DREIDING mechanics

Molecules are most commonly represented on a computer graphics screen using stick or space-filling representations, which are analogous to the Dreiding and Corey-PauUng-Koltun (CPK) mechanical models. Sophisticated variations on these two basic types have... 

DPD (dissipative particle dynamics) a mesoscale algorithm DREIDING a molecular mechanics force field... 

EDTA, leading to a postulate that more than one equivalent of Ca2+ can be captured by X (e.g. one Ca2+ sequestered by the three amines and the three carboxylates and another Ca2 + by the remaining half the donor groups), as the Dreiding model suggests. The fact that there was no interaction at neutral pH of X with phosphate or oxalate anions was separately confirmed. Thus, the dissolution of Ca3(P04)2 and Ca(C204) is entirely due to the cation complexation mechanism. 

To avoid these difficulties the concept of the stereomodel4 was introduced, i.e., a geometric figure, W hich contains only the information required in a particular context. Thus, the formulas above describe different models of dimethyl ei.s-l,2-cyclohexanedicarboxylate, formula 1 contains information about the conformation and configuration, while formula 2 contains information about the configuration of the molecule only. The term stereomodel should not be confused with mechanical model (i.c., a Dreiding model). However, mechanical models are very useful representations of stereomodels. 

A number of functions with multiple minima have been proposed to model the valence angles around metals. The molecular mechanics program DREIDING, based on a generic force field, uses a harmonic cosine function (Eq. 2.16)1321. 

The Dreiding 2.21 force field [168] has been used for the molecular mechanics calculations. Dreiding is a general force field well optimized for small molecules with C, H, N, O and S, that has been widely used for polymers [169, 170]. The total potential energy E was calculated as the sum of various energy contributions as follows. 

High quality computer graphics is now widely available and is used as an aid in visualizing molecules, molecular processes, and intermolecular interactions. In some cases molecular graphics has replaced the building of physical (e. g., Dreid-ing) models but the potential applications are much greater. In order to visualize molecules they need to be constructed in a reliable manner and molecular mechanics is an ideal tool for doing so. 

Robinson and Whalley [195] interpreted the mechanism of conformational transmission in two ways. Inspection of a Dreiding model reveals that a change from to hybridisation at C(2) is accompanied by a slight flattening of the... 

Lin and Marks have considered olefin insertion into the actinide-hydrogen bonds of Cp2An(H)(OR) complexes [Cp = ti -(CH3)5C5 An = Th, U R = achiral or chiral group].Calculations included molecular mechanics analysis of the interaction of Cp U(H) [l(S)-entfo]-bornoxide with norbor-nene. The DREIDING and MMP2 force fields were used to calculate the relative energetics of olefin approach trajectories toward the U center. Three reaction pathways were considered. The authors note that whereas this method is approximate, the energetically favored pathway corresponds to the stereo-chemically favored course of the reaction. 

Another fragmentation on the way to muscone (119) has been used by Dreiding, ° starting with epoxy tosylate (126 Scheme 41) to furnish dione (129). Possible mechanisms have been discussed in detail, with the most probable intermediates being (127) and (128) since the H NMR data show that the C(l)—C(12) bond is almost antiperiplanar to the C(13)—OTs bond. 

As everyone knows who has handled mechanical molecular models, such as Dreiding models, bond distances and angles alone do not, in general, completely define the three-dimensional structure of a molecule, i.e. models constructed with fixed values of of bond distances and angles are generally not rigid. In order to make them so, we need to fix some of the torsion angles as well. How many ... 

With all reagents generated by addition of chiral materials to L1A1H4, their exact structure must be determined before facial and orientation preferences can be determined for a given substrate. As illustrated by Alpine borane , the mechanism of hydride transfer must also be known. When these parameters are known, careful examination of models (Dreiding models or computer generated modeling) should determine the actual steric interactions. A casual inspection is usually insufficient for accurate predictions however. 

Molecular mechanics Simulation based on harmonic forcefields, using classical mechanics to predict structure and dynamics. Forcefields inelude Dreiding, UVFF, CVFF, etc. ... 

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