Donor interaction

The relative basicity and acidity of isothiazole and its methyl derivatives have been compared by IR spectroscopy (77MI41702). The isothiazoles, dissolved in inert solvents (e.g. CCI4, CS2) containing traces of butanol (a proton donor), interact with the butanol OH... 

P,0-Heterocycles with P-atom hexacoordinated owing to donor interaction, participation in enzymatic reactions 98ACR535. 

Electron density is transferred from a Lewis donor to a Lewis acceptor, here shown for an amine (donor) interacting with a phosphenium cation (acceptor). The lone pair orbital at the amine dives into the emptyp-orbital of the phosphenium cation, hollowing the ideas of Mulliken the donation towards an acceptor can be viewed as sketched in Scheme 2. 

The temperature at which a cycloaddition reaction of a neopentylsilene takes place (detected by the elimination of LiCl) has turned out to be dependent on the reaction partners added as substrate. This implies that an interaction between the substrate and A or B or the substrate and C occurs somewhere along the reaction pathway depicted above. For the system Cl3SiCH=CH2/LiBut/R2C=NR it was observed that the imine initiates and supports the salt elimination from the species A/B. Based on the knowledge that silenes are stabilized by external donors [1] we conclude that with carbon unsaturated compounds x-donor interactions instead of cr-donor complexes may be possible as well for the lithiated species (D) as for the silene itself (E). 

Experiment 1. Visual observation of secretory cells in luminescence microscope Various types of secretory cells in allelopathically active plants contain fluorescing secondary products (Fig. 1). Secretions from the above ground parts of plant (in leaves, flowers, stems) were concentrated in secretory hairs and glands. Whereas secretions of roots are in secretory reservoirs and idioblasts (ordinary cells which accumulate secretory products) or may be released by the secretory surface of the root tip (Fig. 1.). The fluorescence appears to change, when allelopathically active cell of other plant species (cell-donor) interacts with acceptor cell (Roshchina and Melnikova, 1999). 

The formation of a coordinate bond is the result of the donation and acceptance of a pair of electrons. This in itself suggests that if a specific electron donor interacts with a series of metal ions (electron acceptors) there will be some variation in the stability of the coordinate bonds depending on the acidity of the metal ion. Conversely, if a specific metal ion is considered, there will be a difference in stability of the complexes formed with a series of electron pair donors (ligands). In fact, there are several factors that affect the stability of complexes formed between metal ions and ligands, and some of them will now be described. 

The effect of donors on the catalyst activity can be explained by assuming that the dimeric complex is not an active catalyst (Cramer s kinetics indicate a monomeric Rh species as active catalyst see Section II,B,2) and that 14 with a free coordination site for ethylene is the active catalyst, while 15 with both coordination sites occupied by donors is catalytically inactive. When D is a weak donor, such as ketone or ether (see Fig. 5d), the reaction rate increases, slowly reaching a maximum and leveling off at the maximum as the concentration of the donor is increased. It can be speculated that these donors interact with the catalyst only to the extent that they break up the dimer 8 to form 14, but that... 

The irregular shape of the CT curve near Req reflects competition of unfavorable donor-donor interactions (steric repulsions) and favorable donor-acceptor... 

We conclude that L2a-Qb donor-donor interactions are generally ineffective at lowering the total variational energy,28 whereas L2a-f2b donor-acceptor interactions are universally stabilizing. Comparison of Fig. 3.2 (or Fig. 1.3) with Fig. 3.13 shows clearly how this fundamental difference arises from the Pauli restriction on orbital occupancies. 

Comparison of the binding energies AE for Ir+ and Au+ species shows that the latter are much more weakly bound (by roughly 60-80 kcalmol-1) for all the bidentate ligands. This large difference merely reflects the fact that a two-pair donor interacts more effectively with a two-pair acceptor (e.g., Ir+) than with a one-pair acceptor (e.g., Au+), a simple consequence of the chemical donor-acceptor... 

When the molecule has an especially weak bond together with a higher energy 7t -otbital, the potential energy scheme for bond dissociation can resemble Figure 4.5(b). The approaching radical-anion electron donor interacts directly with the... 

For the case of one donor interacting with several nearby acceptors, the total FRET efficiency of the system involves the sum of n individual interactions... 

To find out applications and rules of the metala-logy principle, we systematically investigated the influence of HOMO/LUMO- or LUMO/HOMO-perturbations (dual model) as well as relative donor/acceptor- or acceptor/donor-interactions (double-dual model) in metal-complexesin their model-reactions and in metal catalysis The strategy we followed is depicted in Scheme 2.2-2. For our purposes, we separated the studied catalytic system into two r-systems (substrates S Case I),... 

As shown in Fig. 3, Lewis acids (i.e., metal ions and hydrogen bond donors) display syn or anti stereochemistry as they interact with the carboxylate anion. However, in a study of enzyme active sites. Candour (1981) first noticed that hydrogen bond donors to the carboxylates of aspartate and glutamate residues preferentially occur with syn stereochemistry. As a carboxylate-hydrogen bond donor interaction COg-H... 

As for carboxylate-hydrogen bond donor interactions, carboxylate-metal ion interactions are expected to be most favorable with syn stereochemistry. In a survey of the Cambridge Structural Database, Carrell et al. (1988) presented a stereochemical analysis of carboxylate—metal ion interactions which supports this expectation (Scheme 1). These investigators found that the syn-oriented lone electron pair of the carboxylate... 

The first two terms represent van der Waals interactions between the adsorbed SOC and the surface, which would apply to all SOC. The second two terms represent Lewis acid-base interactions, which can be important for compounds containing O, N, or aromatic rings, for example, the adsorption of alkyl ethers on the polar surface of quartz. The y coefficients (in mJ m 2) describe the surface properties, where yvdw is associated with its van der Waals interactions with adsorbing gases, y describes its electron-acceptor interactions, and y describes the electron-donor interactions of the surface. On the other hand, the properties of the adsorbing species are described by In pL for the van der Waals interactions and by the dimensionless parameters ft and which relate to the electron-donor and electron-acceptor properties (if any), respectively, of the adsorbing molecule. 

As anticipated above, the reactivity of the cyano complexes of transition metals are strongly influenced by the structure of the medium, namely the nature of the solvent (specific cyano-donor interactions), or the type and concentration of the counterions (15). Both of these factors have a profound influence in the electronic structure, and determine the observed changes in reactivity, particularly in... 

Wozniak and coworkers described recently the first heterodinuclear bismacrocyclic transition metal complex 34 + (Fig. 14.5) that exhibits potential-driven intramolecular motion of the interlocked crown ether unit.25 26 Although the system contains transition metals, the main interaction between the various subunits, which also allowed to construct catenane 34+, is an acceptor-donor interaction of the charge transfer type. 

Figure 4.10. (a) Sigma-type donor interaction between the bond and the LUMO, cr, of a polarized a bond (shown as a p orbital). (type substituent, or cr of a polarized cr bond. 

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