Donor-acceptor complex potentials

The strength of the complexation is a function of both the donor atom and the metal ion. The solvent medium is also an important factor because solvent molecules that are potential electron donors can compete for the Lewis acid. Qualitative predictions about the strength of donor-acceptor complexation can be made on the basis of the hard-soft-acid-base concept (see Section 1.2.3). The better matched the donor and acceptor, the stronger is the complexation. Scheme 4.3 gives an ordering of hardness and softness for some neutral and ionic Lewis acids and bases. 

An initial osmium tetraoxide/olefin complex (in Scheme 21) is not generally disputed and is considered a donor/acceptor complex between an alkene as electron donor and 0s04 as an electron acceptor (with a reversible reduction potential E ed = —0.06 V versus SEC),217 e.g.,... 

In principle, the behaviour of any molecular species in forming donor-acceptor complexes depends on its ionization potential, electron affinity and polarizability. However, the donor (or acceptor) ability of a substance depends strongly on the requirements and properties of its partners. The same compound may act as a donor towards strong acceptor compounds or as an acceptor towards donor compounds. This is the case of the TT-amphoteric p-tricyanovinyl-AA/V-dimcthylaniline (41) which is a donor towards 2,4,7-trinitrofluorenone and an acceptor towards /V,/V-dirnclhy Ian Mine138. 

The dicarboxonium ions would be useful intermediates for the diacylation of aromatics. The 1,2-dicarboxonium ion (oxalyl dication, 17) has yet to be experimentally obtained. The ionization of the oxalyl fluoride in SbFs presumably forms the donor-acceptor complex, 18, which spontaneously decomposes to CO and COF2. The expected oxalyl dication (OCCO), 17, was not observed although theoretical calculations at MP2/6-31G level indicate 17 to be a minimum on the potential energy surface. 

The ability of molecules to form donor-acceptor complexes depends not only on their ionization potential, electron affinity and polarizability, but also on the requirements and properties of partners. 

Although the fully formed dicationic structure (12) is not formed, the donor-acceptor complex 11 may have partial superelectrophilic character by interaction with SbFs. The adamanta-l,3-diyl dication 12 has been found to be the global minimum structure on the CioHi42+ potential energy surface.5 Theoretical studies at the B3LYP/6-31G level have shown 12 to be 0.4kcal/mol more stable than the isomeric 1,4-dication... 

The reaction of benzo[A]-l,3-diazasilole 85 with lithium alkyls yields the insertion product 112. It was suggested that the initial step of this reaction is the formation of the donor-acceptor complex 113 (Scheme 10) <2002JOM272, 2002JOM150>. The tetracoordinated silicon compounds 112 might have synthetic potential as silylene transfer reagents. 

V [10], Toluene is oxidized at higher potentials (1.98-2.3 V) [19]. However when the solution contains more readily anode-oxidizable components, such as ethanol and fullerene, oxidation products can react with toluene present in the solvate shell of the combined donor-acceptor complex. 

By rough count, more than 50 miscible systems have been reported in the literature, and from intensive studies of these systems a more optimistic view of the potential for miscibility is beginning to develop. Most of these miscible polymer pairs have chemical structures that are capable of forming strong specific interactions such as donor-acceptor complexes and hydrogen bonds. While they have not all been completely studied, those that have show behavior which can only result from the presence of exothermic or negative heats of mixing. 

We consider a generic donor-acceptor complex solute at infinite dilution in a polyatomic solvent. Both the solute and solvent molecules are represented by rigid and non-polarizable ISM models. In the ISM models the potential energy of interaction between two molecules is a sum of pairwise-additive site-site terms, including Coulombic interactions between partial charges located at the molecular sites. Throughout the paper the subscript A refers to interaction sites of the solute, while the subscript aj refers to interaction site j of solvent molecule a. 

This paper summarizes chemical grafting techniques explored in this laboratory that have potential biomedical application. These reactions, initiated by ceric ions, persulfate-bisulfite redox systems, or the presence of comonomers forming donor-acceptor complexes, were carried out in an aqueous environment under conditions which, with suitable modifications, might be tolerated in vivo. Grafting onto tissue surfaces by means of ionizing radiation will not be discussed since techniques for avoiding undesirable side reactions have not yet been developed. 

In a more recent study. Nelson and Yang [494] pre.sented a surface complex-ation model to describe the effect of pH on adsorption equilibria of chlorophe-nols, i.e., the electrostatic effect they also discussed the potential importance of 7t-7t interactions and donor-acceptor complex formation but could not distinguish between the two and concluded, somewhat vaguely, that [t]hese proposed mechanisms provide plausible explanations for the surface complexation reactions between chlorophenols (neutral or anionic forms) and the surface of activated carbon (acidic or basic sites). ... 

Order-disorder phase transitions are especially common in crystalline 7T-donor acceptor complexes between planar polycyclic aromatic hydrocarbons and other organic compounds. The disordered phase can sometimes be characterized in terms of either a static- or a dynamic-disorder model, as shown in Figure 13.2. The dynamic-disorder model consists of disordered components in motion within the confines of a broad well in the potential energy curve, whereas the static disorder model requires that the disordered components be localized in two or more sites in the asymmetric unit, within one or another of the wells of a multiwell-potential energy curve. When the possible sites for static disorder are not resolved by the effective resolution of the data set, it is difficult to choose between these models. This turned out to be true for an anthracene-tetracyanobenzene complex studied at several temperatures above and below the transition temperature Tj, of 206 It was found ° ° ... 

Zacharias, D. E., Prout, K., Myers, C. B, and Glusker, J. P. (1990) Structure and molecular orbital studies of potentially mutagenic methylchrysenes and their TT-TT electron donor-acceptor complexes, Acta Cryst. B47, 97-107 (1991). 

In order to get some information about the fate of silylenes S-la-d in the presence of a second molecule of methyl halide 6a-d, we checked whether silylenes S-la-d can experience stabilization by donor/acceptor interaction with 6a-d. Indeed, the two partners form weak donor/acceptor complexes 7a-d. That means that if S-la-d is created in a matrix at very low temperature in the presence of an excess of a methyl halide 6a-d, complexes like 7a-d should be present. Such a solvation might be the prerequisite for the direct synthesis of silanes 8a-d. These compounds represent the global minima on the CiHaSiX potential energy surfaces and are expected to be generated fl-om the two educt molecules S-la-d and methyl halide 6a-d in rather exothermic (AH, = 65-95 kcal moP ) processes. In the chlorine series (Scheme 1) the value is 73.9 kcal moP. ... 

Before 1990 there were no accurate experimental or theoretical values for the Ea of AGCUT. It was recognized that ionization potentials and electron affinities were important to charge transfer in biological processes, but there were three potential measures of the Ea. These were donor acceptor complex data, reduction potentials, and theoretical calculations, each of which resulted in different measures of the Ea. Much of our work during the past decade has attempted to reconcile these differences. 

This book is based on the reactions of thermal electrons with molecules. The ECD, negative-ion chemical ionization (NICI) mass spectrometry, and polaro-graphic reduction in aprotic solvents methods are used to determine the kinetic and thermodynamic parameters of these reactions. The chromatograph gives a small pure sample of the molecule. The temperature dependence of the response of the ECD and NIMS is measured to determine fundamental properties. The ECD measurements are verified and extended by correlations with half-wave reduction potentials in aprotic solvents, absorption spectra of aromatic hydrocarbons and donor acceptor complexes, electronegativities, and simple molecular orbital theory. 

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