Formation of a donor-acceptor complex

The reaction is initiated by formation of a donor-acceptor complex 4 from acyl chloride 2, which is thereby activated, and the Lewis acid, e.g. aluminum trichloride. Complex 4 can dissociate into the acylium ion 5 and the aluminum tetrachloride anion 4 as well as 5 can act as an electrophile in a reaction with the aromatic substrate ... 

We have also used poly(propynoic acid) in our studies of the photochemical interaction of PCSs with dienophiles, such as maleic anhydride, tetracyanoethylene, and styrene. This photochemical reaction of Diels-Alder type is accompanied by the breakdown of the conjugation system and the formation of slightly colored adducts266. Together with the cycloaddition reaction, photodegradation of PPA and its adducts takes place. A cycloaddition reaction is always preceded by the formation of a donor-acceptor complex of a PCS with a dienophile. 

Currently this model is one of the most commonly used in the theory of free-radical copolymerization. The formation of a donor-acceptor complex Ma... iVlbetween monomers Ma and in some systems is responsible for a number of peculiarities absent in the case of the ideal model. Such peculiarities are due to the fact that besides the single monomer addition to a propagating radical, a possibility also exists of monomer addition in pairs as a complex. Here the role of kinetically independent elements is played by ultimate units Ma of growing chains as well as by free (M ) and complex-bound (M ) monomers, whose constants of the rate of addition to the macroradical with a-th ultimate unit will be... 

Donor-acceptor complexes. A colorless hexane (or dichloromethane) solution of osmium tetraoxide upon exposure to benzene turns yellow instantaneously owing to the formation of a donor/acceptor complex,218 i.e.. 

The exposure of a colorless solution of anisole to iodine monochloride (IC1) in dichloromethane leads to the appearance of a new electronic absorption band (lmax = 350 nm) arising from the formation of a donor/acceptor complex,225 i.e.,... 

Figure 5.19. Illustration of the formation of a donor-acceptor complex by the sequential adsorption of trimethylamine and boron trifluoride. The Lewis-basic trimethylamine forms a dative bond with the electrophilic Si dimer atom, and the Lewis-acidic boron trifluoride bonds to the nucleophilic Si dimer atom [278].

According to a possible mechanism, transfer hydrogenation requires a catalyst-mediated formation of a donor-acceptor complex, followed by a direct hydrogen transfer. An alternative possibility is a simple consecutive dehydrogenation-hydrogenation process. While the former mechanism on palladium is supported by numerous experimental evidence,78 direct hydrogen transfer on nickel was disproved.79... 

Much experimental evidence indicates that Pd mediates the formation of a donor-acceptor complex followed by a direct hydrogen transfer36. This process, however, was disproved in the disproportionation of 1,4-cyclohexadiene (a special case of transfer hydrogenation) over colloidal nickel40. Another possibility is a consecutive dehydrogenation-hydrogenation process. 

Oxidation of chiral esters of phenylacetic acids. These esters can be converted into acetates of mandelic esters by oxidation with DDQ in acetic acid. The reaction is diastereoselective when carried out on esters of chiral alcohols, of which 8-phenylmenthol is the most useful. The presence of substituents on the phenyl group has slight effect on the diastereoselectivity, which depends on formation of a donor-acceptor complex between the substrate and the quinone with removal of a hydrogen atom. The acetoxy group then enters from the opposite, more bulky face. 

The formation of a donor-acceptor complex is described as an equilibrium process characterized by equilibrium constant. The presence of a solvent affects the complexation constant describing the equilibrium between the individual components of the complex. This is due to a competition of the solvent molecules toward each component of the complex. The solvent does not have to be a charge-transfer competitor. Competitive interactions such as hydrogen bonds can also affect the equilibrium. When the equilibrium constant of the complexation is quite low, the influence of the solvent is very significant, due to its overwhelming concentration compared to the concentration of the complex. For example, dioxane or ether are known to be effective n-donors chloroform and methylene chloride have proved to participate in hydrogen bonds with n-donor molecules and carbon tetrachloride behaves as an electron acceptor [83]. 

Scheme 1.36. Formation of a donor-acceptor complex that then homopolymerizes as a route to formation of an alternating copolymer.

Currently this model is one of the most commonly used in the theory of free-radical copolymerization. The formation of a donor-acceptor complex Ma... 

Switchable binding, the formation of a donor-acceptor complex, intramolecular translocation, or a change of redox state are the triggered functions characterized by electroanalytical or spectroscopic techniques [31-34]. 

The catalytic activity of metal ions originates in the formation of a donor-acceptor complex between the cation and the reactant, which must act as a Lewis base. The result of the complexation is that the donor atom becomes effectively more electronegative. All functional groups that have unshared electron pairs are... 

The free-radical polymerization of NVP is rather complex but its liability to be polymerized by its own peroxide is well documented as well as its strong tendency for chain transfer during polymerization However, retardation by oxygen has also been claimed Alternatively, the formation of a donor-acceptor complex has been proposed which could yield anionic and cationic species,... 

This could be formation of a donor-acceptor complex, an acid-base interaction or a chemical reaction. Measurement of the extent or rate of that reaction would provide a measure proportional to the probability W(0) of cyclization or the dynamics of cyclization. The meaningful experimental quantities are Key and key. The experiments must be carried out in such a way that either of these values can be obtained. 

Probably, the reaction is preceded by the formation of a donor-acceptor complex, and the elementary act represents the electron transfer from the n-bond to the O—O group followed by its homolysis... 

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