Strain Coulomb interaction

It follows from the above X-ray data that betaines I and II have some structural peculiarities. Two main peculiarities are especially pronounced for betaines I. These compounds have the sterically strained gauche-conformation of the main chain due to the intramolecular Coulomb interaction of the cationic and anionic centers and noticeable distortions of the bond lengths in it. In Section 5 we discuss how these peculiarities of the betaine structure reflect their reactivity. 

The molecular mechanics energy of a molecule is described in terms of a sum of contributions arising from distortions from ideal bond distances ( stretch contributions ), bond angles ( bend contributions ) and torsion angles ( torsion contributions ), together with contributions due to non-bonded (van der Waals and Coulombic) interactions. It is commonly referred to as a strain energy , meaning that it reflects the strain inherent to a real molecule relative to some idealized form. 

The propagation step is fast, aided by the coulombic interaction between the carbo-cation and the negatively polarized ether oxygen, and the strain in the three-membered ring. Termination may occur by the reaction of the carbocation with an adventitious nucleophile (a base, for example) or, very occasionally, with the anion of the initiator. ... 

In an analysis in 1973 of the effect of packing on the conformation of triphenylphosphine, Brock and Ibers used the 1972 version of Busing s program WMIN. ° The calculations extended beyond the minimization of close contacts between rigid molecules, taking into account internal molecular strain, and van der Waals and Coulomb interactions. 

The primary acceptors of the two plant photosystems differ fundamentally from each other, no doubt because of their different redox midpoint potentials (about -100 to -200 mV for PS II, -705 to -730 mV for PS I [R3-R5]). In PS I two iron-sulfur (ferredoxin-type) proteins, and Fg, with characteristic EPR spectrum in the reduced state ( m between -450 and -550 mV), have been observed (Fig. 2) that function either parallel or in series (see Ref. R5 for a recent review). The shape of the spectra of the two ferredoxin-type acceptors and in particular their principal g values depend on whether one or both acceptors are reduced (Fig. 2). It is unlikely that this is due to a magnetic interaction, as the differences depend linearly on the microwave frequency, i.e. on the applied magnetic field (exchange and dipolar interactions are independent of field Table 3) [16,42], Possibly, Coulomb repulsion causes strain-induced g shifts. 

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