covalent interactions between silicon atoms (Stillinger and Weber 1985) to take into account the directed covalent bonds, interactions between three atoms have to be considered. This potential is well-tested and provides a good description of both the crystalline and... 

One area where the concept of atomic charges is deeply rooted is force field methods (Chapter 2). A significant part of the non-bonded interaction between polar molecules is described in terms of electrostatic interactions between fragments having an internal asymmetry in the electron distribution. The fundamental interaction is between the Electrostatic Potential (ESP) generated by one molecule (or fraction of) and the charged particles of another. The electrostatic potential at position r is given as a sum of contributions from the nuclei and the electronic wave function. 

The function Unb is used for interaction between the indicated EVB atoms while t/ b is used for nonbonded interactions between other atoms which are not bonded to each other or to a common atom. The interactions between the EVB oxygens are modeled by the corresponding 6-12 potential. 

Like the polymethylene hydrocarbons, acyclic carbohydrates and alditols tend to adopt the planar, zigzag conformation wherein all of the carbon atoms lie in the same plane. " However, non-bonded interactions between parallel hydroxyl groups in the 1,3 positions (sy/i-axial interaction) are the most highly destabilizing, and, in xylitol and ribitol, this... 

EFP parameters for a particular fragment are generated for a given atomic basis set, they can be used in a variety of applications. The various components of the non-bonded interactions between molecules are evaluated using the EFP2 generated parameters. The procedure has been described in elsewhere [36] only the main points are summarized below. 

The staggered conformation is likely to be the more stable of the two as hydrogen atoms on one carbon are then as far away from those on the other as they can get (0-310 nm 3-1 A), and any so-called non-bonded interaction between them is thus at a... 

To determine the BEs (Eq. 1) of different electrons in the atom by XPS, one measures the KE of the ejected electrons, knowing the excitation energy, hv, and the work function, electronic structure of the solid, consisting of both localized core states (core line spectra) and delocalized valence states (valence band spectra) can be mapped. The information is element-specific, quantitative, and chemically sensitive. Core line spectra consist of discrete peaks representing orbital BE values, which depend on the chemical environment of a particular element, and whose intensity depends on the concentration of the element. Valence band spectra consist of electronic states associated with bonding interactions between the... 

The unusually facile formation of a disulfonium dication from sulfide 10 is the result of stereochemical features of the eight-membered ring, which favor the formation of a transannular bond.31 According to X-ray data (see in Chapter 7.1 Table 1), the distance between the two sulfur atoms in 1,5-dithiacyclooctane 10 is smaller than the sum of their van der Waals radii (3.75 A), which results in a strong non-bonded interaction between the atoms confirmed by photoelectron spectroscopy and mass spectrometry.32 33 This interaction and the sulfur-sulfur distance can be decreased as a result of bond formation with an electronegative substituent as in sulfoxide 13 or sulfoximine 14.34,35... 

Formally, the lone pairs on molecular nitrogen, hydrogen cyanide, and carbon monoxide are sp hybrid orbitals, whereas NLMO hybridizations calculated even lower p contributions. Hence, these lone pairs have low directionality, the electron density remains close to the coordinating atom and interaction between the lone pair and the Be2+ is comparatively weak. The Be-L bonds are easily disrupted and ligand exchange consequently can proceed with a low activation barrier. A high degree of p character, on the other hand, means that the lone pair is directed toward beryllium, with electron density close to the metal center, and thus well suited for coordination. 

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