Donor-acceptor relationship

The series of neutral B-containing carbocycles as complex ligands within the theme of metal-boron donor-acceptor relationships concludes with the 4,5-dihydro-borepines. l-Phenyl-4,5-dihydroborepine is able to substitute pyridine, acetonitrile or CO... 

Figure 3.91 A schematic depiction ofNBO donor-acceptor relationships connecting one-center (n), two-center (c), and three-center (tu and t) orbital types. ...

The axial preference of R=f-Bu in G is dramatic evidence for the utility of recognizing donor-acceptor relationships in designing specific molecules. 

A compound that is transparent within a spectral domain when in its isolated state can sometimes absorb when in the presence of a species with which it can interact through a donor-acceptor relationship (D-A). This phenomenon is related to the passage of an electron from a bonding orbital of the donor (which becomes a radical cation) to an unoccupied orbital of the acceptor (which becomes a radical anion), which has a close energy level (Fig. 11.6). The position of the absorption band in the spectrum is a function of the ionisation potential of the donor and the electron affinity of the acceptor. The value of e for these transitions is usually large. 

The so-called lithium hydrogen bond, Li-H- Li-H, occurs in the hypothetical linear (LiH)2 dimer. The inner Li atom is electron-deficient, and the inner H atom is sufficiently electron-rich to act as a donor in the formation of an inverse hydrogen bond. The calculated bond lengths (in pm) and electron donor-acceptor relationship are illustrated below ... 

Increasing the electron-accepting character of an electron acceptor monomer would result in a greater separation in the donor—acceptor relationship with a given electron donor monomer. As a result there would be an increased tendency for alternation in the copolymerization. 

Fig. 6. "B-NMR data for 2-diethylboryl-5-methyl thiophene (a) and its pentacarbonyl-chromium complex (b). In the latter, donor-acceptor relationship between boron and the carbonyl group is postulated to account for its higher field nB shift (c).

The donor-acceptor relationships include oxidation-reduction, complexforming, nucleophilic, electrophilic, acidobasic and other processes. A general principle of this theory, from the viewpoint of reactivity and stability of products, is that behave differently in waters. The dependence on pH of the concentrations of the various species is solved by calculation or graphically. 

Much research in the greater polymer science literature is dedicated to the expansion of knowledge into materials appropriate for biomedical applications. For polyphosphazenes, much of the work only has been reported in the past two decades. A recent review outlines phosphazenes and other polymers for their use in biomedical research. Additionally, there were many individual contributions that will be discussed in this chapter. Perhaps one of the simplest phosphazene to be studied from a biological perspective is poly[bis-methylaminophosphazene], as the hydrochloride salt. Interactions between this polymer and DNA were studied by thermal analysis where two functions were noted an electrostatic interaction and a donor-acceptor relationship. It was proposed that the electrostatic interaction serves to stabilize the the helical conformation of the DNA, while the donor-acceptor interaction serves to destabilize the couple. 

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