Interaction energy steric repulsion

ADF calculates various chemically meaningful terms that add up to the bond energy, with an adaptation of Morokuma s bond-energy decomposition to the Kohn-Sham MO method. The individual terms are chemically intuitive quantities such as electrostatic energy, steric repulsion, Pauli repulsion, and orbital interactions. The latter are symmetry decomposed according to the Ziegler transition-state method. ... 

Try to explain the conformational preference in terms of steric repulsion. Which ring atom(s) in the higher-energy conformer approach the CH3 group most closely (Make sure that you find all significant nonbonded interactions.) Which of these interactions are absent in the lower-energy conformer Can interactions that appear in both conformers account for the conformational preference ... 

The parameter redundancy is also the reason that care should be exercised when trying to decompose energy differences into individual terms. Although it may be possible to rationalize the preference of one conformation over another by for example increased steric repulsion between certain atom pairs, this is intimately related to the chosen functional form for the non-bonded energy, and the balance between this and the angle bend/torsional terms. The rotational banier in ethane, for example, may be reproduced solely by an HCCH torsional energy term, solely by an H-H van der Waals repulsion or solely by H-H electrostatic repulsion. Different force fields will have (slightly) different balances of these terms, and while one force field may contribute a conformational difference primarily to steric interactions, another may have the... 

Let us now turn our attention to an interpretation of Ycr particularly to the question of what numerical values might be appropriate under certain conditions. Based on the discussion above, we would expect to find that values in excess of 10 kg/mol-ns would be appropriate for materials below Tg. What we seek is a method of checking this prediction by calculating an approximate value from molecular parameters. To do this we will consider the repulsive interaction as largely a steric one due to the van der Waals repulsions of a pair of chain elements. To the extent that this picture applies, we can calculate an approximate 7c by expanding the van der Waals pair interaction, energy,... 

An estimate of the energy of steric repulsion may be obtained by comparing the observed heat of polymerization with the value calculated on the assumption that the interaction energy between substituents is zero. For the latter purpose, we consider the following steps... 

The pair potential of colloidal particles, i.e. the potential energy of interaction between a pair of colloidal particles as a function of separation distance, is calculated from the linear superposition of the individual energy curves. When this was done using the attractive potential calculated from London dispersion forces, Fa, and electrostatic repulsion, Ve, the theory was called the DLVO Theory (from Derjaguin, Landau, Verwey and Overbeek). Here we will use the term to include other potentials, such as those arising from depletion interactions, Kd, and steric repulsion, Vs, and so we may write the total potential energy of interaction as... 

Primary steric effects are due to repulsions between electrons in valence orbitals on adjacent atoms which are not bonded to each other. They are believed to result from the interpenetration of occupied orbitals on one atom by electrons on the other, resulting in a violation of the Pauli exclusion principle. All steric interactions raise the energy of the system in which they occur. Their effect on chemical reactivity is to either decrease or increase a rate or equilibrium constant depending on whether steric repulsions are greater in the reactant or in the product (equilibria) or transition state (rate). 

The near-zero energy uncovered for interaction of two trimethylsilyl groups attached to the same carbon warrants additional comment, in that severe steric repulsion might have been anticipated between the two bulky substituents. As mentioned previously, trimethylsilyl is both a o-donor substituent and a n -acceptor substituent. Placed on a tetrahedral carbon center, this suggests that K donation from one substituent be followed by a acceptance from the other substituent, and vice versa. 

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